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Effect of Winter Wheat Cultivar Mixtures on Leaf Rust Severity and Grain Yield. T. Mahmood, Former graduate student, Texas Agricultural Experiment Station, Texas A&M University Research and Extension Center, Dallas 75252; David Marshall(2), and M. E. McDaniel(3). (2)Associate professor, Texas Agricultural Experiment Station, Texas A&M University Research and Extension Center, Dallas 75252; (3)Associate professor, Department of Soil and Crop Sciences, Texas A&M University, College Station 77843. Phytopathology 81:470-474. Accepted for publication 18 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-470.

Three different experiments involving winter wheat cultivar mixtures and their component purelines were conducted at McGregor, TX, in the 19861987 and 19871988 growing seasons. The same experiments were also conducted during 19871988 at Dallas, Prosper, Stephenville, and Uvalde, TX. In three-way mixtures with the leaf rust susceptible cultivar TAM 107 and the moderately resistant wheats, Collin and TX71C8130R, disease severity and area under the disease progress curve (AUDPC) were reduced in all locations and years compared with the mean of the component cultivars, with the exception of one mixture at Stephenville in 19871988. Additionally, grain yields and thousand kernel weights were higher in the mixtures as compared with the component cultivars in most cases. Another three-way mixture experiment used the moderately resistant cultivar Thunderbird with the susceptible cultivars Mustang and Vona. In this experiment, disease severity and AUDPC were reduced in all mixture-component comparisons. The third experiment used two-way mixtures of the moderately resistant cultivar Siouxland and the susceptible cultivar Hawk. Reductions in disease and increases in yield were found in several of these mixtures as compared with the component cultivars. Overall, there was a mean reduction in AUDPC of 32% in the mixtures compared with the mean AUDPC of the component cultivars. The AUDPC in the mixtures was always less than that of the most susceptible cultivar grown in a pure stand. Mixtures were equal to or better than the mean grain yield of their component cultivars in 68% of the comparisons. The reduction in leaf rust in mixtures was more accurately expressed in higher thousand kernal weight than in overall grain yield.

Additional keywords: Puccinia recondita.