EFFECTS OF SINGLE OR DOUBLE INFECTIONS WITH HELMINTHOSPORIUM-AVENAE AND BARLEY YELLOW DWARF VIRUS ON YIELD COMPONENTS OF OATS

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 (Helminthosporiu m 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 g rowth 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 ye ar. 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 betwee n date of inoculation and BYDV infection were significant for seeds pe r panicle and total yield. Earlier inoculations were associated with l arger reductions in yield. No H. avenae-by-BYDV interactions occurred.