RESISTANCE OF WINTER-WHEAT TO CEREAL LEAF BEETLE (COLEOPTERA, CHRYSOMELIDAE) AND BIRD CHERRY-OAT APHID (HOMOPTERA, APHIDIDAE)

Resistance tests based on estimation of leaf-feeding damage by cereal leaf beetle, Oulema melanopus (L.), and infestation by bird cherry-oat aphid, Rhopalosiphum padi (L.), were conducted on 26 winter wheat gen otypes over a 3-yr period. Grain yield and thousand-kernel mass were m easured in infested and non-infested control plots in cages covered by insect nets. Highly significant differences were found between genoty pes in feeding damage by cereal leaf beetle and infestation by bird ch erry-oat aphid. The most resistant genotype had 7.4% leaf-feeding dama ge by cereal leaf beetle and the most susceptible 69.4%. Values of inf estation by bird cherry-oat aphid varied between 25 and 79.2%. Yield r esponse was more sensitive indicator of genotype reaction than the 1,0 00-kernel mass. Yield of the most tolerant genotype was reduced by 26% , whereas the 1,000-kernel mass was reduced only 23%. The maximum loss es were 63% in yield and 50% in 1,000-kernel mass. A close correlation was found between infestation severity by bird cherry-oat aphid and y ield reduction (r = 0.7572), but feeding by cereal leaf beetle did not significantly affect yield. Trichome length of the flag leaf exhibite d a significant correlation with feeding damage by cereal leaf beetle (r = -0.7161), but neither trichome density nor length influenced the infestation by aphids. Principal components analysis and multiple regr ession analyses were performed to determine the relationships among te sted characteristics and to quantify the effect of leaf-feeding damage by cereal leaf beetle, infestation by bird cherry-oat aphid, Fusarium spp. infection, heading date, and plant height on grain yield and 1,0 00-kernel mass. Among the variables examined, infestation severity of R. padi had the highest relative importance and direct effect on both yield reduction and 1,000-kernel mass.