Adaptation of Kharif Rice Crop to Low Light Intensity in Field Condition of Assam
Rice (Oryza sativa L.) grown in winter season in tropical and subtropical regions suffers from adverse climatic condition, which is characterized by overcast sky posing low sunshine hours during the vegetative to reproductive growth stages of the crop. Rice plant requires about 1500 bright sunshine (BSS) hours (PPFD>1000µMs-1m-1) for the period from transplanting to maturity. Instead, prevalence of only about 800-900 BSS hours (PPFD<500 µMs-1m-1) during August to December in places like Northeastern region of India hampers not only the physiological efficiencies, but also the nutritional quality of grain, and ultimately the productivity of winter rice crop. In this context, one hundred rice germplasm, (fifty collected from AAU, Assam, and another fifty germplasm from NRRI, Cuttack), were screened for adaptation to low light intensity in filed condition at ICR farm, AAU for the two consecutive kharif seasons of 2016 & 2017. In general, low light provided at 40 days after transplanting, by 35% shade net, erected at 1.8m above the ground by bamboo frame, reduced many physiological parameters except internodes length, chlorophyll contents and spikelet sterility. However, some of the varieties produced higher yield and its attributes under low light condition. Based on the two year’s pool data, the short duration variety BVS1 produced the highest economic yield under normal (7.18 th-1) and low light (5.88 th-1) conditions in both the years. Similarly, a long duration genotype viz., Aki Sali, too, produced higher economic yield under both normal (5.75 th-1) and low light (3.80 th-1) conditions. Even, the low light tolerant check variety Swarnaprabha, produced lower yield both under normal (2.40 th-1) and low light (1.73 th-1) than BVS-1 and Aki Sali in the investigation. The low light susceptible check variety IR-8 produced lower yield (2.35 th-1 & 1.94 th-1only) under normal and low light conditions respectively. The contrasting genotypes under low light condition are BSV-1 (5.88 th-1, 18.07 % reduction) and Misi Sali (0.28 th-1 with 93.98% yield reduction), whereas the contrasting ones under normal light condition are BSV-1 (7.18 th-1) and Bhagawanti (3.14 th-1 with 74.30% yield reduction). The physiological attributes supporting higher economic yield of the tolerant varieties (BVS-1& Aki Sali) under low light condition are higher panicle length, individual panicle weight, lower sterility, higher HI and Chlorophyll contents. The other morpho-physiological characteristic of the tolerant varieties are more internode length, lower SLW, and higher tiller number. A significant positive correlation of yield attributes with grain yield at normal light, and mostly a negative correlation of the parameters of the germplasm were found at low light conditions.
Keywords - Low Light, PPFD, Chlorophyll, SLW, Inter Node Length, HI, Panicle Length and Weight, Sterility, HD Grains