CONSERVATION OF PLANT GENETIC RESOURCES

 

C Kameswara Rao

Foundation for Biotechnology Awareness and Education, Bangalore, India

 

All life that constitutes Biodiversity depends on plants, the most crucial components of ecosystems in which all microorganisms, animals and humans, live.  Direct threats to plant survival are a combination of habitat loss, aggressive alien species, over exploitation and climate change.  The fundamental causes of these threats are rooted more in uncontrolled population growth, short sighted policies, ignorance or greed.  The consequent socio-economic factors are difficult to control. 

 

Loss of plants leads to worsening food insecurity, increasing vulnerability to disease, lower material wealth, deteriorating social relations and restricted freedom of choice and action.  Despite such deep reliance on plants, continued misuse of ecosystems has taken us to a crisis point.  

 

Conservation of species, particularly the agriculturally important ones which have an impact on human well being, has now attained paramount importance, in our efforts to provide for the sustainable utilization of biological resources, by preventing further loss. 

 

In plants and animals, the DNA is the genetic material that maintains the organismís continuity from generation to generation.  While a genome is one set of all genes of an organism, a gene pool is all the genes in a population of that species.  

 

The genetic material of many organisms is of immense value and needs to be preserved for the benefit of the future generations.  Plant genetic resources should be available for use in research and breeding in agriculture and forestry.  These are a) actual currently cultivated varieties (cultivars), b) once favoured but now discontinued old cultivars, c) locally developed and preferred varieties called landraces that are or were grown and c) wild relatives of crop species. 

 

The cells (including pollen), tissues, organs, whole single or few celled organisms, seeds or other propagules that serve as a means of regenerating the whole organism, constitute the germplasm which is preserved by various means in controlled storage facilities called biobanks or germplasm banks.  These are variously called as seedbanks, in vitro banks, gene banks and DNA banks, depending upon the material that is conserved in them.    Currently, extracted and preserved DNA cannot be used to regenerate the whole organism, but any chosen gene can be isolated for use in genetic engineering.

 

Several pressing considerations necessitate biobanking, of which the following are more significant:

 

a)     It is estimated that 60,000 to 1,00,000 plant species, with diverse economic uses,  are under threat of extinction and need to be protected.

b)     About three-quarters of crop biodiversity has been lost in the last century.  Eighty per cent of maize varieties known in the 1930s in Mexico no longer exist and in the USA 94 per cent of varieties of peas are no longer grown.

c)     During the past 50 years many high yielding and/or otherwise better varieties particularly those with higher pest and disease tolerance, have continuously replaced the once favoured cultivars and landraces. 

d)     The dropped varieties may contain genes affording advantages to future agriculture.  For example, the genes for resistance against the late blight fungus that caused the Irish potato famine in 1845 were taken from South American potato varieties, not in active cultivation.

e)     Wild relatives of crop species may contain genes useful in crop improvement. The genes for resistance against red rot of sugarcane that causes heavy losses were introduced from a wild relative (Saccharum spontaneum).

f)       The Centres of Origin of the species that gave rise to crops and the original Centres of Domestication of crop varieties are a reservoir of crop genetic resources, most of which have already been lost and the rest need to be conserved.  

g)     Economics encourage farmers to drop crops and many farms now grow just one or two crops, with very high efficiency.  But on account of genetic uniformity, these crops may become vulnerable to the changes in the habitat, and pests and diseases.  Conservation of crop genetic resources is an insurance against such risks to food security. 

h)     Farmers have long stopped conserving seed for any reason.

 

Germplasm banking is a system to conserve crop varieties and their wild relatives, protecting them from the vagaries of climate, politics and human error. 

 

APPROACHES TO SPECIES CONSERVATION

 

There are two main approaches to conservation wild or cultivated species:

 

In situ conservation: Conservation in the natural habitats, where evolutionary progression continues.  Over a period of time and several generations, the species/variety may change its genetic and morphological composition and even the desired traits may be lost, if they do not have any advantage to the species in that environment.  While whole populations of wild plant species can be conserved in bioreserves, cultivated species have to be cultivated and so are not amenable for in situ conservation. 

 

Ex situ conservation: Conservation away from the natural habitats, which requires appropriate techniques for long term preservation of the seed or other material in biobanks.   On account of removal from the natural habitat, there is cessation of evolutionary progression, but the desired genes would be preserved.  The seed and other propagules may lose their viability sooner or later, but tissue culture methods may help in the revival of the material, if preservation techniques are appropriate.  Genetic engineering techniques would help in the recovery of the desired genes and their use in developing transgenics of the same or another crop.  While small populations of wild plant species can be grown in botanic gardens, cultivated species offer problems.  Ex situ conservation requires continuous professional attention, elaborate infrastructure and heavy financial inputs.

 

Since each has some disadvantages and some special advantages, a judicious combination of both in situ and ex situ approaches is needed for successful conservation of species.

 

September 21, 2008

 

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CONSERVATION OF PLANT SPECIES IN DNA BANKS