THE QUANTUM YIELD OF PHOTOSYNTHETIC ELECTRON-TRANSPORT EVALUATED BY CHLOROPHYLL FLUORESCENCE AS AN INDICATOR OF DROUGHT TOLERANCE IN DURUM-WHEAT

The chlorophyll fluorescence parameters Delta F/Fm' and Fv'/Fm', relat ed respectively to the quantum yield of photosynthetic electron transp ort and to the efficiency of excitation capture by the open centres of photosystem II, have been evaluated as possible indicators of drought tolerance in durum wheat. Delta F/Fm' and Fv'/Fm' measurements were c arried out on excised leaves, both control and dehydrated, of 25 culti vars. Delta F/Fm' and Fv'/Fm' values were obtained at two times after the start of fluorescence measurement: at 14 s, i.e. during the induct ion curve (Delta F/Fm'(14s) and Fv'/Fm'(14s)) and at 200 s, i.e. at st eady state fluorescence (Delta F/Fm'(200s) and Fv'/Fm'(200s)). In dehy drated leaves a mean significant decrease of 20 % (P < 0.001) was obse rved in Delta F/Fm'(14s) values. In contrast, no great differences wer e observed between control and dehydrated leaves with regard to Delta F/Fm'(200s), Fv'/Fm'(14s) and Fv'/Fm'(200s). The percentage decrease o f Delta F/Fm'(14s) after dehydration was correlated with the drought s usceptibility index (DSI) of the cultivars, evaluated on a yield basis and a significant correlation (r = 0.72, P < 0.001) was found.