MILD DROUGHT IN INTERACTION WITH ADDITIONAL NITROGEN DOSE AT GRAIN FILLING STAGE MODULATES 2ACETYL-1-PYRROLINE BIOSYNTHESIS AND GRAIN YIELD IN FRAGRANT RICE

Abstract

Field experiments were conducted to investigate the influence of varying levels of water and nitrogen at grain filling stage on 2-acetyl-1-pyrroline (2-AP) content, enzymes activities and grain yield of fragrant rice (Oryza sativa L.). Two fragrant rice cultivars i.e., 'Basmati 385' and 'Nongxiang 18', were grown under two water treatments i.e., W1: well-watered (water layer 4-6 cm) and W2: mild soil drought, (the soil water potential was -(25 5 kPa)) from full heading stage to maturity during early and late season, 2014 at South China Agricultural University, Guangzhou, China. Two nitrogen levels i.e., N1: 15 kg hm -2 and N2: 30 kg hm -2 were applied at heading stage. Results showed that the W2 and N1 treatment improved 2-AP content in brown rice for both cultivars. Higher 2-AP content was observed in the W2N1 treatment in 'Basmati 385' (26.22 and 136.29 ng g -1 ) and 'Nongxiang 18' (23.47 and 66.48 ng g -1 ). Moreover, 2-AP content in brown rice showed positive correlation with proline dehydrogenase (PDH) activity whilst showed negative correlation with proline content in grains during both seasons. In addition, 2-AP content in brown rice showed significantly negative correlation with proline for early season, but significant and positive correlation with PDH activity in grains for late season. During early season, all treatments were found no statistically difference for grain yield of both rice cultivars, whereas the highest grain yield i.e., 7.39 and 8.07 t hm -2 was obtained under W2N1 treatment in 'Basmati 385' and 'Nongxiang 18', respectively during late season. In conclusion, mild drought conditions in combination with the N application at 15 kg hm -2 at grain filling stage could promote grain yield and 2-AP content in brown rice.