Performance of North American and Australian lucernes in the Queensland subtropics. 3. Yield, plant survival and aphid populations in raingrown stands

Abstract

Twenty-three North American and up to five Australian lucerne lines were evaluated for dry matter yield, plant persistence and aphid resistance at three sites under raingrown conditions in southern Queensland. The experiment at Toowoomba was conducted over 3 years, but those at Mitchell and Biloela were terminated after 1 and 2 years, respectively, because of poor plant survival caused partly by dry conditions. In the subhumid environments at Toowoomba and Biloela, lucerne yield was strongly associated with lucerne population decline. At Toowomba, where there was least confounding with nonordered variation, yield was also positively associated with decreasing winter dormancy. There, persistence (and therefore yield) was associated with resistance to both anthracnose and Phytophthora root rot. No line possessed high levels of combined resistance to these diseases. In the semi-arid environment at Mitchell, the highest yields were obtained from non-dormant lines. Root canker reduced lucerne yield at this site. Large populations of spotted alfalfa aphid developed on susceptible lines and of blue-green aphid on all lines. However, no effects on the dry matter yield or persistence of any lines were measured.