Influence of leaf position on yield loss caused by wheat leaf rust in single tillers

Abstract

The average disease severity estimated on the upper three leaves of spring wheat resulted in a significant correlation between leaf rust severity and loss in grain weight ( R 2 = 0.90) and 1000-kernel weight ( R 2 = 0.89). High R 2 values and significant regression coefficients alone, however, are insufficient to validate a disease-loss model; additional important criteria are the absence of heteroscedasticity and presence of a functional relationship between disease and loss. These criteria were obtained by determining the separate contribution of leaves to total grain weight of single tillers. The flag, penultimate and antepenultimate leaf positions, respectively, were found to contribute 26, 12 and 3% to potential grain yield per tiller. An effective severity [leaf contribution × severity (SEV-c)] was obtained which had a one-to-one relationship with yield loss in grain weight. The effective severity could be used, therefore, to predict yield loss in total grain weight; it was possible to predict yield loss by knowing the disease severity on the three upper wheat leaves and each leaf's potential contribution to grain yield. A good correlation was also found between yield loss and the effective severity adjusted for leaf area (SEV-c+ A), suggesting that SEV-c+A, can be used in the place of SEV-c, especially when leaf area varies.