VIEW ARTICLE

Disease Detection and Losses

A Multiple Regression Model to Estimate the Contributions of Leaves and the Effects of Leaf Rust on Yield of Winter Wheat. K. V. Subba Rao, Former graduate research assistant, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803, Present address: Department of Plant Pathology and Crop Physiology, Louisiana State University, Baton Rouge 70803; X. B. Yang(2), G. T. Berggren(3), and J. P. Snow(4). (2)Former graduate research assistant, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803, Present address: Foreign Disease-Weed Science Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Fort Detrick, Building 1301, Frederick, MD 21701; (3)(4)Professors, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803. Phytopathology 79:1233-1238. Accepted for publication 13 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1233.

The contributions of each wheat leaf to tiller grain yield of cultivar McNair 1003, susceptible to prevalent leaf rust races, and the effect of leaf rust on each leaf were determined by defoliation and inoculation in 1986-87 and 1987-88 winter wheat-growing seasons. The 10 treatments included in the experiment involved removing/retaining flag (F), F-1, F-2, and F-3 leaves in different combinations from both rusted and control tillers. Maximum losses due to leaf rust in tiller grain weight, tiller grain number, and 1,000-grain weight were, respectively, 27.0, 19.0, and 24.0% in 1986-87 and 24.0, 23.0, and 18.0% in 1987-88. Maximum losses in tiller grain weight, tiller grain number, and 1,000-grain weight due to defoliation in rusted treatments were, respectively, 56.7, 46.4, and 29.8% in 1986-87 and 38.8, 27.8, and 19.9% in 1987-88; in control treatments losses were, respectively, 58.8, 41.6, and 38.1% in 1986-87 and 51.1, 35.6, and 31% in 1987-88. Defoliation of F in 1986-87 and F and F-1 in 1987-88 caused significant reduction of all the three yield components measured. Contributions to yield of the different parts of the tiller towards grain weight were estimated by the following regression model: Y_ij = ß₀ + ß₁F_i + ß₂(F – 1_i) + ß₃(F – 2_i) + ß₄(F – 3_i) + e_ij, in which ß₀, ß₁, ß₂, ß₃, and ß₄ are the absolute contributions of the nonfoliar parts, F, F-1, F-2, and F-3 leaves, respectively, of the i^th tiller in the j^th treatment. The partial regression coefficients for the nonfoliar parts, F, F-1, and F-2 of the tiller were, respectively, 0.98 ± 0.08, 0.78 ± 0.13, 0.41 ± 0.19, and 0.23 ± 0.27 in the rusted treatments of 1986-87; 1.21 ± 0.07, 0.79 ± 0.11, 0.42 ± 0.13, and 0.34 ± 0.13 in the control treatments of 1986-87; 0.80 ± 0.05, 0.42 ± 0.09, 0.22 ± 0.09, and 0.14 ± 0.14 in the rusted treatments of 1987-88; and 0.87 ± 0.04, 0.44 ± 0.06, 0.28 ± 0.07, and 0.12 ± 0.07 in the control treatments of 1987-88. Paired t-tests for the estimated relative contributions of the leaves between rusted and control treatments each year were not significant, indicating that leaf rust does not alter the relative contribution of leaves of tiller to yield. The regression between the relative healthy area duration for each leaf and tiller grain weight was highly significant (P = 0.0001) with an adjusted R² of 0.84 and 0.91 for rusted and control treatments, respectively, in 1986-87 and 0.67 and 0.88, respectively, in 1987-88.