Genetic diversity analysis and RAPD marker

low genetic divergence of varieties can be appreciated in the background of tree

gene flow that might have occurred in the course of mulberry varietal selection

and breeding. Almost all the varieties under different species intercross with each

other to produce fertile hybrids obscuring the species delimitation at varietal level.

In fact, most of the mulberry varieties are the selection from open-pollination

hybrids. This view has been confirmed by Sharma et al., (2000) while assessing the

genetic diversity in mulberry germplasm using florescence-based AFLP markers

showed high similarity among cultivated mulberry varieties of diverse geographic

origin. The study also confirmed that the mulberry improvement has taken place

utilizing a narrow genetic base.

The varied genetic distance values in comparison with parents and progenies to

progenies are explained in terms of recombinations and independent assortment

of those RAPD markers. The genetic distance values between Mysore Local and

progeny 41(P ₄₁ ) was higher than that of parental combination (0.200). Comparison

of V-1 with progenies revealed a lower genetic distance than its parental

combination. Among progenies P ₄ and P ₃₈ exhibited highest genetic divergence

(GD) of 0.278. Few of the progenies were having similar genetic make-up (GD -

0) based on the limited number of RAPD markers under consideration.

Heterozygosity among cultivated mulberry varieties due to out-breeding behavior

has been well recorded as in the case of most of the tree species (Tikadar et al.,

1999). Evolution of homozygous lines through selfing has not been successful

party due to dioecious nature of mulberry varieties. Even in case of monoecious

varieties, the selfed lines could not be maintained beyond S ₂ or S ₃ generations

probably because of the expression of deleterious genes and intrinsic requirement

of heterozygosity for mulberry growth and development. To attain reproductive

maturity mulberry plant takes quite some time (anywhere between 2 to 3 years) and

hence breeding is somewhat time consuming and laborious. Based on these facts

and assumptions, molecular markers are thought as an alternative for generation of

genetic information in mulberry and can be used as a tool to study its inheritance

pattern.

RFLP and SSR markers are co-dominant and are only advantageous where F ₂

generation can be easily obtained. As discussed, generation of F ₂ population in

mulberry is quite demanding or even impossible. RAPDs are known to be dominant

markers, which can seriously restrict its use in segregation analysis. However,

parental mulberry varieties have been originated from open crosses for a long

time and hence it shows immediate segregation when crossed. This is an evidence

for very high level of heterozygosity in parents. Perhaps lack of co-dominance

with RAPD markers might not represent such a disadvantage for crosses involving

heterozygotes. Carlson et al., (1991) showed the appropriateness of this technique

in the study of segregation of RAPD markers in F ₁ progeny of conifers. He also

Int. J. Bioinformatics and Biological Sci.: v.2 n.1&2, p. 23-39. March & June 2014

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