Tamarind monograph.pdf - Crops for the Future

Chapter 7. Genetic Improvement
7.1 Introduction
H.P.M. Gunasena and D.K.N.G. Pushpakumara
Although tamarind is an ancient domesticate, little attempt has been directed
to its genetic improvement. This is understandable because tree
improvement research that combines developmental and operational phases
is time consuming and the large scale cultivation of tamarind is still in its
early stages. Indigenous farmers have however selected planting materials
from natural populations based on desirable and observable characteristics
but such phenotypic selection means the growing stocks are virtually wild.
Tamarind was recorded over a century ago as a variable species especially
for pulp colour and sweetness (von Mueller, 1881). Since there is such
extensive variation in characters such as foliage, flower and pod production
and timber quality (Table 7.1), there is a considerable scope to improve the
species. Improvement holds the key for boosting productivity and yield of
the orchards and involves development of genotypes possessing desirable
characters like fast growth, good tree form, high yield and resistance or
tolerance to major pests, diseases and drought (Radhamani et al., 1998).
Since the variation in pod length and pod width was found to be genotypic
(Shivanandam and Raju, 1988; Hanamashetti, 1996). Similarly for other
trials the potential for improvement depends on sampling the genetic
variability available within and between populations. Hence, knowledge of
genetic variation and structure of a species and genetic parameters of
important traits are essential to develop effective improvement and
conservation strategies.
7.2 Understanding the variations
The apparent high observable variability within and between populations
(Table 7.1) indicates that speedy benefits may be obtained by selecting
superior trees within provenances and propagating such stocks as clones. A
considerable variation in growth characters such as shoot length, root length,
germination percentage, plant height and pinnae per plant has also been
observed in different populations (Challapilli et al., 1995; Bennet et al.,
1997; Divakara, 2002; Shanthi, 2003). Recent studies on isozyme analysis
of ten tamarind populations from Coimbatore, India identified 12 loci with
25 alleles (Shanthi, 2003). All populations had more than 50% polymorphic
loci (range from 50-75%). The mean number of alleles per locus was 1.85
(range from 1.6-2.0). Mean heterozygosity observed among 10 populations
ranged from 0.085-0.154 whilst mean heterozygosity expected according to
the Hardy-Weinberg equilibrium ranged from 0.163-0.258.
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