Plant Tissue Culture in Forestry: An Overview

The below mentioned article provides an overview on the plant tissue culture in forestry.

Introduction:

Forest is important renewable natural resources for man, because it provides several forest products like fuel, timber, lumber, paper, fodder etc.

Forest has also other uses such as recreation, wildlife habitat, air and water sheds. From ecological viewpoint, forest regulates the level of rainfall necessary for the existence of vegetation on earth. It also helps in recycling moisture.

Forest checks flood, drought and soil erosion. But the increasing world population re­quires more food, fuel and space for habitation. Hence indiscriminate deforestation by man for his own interest i.e. for agriculture, construction and habitation purposes ultimately reduces the forest covered area on earth.

It is feared that in the coming decades, there is going to be an acute shortage of forest products and the ecological balance will be lost. So deforestation should be stopped. One method of avoiding this situation is afforestation with superior genotype and the conservation of forest by adopting some scien­tific and technical measures. The most common traditional measure is the rapid propagation and plantation of forest trees. Many forest trees are propagated vegetatively by cuttings, grafting, layering’s etc.

These methods produce the plant geneti­cally alike to the parent plants, but there are some difficulties. Only a small number of plants can be produced by this way and it takes years to build up enough stock for planting in fields or forests. Sometimes the method proves to be im­possible.

The long life cycle of trees also makes development of superior varieties a very lengthy and tedious process. Traditional methods of tree breeding and improvement, particularly in the area of genotype evolution with respect to grow­th rates, cold hardiness, disease resistance, tol­erance to draught or chemicals may take many years to produce a desired hybrid and sometimes it is not easy to raise such improved tree hybrid.

Again there are some problems to propa­gate forest trees from seeds. Even storage of seeds for longer period is not feasible to preserve the germplasm. In recent years, another technique called plant tissue culture has been developed which could be an answer to problems faced by the traditional procedures. Plant tissue culture has a great potential to improve traditional methods of tree breeding. This tech­nique may dramatically reduce the time to pro­duce new varieties.

Plant tissue culture is very useful for mass clonal propagation of forest trees. In vitro the rate of multiplication cannot be ex­pected by any of the in vivo methods of clonal propagation. Multiplication cycle is very short. In tissue culture, plant multiplication can con­tinue throughout the year irrespective of the sea­son. It is also feasible to preserve just the germplasm in a deep-freeze as mass of the cells and later grow a complete plant in tissue culture. So millions of potential forest trees could be stored in a few test tube.

Scope of Tissue Culture in Forestry:

Some aspects of plant tissue culture have already been employed in forestry such as:

1. Micro propagation

2. Apical meristem culture

3. Embryo culture

4. Protoplast and somatic hybridization

5. Isolation of haploidy

Micro propagation is employed for the pro­duction of rapid clonal propagation of selected plant species.

Micro propagation generally in­volves several steps:

(a) The mother plant is selected for yield and quality

(b) The growing tissue (e.g. vegetative buds, nodal cuttings, petioles etc.) is dissected

(c) Surface sterilization of tissue

(d) Inoculation of tissue on a defined medium

(e) Resulting shoots are multiplied by subcul­ture in fresh medium the operation being repeated many times

(f) Shoots are then rooted

(g) After development of root system plants are transferred to small pot and to the field.

By this technique a million-fold annual in­crease in the rate of artificial plant propagation over conventional methods of vegetative propa­gation is possible. This technique has now been exploited in accelerating tree improvement pro­grammes for forest trees.

Apical meristem culture is very useful for the production of virus-free plants. Generally the apical meristem is free from virus infection. Plants obtained from such meristem through tis­sue culture are usually free of viruses. This tech­nique has now been commercialized for produc­tion of virus free forest trees. One of the procedures commonly employed in plant breeding programmes for improvement of trees is by hybridization which in many cases involves wide crosses between plants belonging to different varieties or species.

However, due to several reasons, embryos abort at an early stage. The use of embryo culture can overcome post- pollination incompatibility to enable rescue of in­terspecific hybrids and allow the genetic base of tree species to be significantly broadened. There are some reports on breeding of forest tree hy­brids by embryo culture.

Protoplasts are the naked plant cells (cells without cell wall) and plantlets can be regener­ated from a protoplast. Somatic hybridization is a technique by which somatic or gametic cells of different plants are fused and plantlets raised from fused protoplasts.

Somatic hybridization also provides a mechanism to broaden the germplasm base. Protoplast fusion enables the re­ciprocal exchange of cytoplasmic organelles and possible genetic recombination between geneti­cally dissimilar mitochondria or chloroplast genomes. Though extensive studies are in pro­gress few works have been done on isolation and regeneration of protoplasts from forest trees.

Plants can also be raised from isolated mi­crospore or from anthers by tissue culture. This technique has enhanced the capacity to gener­ate large number of haploid plants. Haploids enable the achievement of rapid homozygosity, enhanced selection efficiency for recessive genes and breeding at a dialletic stage for autopolyploid species. This technique appears to have the best prospect for utilization in forest tree improvement plan in the near future.

Brief Past History:

R. J. Gautheret (1934):

First cultured cambium tissue of some tree species (Salix capraea, Populus nigra) on Knop’s solution contain­ing glucose and cysteine hydrochloride and noted that the tissues proliferated for a few months. The addition of B-vitamins and IAA enhanced considerably the growth of Salix cambium.

R. J. Gautheret (1940):

First reported the organogenesis in cambial tissue of Ulmus campestris in culture. He obtained buds in vitro from cambial tissue.

E. A. Ball (1950):

First obtained buds from callus tissue of Sequoia sempervirens (a gymnosperm) having greater life span.

E. C. Stone and J. W. Duffield (1950):

Have described a case of breeding hybrid seedling from Pinus lambertiana x P. armandi and P. lambertiana x P. koraiensis crosses by planting embryos encased in the gametophytic tissue on agar slant. As both P. armandi and P. koraien­sis are blister rust resistant, these attempts con­stitute a significant achievement towards breed­ing a disease-resistant line.

P. G. Haddock (1954):

Reported a suc­cessful rearing of excised embryos of Pinus lam­bertiana completely free of mega-gametophyte by tissue culture.

L. L. Winton (1968):

First reported the regeneration of true triploid plant from the callus tissue of Populus tremuloide.

H. E. Sommer (1975):

The first gymnos­perm plantlets were obtained by Sommer from cultured excised cotyledons and hypocotyls of Pinus palustris.

W. J. Kaiser and L. R. Teemba (1979):

Reported the virus free plant from apical meristem culture of Cassava (Manihot escu- lenta).

E. A. Shahim and J. F. Sliepard (1980):

They reported mesophyll protoplast isolation, proliferation and shoot formation from Cassave (Manihot esculenta).

P. K. Gupta, A. F. Mascarenhas, A. L. Nadgir and V. Jagannathan (1980, 1981):

Obtained the clonal propagation of Tectona grandis and Eucalyptus citriodora.

C. H. Chen (1982):

Obtained haploid plants from anther culture of rubber tree.

Conclusion:

It is well known that our underground fossil fuel is limited and un-renewable. So forest prod­ucts are the only alternative way to meet our fuel requirement. At the same time, deforestation is continuously destructing our ecological balance and causes natural calamities in every year.

So major efforts should be given to improve the field performance of tissue culture derived plantlets for rapid clonal propagation so that the cost and benefit become easily accessible for commercial purposes. On the other hand, the future of for­est tree tissue culture does not stop at merely producing clonal plants.

Continuing progress in the field of genetic engineering should soon en­able scientists to carry out breeding within the test tube. New genetic information could be in­troduced directly into cells by using protoplasts or cells of different chosen strains.