Effect of different infestation levels of the greenbug, Shizaphis graminum (Rondani, 1852) on susceptible and resistant sorghum genotypes

Abstract

The sorghum genotypes were planted in pots. Plants were covered with circular cages, made of a wire frame and a fine cloth. In the first experiments, using only the susceptible genotype (BR 601) plants were infested by placing a density of zero, five, ten, fifteen, 20 e 25 insects per plant eleven days following planting. The individuals were seven days old. The resistant genotype TX 2567 were included in the second experiment, using in this case zero, ten, 20 and 30 greenbugs per plant. Different plants were infested 16, 26 and 36 days following planting. Evaluations were based in a visual damage scale from zero (no damage) to nine (over 81% plant necrosis) and in the growth difference between infested and non-infested plants. It was concluded that under an initial infestation of ten greenbugs per plant the susceptible plants are killed in 21 days but the resistant ones, even with an initial infestation of 20 greenbugs per plant, stay alive at least for 28 days and with an increase in size of 68.6% in relation to uninfested plants. It was also concluded that resistant or susceptible plants, are able to stay alive for a longer period, under the same initial infestation, when the infestation occurs in older plants.