Host resistance and fungicide control of leaf rust ( Puccinia hordei) in barley ( Hordeum vulgare) and effects on grain yield and yield components

Abstract

The effectiveness of varying levels of host resistance in five barley ( Hordeum vulgare L.) genotypes and three fungicide application protocols on the control of leaf rust (caused by Puccinia hordei G. Otth) and losses in grain yield, test weight, and 1000-kernel weight was evaluated in field experiments at two locations over four crop years. Fungicide treatments applied to all barley entries at each location and each year included a non-treated control, a single threshold-based application of triadimefon (140 g a.i. ha −1), and a complete control treatment comprised of multiple applications of triadimefon to emulate a disease-free environment. Leaf rust severity was assessed using the James [1971. A Manual of Assessment Keys for Plant Diseases. Canada Dep. Agric. Publ. 1458. The American Phytopathological Society, St. Paul, MN.] scale (0–25%) at three to four plant growth stages and data were used to calculate mean rust severity (MRS) and area under the disease progress curve (AUDPC). Leaf rust epidemics were severe in 1 (1995) of the 4 years of the study, and the treatment effect on grain yield was significant at one location (Warsaw). The susceptible cv. Wysor had a grain yield loss of 33% and MRS was 9.25% (34.23% in modified Cobb scale) at this location. In 2 (1995 and 1997) of 4 years of study, significant ( P ⩽ 0.05 ) negative correlations were obtained between MRS and grain yield, test weight, and 1000-kernel weight of cv. Wysor at both locations. In the other 2 years (1994 and 1996) when leaf rust epidemics were mild, these correlations were mostly non-significant. In general, fungicide treatment significantly ( P ⩽ 0.05 ) reduced MRS and AUDPC and reduced losses in grain yield, test weight, and 1000-kernel weight for the susceptible and moderately susceptible cultivars compared with the non-treated control. The cv. Starling, possessing adult-plant resistance, did not consistently benefit from fungicide application. There was no benefit from fungicide application for control of leaf rust in the resistant line VA92-42-46. In general, the complete-control fungicide treatment did not result in further significant reduction in leaf rust or losses in grain yield compared to threshold-level fungicide applications.