Interestingly, the genotypes in the two groups (resistant and susceptible) were represented by three different categories. A set of six genotypes, three belonging to each of the resistant [N-3, MZD-3, and AH 918 (F)] and susceptible [CM 213, MZP-1C and AH 421 (F)] groups were chosen for analyzing genetic relationship. Particulars of these genotypes are as follows: N-3-NEH race from Nagaland; MZD-3-Interspecifc derivative from Z. maize X Z. diploperennis; AH 918 (F)-Female parent of an experimental hybrid; CM 213 -Female parent of a released single cross hybrid; MZP-1C -Derivative of inter-specific cross Z. maize X Z. parviglumis; AH 421(F) -Female parent of an experimental hybrid. Data on morphological characteristics as well as those generated by polymorphism survey using SSR (Simple Sequence Repeats) were used to analyze genetic relationships. Of the 36 SSR markers used, 17 were found to be effective in detecting polymorphism. The similarity matrix was analyzed by NTSYS-PC Version 2.02 (Rohlf, 1992, Exeter Pub. New York) by employing UPGMA with average linkage (Sneath and Sokal, 1973, Numerical Taxonomy, W.H. Freeman & Co., San Francisco).
The clustering pattern obtained individually with a morphological or molecular marker was compared with that obtained by using both in combination. Interestingly, grouping of genotypes followed a common pattern and reflected the response of genotypes to BSDM also (Fig. 1). Thus, a relatively small number of SSR markers (17) in combination with morphological markers enabled meaningful grouping. Improvement in clustering may be expected by analyzing a greater number of polymorphic SSR markers, as there is limited scope for further increasing the number of easily discernible morphological characters.
The present study highlighted the diversity in the material chosen with respect to BSDM disease. For a better understanding of the mechanism of disease response and for increasing the precision in incorporating disease resistance, molecular markers like SSRs may be effective tools. In this endeavor, considering information regarding the level of heterozygosity and polymorphism, AH 918 (F) and CM 213 are potential lines for further studies.
1. Dendrogram depicting genetic relationships among selected maize
lines based on SSR + morphological data.
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