Inheritance of resistance to head bugs and its interaction with grain molds in Sorghum bicolor

Sorghum head bug, Calocoris angustatus Lethiery is one of the most importan t pests of grain sorghum in India. Head bug damage increases the severity o f grain molds, which renders the grain unfit for human consumption. Therefo re, we studied the gene action for resistance to head bugs and grain molds in a diverse array of male-sterile lines and testers in a line x tester mat ing design under natural infestation. Mean squares for parents, parents vs crosses, lines, testers, and lines x testers were significant for head bug damage and grain mold severity. General combining ability (GCA) effects wer e significant and negative for ICSA 88019 for head bug damage, and ICSA 880 19 and ICSA 88020 for grain molds (except for ICSA 88020 in 1993). General combining ability effects were positive for ICSA 42 and 296 A. GCA effects of lines and testers for head bug damage and grain mold severity were in th e same direction (+ve or -ve). Head bug damage in the grain was significant ly correlated with grain mold severity. Testers IS 8891, IS 15107, and TAM 2566 (with colored grain and less susceptibility to molds) produced mold-re sistant hybrids in combination with all the male-sterile lines, while the r everse was true in the case of Swarna and ICSV 112. Resistance to head bugs showed dominance to partial dominance type of gene action, while in the ca se of grain molds, it showed dominance to overdominance. Resistance to thes e pests is governed by both additive and nonadditive types of gene action. The implications of these results are discussed in relation to need for cro p improvement in sorghum.