Causes of sterility in rice under salinity stress

Abstract

Effect of salinity at 50 mM NaCl level on Pollen Viability, Chlorophyll, Na+, K+, Photosynthesis (pn), Carbohydrate content of different floral parts and Starch synthetase activity at midmilky stage of developing grains of IR-28 were analyzed, to find out the causes of sterility in rice under salt stress. Salinity induced changes on floral characteristics i.e. panicle length, number of primary and secondary branches of panicles were also studied. The yield components like filled seeds / panicle, un-filled seeds /panicle, total seeds / panicle, total seed weight / panicle and 1000 seed weight were also recorded at maturity. The results showed significant inhibition in pollen Viability, Chlorophyll; K+ in Flag leaf, third leaf, primary branches, and panicle stalk. On the other hand significant increase in Na+ content in different leaves and all the floral parts was observed. This could be one of the reasons of sterility in rice. Further analysis was done to see the effect of salinity on photosynthate translocation in panicle branches & developing spikelets, carbohydrate content of different vegetative parts. The data suggest that reduction in grain number and grain weight in salinized panicles was not merely due to reduction in Pollen Viability, reduction in pn and higher accumulation of Na+ & less K+ in different floral parts but also due to higher accumulation of Photosynthates (sugars) in Primary & Secondary panicle branches, panicle main stalk and panicle stem coupled with reduced activity of starch synthetase in developing grains. From these data it was inferred that this could possibly be due to higher accumulation of Na+ in floral parts, thus reducing the availability of glucosyle donors for starch synthetase activity to transfer the glucose moiety from ADP-G to starch primer in developing grains resulting in failure of seed set.