Agricultural Sciences: Techniques and Innovations Vol. 11

This pot experiment evaluated the effects of salt stress and foliar application of exogenous proline on three lowland rice cultivars during the reproductive phase. Plants of CNT1, PT1 and IN35 were grown under four sodium chloride levels (0, 50, 100 and 150 mM NaCl) and received four proline concentrations (0, 50, 100 and 150 mM), applied once at the heading stage before flowering. Physiological and biochemical traits were measured after proline application, whereas yield and yield-related traits were recorded at harvest. Pollen viability and proline gene expression responses were also assessed under the imposed treatments. Salinity produced cultivar-dependent effects on chlorophyll b, total chlorophyll, starch content, pollen viability and agronomic performance. Most yield and yield-component traits declined from 50 mM NaCl, while the harvest index declined more clearly at higher salinity levels. Among the cultivars, IN35 generally maintained higher grain yield per plant, productive tillers, filled grain percentage, 1000-grain weight, straw dry weight and harvest index than CNT1 and PT1. Exogenous proline increased chlorophyll traits and improved filled grain percentage, panicle length and grain yield per plant, with responses varying according to cultivar and salinity level. Pollen viability also improved after proline application under several salt-stress conditions. Reported proline gene expression differed among cultivars and treatments, with higher expression values observed in IN35 than in the Thai cultivars under stronger salt stress. Overall, the results indicate that exogenous proline may partially reduce salt-stress effects during the reproductive phase of rice, but the response depends strongly on cultivar and stress intensity.