Susceptibility of mango (Mangifera indica L.) to cold-induced photoinhibition and recovery at different temperatures

Cold-induced photoinhibition of photosynthesis and recovery from photoinhibition in mono- and poly-embryonic mango cultivars were investigated under field and controlled temperature and light conditions. Photoinhibition, measured as a decrease in the ratio of variable to maximum chlorophyll fluorescence emission (Fv/Fm), occurred in trees growing in the field in winter and early spring. Fv/Fm ratios of all cultivars began to decrease from about 0.49 in May, reaching minimum values of about 0.33 in mid July, and then gradually increased to around 0.68 and exceeded pre-winter values by early November. A seasonal change of leaf chlorophyll content in all cultivars followed a similar pattern to the changes in Fv/Fm ratios during winter. Susceptibility to cold-induced photoinhibition and a reduction in leaf chlorophyll content were greater in poly-embryonic cultivars than in mono-embryonic cultivars. There was a positive linear relationship between the minimum air temperature the night before the measurement and the leaf Fv/Fm ratio (r(2) = 0.62-0.70). In controlled environmental experiments, poly-embryonic cultivars were also more susceptible to photoinhibition than mono-embryonic cultivars. When held at 10 degrees C and irradiated with a photosynthetic photon flux (PPF) of 450 mu mol/m(2).s, photoinhibition in detached leaves increased linearly with time. The extent of the reduction in Fv/Fm ratios induced by 6 h irradiation was 43% and 56%, respectively, in mono- and poly-embryonic cultivars. Recovery from photoinhibition in detached leaves was promoted by exposure to a PPF of 20 mu mol/m(2).s for 24 h at 20 degrees C. Negligible recovery occurred in photoinhibited leaves maintained at 10 degrees C