In this article we will discuss about:- 1. Elements of Tree Improvement Programme 2. Achievements in Tree Improvement 3. Peculiar Problems 4. Advantages 5. Disadvantages.
Main objectives of the tree improvement are to maximize the gain per unit time and space via selection and development of improved genotypes and to maintain large and diverse genetic base for continuing successful tree improvement programme.
Elements of Tree Improvement Programme:
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According to Wellendorf (1991), the main elements of tree improvement programme are:
i. Tree improvement strategy
ii. Forest tree population
iii. Management
iv. Research and development
i. Tree Improvement Strategy:
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The first step is the identification of species on the basis of its value which can be assessed on the basis of its use in plantation programme, market value and consumption pattern and users preference. After identification of the species possible gains and risks are assessed. Possible gains and risks will depend upon end use characters of interest, their genetic variation, their heritability’s, rotation age and type of value found in value production i.e. commercial subsistence or environmental.
The risk of tree improvement is associated with the situation where non local seed sources are used without testing or based on short term testing. Risks also increase when breeding and seed production is based on few individuals.
The tree improvement strategy depends upon availability of investment capital. The traditional area of tree improvement is industrial plantations. In developing countries like India, private companies are investing in short rotation forestry. In case of social forestry sector, investment to finance the tree improvement is not generally available. Here low cost tree improvement options can be explored.
The tree improvement options like low level improvement programme (seed collection from identified sources/seedling and clonal seed orchards) or high level improvement programme (advance generation tree improvement) will depend upon ease of breeding of the identified species, its value and availability of investment capital.
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ii. Forest Tree Population:
Forest tree populations are the basic resources of tree improvement. Their structure and handling is the core of tree improvement.
iii. Management:
Management aspects which include human and organizational base for tree improvement activities.
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iv. Research and Development:
Research and development which are necessary for solving key problems in tree improvement.
Achievements in Tree Improvement:
Tree improvement work in India was started by Prof. Champion who realized the importance of geographical variations and application of the knowledge of forest genetics during 1930. He established a provenance trial of chir pine at New Forest, Dehradun and found that spiral gains in chir pine are inherited.
Laurie during the same period established an all-India Teak provenance trial, which remained the most important one in Asia. Forest Research Institute, Dehradun opened a Forest Genetics section during 1959-60 attached to Botany Branch under the then Directorate of Biological Research at FRI.
In the year 1961 Prof. J. D. Mathews an expert from FAO suggested initially to work on some priority species viz. Tectona grandis, Bombax ceiba, Pinus spp. Dalbergia sissoo, Santalum album, Morus alba and Pterocarpus santalinus. During Vth plan period a central sector schemes were initiated in collaboration with Danish International Developmental Agency (DANIDA) as “Indo-Danish Project on Seed Procurement and Tree Improvement” under which tree improvement was carried out on Pinus roxburghii, P.wallichiana, Cedrus deodara, Dalbergia sissoo, D.latifolia, Albizia lebbek, Tectona grandis, Bombax ceiba, Gmelina arborea.
i. Provenance Trials:
Provenance trials have been carried out in number of species. A test consisting of 75 provenances Tectona grandis was established in 1971 by DANIDA on 50 sites in 16 countries. The trial was evaluated in 1983. A provenance trial consisting of 23 provenances from four states was established at Forest Research Institute, Dehradun in 1981. In 1995, trial of 30 neem provenances was established under International Neem Network where 21 countries are participating.
ii. Seed Stands and Seed Production Area (SPA):
Seed stands have almost selected in every state. Approximately 15,000 ha of seed stands have been selected [Tectona grandis (9358 ha), Pinus roxburghii (2934.2 ha), Eucalyptus spp. (99.44 ha) etc.]. The total area under SPA is 1225.6 ha [Azadirachta indica (87ha), Dalbergia sissoo (173 ha), Tectona grandis (433 ha), Eucalyptus tereticornis (42 ha) etc.].
iii. Plus Tree Selection:
Selection of plus trees through comparison method have been reported in number of species such as Pinus roxburghii, Populus ciliata, Pinus gerardiana in Himachal Pradesh; Dalbegia sissoo in Punjab, Haryana, Maharashtra; Tectona grandis in Andhra Pradesh, Karnataka, Maharashtra, Kerala, Madhya Pradesh; Casuarina equisetifolia in Andhra Pradesh, Tamil Nadu; Bombax ceiba in Maharashtra and Kerala etc.
A total of 1200 plus trees of different species have been selected. Prominent species are Tectona grandis (714), Bombax ceiba (62), Dalbergia sissoo (53), Gmelina arborea (60), Pinus roxburghii (186) etc.
iv. Seed Orchards:
Seed orchards have been raised by different institutions. About 511 ha of seedling and clonal seed orchard of 17 priority species have been raised. In Andhra Pradesh, more than 250 ha of clonal orchard of Tectona grandis have been established. Bihar has established more than 134 ha of teak seed orchard. Similarly large scale orchards of teak have been raised in Karnataka, Maharashtra and Madhya Pradesh.
Forest Department, Arunachal Pradesh has established clonal orchard of Gmelina arborea, Bombax ceiba, Terminalia myriocarpa and Chukrasia tabularis. In Himachal Pradesh, clonal seed orchards of Grewia optiva, Bauhinia variegata and Dalbergia sissoo have been raised by Department of Tree Improvement, Dr. YS Parmar University of Horticulture and Forestry. Himalayan Bioresource Institute, Shimla has established seedling seed orchards of Dalbergia sissoo.
v. Clonal Forestry:
Wimco during 1980’s introduced four clones of Populus deltoides from Australia, out of which two outstanding clones G-3 and G-48 laid the foundation of large scale poplar plantation in India. Since then large number of clones have been developed by FRI, Dehradun, State Agricultural Universities, Wimco etc. Wimco has got registered six new clones WSL-22, WSL-27, WSL-32, WSL-37, WSL A-26 and WSL A- 49 with International Poplar Commission, Italy. Punjab Agricultural University, Ludhiana has released several clones of poplar (PL series) for cultivation in Punjab. Dr Y. S. Parmar University has released many clones of Populus ciliata, P. deltoides and hybrids of P. ciliata x P. maximowiczii.
The Department of Tree Improvement, Dr YS Parmar University, has been in the forefront of improvement and breeding of Salix. The clonal archive of Salix contains more than 250 clones of 40 species covering different countries. Seven promising clones namely J- 7999, NZ-1140, 13/25, J-194, J-795, SI-63-007 and PN-731 have been recommended for cultivation. About 5000 hybrid plants have been raised through controlled breeding.
The genetic improvement for higher productivity of Eucalyptus through breeding approaches was initiated during 60’s and has been continuing with strength till now. A series of F1 hybrids, popularly known as FRI 4, FRI 5 to FRI 15, were developed at FRI by using different species combinations. Some of the hybrids have shown pronounced and sustained degree of superiority in growth parameters.
ITC, Bhadrachalam has pioneered clonal Euclyptus in India. Clones like 3, 6, 7, 10, and 27 developed at Bhadrachalam formed the basis of initial clonal plantation since 1992. Later on clones like 2045, 2070, 2155 were developed and are being planted on large scale. More than 40 million plants of fast growing Eucalyptus are being produced every year in India.
Peculiar Problems in Tree Improvement:
As mentioned by Wright (1976), although genetic principles are same for trees, men and fruit flies, the inheritance pattern, method of experimentation vary considerably among these groups. Due to long life of forest trees, the generation interval is quite large giving rise to peculiar problems in the improvement of forest trees.
He has outlined some peculiar problems related to forest genetics:
i. Indirect Evidence:
Since most of the characters are under control of genes and environment, the genetic control of these characters is identified by progeny testing i.e. growing and measuring the off springs of trees under similar conditions in replicated environment.
ii. Uncertainty and Need for Continuous Experimentation:
Generalization that taller trees will produce taller offspring does not always hold true. Offspring of taller trees may grow 1 per cent taller than the offspring of average trees; however the offspring of some trees may grow 5 per cent faster than average. Thus one can obtain 1 per cent gain by using general rule, but he must test the offspring of each parent to obtain full 5 per cent gain.
iii. Time Element:
Trees are long lived species which require several years to produce the seed. Species such as Eucalyptus take 3-4 years to produce seed whereas some pines may take 10-30 years to produce seed. However, early flowering can be induced by grafting and nutrient management in some species. Also juvenile mature correlations can help in reducing generation interval.
iv. Necessity for Seed Production:
Though most of the trees are not grown for seed yet a tree breeder must dilute some part of his work with experiments on simulation of flowering and fruiting.
v. Scarcity about Basic Information:
Field crops like wheat, maize, rice etc. have been extensively studied crops. In these crops, genes controlling different characters have been identified on particular chromosomes. Transgenic plants have been produced in number of plant species. There is lack of basic information on most of the forest tree species.
Clonal Forestry:
Vegetative propagation is one of the important tools in tree improvement. It can capture both additive and non-additive genetic variance thus maximizing gains in tree improvement programmes. It has been widely used in short rotation forestry. Poplars, Willows, Eucalyptus etc. are mass produced through vegetative means.
Besides its role in production forestry, it can be used to preserve genotypes in clonal banks, for establishing seed orchards and transferring traits which have low heritabilities. In species where vegetative propagation is feasible, best trees can be vegetatively propagated for substantial gains.
Different types of vegetative propagation methods like grafting, rooting of cuttings, air layering, tissue culture, meristem and cell culture are available. Despite its advantages, vegetative propagation is dead end to breeding. Gains through clonal forestry decline over time unless backed by continued breeding and testing.
Advantages of Tree Improvement Programme:
i. Change in genetic makeup of trees is permanent.
ii. By means of vegetative propagation, developed material can be kept for indefinite time.
iii. Greatest genetic variability is present in most tree stands, which is not changed by action of people.
iv. The wide genetic variation enables wide adaptability.
Limitation of Tree Improvement Programme:
Though there are great advantages of tree improvement programme, it has some limitations also.
i. Requirement of large area for storage and testing of desirable genetic material.
ii. Large size of trees create problems to carry out different breeding activities e.g. measurement of length, diameter, crossing and seed collection.
iii. The cost and effort of producing new seed crop is large.
iv. Different trees possess different growth curves. Therefore juvenile mature correlations are not satisfactory for growth characteristics.
v. Lack of availability of seed with known or desired genetic background.
vi. Requirement of good permanent record because tree improvement is a long term process.