Contents - Faperta

Physico-Chemical and Molecular Markers for Resistance to Insect Pests 187
in accurately and precisely phenotyping such traits, which confound the development of
effective MAS systems. The quality of an MAS program can only be as good as the quality
of the phenotypic data on which the development of that marker was based. Therefore, it
is essential to use large mapping populations characterized across seasons and locations,
using well-defi ned phenotyping protocols. Nevertheless, when confi dence limits are calculated
for the QTL positions, they might cover several intervals or entire chromosome
arms, if the heritability of the trait is low (Hyne et al., 1995). Fine mapping of such large
QTL intervals, by phenotypic screening of several hundred individuals exhibiting molecular
marker evidence of genetic recombination in the interval of interest, is then required
to obtain tightly linked fl anking markers that can be exploited in MAS.
Conclusions
A good beginning has been made in developing genetic linkage maps of many crops.
However, the accuracy and precision of phenotyping for resistance to insect pests remains
a critical constraint in many crops. There is a need to focus on developing innovative
solutions to this problem. Improved phenotyping systems will have substantial impact on
both conventional and MAS to breed for resistance to insect pests, in addition to the more
strategic research that feeds into these endeavors. MAS has had a dramatic impact,
particularly in the private sector, in breeding for disease resistance and quality traits where
simply inherited components could be readily identifi ed. The same potential may be
achieved in the case of more complex traits such as resistance to insect pests and abiotic
stresses. However, the practical and logistical demands for developing and implementing
molecular breeding systems for these traits are quite complex. There is a need to use MAS
to develop cultivars with improved resistance to insect pests and to strengthen Bt transgenic
crops through introgression of other components of resistance through MAS. There
are very few reports concerning the application of MAS for resistance to insect pests.
However, those available fail to demonstrate an increase in effi ciency of MAS over conventional
breeding approaches, although combining MAS with conventional approaches has
given better results. Thus, not only is there a need for precise mapping of the QTLs associated
with resistance to insects, but also the development of a new par adigm in breeding
based on re-engineering breeding programs to make best use of molecular marker data.
Only a combination of conventional and molecular approaches can accelerate the progress
in developing cultivars with insect resistance to increase crop productivity and improve
livelihoods of the rural poor.
References
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Ahmad, F., Gaur, P.M. and Slinkard, A.E. (1992). Isozyme polymorphism and phylogenetic interpretations
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