PHOTOSYNTHETIC RESPONSE OF TOMATO PLANTS TO VASCULAR WILT DISEASES

Greenhouse experiments were conducted to study the chronology of effec ts on gas exchange and chlorophyll-a fluorescence, visible symptoms an d hyphal colonization in plants of the susceptible tomato cultivar Bon ny Best inoculated with tracheomycotic fungi Fusarium oxysporum f. sp. lycopersici or Verticillium albo-atrum. The net photosynthetic rates and related parameters of healthy (uncolonized and asymptomatic) leave s of infected plants were affected by both the parasites. In the first uncolonized leaf, net photosynthesis was depressed in different ways: in Fusarium-infected individuals, the maximum detrimental effect was observed a week after inoculation, while in Verticillium-infected plan ts the most severe depression was detected 21 days after inoculation. The behaviour of the physiological parameters investigated, together w ith the data relative to chlorophyll fluorescence measurements highlig hted the fact that the depression in photosynthetic activity was cause d by different concomitant factors in Verticillium-infected plants and was due mainly to drought stress in plants inoculated with Fusarium. (C) 1997 Elsevier Science Ireland Ltd.