EFFECTS OF VERTICILLIUM-DAHLIAE ON GAS-EXCHANGE OF POTATO

Growth-chamber and field experiments were conducted to determine the effects of Verticillium dahliae on gas exchange of potato. Infection caused lower stomatal conductance, lower transpiration, and higher leaf temperature in leaves of all ages. Infection reduced carbon assimilation rate in high light, but reductions were not always observed in low light. Infection did not affect dark respiration. Intercellular CO2 concentration was decreased and leaf water use efficiency was increased in diseased nonsymptomatic leaves. However, diseased chlorotic leaves often did not show this effect. The rate of stomatal opening in the morning was slower for diseased leaves compared with nondiseased leaves. Infection did not affect the relationship between assimilation rate and stomatal conductance in high light. Changes in gas exchange caused by infection with V. dahliae matched previously reported effects of drought on potato gas excange.