Diversity analysis using ISSR markers for resistance to shoot pests in sorghum

Shoot flies and stem borers are key shoot pests that destabilize the yield of sorghum [Sorghum bicolor (L.) Moench] across the semi-arid tropics of Asia and Africa. Progress in building up genetic resistance through breeding programs is slow, which can be attributed to the moderate levels of resistance conferred by the resistance sources in use. Genetic diversity analysis of resistant and elite genotypes is essential in designing breeding programs for resistance to the above pests. In the present study, the genetic diversity of seven genotypes resistant to shoot fly and/or stem borers, a susceptible control genotype and two susceptible elite hybrid parental lines was analyzed using PCR amplification product differences revealed by 26 ISSR primers. Cluster analysis based on ISSR markers resulted in two major groups, (i) resistance sources, and (ii) the susceptible control and hybrid parental lines. It was interesting to note that (a) the susceptible elite hybrid parents and susceptible control were genetically similar, and (b) resistance sources were genetically diverse as a group, offering the possibility that they may have diverse resistance mechanisms. Two improved resistance sources, which are products of crosses between durra race resistance sources and agronomically elite caudatum race materials, bridged two sub-groups of resistance sources. A primer (UBC827) showed the highest PIC value (0.98), thus detecting to the highest level of polymorphism. (AC)(n)-based primers detected higher levels of polymorphism than others used in this study, and can be recommended for future use. Incorporation of multiple resistant sources in crossing, and pyramiding of genes for resistance in the subsequent generations would help in improvement of shoot fly and stem borer resistance in the elite lines. Breeding strategies to utilize these resistant lines are discussed. (C) 2011 Elsevier Ltd. All rights reserved.