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Environmental Influence on the Infection of Wheat by Mycosphaerella graminicola. A. M. Magboul, Assistant professor, Department of Plant Protection, King Faisal University at Al-Hassa, Saudi Arabia; S. Geng(2), D. G. Gilchrist(3), and L. F. Jackson(4). (2)(4)Professor and agronomist, respectively, Department of Agronomy and Range Science, University of California, Davis (UCD), CA 95616-8515; (3)Professor, Department of Plant Pathology, UCD. Phytopathology 82:1407-1413. Accepted for publication 17 August 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/Phyto-82-1407.

Mycosphaerella graminicola (anamorph, Septoria tritici), the causal agent of Septoria tritici blotch on wheat, can cause a significant yield loss for most commercially grown wheat cultivars and in many wheat-growing areas. Environmental factors which affect infection and disease development such as light intensity, temperature, and moisture have been studied extensively. Yet, reports on specific effects of temperature and leaf wetness period on the infection process are limited. The objectives of this study were to quantify the effect of temperature and duration of leaf wetness and their interaction during the infection process on major disease components, to study the dynamic characteristics of these disease components, and to derive a mathematical expression for each disease component, as a function of infection temperature and leaf wetness period. Results showed that temperature is a critical determinant of wheat infection by M. graminicola and that the optimum temperature for the infection process does not depend on leaf wetness period. Furthermore, the initial conditions of temperature and leaf wetness period following inoculation not only affect the rate of disease development but also the asymptotic level of disease severity that ultimately may be achieved. Except for lesion length, the maximum rate of increase in all disease components responds linearly to changes in leaf wetness period, and quadratically to changes in temperature. The rate of lesion length expansion is mainly influenced by postinfection conditions. Of the four components of Septoria tritici blotch of wheat studied, lesion unit (number of average-sized lesions) per square centimeter is the most sensitive indicator of a successful infection.

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