EFFECTS OF DROUGHT ON CHLOROPHYLL FLUORESCENCE IN POTATO (SOLANUM-TUBEROSUM L) .1. PLANT WATER STATUS AND THE KINETICS OF CHLOROPHYLL FLUORESCENCE

The slow kinetics of chlorophyll fluorescence were examined in seven potato genotypes grown either fully irrigated or droughted from the time of plant emergence. Constant and variable fluorescence (F(o) and F(v) respectively) declined with time in plants from both irrigated and droughted treatments, but the decline was greater in droughted than irrigated plants. However, the yield of variable fluorescence (F(v)/(F(o) + F(v))) was unaffected by the drought treatment. The main effect of drought was upon the quenching of variable fluorescence. Both the half life of the decay of variable fluorescence (q1/2) and the secondary maximum (M) were significantly greater in the droughted plants than in those from the irrigated treatment. Significant differences between genotypes were found for F(v)/(F(o) + F(v)), M and q1/2. Genotype-by-treatment interactions were non-significant for all the variables examined. Changes in chlorophyll fluorescence transients were not closely related to changes in leaf water potential.