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Effects of Pyrenophora teres and Weeds on Barley Yield and Yield Components. J. R. Burleigh, Department of Plant and Soil Science, California State University, Chico, 95929, and Former student, IAV Rabat, Morocco; M. Tajani, and M. Seck. Department de Phytopathologie, Institut Agronomique Veterinaire (IAV), Rabat, Morocco. Phytopathology 78:295-299. Accepted for publication 1 April 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-295.

Combinations of location and fungicide treatments were used to create epidemics of P. teres that had common onset times yet differed in area under the disease progress curve (AUDPC). Regression analysis showed that yield was inversely related to AUDPC when AUDPC ranged from 0.1 to 28.4. When yield decreased with AUDPC so did number of ears and kernel weight. Most of the variation in number of ears and kernel weight was explained by AUDPC and AUWGC (area under weed growth curve) for the growth intervals tillering to booting and tillering to mid-anthesis, respectively. Exponential curves with lower asymptotes at 70 g and 20 ears best expressed the relationships between yield and AUDPC and between number of ears and AUDPC, respectively, while grain weight was a linear function of AUDPC. Weeds also affected yield by reducing number of ears and kernel weight.