ANTIXENOSIS COMPONENT OF RESISTANCE TO CORN PLANTHOPPER, PEREGRINUS-MAIDIS (ASHMEAD) IN SORGHUM

Antixenosis component of resistance to corn planthopper, Peregrinus ma idis (Ashm.) was investigated in 10 selected sorghum genotypes at thre e plant growth stages(30,45 and 60 DAG) under laboratory and field (ra iny and postrainy seasons) conditions. In a free-choice test, the orie ntational and settling responses of nymphs and brachypterous adults on all genotypes although influenced by the olfactory and visual respons es, their feeding was not sustained due to gustatory stimuli indicatin g their significant role in determining the degree of antixenosis. The genotypes IS 18676, IS 19349 and IS 18677 showed a high degree of ant ixenosis in settling fewer nymphs and adults consistently at 30, 45 an d 60 DAG. This finding was supported with low colonization of nymphs, and brachypterous and macropterous adults under field conditions. In a ddition, high degree of antixenosis for oviposition in both laboratory and field tests was evidenced on IS 18676 and IS 19349 at 30,45 and 6 0 DAG, but on SPV 472 and SPV 475 only at specific plant growth stages . The variability in the rate of adult colonization together with suit ability of plant growth stages for oviposition has contributed to vari able degrees of antixenosis for oviposition.