Adverse effect of increase in minimum temperature during early grain filling period on grain growth and quality in indica rice (Oryza sativa) cultivars

Increasing global temperatures have a deterimental effect on rice quality besides leading to yield penalty. Past data shows that minimum temperature has increased more than maximum temperature in India as well as other parts of the world. The effect of this increase in mean minimum temperature on grain growth and quality of indica rice (Oryza saliva L.) cultivars is obscure. Our study submits the evaluation of grain quality of early, mid-early and medium duration indica rice cultivars to moderate increase in mean minimum temperature from anthesis to maturity in two seasons (kharif2014 and 2015). Early duration susceptible cultivars, Vandana and Parijat were significantly affected during the early phase of grain filling resulting in 4.6 and 6.4% decline in test weight and 12-18% in high density grains respectively, when the mean minimum temperatures were >= 25 degrees C. Slower grain growth rate under elevated mean minimum temperature accounted for decrease in dry matter accumulation in these cultivars. In general, percentage chalkiness was less in all the indica cultivars. Head rice recovery was not affected but amylose content reduced in all cultivars with a significant effect on Bakal and Sahbhagi Dhan when minimum temperatures increased by more than 23 degrees C. Rice cooking temperature determined by alkali spreading value was not stable across the environment in early duration cultivars, Vandana and Parijat. Increase in mean minimum temperature elicited the vulnerability of early duration indica cultivars, by adversely affecting quality traits like test weight, high density grains and gelatinization temperature.