Response of rice plants to heat stress during initiation of panicle primordia or grain-filling phases

Leaf photosynthesis, a major determinant for yield sustainability in rice, is greatly conditioned by high temperature stress during growth. The effect of short-term high temperatures on leaf photosynthesis, stomatal conductance, Fv/Fm, SPAD readings and yield characteristics was studied in two Colombian rice cultivars. Two genotypes, cv. Fedearroz 50 (F50) and cv. Fedearroz 733 (F733) were used in pot experiments with heat stress treatment (Plants were exposed to 40°C for two and half hours for five consecutive days) and natural temperature (control) treatment. Heat treatments were carried out at the initiation of panicle primordial (IP) or grain-filling (GF) phases. The results showed that short-term high temperature stress produced a reduction on the photosynthesis rate in both cultivars either IP or GF phases. Similar trends were found on stomatal conductance in all cases due to high temperatures. Although Fv/Fm and SPAD readings were not affected by high temperatures, these variables diminished significantly among phenological phases. 'F733' rice plants showed higher number spikelet sterility due to heat stress treatments. These results seem to indicate that heat-tolerant cultivars of rice is associated with high levels of photosynthesis rate in leaves.