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 parameters affected, sugarcane plants were grown at 15, 27, and 45 degrees for up to 10 months and photosynthetic parameters of the leaves were determined, namely chlorophyll content, Hill reaction, chlorophyll fluorescence parameters concerning photosystem II and electron transport activity, and critical temperature of chloroplast membrane organization. In all cases plants grown at 27 degrees were superior to those grown at 15 or 45 degrees. The photosynthetic performance of plants grown at 45 degrees was superior to those grown at 15 degrees in all parameters, when the plants were young (3 months old). With age some adaptation to the unfavourable temperatures proceeded, indicated by a change of photosynthetic properties in the direction of plants grown at optimal temperature (27 degrees). The adaptation was especially strong for the plants grown at 15 degrees, so that after 9 months their performance was better than that of 45 degrees plants. The conclusions for breeding of more temperature adapted sugarcane plants are discussed.