Phacidiopycnis washingtonensis: Inoculum availability, persistence and seasonal host susceptibility in Washington apple orchards
P. SIKDAR (1), M. Mazzola (2), C. L. Xiao (3). (1) TFREC, Washington State University, Wenatchee, WA, U.S.A.; (2) USDA ARS, Tree-Fruit Research Laboratory, Wenatchee, WA, U.S.A.; (3) USDA ARS, San Joaquin Valley Agricultural Sciences Center, Parlier, CA, U.S.A.
<i>P. washingtonensis</i> infects apple fruit in the orchard but decay symptoms develop during storage. Pycnidia on diseased shoots are believed to be the inoculum source for fruit infection in the orchard. However, the period of twig susceptibility and availability of viable inoculum in the field are unknown. Two separate studies were conducted to assess availability of viable inoculum during the fruit growing season and characterize the seasonal nature of twig susceptibility to infection in the orchard. In a Red Delicious orchard, 2-year-old twigs were wounded, cold-injured and inoculated with the fungus in spring 2011. Over the next 10 months, 1 cold-injured twig from each of 10 inoculated trees was harvested monthly and viability of pycnidia assessed. Viable pycnidia were detected on all twigs at each sampling time. In a second study, twigs were wounded, with or without cold injury, and inoculated every other month over 2 years. Canker development and the presence of pycnidia on each twig were monitored over 6 months. Twigs were most susceptible to infection during spring to early summer. A cold injury treatment facilitated infection establishment and production of pycnidia. Canker development also was observed on non-cold-injured twigs but the production of viable pycnidia was less.Thus, viable inoculum of <i>P. washingtonensis</i> was available during all sampling months, suggesting that viable inoculum is likely not a limiting factor for fruit infection in the orchard.
View Presentation |
