Contents - Faperta

6
Physico-Chemical and Molecular Markers
for Resistance to Insect Pests
Introduction
Because of environmental and human health problems associated with excessive use of
pesticides, there has been an increased emphasis on alternative methods of controlling
insect pests, including host plant resistance to insects, which can play a pivotal role in
integrated pest management. Sources of resistance to insects have been identifi ed long
ago, but these have not been used effectively in crop improvement, because the levels of
resistance are either too low or it is not possible to screen the test material under uniform
and optimum insect infestation levels to identify lines combining desirable agronomic
traits and resistance to insect pests (Sharma and Ortiz, 2002; Sharma et al., 2005). Thus,
there is a need for improving the accuracy and precision of phenotyping for insect resistance.
Once the phenotyping systems are developed, molecular markers can be used to
accelerate the pace of development of insect-resistant cultivars, dissecting the genetic basis
of resistance, identifying the location of underlying genes, and understanding the nature
of gene action (Sharma et al., 2002).
Screening of germplasm collections has resulted in identifi cation of accessions with
moderate to high levels of resistance against several insect species in different crops (Smith,
1989, 2005; Panda and Khush, 1995; Sharma and Ortiz, 2002; Sharma et al., 2005). However,
large-scale screening of thousands of germplasm accessions for insect resistance probably
has resulted in missing many germplasm accessions with diverse genes for insect resistance
(Clement and Quisenberry, 1999). Many of the identifi ed sources of resistance have
not been used widely because the levels of resistance are either low or it has not been possible
to transfer the genes for insect resistance into high-yielding cultivars because of linkage
drag. To overcome these problems, marker-assisted selection can be used as a powerful
tool in terms of pyramiding resistance genes, and identifying segregants not carrying
undesirable traits (provided there are no pleiotropic effects of the insect resistance genes).