ABSTRACT
Evaluation of germplasm collections have resulted in identifi cation of several sources of resistance to insect pests in different crops (Panda and Khush, 1995; H.C. Sharma and Ortiz, 2002; Smith, 2005). However, screening of thousands of germplasm accessions probably has resulted in missing many germplasm accessions with moderate levels of resistance, but with different genes for insect resistance (Clement and Quisenberry, 1999). The identifi ed sources of resistance have not been used widely because of low heritability or linkage drag. Varieties with resistance to insect pests have been identifi ed and released for cultivation in different crops (Panda and Khush, 1995). However, the levels of resistance in most of the varieties released for cultivation are low to moderate. Therefore, there is a need to increase the levels and diversify the basis of resistance through exploitation of resistance sources in cultivated germplasm and wild relatives of crops with different mechanisms of resistance. The progress in developing crop cultivars with resistance to insects has been quite slow because of lack of information on the mechanisms that contribute to insect resistance, the numbers of genes involved, and the nature of gene action (Smith, 2005). Lack of such information reduces the effi ciency of breeding for insect resistance and confounds the development of effective marker-assisted selection systems. There is a need to understand the mechanisms and inheritance of resistance to insects to identify molecular markers associated with different mechanisms of resistance. Such an information will also be useful to plan appropriate strategies for marker-assisted introgression of insect resistant genes into high yielding cultivars, understand the nature of gene action, number of genes involved, and pyramiding of resistance genes to develop cultivars with stable and durable resistance to insect pests.
