Effects of Single or Double Infections with Helminthosporium avenae and Barley Yellow Dwarf Virus on Yield Components of Oats. M. L. Sommerfeld, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. F. E. Gildow, and J. A. Frank. Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 77:741-744. Accepted for publication 4 February 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0741.

Field experiments were conducted over 2 yr near State College, PA, to study the effects on yield components of spring oats (cultivar Noble) of single and dual infections with Pyrenophora avenae (Helminthosporium avenae) and barley yellow dwarf virus (BYDV) (PAV-NY isolate). Oats were inoculated with BYDV 4 or 6 wk after planting and with H. avenae 6 or 8 wk after planting. Although the average percentage of leaf area covered with Helminthosporium leaf blotch lesions approached 14% at growth stage 11.1 and rose to 30–50% after stage 11.2, infection with H. avenae had no significant effect on any yield component in either year. BYDV infection reduced the number of tillers and panicles by 15%, the number of seeds per panicle by 18%, thousand-kernel weight by 5%, and total yield by 33% compared to control plants. Interactions between date of inoculation and BYDV infection were significant for seeds per panicle and total yield. Earlier inoculations were associated with larger reductions in yield. No H. avenae-by-BYDV interactions occurred.