FIELD-RESISTANCE TO RUSSIAN WHEAT APHID IN BARLEY .2. YIELD ASSESSMENT

Host-plant resistance could reduce yield losses due to feeding of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), on barley (Hordeum vulgare L.). Most RWA screening procedures rely on differential expression of foliar RWA feeding symptoms to identify resistant genotypes. This study was conducted to determine if field expression of foliar symptoms in barley is a good indicator of yield reduction due to RWA feeding damage. Spring barley genotypes representing a range in foliar symptom expression were evaluated in the field in infested and uninfested hill-plots in summer 1989 (14 genotypes) and winter 1990 (19 genotypes). Plants were scored for foliar symptoms on a 1 to 6 scale (1 = no symptoms). Grain yield (GY), spike number (SN), 100-kernel weight (KW), and straw yield (SY, 1990 only) were measured. Reduction in GY among genotypes due to RWA feeding ranged from -10 to 48% in 1989 and from -17 to 59% in 1990, and was highly correlated (r = 0.7 1, df = 31, P < 0.01) with foliar symptom scores. Reduction in SN ranged from -3 to 42% in 1989 and from -14 to 39% in 1990, and was also highly correlated (r = 0.77, df = 31, P < 0.01)) with foliar symptom scores. Kernel weight was unaffected by RWA infestation. Reduction in SY ranged from -16 to 43% and was correlated (r = 0.65, df = 17, P < 0.01) with foliar symptom scores. Visual rating based on foliar RWA feeding symptoms in artificially infested hill-plots in the field was an effective method to identify genotypes that show minimal yield reduction under RWA infestation.