ibclogo XVI International Botanical Congess


Abstract Number: 4882
Poster No. = 2504


FACTORS INFLUENCING ASCOCARP FORMATION AND DEVELOPMENT IN MICROSPHAERA PULCHRA OF FLOWERING DOGWOOD


Margaret T. Mmbaga & Hongyan Sheng, Tennessee State University, Nursery Crop Research Station, 472 Cadillac Lane, McMinnville, TN 37110


Ascocarps of Microsphaera pulchra constitute the main mechanism for winter survival and source of primary inoculum for powdery mildew in Cornus florida. Ascocarp formation occurs late in the season and may be influenced by host physiology and /or environmental factors. A study on the effect of temperature and day length on ascocarp formation showed that cool temperatures were important in ascocarp formation. Ascocarps developed at 23/150C and 18/100C and 12, 11 and 10 hr day-lengths, but did not develop at 28/20C at any day- length. Ascocarp development was best at 23/150C and 12 hr day-length. Ascocarp initials were observed four weeks after treatments started, some matured in five weeks. Plants left outdoors in natural environment developed ascocarp initials when maximum temperatures dropped below 260C for several weeks. By this time, all leaves in the cool temperature treatments had abundant mature ascocarps. Ascocarp initials (cream colored) cannot survive below-zero temperatures, but more completely mature ascocarps (brown-black) can survive freezing temperatures. Since time is a factor in the maturation of ascocarps to a level that can survive winter, the timing of ascocarp formation and development have significant implications on primary inoculum density.


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