SORGHUM RESISTANCE TO INSECT PESTS

Scope and Method of Study. The research was conducted to study varietal resistance and inheritance of resistance in sorghums to the sorghum midge, Contarinia sorghicola (Coquillet); the greenbug biotype E, Schizaphis graminum (Rondani); and the chinch bug, Blissus leucopterus leucopterus (Say). Also the mechanisms of resistance in sorghums to greenbug biotype E were investigated. The feasibility of transferring resistance to the three kinds of insect pests to high yielding varieties was determined.;The inheritance of resistance in PI220248 and PI264453 to greenbug biotype E was probably controlled by a single dominant gene pair. There should be little difficulty in developing sorghum varieties resistant to greenbug biotype E by using the resistant varieties in this study. The mechanism of resistance in PI220248 showed the highest degree of antibiosis with high levels of nonpreference and tolerance as well. PI264453 was also high in all three components. J242, another resistant variety, had moderate levels of the three components and suffered moderate injury.;In the chinch bug resistance study, sorgo and kafir had higher resistance than other sorghum types. Wonder Kafir CI 872 showed the most resistance at the seedling stage in confinement tests. The inheritance of resistance to the chinch bug is not completely understood. However, it is evident that resistant plants can be identified in segregating populations, so there should not be much difficulty in transferring chinch bug resistance to high yielding varieties.;Although resistance to the greenbug and to the chinch bug can be more readily transferred to the progeny of a cross than resistance to sorghum midge, it should still be possible to combine resistance to all three insect pests in superior lines through present breeding techniques.;Findings and Conclusions. The resistance to the sorghum midge in SCO175, SCO423, AF-28 (derivative), and SGIRL-MR-1 sorghum varieties was controlled by recessive genes at more than one locus, and the inheritance was not simple. It appears to be difficult to transfer genes for resistance into agronomically acceptable sorghum by simple hybridization. Small glumes of the spikelet in sorghum might be used as an index character to select sorghum midge resistance in segregating generations when there is a lack of midge infestation.