SHOOT LENGTH AFFECTS SUSCEPTIBILITY TO MUMMY BERRY BLIGHT WITHIN HIGHBUSH BLUEBERRY CULTIVARS

Shoot growth of six blight-resistant highbush blueberry (Vaccinium cor ymbosum L.) cultivars and of one susceptible cultivar was manipulated during the primary infection period of mummy berry disease to determin e if some portion of the observed resistance was based on disease avoi dance, In experiments across 2 years, resistant cultivars either incre ased continually in susceptibility or exhibited a peak and then decrea sed in susceptibility as shoots elongated. In a larger experiment that included both susceptible and resistant cultivars, peaks of susceptib ility were identified for 'Bluejay', 'Darrow', and 'Jersey'. In contra st, general decreases in susceptibility were identified for 'Duke', 'B lueray', and 'Croatan' as shoots elongated, Shoot lengths associated w ith peak susceptibility varied among and within cultivars across exper iments, The increases in susceptibility observed at longer shoot lengt hs were generally small, This finding suggests that cultivars identifi ed as resistant have intrinsic levels of resistance, but maturity and general condition of the plant tissue can also affect disease levels.