Resistance to Phomopsis stem blight reduces the lupinosis toxicity of narrow-leafed lupin stems

Abstract

To determine if resistance to Phomopsis stem blight reduced the lupinosis toxicity of stems in sheep, we tested mature, dry stems of several selected lines of Lupinus angustifolius L. (narrow-leafed lupin). Resistance was defined as a significant reduction in Phomopsis stem blight symptoms on mature, dry stems compared with susceptible cultivars. Six experiments were conducted at 4 sites in Western Australia in 1983 and 1984. Mature, dry stems were collected from field plots of resistant and susceptible lines for assessment of the frequency of isolation of Phomopsis leptostromiformis (Knhn) Bubak from stem tissue and toxicity to sheep 0 and 14 weeks after the normal time for seed harvest. In both years, P. lepto-stromiformis was isolated with high frequency from susceptible cultivars but with reduced frequency from only some resistant lines. Similarly, toxicity was significantly reduced in some but not all resistant lines. The variation in toxicity among lines could not be fully explained by their relative resistance or frequency of isolation of P. leptostromiformis. Symptoms of Phomopsis stem blight, frequencies of isolation of P. leptostromiformis, and toxicity increased from 0 to 14 weeks after normal harvest time. New lupin lines resistant to Phomopsis stem blight will require testing in field grazing experiments at several sites and for many seasons to confirm their potential for reducing the occurrence of lupinosis.