Rice (Oryza sativa L.) is the most important food crop cultivated worldwide and forms the staple diet for 2.7 billion people globally (40% of the world’s population). Rice is the most important cereal crop of the Eastern and North-Eastern India. About 80% of the rice area in Eastern and NE India are rain-fed which are exposed to a variety of abiotic stresses among which low light intensity is the most prevalent. Low light stress is a critical abiotic stress that reduces rice yield and quality. Since the growth and yield of rice crop are significantly affected by low light stress, the molecular mechanism of low light adaptation/resistance has been of great interest. Therefore, it is important to identify genotypes with specific adaptive features (low light intensity tolerance) to mark and introgress the responsible traits into high yielding varieties. Fifty rice genotypes were evaluated for 13 agro-morphological and physiological characters under two different environmental conditions (normal light and low light) to see the effect of light intensity on the studied traits. Data obtained was subjected to various statistical analyses of which the tolerant and the susceptible genotypes were identified. Inside greenhouse (low light condition), the mean monthly light received by the genotypes ranged from 1000-4000 W/m2; while it varied from 5000-9000 W/m2 outside greenhouse (control condition).The outcome of the study indicated that there was a general trend of increase in plant height of the genotypes under low light condition, highest being in Kba Sawrit-B (+85.8 cm),. Also, there was a general decrease in panicle weight, panicle length, number of spikelets/panicle, spikelet fertility and total number of grains. The grain weight/plant showed a general decrease in all the genotypes under low light condition and as was harvest index. The present study confirms for the first time that the susceptibility/resistance indices calculations developed for drought can very well be applied to low light intensity stress. Analysis of data through calculation of correlation coefficient, PCA and analysis of resistance/susceptibility indices identified some genotypes like IRCTN 91-84, IRCTN 91-94, RCPL 1-4C, RCPL 1-9C, etc. to be the promising genotypes for low light tolerance. The genotypes such as Kuki, Tami Hikari and Kba Sawrit-B were found to be the most susceptible genotypes for low light intensity.
One of the most significant findings of the study is that IRCTN 91-84 (7.39) is a unique genotype (most tolerant genotype to low light intensity) and can be utilised for breeding for low light resistance.
Keywords: Low light intensity; abiotic stress; correlation coefficient.