CLEISTOTHECIA OF UNCINULA-NECATOR - AN ADDITIONAL SOURCE OF INOCULUM IN ITALIAN VINEYARDS

Density and viability of populations of cleistothecia of Uncinula neca tor from bark, leaves, and soil were determined in three vineyards in the Florence and Siena provinces of Tuscany for 3 years. A higher dens ity of cleistothecia was found on fallen leaves than on bark. However, the percentage of viable cleistothecia was higher on bark. No viable cleistothecia were recovered from soil. U. necator overwintered as myc elium in dormant infected buds, which gave rise to flag shoots, only i n Santa Cristina, where 20 acid 92 flag shoots per hectare were detect ed before bloom in 1994 and 1995, respectively. Disease incidence and severity increased similarly at Corti, Fornace, and at Santa Cristina, although powdery mildew epidemics started from ascospores only in Cor d and Fornace, whereas flag shoots were present at Santa Cristina. Cle istothecia were formed in autumn in both 1994 and 1995, and their disp ersal started in late September to mid-October, with the maximum numbe r of cleistothecia trapped in funnels during the second half of Octobe r. Cleistothecia appear to function as the sole source of primary inoc ulum for grape powdery mildew in some Italian vineyards and serve as a dditional sources of inoculum where the pathogen also overwinters in i nfected buds. In Australia but not in New York, the pathogen also over winters as cleistothecia on fallen leaves.