|Seasonality of canker induction and expansion by Neofabraea perennans and Cryptosporiopsis kienholzii in apple trees|
C. AGUILAR (1), M. Mazzola (2), C. L. Xiao (3). (1) WSU Tree Fruit Research & Extension Center, Wenatchee, WA, U.S.A.; (2) USDA-ARS Tree Fruit Research Lab, Wenatchee, WA, U.S.A.; (3) USDA-ARS, Parlier, CA, U.S.A.
In the U.S. Pacific Northwest, bull’s-eye rot is a major postharvest disease of apples and other pome fruit. Four closely related fungi belonging to <i>Neofabraea</i> or related genera are known to cause this disease. Depending upon species, these fungi overwinter either as saprophytes of organic plant debris on the orchard floor, or as mycelium in cankers of infected trees. <i>N. perennans</i> and recently described <i>Cryptosporiopsis</i> <i>kienholzii</i> are two bull’s-eye rot-causing pathogens that are prevalent in pome fruit production areas of central and eastern Washington State. While <i>N. perennans</i> is known to cause perennial canker in apple trees, the canker-inducing status of <i>C. kienholzii</i> and its survival in the orchard remains unknown. Twigs of ‘Red Delicious’ and ‘Fuji’ apple trees were inoculated in the orchard with mycelial plugs of either <i>N. perennans</i> or <i>C. kienholzii</i> throughout the year for two years and monitored for canker expansion on a monthly basis up to six months post inoculation. Twigs were harvested on the final month of measurement, during which re-isolation of fungi from diseased twigs was attempted. Preliminary data from this experiment suggests rapid growth and expansion for cankers induced by either species during the months of April and October. Inoculations conducted during hot summer and freezing cold winter months seemed to be the least conducive for canker growth. However, both fungi were capable of surviving as mycelium in twigs throughout the year.