SEASONAL FLUCTUATIONS IN KIWIFRUIT PHYLLOSPHERE AND ICE NUCLEATION ACTIVITY OF PSEUDOMONAS VIRIDIFLAVA

Abstract

Seasonal fluctuations of Pseudomonas viridiflava, the causal agent of bacterial blight, were investigated on the kiwifruit phyllosphere in relation to ice nucleation activity, at different sites in central Italy (north of Latium), from October 1995 until September 1996. The pathogen was detected during the different seasons on leaves, twigs, buds and fruits with population values ranging between 1.1x101 and 2x106 cfu cm-2 with maxima in spring and autumn. The pathogen was also present in significant amounts in several winter and summer months. No P. viridiflava was detected on flowers. Most of the bacterial isolates showed ice nucleation activity, manifested at relatively low concentrations (104 cfu ml-1) and at temperatures slightly below 0°C (-3 °C). Epidemiological implications are discussed.