Contents - Faperta

Mechanisms and Inheritance of Resistance to Insect Pests 135
has been stopped because of its susceptibility to southern corn leaf blight, Bipolaris maydis
(Nisikado and Miyake), which severely damaged maize crop in the United States in the
1970s (Tatum, 1971). In pearl millet, most of the hybrids are based on A 1 cytoplasm (Burton
and Athwal, 1967), and the hybrids based on 111A CMS line are less susceptible to the
Oriental armyworm, Mythimna separata (Walker) than those based on 5141A and 5054A
(H.C. Sharma, Bhatnagar, and Davies, 1982). Most of the sorghum hybrids are based on
Milo (A 1) cytoplasm (Stephens and Holland, 1954), and a large number of these hybrids are
highly susceptible to insect pests. Sorghum lines KS 34 to 39 are as susceptible as CKA
(Combine Kafi r-based CMS lines) to greenbug, S. graminum (Ross and Kofoid, 1979).
Cytoplasmic male-sterile lines are more susceptible to insects than the corresponding
maintainer lines, suggesting that resistance to insects is infl uenced by the interaction of
factors in the cytoplasm of the maintainer lines and the nuclear genes (H.C. Sharma, 2001;
H.C. Sharma et al., 1994, 2004). Resistance to sorghum shoot fl y, A. soccata, sorghum midge,
S. sorghicola, sugarcane aphid, Melanaphis sacchari (Zehntner), and shoot bug, Peregrinus
maidis Ashmead, in F 1 hybrids of sorghum is infl uenced by CMS lines, while resistance to
spotted stem borer, C. partellus is infl uenced by the restorer lines (H.C. Sharma et al., 2004;
Dhillon et al., 2006a, 2006b). Hybrids based on insect-resistant male-sterile and restorer
lines are resistant, while those based on insect susceptible CMS, and resistant, or susceptible
restorer lines are susceptible to shoot fl y, sugarcane aphid, shoot bug, head bug, and
midge (H.C. Sharma et al., 1996, 2000a; Dhillon et al., 2006a, 2006b). A 4M and A 4VzM cytoplasms
in sorghum are less susceptible to shoot fl y than the A 1, A 2, and A 3 cytoplasms
(Dhillon, Sharma, and Reddy, 2005; Dhillon et al., 2005; H.C. Sharma et al., 2005c). To overcome
the problem of a narrow genetic base based on a single source of male sterility, efforts
should be made to transfer the insect resistance genes into diverse genetic backgrounds or
discover new sources of male-sterility that are less susceptible to insect pests.
Genetics and Inheritance of Resistance to Insect Pests
Information on genetics and inheritance of resistance to insect pests is important in crop
improvement, which indicates the degree of ease or diffi culty involved in incorporating
the resistance genes into the improved cultivars. Resistance to insects may be dominant or
recessive. The general combining ability (GCA) of a cultivar to transmit resistance to the
progeny is determined from the average resistance levels of the F 1 and F 2 plants in all
crosses involving a particular genotype, while the specifi c combining ability (SCA) is a
measure of the amount of resistance transferred by a genotype in a single cross to a
particular parent. Heritability or variation observed in the progeny of a cross is another
measure of inheritance of resistance, which may be affected by several factors. When several
different alleles from genes in resistant plants contribute to variation for resistance to
an insect species, these are called additive effects. Epistatic effects of alleles may also
contribute to variation. The genetics and inheritance of resistance to insects has been discussed
by Khush and Brar (1991), Panda and Khush (1995), and Smith (2005). Information
on inheritance of resistance to insects in different crops is discussed below.
Rice
Many genes have been identifi ed in rice that contribute for resistance to brown planthopper,
N. lugens, green leafhoppers, Nephotettix cincticeps Uhler and N. virescens, gall midge,