Contents - Faperta

154 Biotechnological Approaches for Pest Management and Ecological Sustainability
Varieties with resistance to insect pests have been identifi ed and released for cultivation in
different crops (Panda and Khush, 1995; Sharma and Ortiz, 2002). However, the levels of
resistance in some 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 to insect pests
through exploitation of resistance sources in the cultivated germplasm, wild relatives of
crops, and genetic engineering of novel genes from unrelated species to make host plant
resistance an effective weapon for pest management.
The last decade has seen rapid progress in molecular biology, with whole genome
sequencing of model organisms such as humans, Saccharomyces, Arabidopsis, and Oryza
(Chalfi e, 1998; Sherman, 1998; Palevitz, 2000; Shoemaker et al., 2001; Piskur and Langkjaer,
2004). Systematic whole genome sequencing will provide critical information on gene and
genome organization and function, which will revolutionize our understanding of crop
production and ability to manipulate traits contributing to crop productivity (Pereira,
2000; Crouch et al., 2005). The advances in genome sequencing in major crops will have
substantial spillover effects on lesser-studied crops. Recombinant DNA technologies will
allow identifi cation of specifi c chromosomal regions carrying the genes associated with
resistance to the target insect pest (Karp et al., 1997). There are many types of DNA markers,
and each of these have a different set of advantages for any particular application in
linkage mapping and marker-assisted selection (MAS) for resistance to insect pests. Once
genomic regions contributing to the trait of interest have been identifi ed and the alleles at
each locus designated by molecular markers, they can be transferred into locally adapted,
high-yielding cultivars by crossing, and following the marker(s) through subsequent generations
of inbreeding or backcrossing. Wild relatives of crops also contain alleles of importance
for resistance to insect pests. Since these alleles are often recessive, they can only
effectively be utilized in crop breeding programs through MAS (Xiao et al., 1996; Mifl in,
2000). Molecular markers can be used to:
• Estimate genetic variances (Bai, Michaels, and Pauls, 1998).
• Predict hybrid performance (Bohn et al., 1997).
• Estimate the number of genes in which the parents differ (Kisha, Sneller, and
Diers, 1997).
• Identify quantitative trait loci (QTL) associated with resistance to insect pests
(Peirera, 2000).
Genetic maps based on recombination frequencies are an important tool in crop improvement
(Karp et al., 1997; Mohan et al., 1997). At times, there may be discrepancies in physical
and genetic maps and, therefore, it is important to correlate genetic and physical maps for
mapping and isolating the genes of interest. Physical or genetic mapping can be accomplished
by using:
• Terminal defi ciencies (B.Y. Lin et al., 1997).
• Translocation lines (Kunzel, Korzum, and Meister, 2000).
• Pulsed fi eld gel electrophoresis (Bonnema et al., 1996).
• YAC and BAC contiguous DNA sequences (Kurata et al., 1997; Dunford et al.,
2002).
• Genomic introgression (Humphreys et al., 1998).
• Fluorescence in situ hybridization (FISH) (J. Jiang and Gill, 1994; Kim et al., 2004).