SIGNIFICANCE OF SEED PATHOLOGY IN FOREST TREES

Introduction

The ever-increasing impact of human activities on the environment makes the conservation of natural resources, including biological diversity, an urgent and critical task leading to changes and introduction in the flora and fauna in forest with the new pathogens or virulent races of the pathogens leading to newer diseases, which may be severe and thus lead to substantial losses.

Importance of Forest Pathology

The science of Forest Pathology as profession began when a Germen forester Robert Hartig, fathered forest pathology as a science in the 1870s. Forest pathology is the branch of plant pathology that deals with diseases of woody plant growing in natural forests, in plantation, in urban environment and microbiological deterioration of forest product after harvests. Danida Forest Seed was established in 1968 as Danish / FAO Forest Tree Seed Centre. The name was subsequently changed to Danida Forest Seed Centre (DFSC) in 1981. The main objectives of DFSC are to promote supply, production and use of genetically and physiologically improved seed material for tree planting programme in forestry and agro-forestry in developing countries.

Diseases of forests are caused by fungi, bacteria, nematodes, seed plants, viruses,mycoplasmas, as well as unfavorable environmental factors including heat, cold, drought, flooding, air pollution, nutrient deficiencies, and adverse physical factors or toxic substances in soil. Devastating losses due to diseases such as Dutch elm disease, Chestnut blight, pine blister rust, oak wilt, Cyprus canker, etc., in trees have been experienced from time to time.

Deterioration of tree seeds by fungi involves problems that differ in many aspects from those of grains. For example, tree seeds are exposed to many conditions before storage that permit the development of mold fungi. Hence, it is important to know the characteristics of fungi associated with important tree species, what damage they cause, where and when and under what circumstances the damage occurs, and what could be done to prevent the damage.

The science of tree seed pathology is still very young. The occurrence and distribution of most of the tree seed pathogens is well realized but there is very little understanding of their impact on seed production, seed quality and seed viability. Interest in these problems has been growing steadily in the past few decades, but recently this interest has changed in to serious concern mostly because of the problems encountered in the renewal and management of the forests, which are a major resource worldwide.

Since the inception of the forest pathology, pioneering studies have been carried out on many disease problems of seeds, seedlings in nurseries, plantations and natural forests and their management. Significant contributions were made on the aspects of timber pathology and mycorrhizae. More than 160 fungi causing diseases and decays of both hardwood and soft wood species were studied. Seeds of mandated tree species were screened for seed borne pathogens and their management was evolved to minimize losses in storage and nursery. In Dalbergia sissoo among the the nursery diseases, the most notable ones are damping-off, and Rhizoctonia leaf and web blight (Mehrotra, 1998). The Melampsora rust (Pei and McCracken, 2005), Uredo sissoo, Maravalia achroa and Maravalia pterocarpi have also been reported to cause foliage infections in nursery seedlings. A Meliola sp. causes a sooty mould of seedlings. Certain seedling diseases like Rosellina root rot poplar scab (also known as ‘Summer Leaf Drop’) caused by a fungus Venturia populina (anamorph Pollaccia elegans), Bipolaris leaf blight diseases of poplars, Cylindrocladium leaf and twig blight of eucalypts and Pseudocercospora needle blight of pines have been investigated and management have been worked out extensively.

In plantations, some of the important diseases include Trichosporium wilt of Casuarina equisetifolia, Fusarium wilt of Dalbergia sissoo, pink disease of Eucalyptus, Ganoderma root rot of hard wood species, partridge root rot of Shorea robusta caused by Aurificaria shoreae, root rot of Gmelina arborea by Poria rhizomorpha, root rot of Cedrus deodara by Heterobasidion annosum,Armillaria root rot of Abies pindrow, Picea smithiana and Cryptomeria japonica and brown root rot of poplars caused by Phellinus noxius.

The importance of forests pathology is a function of the economic and aesthetic value of trees and forest products. Disease losses occur virtually in every forest stand in every region of the world. Diseases cause greater growth loss than fire, insects, animals, or weather. Health and vigor of seedlings and their further growth are to a considerable extent dependent on the quality of seeds since seedlings grown from the seeds are the primary source of pathogens. In the past, damping-off fungi, cone rust, a number of cone and seed insects in pines, and fungal damages to acorns (oak), hazelnuts, chestnuts, walnuts and seeds of birch and elm were considered the only major problems in seed and seedling production. Many fungi have now been isolated and studied for their effects on seeds of both conifer and hardwood tree species. Diseases operate in many ways to reduce the yield and quality of timber and other values of trees. Losses begin with seed abortion and deterioration in the germinabilty of seeds and the survival of seedlings. Root pathogen, e.g. Fomes annous and Poria weirii, kill or decrease tree growth. Bark and cambial parasite, e.g. Nectria galligena and Strumella coryneoidea, can girdle and kill trees or produce lesions that lead to decay. Wood discoloring and rotting fungi, e.g. Fomes pini and decrease the merchantability of wood in conifers and hard woods. Foliage diseases, such as Elytroderma deformans needle blight in ponderosa pine and sycamore anthracnose decrease the amenity value of trees, decrease their growth and some times kill them.

Seed borne infection, causing seed quality losses of Botryodiplodia theobromae on Swietenia macrophylla; Colletotrichum gloeosporoides on Dalbergia cochinensis; Alternaria longissima on Bauhinia sp.; Pestalotiopsis sp. on Cassia bakeriana; Macrophoma sp. on Eucalyptus camaldulensis and Fusarium sp. on Shorea obtuse has been observed.

Significance of Forest Seed Pathology

Fungal diseases are serious problems in regeneration and, some times, can cause heavy mortality in nurseries and become established on seedlings. Apart from seed borne fungal pathogens, soil borne pathogens also have been found to cause seedling mortality in forest nurseries. These seedlings being tender in tissues often face difficulty in establishing themselves. Such substandard seedlings when used as planting stock further spread the disease to plantation and forest causing heavy damages.

Fungi associated with tree seeds vary in different host species, in different regions and in different years (Mittal et al., 1990). Nearly all seeds carry spores of various microscopic fungi either on the surface or within the seed. Superficial mycelium is almost always found because of the ready adhesion of spores to the uneven surface of the seeds. In Norway, spruce and Scotch pine seeds, Sirococcus strobilinus spore load can be as high as 150,000 spores and in some seed lots several hundred thousand spores/gram seed. Under favorable conditions, some spores germinate, the mycelium penetrating into the cotyledons of the seed and feed on the embryo. Several kinds of fungi can be associated with tree seeds. Depending upon their location, the seed-borne fungi can, in general, be classified in two groups: externally seed borne and internally seed-borne. An extensive study on seed borne fungi and their management has been carried out at Danish Forest Seed Centre, Denmark with a view to maintain the quality of tree seeds (Rees and Phillips, 1986).

Externally seed borne fungi are those that survive on the upper surface of the seeds. Examples are Botryosphaeria, Botrytis, Fusarium, Mucor, Phialophora, Rhizopus, and Trichothecium, etc. They are not usually host specific and may involve more than one host species. A rich microflora has been recorded in Albizia lebbeck seed samples comprising Aspergillus, Chaetomimum, Rhizopus., Penicillum which occurred in a range of 21-48 per cent (Mohanan et al., 2005).

Internally seed-borne fungi include species of Alternaria, Aspergillus, Botrytis, Botryodiplodia, Caloscypha, Cephalosporium, Fusarium, Phoma, Schizophyllum and Sirococcus. These may cause deterioration of seed quality and pre- or post-emergence mortality of seedlings. Symptoms of seed-borne diseases are usually divided into pre- and post-emergence damping-off. The former consists of reduced emergence and decay of the radicle just emerged from the seed coat; the latter is subdivided into root rot, cotyledon rot, and basal stem rot after the seedlings emerge from the soil. Reduction in seed germination, decay and loss of viability of seeds during storage, and the diseases of seedlings are among the major problems brought by fungal pathogens.

Losses Due to Seedborne Fungi in Tree Seed and Seedling Diseases

Damping Off
Pre- and post-emergence damping off caused by various fungi are the most dangerous diseases affecting conifers as well as hardwood species. Fusarium solani, is a soil inhabitant, in the seeds of Leucaena and Agathis which caused post- emergence damping-off in the nursery and in the out planted seedlings. Fusarium-contaminated seed with species like Fusarium oxysporum, Fusarium equiseti, Fusarium verticillioides, Fusarium incarnatum and Fusarium acuminatum cause high damping-off losses in Pinus ponderosa (Salerno and Lori, 2008).

Seedling Blight
Sirococcus blight caused by the seed-borne fungus Sirococcus strobilinus is an important disease of seedlings of several spruce and pine species and of Pseudotsuga. The pathogen attack very young seedlings, killing the primary needles from the base upward. Dead seedlings remain upright and small, black pycnidia usually form at the base of infected needles. Diseased seedlings usually occur randomly, characteristic of seed-borne diseases. Pinus ponderosa show seedlings chlorosis due to seed-borne Fusaria species, like F. oxysporum, F. equiseti, F. incarnatum, F. acuminatum and F. verticillioides. Rhizoctonia solani (Thanatephorus cucumeris) has been found to cause the leaf blight of Cassia fistula, Bauhinia variegata, Dalbergia sissoo and Populus deltoides in the nurseries in western Uttar Pradesh, India. The disease caused blighting and webbing of leaves forming cobweb-like structures. The disease caused premature defoliation and group infection of seedlings due to lateral spread of the disease through contact of the overlapping foliage of the adjoining seedlings (Mahrotra 1998). Leaf spot and leaf blight of Dendrocalamus strictus and due to Cercospora apii and Myrothecium roridum; root rot of Hardwickia binata (Fusarium oxysporium) and leaf blight of Terminalia catappa (Fusarium solani) are important seedling diseases. Myrothecium roridum has also been found to cause leaf spot in Bombax ceiba (Sharma et al., 1985) and Pterocarpus marsupium (Ali and Sharma, 1996). Cercospora dehraduni, a new species from India has been reported (Mishra, 2001).

Seedling Wilt
Another important disease transferred by seeds is the Tracheomycosis wilting of plants. This symptom can be elucidated as a reaction of the host to the irritation by the parasite wherein the typical blocking of trachae by thalli, and a yellowish brown, rubber-like substance filling the adjacent parenchymatous cells, are produced. Reduced seedling height and leaf symptoms (chlorotic and necrotic lesions and malformed leaves) are also sometimes observed in seedlings raised from the fungus-inoculated seeds of Acer saccharum (Picea glauca and Pinus strobes). A new seedling wilt disease of Dalbergia sissoo in India has been identified as Fusarium oxysporum (Harsh et al., 1992). A seedling disease causing collar rot in Azadirachta indica due to Fusarium semitectum has been reported causing 3 to 66 per cent seedlings mortality in 2 to 3 months old seedlings (Uniyal, 1999). Fusarium solani has been found to cause root rot and seedling blight of Azadirachta indica, Eucalyptus camaldulensis and Paraserianthus falcataria ( Sankaran et al.,1986). Acacia koa seedling wilt due to Fusarium oxysporum f. sp. koae has been reported in Gardner (1980).

Germination Reduction
The extremely common and numerous mold fungi, are the species of Mucor, Rhizopus, Trichothecium, Botrytis, Penicillium and others, which colonize the surface of several tree seeds and get into the surface tissues. Saprophytic fungi, such as, Aspergillus spp., Mucor spp., Rhizopus sp., Trichoderma sp., and Cladosporium sp. grow on seed coat under favorable conditions, and may invade tissues of the germinating seeds and kill the seedlings. The seed coat microflora could thus, be directly responsible for the weakening of seed vigor, predisposing it to the attack of soil-borne pathogenic fungi. Certain Fusarium spp. isolates and tested, through inoculation on Pinus patula seeds, reduce germination, and cause damping-off of seedlings but do not affect seed germination or seedling growth. Leucaena seeds infected by Colletotrichum graminicola fail to germinate, and if the infection is carried to the nursery, seedlings under moisture stress succumbed to the damping-off disease. Botryodiplodia theobromae, which causes black dry rot in mahagony (Swietania macrophylla) could cause upto to 92 per cent seed deterioration. The causal agent of pitch canker disease of pines, Fusarium subglutinans f.sp. pini has been a new introduction to California (Storer et al., 1998). The pathogen is seed-borne in Monterey pine (Pinus radiata). Seeds from infected branches show up to 83 per cent of infection. Seedling emergence is significantly reduced in infested pine seeds compared with 67 per cent for uninfested seeds. The fungus is more frequent on seedlings originating from diseased branches than from symptomless branches. However, seeds from symptom less branches produced asymptomatic but infected seedlings in Monterey pine.

Decay and Loss of Viability During Storage
Storability of seeds is dependent upon temperature, time, relative humidity and method of storage as well as the moisture content of, and initial fungal inoculums on, seeds to be stored. Improper storage of cones cause heating of cones as a result of biological activity and these cones suffer more damage by fungi. The storage containers also affect the seed mycoflora. Storage of achenes of Platanus occidentalis at low temperature (2°C) show no loss in germinability even after 7 months. While at 20°C and 30°C germinability decreases and most fungi on achenes increase with the increase in temperature, relative humidity and time of storage.

The seeds in Pseudotsuga menziesii cones are safely stored for 225 days under operational conditions and are often free of diseases but when stored after extraction, 56 per cent of them became diseased. Therefore, subfreezing temperatures has been suggested for storing tree seeds at to maintain their germinability of the extracted seeds of Pseudotsuga menziesii, immediately after their removal from the cone to inhibit further fungal activity within the seed.

Seed Health Testing for Forest Seed

Most of the forest pathology is found to be confined to seed-borne fungi only. Seed-borne fungi testing include isolation and study of fungi during processing, storage, germination and seedling growth. The seed-health testing methods include direct observation, washing test and incubation methods (blotter and agar plate) for seeds, and seedling symptom test and growing-on test for seedlings (International Seed Testing Association, 1993).

Some special methods like dilution plate method, ultrasound technique, isozyme patterns, seed tissue excision, seed sectioning, radiography, and ELISA technique have also been discussed. The ISTA recommendations for germination testing, which are more clearly available for agricultural crop seeds, are usually followed as standard practices. Seed size and, sometimes, unavailability of tree seeds in large quantities makes it difficult to use large numbers of seeds in testing. Therefore, it is important to find out (standardize) how many seeds of a tree species should be tested and in how many replicates. For many years, it has been difficult to secure accurate, maximum germination of all viable seeds or achieve the true planting value of forest tree seeds. For example, the dormant nature of the seeds of Abies balsamea, A. fraseri, and other Abies species, which require a moist pre chill treatment of 21 to 28 days or more at 3 to 5°C, together with fungal contamination and growth during the 2-month overall test duration, have been responsible for sometimes erroneous, erratic, or negative germination results. Another problem generally encountered in seed testing involves seed pretreatment. Some scientist use 0.5 per cent sodium hypochlorite solution for 2 to 3 minutes for surface sterilization of diseased red pine seedlings. For testing pathogencity through artificial inoculation of seeds with some seed-borne fungi, different methods for seed inoculations are employed. Several workers have attempted rolling of seeds on fresh fungal cultures, whereas others used spore suspensions. At several platforms, a controversy existed over the method of inoculation and the testing environment, which need to be standardized for different types of seeds. The reduction of germination under conditions of artificial infection does not correspond exactly to the reduction of germination that occurs under conditions of natural infection. Under natural conditions, the various microorganisms on seeds interact within themselves and with the microorganisms present in the soil or growing media. Such an interaction is often even antagonistic, which affects the ability of individual microorganisms to develop rapidly and to infect seeds. Often, in artificial inoculation studies, the conditions for facilitating microbial growth are provided. This suggests a need for testing the pathogenicity of various fungi in natural soils or growing media under greenhouse or field conditions.

Molecular Techniques for Seed Health Testing
A number of molecular techniques have been developed or are underway for detection of seed borne pathogen in agricultural crops. Nevertheless, there is need to standardize the molecular and serological techniques, which are more sensitive and quicker for detection of seed borne pathogens in forest seed crops. These techniques may support to screening the material for diseases of significance even in vegetative propagating planting material for sanitary and phytosanitary reasons. Molecular-based identification and phylogeny of Armillaria species has been carried out by Keca et al. (2006).

Management of Seedborne Infection in Trees

Seed Collection, Processing and Storage
Collection of seeds from healthy, disease-free areas or orchards; collection from healthy trees, healthy cones or acorns at the appropriate time; collection from tree and not from ground or from squirrel caches, etc.; transport of cones or seeds in well aerated, clean, dry containers or bags; avoiding damage to seeds during extraction and processing; and use of optimum seed extraction and storage conditions, all need be studied for different forest tree species and considered important for prevention of fungal infections on seeds.

Surface Treatment
Although adverse effects on seed germination have sometimes been reported, seed treatment with sterilants to reduce or eliminate fungal contamination has been considered necessary for production of healthy seedlings at several nurseries. For sterilizing conifer seeds with minimal stimulation or retardation to them, an immersion of the seeds in a commercial detergent followed by treatment with 30 per cent hydrogen peroxide has been recommended. Hydrogen peroxide treatment (30 per cent for 45 minutes) improved the total germination in tree seed. In Tectona grandis, surface sterilization helps to control most spermoplane microflora. Sulphuric acid seed treatment reduces seed mycoflora and increases the per cent germination of the seed. Emerging seedlings in such treatments are healthy and are free from storage fungi (Mohanan et al., 2005). In general, hot water and acid treatment enhance seed germination and reduce the number of spermoplane mycoflora and their intensity in tree seeds.

Chemical Management
Coating seeds with a repellent against birds and small rodents and a fungicide against damping-off has been a common practice in forest tree nurseries at several places. Although a lot of literature on chemical seed treatment and control of seed-fungi has accumulated, most studies confine to conifers. The sulphuric acid treatment to Araucaria excelsa seeds, which has been prescribed by quarantine regulations against Cryptospora longispora, was found effective in eradicating the seed-borne fungi but the acid was detrimental to seed germination. PCNB dust (70 to 75 per cent) applied to the seed of Balsam, Fraser, and Grand firs gives excellent control of Rhizoctonia solani without any injury to the germinating seedlings. In different tree species (Cedrus deodara, Eucalyptus citriodora, E. hybrid, Pinus roxburghii, P. wallichiana, and Shorea robusta), seed treatment with Brassicol, Bavistin SD and Dithane M-45 as seed dressers could be used to effectively for the control of the most common seed-borne fungi. Effective control of Aspergillus niger on the seeds of Shorea robusta has been found with Bavistin SD or Brassicol seed treatment. The combined use of Benlate (0.15 per cent) and Dithane M 45 (0.15 per cent) has been found to effectively control for several fungi such as, Botryodiplodia theobromae, Colletotrichum gloeosporoides, Fusarium spp., Macrophomina phaseolina, Pestalotia sp., Phoma sp. and Phomopsis sp., on the seeds of Acacia auriculiformis, Albizzia spp., Gmellia arborea, Leucaena leucocephala and several Pinus spp.

Since detrimental effects of chemical seed treatment on seed germination and seedling quality have also been reported, it is desirable that lower concentrations, which should not be phytotoxic, be tried. Captan at concentrations up to 2,500 ppm did not affect seed germination of Pinus resinosa; however, concentrations of 500 ppm or higher injured roots, stems and cotyledons in young seedlings. Root injury consisted of collapse of root hair cells epidermal cells, and cortical cells; and the cotyledon injury included the collapse of epidermal and mesophyll cells. Ziram and Bavistin have been found effective for management of collar rot in Azadirachta indica ((Uniyal, 1999). Collar rot of Bauhinia purpurea caused by Rhizoctonia solani was recorded for the first time in India. The fungus also attacked cotyedons and caused rotting to varying extent. The disease was effectively controlled by seed treatment with Thiride @ 6g/kg and soil drenching with Dithane M-45 (0.3 per cent) @ 20 ml per tube in root trainers prior to sowing of seeds. The seedling wilt of Dalbergia sissoo, which is severe during summer, and high temperature and moisture favour the disease development is effectively reduced with soil drench with 0.2 per cent Bavistin or seed dressing with 0.2 per cent Topsin-M (Harsh et al., 1992). To safeguard the seeds against spermoplane microflora and also to check the seedling diseases in nursery, Chacko and Mohanan (2002), suggested the use of thiride or captan 2g/kg seeds for D. sissoides seed treatment. The use of Dithane M-45, Bavistin and Captan, a general seed dressing recommendation, for management of seed mycoflora and to improve seed germination and emergence of healthy seedlings in Populus deltoids has been made by Day and Debata (2000).

Legislation

Vigorous implementation of the seed laws, such as the Seed Acts and Seed Certification Programmes for quality evaluation and management for forest seed need to be standardized. Moreover, seed collection, seed sampling, extraction, storage and movement need to be standardized keeping in mind the phytosanitary issues.

Conclusion

There is an increasing awareness worldwide that unless we intensify efforts at gene conservation, reforestation and intensive forest management, serious depletion of the world’s forests will result. Although reforestation is recognized as an essential activity, an adequate supply of seeds of high quality and high genetic potential is often a limiting factor in many countries. This emphasizes the need for organized seed production and seed research to resolve many problems related to reforestation. Several fungi have been studied on tree seeds; they vary in different host species, in different regions and in different years. Even the detrimental effects to seeds during germination and storage, and to seedlings in nurseries, vary in different host species and environments. With the favorable environment in the tropics, viz. high atmospheric temperatures coupled with high humidity, damage to seeds and seedlings is greater. Biotic factors like squirrel and seedbug damages, and abiotic factors like time and method of collection, shipment, extraction, processing, testing, and storage of seeds, all affect the occurrence of fungi in seeds. Improvement in these practices, use of surface sterilants and/or fungicides and following legislated practices like quarantine will help in the worldwide management of seeds.

References

Viewpoint: Implementation of Forest Tree Seed Certification and Legislation in India- What Are We Waiting For?

Introduction

Forest Tree Seed Certification in India – a Brief History

The subject of seed certification in Indian forestry has a long history and has been reviewed earlier (Thapliyal, 2007). Champion (1930) and Dent (1948) were pioneers in emphasizing the importance of ‘seed origin’ and quality of parent trees in plantation forestry in India. Taking a clue from them, an all India symposium at the Forest Research Institute, Dehradun in 1958 recommended for creation of a seed testing and certification agency at the institute. Later, British forest geneticist, Dr. J.D. Mathews developed a tree improvement programme for a few select Indian species which involved development of seed certification procedures, notably for teak, a register of tree and seed sources, seed production areas, etc. was recommended to be maintained. It was proposed that all teak seed used in India be collected from seed production areas SPAs and passed through the seed certification procedure (Kedarnath and Mathews, 1962).

The subject of forest tree seed certification was revived after a 15 year hiatus in 1976 when the Indo-Danish Project on Seed Procurement and Tree Improvement (IDPSPTI) was taken up. The project took a scheme for the control of forest reproductive material moving in international trade proposed for universal adoption by the ‘Organization of Economic Cooperation and Development (OECD, 1974). The project brought out a publication titled ‘A seed zoning system in India’ (Gopal and Pattanath, 1981) and organized working group meetings with the state forest departments with action plans for execution at state and national level. Provenance trials at national level were taken up for some selected species and lists of selected sources of some priority indigenous species were compiled. Information regarding plus trees, seed stands and seed orchards were also compiled and maintained in standard forms. The project came to an end in 1986.

In 1988, the National Wasteland Development Board, Ministry of Environment and Forests, Government of India prepared a scheme entitled ‘Central Sector Scheme for Production, Certification, Storage and Distribution of Forest Seeds’, under which funds were provided to interested states for the establishment of ‘seed collection cells’.

Tree improvement activities were taken up once again in 1993 under the World Bank aided ‘Forestry Research, Education and Extension Project’ (FREEP, 1993-2000). This project, however, was named as the ‘Planting Stock Improvement Project’. Main activities included creation of seed production areas, selection of plus trees, etc. but the major emphasis was on the creation of vegetative multiplication gardens from plus trees. It was in this project that for the first time rouging of undesirable trees was taken up on a large scale in the selected stands for conversion into SPAs.

Similar developments can be traced in respect of forest tree seed technology. The importance of seed technology in plantation programmes in India was discussed in the Sixth Silvicultural Conference at FRI, Dehradun in 1945 and later by Dent (1948). In the All- India Symposium organized by the Forest Research Institute at Dehradun in 1958 resolution regarding the establishment of a seed testing laboratory at FRI was passed and subsequently first seed testing laboratory in forestry was established at FRI, Dehradun in the year 1962. This laboratory brought out a set of recommendations for the testing of tree seeds of more than 100 species from the Indian sub-continent (Thapliyal et al., 2003).

Following inputs provided by a paper ‘Organization of Seed Testing Laboratories’ (Thapliyal and Rawat, 1986) presented at the ‘National Seminar on Forest Tree Seed, Hyderabad, 28-30 January 1986 (1986) led to the drafting of a ‘Central Sector Scheme for Production, Certification, Storage and Distribution of Forest Seeds’, as mentioned above. It was through this scheme that funds were made available for setting up seed testing laboratories, apart from seed collection cells, in the state forest departments. Seed testing laboratories were also established at agricultural universities and some institutes through the Research Grant Fund of the Forestry Research, Education and Extension Project of ICFRE (Thapliyal, 1997). A number of training programmes in tree seed technology beginning 1990 were run for the state forest department officials in order to create technical manpower to take up seed collection, processing and routine seed testing in these laboratories.

Thus over the years, since the visit of J.D. Mathews, the task of marking of plus trees, establishment of seed production areas and seed orchards has been going on unabated (Emmanuel et al., 1992; Gurumurthi, 1992). Two reports emanating from the Indian Council for Forestry Research and Education, (ICFRE), Dehradun listed plus trees, seed production areas, clonal and seedling seed orchards and provenance trials of a number of species undertaken by a chain of ICFRE institutes in various parts and states of the country (Sharma et al., 2002; Katwal et al., 2003). This is in addition to the selection work done by the state forest departments. Seed testing laboratories and seed collection cells in the ICFRE institutes and in some of the state forest departments have also been duly established.

Present Status of Tree Seed Certification

According to Barner (1975), a comprehensive forest tree seed certification scheme should encompass the following elements:

Planning
1. Preparation of maps showing distribution of important species.
2. Delimitation of the regions of provenances of these species.
3. Delimitation of major regions of afforestation and reforestation.
4. Estimation of demand and supply of seed and plants.

The Indo-Danish Project on Seed Procurement and Tree Improvement proposed the concept of ‘Seed Zones’ in place of the ’Regions of Provenances’. The data with regard to points 3 and 4 is expected to be available with the state forest departments.

Implementation
1. Organization and management.
2. Classification and approval of sources.
3. Recommendation for choice of provenances and transfer of reproductive material.
4. Production and control procedures.
5. Data recording and documentation.
6. Marketing of reproductive material.

Organization and Management
The following responsible authorities may be appointed for the implementation of a seed certification scheme

a. Designated authority
This may be called as certification agency or management committee at central and states level, appointed and be responsible to the government.

b. Advisory committee
Constituted by equal representation of foresters, industry, research and seed traders.

c. A working group on approval of sources
Appointed by the designated authority, the members of the group include people having practical experience in the fields of silviculture, provenance research, forest tree breeding and genetics, forest mensuration and utilization.

d. Inspectors
Should be professional foresters or personnel with special training, acting on behalf of the designated authority.

The Indo-Danish Project with representation from the Government of India and state forest departments constituted a designated authority, an advisory committee and working groups during the initial project period. On points 3, 4, 5 and 6, scant details are available except may be for teak in some states.

From the foregoing, it is apparent that some spade work for embarking on a forest tree seed certification programme in the country is in place and the existing gaps and remaining tasks can be accomplished through a seed certification agency whenever constituted.

Seed Legislation
Seed legislation has been enacted in most countries around the world to provide guideline and controls to ensure that the purchaser of seed receives a produce that is true to description and of known quality.

In agriculture, with a view to regulate the quality of seed of any kind or variety to be sold, Seed Act, 1966 was passed by the Parliament which came into force from 1969. Under the Act, the term ‘seed’ includes seeds of crops including edible oilseeds, seeds of fruits and vegetables, cotton seeds, fodder seeds, seedlings, tubers, bulbs, rhizomes, roots, cuttings of all types, grass and other vegetatively propagated material of food crops and cattle fodder. The law provides for initiating comprehensive seed certification of improved varieties and the enforcement of seed control programmes of all seeds sold through the commercial channels for sowing purposes. Under Section 3 of the Act, the central government has constituted a Central Seed Committee to advise the central and state governments on matters arising from the administration of this Act and to carry out other functions assigned to it by or under the Act. This committee is assisted by the various sub-committees at the central level and state sub-committees at the state level in the discharge of its functions. The Seed Act, 1966 was further amended in the year 1972 to provide for the establishment of a Central Seed Certification Board to advise the central government and the state governments on all matters relating to seed certification. Similar organizational set up may be required for the administration of an Act related to forest tree seeds.

The purpose of seed legislation is to provide legal support to seed certification and is not in itself a part of certification. Legislation places responsibility on the seller to ensure that the seed conforms to the statements made about it or meets certain established standards. For example, if a seed vendor claims to sell ‘certified seed’ provisions under the seed act can be invoked to ascertain whether this seed actually belongs to the said category and really comes from trees in a seed orchard, or from superior (plus) trees in natural stands with artificial pollination. The same will apply to selected seed (seed produced from a SPA) whether the SPA/seed orchard in question maintains minimum standards regarding rouging and an effective pollen dilution zone among other requirements, as laid down under the OECD Scheme

Apart from the fine details as cited above, the accurate and adequate records about a seed-lot not only enhance the value of seed service but also help seed legislation. All phases of seed operations, from field harvesting to nursery sowing, must be linked by a comprehensive system of records, which on request can be made available for inspection. The most important information about a seed lot which every user would expect to receive with the seed includes the seed lot identity number (Thapliyal, 1994), information on seed origin, year of ripening and an estimate of the quality of seed (viable seed per kg or germinative capacity). Pertaining to germination and purity, there are two main types of seed legislations used, described as ‘minimum standards’ and ‘analytical labeling’. Under the ‘minimum standards’ legislation used in most countries the government sets arbitrary standards for germination and purity, and seed falling below these standards is prohibited from sale. In effect the purchaser is protected from against receiving very poor quality seed. The ‘analytical labeling’ provides specific information on seed quality and the same is printed on seed parcels. This legislation has been enacted in all states of Australia and applies to seed sold in the state for the purpose of sowing (Blackstock, 1987).

Under the Seed Act, seed testing must be carried out in laboratories duly notified under the Act for labeling requirements. These laboratories should be adequately equipped and staffed with trained personnel to carry out accurate and reliable tests. The seed should also be collected by collectors registered by the seed certification agency and extracted, cleaned and packaged in a registered seed extraction plant and stored in a registered seed storage facility for the satisfaction of the seed purchaser and also for meeting the legal requirements.

Seed legislation will go a long way in promoting the use of high quality seed in forestry plantations in India but unless the requirements of a comprehensive tree seed certification programme are addressed adequately, the legislation in forestry seed will not serve the desired objectives

References

Barner, H. 1975. The storage of tree seeds. In: FAO/DANIDA Training Course on Forest Seed Collection and Handling, Chiang Mai, 17 February - 13 March 1975. Report. Rome, FAO.

Blackstock, J. 1987. Legal aspects of the use of native plant seed. In: Langkamp, P.J. Ed. Germination of Australian native plant seed. Melbourne, Inkata Press.

Champion, H.G. 1930. Second interim report on the progress of investigation into the origin of twisted fiber in Pinus longifolia Roxb. Indian Forester, 56 (12): 511-520.

Dent, T.V. 1948. Seed storage with particular reference to the storage of seed of Indian forest plants. Indian Forest Records (New Series) Silviculture, 7: 1-134.

Emmanuel, C.J.S.K.; Kapoor, M.L. and Sharma, V.K. 1992. Three decades of forest genetics and tree improvement. Indian Forester, 118: 489-500.

Gopal, M. and Pattanath, P.G. 1981. Certification of forest reproductive material in India, Revised Scheme, 1979 - Seed Zoning System Followed in India. Hyderabad, Indo-Danish Project on Seed Procurement and Tree Improvement. 25p.

Gurumurthi, K. 1992. Baseline studies and basic approaches to tree improvement networking. In: National Network Inception Workshop on Improved Productivity of Man-Made Forests Through Application of Technological Advances in Tree Breeding and Propagation. Coimbatore, 24-25 September 1992. Proceedings. The author.

Katwal, R.P.S.; Srivastava, R.K.; Sudhir Kumar and Jeeva, V. 2003. State of forest genetic resources conservation and management in India (Working Paper FGR/65E). In: Food and Agriculture Organisation of the United Nations. Forest genetic resources working papers. Rome, FAO.Kedharnath, S. and Matthews, J.D. 1962. Improvement of teak by selection and breeding. Indian Forester, 88: 277-284.

Matthews, J.D. 1961. A programme of forest genetics and forest tree breeding. (FAO/ETAF Report No. 1349). Rome, FAO.

National Seminar on Forest Tree Seed, Hyderabad, 28-30 January 1986. 1986. Proceedings, edited by S.N. Rai. The author. 242 p.

Organization for Economic Cooperation and Development. 1974. OECD scheme for the control of forest reproductive material moving in international trade. Paris, OECD. Directorate for Agriculture and Food.

Rudolf, P.O.; Dorman, K.W. and Hitt, R.G. 1974. Production of genetically improved seed. In: Schopmeyer, C.S. Ed. Seeds of woody plants in the United Sates, Washington, DC, U.S. Department of Agriculture. pp. 53-74.

Sharma, M.K.; Singhal, R.M.; Sudhir Kumar and Jeeva, V. 2002. Regional update for India forest genetics resources. In: Twelfth Session of the FAO Panel of Experts on Forest Gene Resources, Rome, 21-23 November 2001. Working papers. Rome, FAO.

Thapliyal, R.C. 1994. Identification of forest reproductive material for certification. In: Joshi, N.K. Ed., New trends. Indian forestry. Dehradun, ICFRE. pp. 89-101.

Thapliyal, R.C. 2007. Forest tree seed testing and certification in India. In: Seminar on Concepts in Forestry Research, Srinagar, 1-3 November 2006. Concepts in forestry research: Proceedings, edited by N.P. Todaria, B.P. Chamola and D.S. Chauhan Dehradun, International Book Distributors.

Thapliyal, R.C. and Rawat, M.S. 1986. Organization of seed testing laboratories. In: National Seminar on Forest Tree Seed, Hyderabad, 28-30 January 1986. Proceedings, edited by S.N. Rai. The author. pp.205-216.

Thapliyal, R.C.; Thapliyal, M.; Rawat, M.S.; Nawa Bahar; Naithani, K.C. and Bist, J.P.S. 2003. A handbook for testing of Indian tree seeds. Dehradun, F.R.I. 40p.

QUALITY SEED PRODUCTION THROUGH HIGH DENSITY SEED ORCHARDS

Introduction

Seed orchard is an area where seeds are mass-produced to obtain the greatest genetic gain as quickly and inexpensively as possible. Seed orchards are the plantations of selected clones or progenies, which are isolated and managed to produce frequent, abundant and easily harvested crops of seeds. Most clonal seed orchards have been established based on some assumptions including (a) all the clones and ramets in the orchard would flower during the same period, (b) have the same cycle of periodic heavy flower production, (c) be completely inter-fertile with all its neighbors and yield identical numbers of viable seed per tree, (d) have the same levels of self-incompatibility and (e) have a similar rate of growth and crown shape as all the other trees. It is almost certain that these assumptions are not virtually satisfied fully. The assumptions of synchronization of flowering and random mating should definitely come true for a seed orchard to be successful.

There are two types of seed orchards namely clonal or vegetative seed orchard and seedling seed orchard. Clonal seed orchards are those established through the use of vegetative propagules such as grafts, cuttings, tissue culture plantlets, etc. These orchards are the most common type used operationally. The seedling seed orchards on the other hand, are established by planting seedlings followed by rouging the poorest trees, generally leaving only the superior most trees of the best families for seed production.

There is no rule of thumb as to the number of clones or families that should be raised in the seed orchard. It has been an accepted fact that about 20 genotypes are sufficient to generate a progeny base broad enough to ensure adaptation of orchard strain to normal planting sites, and to avoid serious inbreeding among the genotype within the orchards. This is premised on the condition that the genotypes as much as possible will all flower in equal abundance at the same time, and the localizing of ramets or progenies in the orchard is minimized to avoid inbreeding. For practical reason, it is advantageous to establish more than 20 genotypes to allow for the loss or rejection of stock-scion incompatibility. Strategically, it is wise to include higher number of genotypes in the first generation orchard if progeny test can be conducted to evaluate the genotypes of a younger age.

Seed orchards are commonly categorized by generation i.e. first, second or more advance generation depending upon how many cycles of improvement a seed orchard has undergone. When seedling seed orchards are the main production populations in a breeding programme, careful planning needs to be done so that advantage can be taken of the fast generation turn over. A basic requirement will be having sufficiently large number of families in the first generation seed orchard to allow for selection and culling in subsequent generations without danger of inbreeding. It must ensure that a large diversity is maintained in each generation by having a representation of at least two thirds of the families of the previous generation (Cameron et al., 1989).

Recurrent selection for general combining ability is the most commonly used breeding strategy when advance generation breeding is undertaken through seed orchards. A single plantation is established per generation which serves first as a progeny test then as a basis for selection and breeding for the next generation and finally as a SSO. The ultimate aim is to obtain maximum gain per unit of time. Thus it is essential that the improved material obtained through recurrent selection be brought into production orchards as soon as possible.

First Generation Orchard
The first-generation orchards are usually established from selections of natural stands or unimproved plantations, most often using individual selection methods. In these orchards, the pedigrees of the parent trees are usually not known. In the first generation orchards the inferior trees after progeny testing are removed by rouging allowing inter mating only amongst the superior trees. The removal of trees for spacing or health reason is simply thinning and cannot be called genetic rouging, because the first generation orchard is started with parents whose genetic worth is not known. The orchards are usually established at a close spacing to allow rouging of poor genotypes, which leave a fully productive seed orchard. Often 50 per cent of the initially established clones are removed. A strategy for developing and testing suitable material for future generations to be designed very early during the first generation breeding programme itself so that broad genetic base is retained and the risk of inbreeding in the advanced generation is reduced. If wider genetic base of economically important traits, such as straightness, wood qualities and growth is to be maintained, it is vitally important to increase genetic variation within the breeding population. The breeding population from which selections are to be made need to be enriched by other material derived from controlled crossings and carefully planned breeding. Each breeding population would effectively provide a base on which successively better production orchards can be established.

1.5 Generation Orchard
It consists of taking the best general combiners from a number of orchards similar in geographic backgrounds and bringing them together into a new, improved first generation orchard. These orchards results in excellent genetic gain and produce improved seed because it is composed of the genetically tested genotypes.

Advance Generation Orchard
The techniques used in the advance generation orchards is similar to those used in first generation orchards but improved selection methods and designs are used to get greatest gain per unit time. Hence, progeny testing is an essential component of an advanced generation orchard as progenies of the best trees through selection create the base material for next generation breeding. An advanced generation orchard is established from selections made from an orchard where pedigree information and performance of the parents in the test environment is known, unlike an early stage orchard where selections from natural stands are tested. In advance generation orchards for maximum efficiency within family selections and out crossing among the final seed producers, it is necessary estimation of genetic parameters and ranking of families. As inferior individuals are removed in the selection for the next generation, there is less tree-to-tree variation for the important traits in the advancing generations and genetic advance is more dependent on family selections (Barnes, 1995). Selection within family can be reduced as the progenies tend to have greater uniformity and hence the number of individuals per family per se need not be very large. Suitable mating designs, which provide reasonable assessment of the breeding value of parents and produce sufficient genetically distinct families to be used for developing an adequate base for advanced generation orchards.

Hybridization Orchards
The occurrence of putative inter-specific hybrids has generated considerable interest in breeding for hybrid production in tree species. Inter-specific hybrids have been reported in pines, eucalypts, acacias and other species when they were introduced to related species. Such hybrids have developed into land races like ‘Mysore gum’ with distinct morphological features and adaptations. Hybrids show best vigour and plasticity when they are introduced to a different environment as new genetic entity with the adaptability of both parent species. Interspecific hybridization is a means of producing a strong heterozygote, which show increased plasticity (Martin, 1989). Crossing should however be performed between species which have an optimum genetic distance and compatibility. Crosses between too close or too distinct individuals will result in inbreeding depression or appearance of abnormal progenies. Apart from tree vigour and adaptability, there are other traits like tree form, resistance to diseases and pests and wood characteristics, which generally have high heritability and can be exploited through hybridization. One of the advantages of creating hybrids is the potential to combine interesting groups of characteristics not found in a pure species (Martin, 1989). Generally F2 hybrids are quite variable but in some species F2 are vigorous as F1. Such F2 hybrids have been used for establishing operational plantations of pines over large areas in Queensland, Australia (Nikles, 1996).

Spontaneous hybrids also occur in overlapping regions of the species in natural distribution. Heterosis depends to an extent on the genetic diversity of the populations crossed and may be expressed in ideal environments. The heterosis may also result from two or more characters complimenting each other, which is an additive gene effect. Thus, depending on the extent to which the parents differ and the direction of the crosses, certain specific crosses may result in increased hybrid vigour.

Genetic trials can be used to compare the gains of the second-generation progeny with those of the first generation as well as progenies of individual plus trees of best natural provenances. Montagu et al. (1998) reported 13-21 per cent improvement in growth of second-generation progenies over that of first generation progenies in Acacia auriculiformis. There were, however, several outstanding trees from natural provenance stands whose progeny out performed the second generation progenies of selected mother trees of SSO. This observation shows that vigour increases with improvement in each generation but it is important to include new selections from natural stands as infusions. Seedling seed orchards established with a poor base of inferior local selections have the drawback that the potential gains from out crossing and intensity of selection within the orchard cannot compensate the original inclusion of poor genotypes in the orchard (Montagu et al., 1998).

In seed orchards establishment, securing full stocking should be the primary concern. Where the field grafting is adopted for establishment, it is advisable to plant two or three seedling stocks in close proximity at each place where successful ramets is desired. This is to allow for grafting failures, culling of incompatible ramets, or selection of best ramets. Orchards established by using potted grafts, balled grafts or seedlings, should adopt a closer spacing to allow for establishment losses.

Individuals selected for clonal propagation in the orchard should be sexually mature to avoid long delays and great height growth before the orchard trees flower {this is unavoidable in seedling seed orchards and orchards established with rooted cuttings from juvenile sources). Besides providing wider spacing and fertilizing in order to enhance early and abundant flowering, it is imperative for one to learn which environmental factors influence seed production. Thus, some preliminary studies on the suitability of the proposed orchard site for seed production are required.

Complete isolation of the orchards from inferior pollens of the same or hybridizing species may not be possible. For tropical pines, it is recommended the minimum isolation distance to be 200m upwind from sources of contamination. Effective pollen dispersion distances of hardwoods are not yet well documented. Therefore, the hardwood seed orchards should as much as possible is distantly separated from sources of pollen contamination. Isolation zones are also required to protect orchards from different physiographic regions and between advanced and early generation orchards. However, some species in the same genus need to be isolated from each other because they flower at different times and they will not cross. This is common in pines.

The size of orchards to be established depends upon the extent of area to be reforested each year and anticipated annual seed yield. It is quite common for initial estimates of the required orchard area to be conservative because of under estimation of future reforestation programme and/or over estimation of seed yield. However, once suitable orchard sites have been developed, it is desirable to reserve large areas in the vicinity to develop later generation orchard, seed extraction plants, nurseries, etc.

Factors Influence Seed Production

Physiological plant factors along with environmental condition influence flowering and seed production. Some trees are alternate bearers while some produce seeds every year. The phenology should be well studied for the species of interest for establishing a seed orchard. Some times brief stress may promote flowering in many plant species.

For some species the reproduction can be hastened by using grafts or cuttings, as the graft retains the physiological maturity needed for flowering. The position of the tree from where the scions are taken also influences the flowering (Schmidt, 1993). The reduction in height of tree is desirable for training of the tree for manipulation of canopy. The grafting of superior scion for tree seed orchards on dwarfing root stock would be required.

The general requirement in the orchard design is to minimize inbreeding and maximize out crossing (Schmidt, 1993). About spacing of seedlings or clones in seed orchards, it is recommended to have trees 10 m apart, and that accounts for about 100 trees per hectare (Schmidt, 1993).

High Density Seed Orchards

Due to land constraints and high population pressure, it might not be possible to have wide layouts for seed orchards and high density seed orchards (HDSO) would replace the conventional orchards. The orchard with high density of trees with intensive fertilizer and water management along with strategic canopy management through tree training will increase quality seed production per unit area substantially. The concept is not very new for horticulture crops where tree canopy is modified to increase the light interception to increase fruit yield. The branches can be trained in a way to increase flowering as well as to practice mechanized collection of fruits and seeds. The intensive management of water and nutrient can be achieved by monitoring of water and nutrient status of the orchards using automated system and their optimum maintenance through drip irrigation. If needed the photoperiodic requirement can also be optimized using artificial lights.

Pruning is generally recommended in the dormant season and it is advisable to remove branches in such a way to allow penetration of more light into the tree canopy. Higher the light interception percentage better will be the fruiting. For achieving this in fruit crop like Avocado the slender pyramidal canopy is maintained through pruning in New Zealand (Thorp et al.). The method described for Avocado was adapted / modified from that described in apple by Tustin (2000).

To have high plant density, orchard should have grafted plants of superior genotype on dwarfing root stocks. The trees should be trained from beginning i.e. at the time of planting so as to avoid crown competition and optimizing the light availability and branch density. Controlled crossing can also be achieved easily because of shorter height of the orchards. High density seed orchard offers flexibility in regulating the contribution of individual genotype in seed production. The equal contribution of pollen can be controlled through selective pruning. The desired clones may be allowed to retain larger crown than the less desired ones. Managing genetic diversity of the seed lot can, thus, be controlled through management of flowering in the orchard. Such types of hi-tech seed orchards needs to be managed by highly qualified and well trained mangers.

Requirements of HDSO
The high density seed orchard needs two major requirements, first trees producing seeds and second is the technical requirement that includes infrastructure and silvicultural management operations. Trees producing genetically superior seeds are the main component of the seed orchard and rest all revolve around it.

Ideotype tree for HDSO

Technical requirements

The utility of high-tech systems for management of orchards have been demonstrated. A spatially variable micro-sprinkler system for orchards was developed and installed for 50 trees in a nectarine orchard with individually addressable micro-sprinkler nodes for each tree. Continuous pressure monitoring allowed fault detection and accurate computation of water discharge by individual micro-sprinklers. The system can precisely control irrigation and fertilization for each and every tree of the orchard (Coates et al., 2005). Monitoring of plantation through satellite has been reported for pine plantation (Joshnston et al., 1997). With advancements in remote sensing technology now it is possible to monitor even one square meter from space.

For shaping the orchard canopy for better light interception, it is essential to have data on growth and development of canopy of species of interest. Folie et al. (2003) conducted a study to work out modeling of crown growth for tropical forest species. It was reported that trees of 60 cm bole diameter would each require 0.009 ha of growing space with a density of about 107 stems ha-1. Stand basal area converge around 31 m2 ha-1. Such a study would help in planning the layout for the planting in high density seed orchards.

Such seed orchards can be planned only with tested superior genotypes and clone as gradual thinning of inferior trees is not part of silvicultural operations for HDSO. Replacement of dead and diseased trees should be done as and when required. It is recommended to go for open pyramid training of trees so as to maximize light interception. The other systems of training may be adapted based on the site location of the HDSO and direction of the sun light.

Applications of Growth Regulators
There are number of growth regulators that are utilized in horticulture for regulating various stages of plant growth. Auxins are known to promote shoot elongation, cytokinins stimulate cell division, gibberellins promote cell division and elongation. Ethylene a gaseous plant hormone promotes fruit ripening and senescence. Inhibitors of gibberelic acid biosynthesis like phosphone D, amo-1618, cycocyl, ancymidol and paclobutrazol are used to inhibit stem elongation (Salisbury and Ross, 1992). Chemicals like ancymidol, butralin, C8—C10 fatty alcohols, chlormequat chloride are commercially used as plant growth retardants (Fishel, 2006). Gibberellic acids have been used for promotion of flowering in seed orchards. The use of growth retardant (paclobutrazol and flurprimidol) was found to prevent the phototropic curvature of new shoot growth toward increased light intensities in etiolated zinnia seedlings and in silver maple. The growth retardants paclobutrazol and flurprimidol application after pruning reduce the shoot growth and reduced the frequency of pruning operations (Sperry and Chaney, 1999). Such treatments can be utilized for shaping up the canopies in high density seed orchards. Studies on effect of growth retardants on flowering and fruiting would help in deciding the type, concentration, timing and frequency of plant growth regulators in seed orchards.

Use of Mulching
Mulching refers to covering of soil surface around plant or tree in a plantation using fabric, plastic metallic, wooden sheets or other material to control weeds and promote tree growth. The mulch prevents loss of moisture from the soil surface, increases the soil temperature (especially when black colour mulch is used), prevents weed growth. Mulches are more popular treatments in fruit than in forestry crops. Weed management through mulching have been reported in many fruit crops (Dale, 2000; Forsella et al., 2003; Starast et al., 2002; Weber, 2003). In orchards of Japanese quince (Chaenomeles japonica), synthetic mulches were found best to control weeds, improve plant growth and yield, and prevented the fruit from getting contaminated by soil (Kviklys et al., 2004). In intensively managed seed orchards, suitable mulch may improve the growth of plants, control weeds and may also promote early ripening of fruits.

Use of Molecular Markers
Molecular markers can be utilized for identification of genetically diverse clone for higher genetic gains, estimating genetic contribution and mating system operating in the seed orchard. Ample published literature is available on different kinds of molecular markers, and their applications (Karp et al., 1997; Farooq and Azam, 2002; Spooner et al., 2005; Semagn et al., 2006).

Conclusion

Seed orchards that are well-planned and managed, whose clones and families are properly evaluated produce good quality seeds, but their cost in absolute terms is high. Normally the cost involved in developing the required seed orchard is high and is imperative that they be associated with a large reforestation programme. Cost of high density seed orchard with satellite and microprocessor based hi-tech management system (Fig.1) would be still higher, however, considering scarcity of land and water resources and huge requirement of quality seeds it is justifiable to evolve our seed orchard to intensively managed high density seed orchards.

Fig. 1. Hypothetical design of high density seed orchard with microprocessor based intensive management system

References