Abstract
Three pot culture experiments were conducted to study the biochemical aspects, growth and mechanisms of salinity tolerance in rice at the Bangladesh Institute of Nuclear Agriculture, Mymensingh during the boro season of 2003-04, 2004-05 and 2005-06. Thirty rice genotypes were first tested for germination and seedling growth at different salinity levels. The germination of all the genotypes was almost normal at low salinity level (upto 4 dSm1) and it was reduced at elevated salinity levels. The percent relative seedling height, root and shoot dry weight and total dry matter under different salinity levels were higher in genotypes PVSB19, Pokkali, PVSB9, PNR519, PNR381 but NS15 showed very poor performance. The highest concentration of Na* was in NS15 and it was lowest in PNR519. Pokkali contained the highest concentration of K and the highest K*/Na* ratio was recorded in PVSB9 followed by PVSB19. Conversely, NS15 contained the lowest amount of K and K*/Na* ratio. Considering the above results, genotypes PVSB9, PVSB19, PNR381, PNR519 and Pokkali were screened as tolerant, Iratom24 as moderately tolerant and NS15 as susceptible. This study demonstrated that plant height, total tillers, root, shoot, and total dry matter, effective tillers, panicle length, spikelet number, filled grain, grain size and grain yield decreased significantly as the levels of salinity increased. As to the morphological characters, Pokkali, PVSB9, PVSB19 showed significantly higher values and the lowest value was recorded in NS15. The genotype NS15 survived upto 6 dSm1 and did not produce any grain at and above 9 dSm1 salinity, while Pokkali and PVSB9 produced grains upto 12 dSm1. Salinity affected significantly leaf chlorophyll, sugar, soluble protein, total amino acid and activities of nitrate reductase and Rubisco in the selected rice genotypes at different days after transplanting. The content of Na+, K+, Ca2+, Mg2+ and Cl in roots, shoots, stem, leaf sheath, leaf blade of rice and grain differed significantly with increasing salinity levels. The ionic ratios of Na+/K+, Na+/Ca2+, Na+/Mg2+, Ca2+/Mg2+ increased in roots and shoots with increasing salinity levels. Finally the effect of supplemental Ca application on mineral composition and growth of two tolerant genotypes Pokkali, PVSB9 and one sensitive NS15 were studied. The concentration of P, S, Na+, Ca2+, Mg2+, Fe2+, Mn2+ and Zn2+ were highest in NS15 and those were lowest in PVSB9 and Pokkali under different salinity and Ca levels. The relative- plant height, total tillers, root and shoot dry weight and total dry matter decreased with increasing salinity levels and these characters increased with increasing supplemental Ca levels significantly. The tolerant genotypes accumulated higher amounts of organic solutes and altered the ionic ratios through dilution of Na+ in shoot. Supplemental Ca ameliorated the deleterious effect of salinity in both tolerant and susceptible genotypes.