Factors Influencing the Outcome of Barley Yellow Streak Mosaic Virus-Brown Wheat Mite-Barley Interactions. Eric. D. Smidansky, Former Graduate Research Assistant, Montana State University-Bozeman, Bozeman 59717. Thomas W. Carroll, Professor Emeritus, Department of Plant Pathology, Montana State University-Bozeman, Bozeman 59717. Plant Dis. 80:186-193. Accepted for publication 7 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0186.

Barley yellow streak mosaic virus (BaYSMV), the cause of disease in barley, is transmitted in nature only by the brown wheat mile (Peirobia latens). Greenhouse and growth chamber experiments were conducted to gain insight into what underlies the reported association between severe BaYSMV-induced disease outbreaks and large mite populations with warm and dry conditions. Experiments were also done to determine the efficiency of the mite as a vector for BaYSMV. The presence of BaYSMV antigen in diseased plants and viruliferous mites was confirmed by enzyme-linked immunosorbent assay (ELISA). Evidence was found for a critical temperature threshold between 21 and 26°C for efficient expression of BaYSMV-induced symptoms in barley. The influence of barley host plants stressed by drought on disease incidence was neutral, positive, and negative at 21, 26, and 30°C, respectively. Applying water periodically to mite egg deposition substrates on the soil surface appeared to reduce the number of eggs deposited. Mite counts were generally higher on BaYSMV-infected barley than on healthy barley. Preadult nonviruliferous mites readily acquired BaYSMV from infected host plants. Adult mites efficiently inoculated the virus into barley plants, and preadults were also able to inoculate the virus. Mite populations were able to expand at temperatures too low to support all but very low incidences of BaYSMV-induced disease in barley. There was also indirect evidence for transovarial passage of BaYSMV to red nondiapausal eggs within the mite vector