GENE-ACTION FOR RESISTANCE IN SORGHUM TO MIDGE, CONTARINIA-SORGHICOLA

Gene action for resistance to sorghum midge (Contarinia sorghicola Cog .) was studied in a diverse array of midge-resistant and midge-suscept ible females and males under natural infestation and under uniform inf estation with a no-choice headcage technique. Gene action for glume an d grain characteristics associated with resistance to sorghum midge wa s also studied to understand their role in expression of resistance to this insect. Gene action for resistance to midge is largely governed by additive gene action. Genotype x environment interaction was signif icant for midge damage rating under natural infestation but nonsignifi cant under no-choice headcage screening, The GCA effects of midge-resi stant cytoplasmic male-sterile (CMS) females (Phl 7061 A and PM 7068 A ) were significant and negative, and such effects for the midge-suscep tible CMS females ICSA 42 and 296 A were positive, Similar results wer e observed for the males (except for CS 3541 and MR 750 for midge dama ge in one out of two seasons), Dominance (mid-parent heterosis) was al so important for midge resistance in some cross combinations, For geno typic nonpreference by the midge females, the SCA effects were greater than the GCA effects, The SCA effects for genotypic nonpreference wer e negative for PM 7061 A, The GCA effects were significant and negativ e for glume length in PM 7061 B, glume hardness for 296 B, and glume h airiness for PM 7061 B, The GCA effects were significant and positive for glume length, glume hairiness, and glume hardness of ICSB 42. Resi stance is needed in both the parents to produce midge-resistant hybrid s.