Photosynthetic performance and adaptation of sugarcane at suboptimal temperatures

Cultivation of sugarcane is limited by moderate chilling temperatures of 15 degrees in subtropical areas of the world, whereas high temperatures seem to pose less problems. To obtain an overview of the physiological parameter s affected, sugarcane plants were grown at 15, 27, and 45 degrees for up to 10 months and photosynthetic parameters of the leaves were determined, nam ely chlorophyll content, Hill reaction, chlorophyll fluorescence parameters concerning photosystem II and electron transport activity, and critical te mperature of chloroplast membrane organization. In all cases plants grown a t 27 degrees were superior to those grown at 15 or 45 degrees. The photosyn thetic performance of plants grown at 45 degrees was superior to those grow n at 15 degrees in all parameters, when the plants were young (3 months old ). With age some adaptation to the unfavourable temperatures proceeded, ind icated by a change of photosynthetic properties in the direction of plants grown at optimal temperature (27 degrees). The adaptation was especially st rong for the plants grown at 15 degrees, so that after 9 months their perfo rmance was better than that of 45 degrees plants. The conclusions for breed ing of more temperature adapted sugarcane plants are discussed.