Genotypic variations in growth, mineral composition, photosynthesis and leaf metabolism of Indian mustard under sodicity stress

Responses of five genotypes (Varuna, CZM-2, Pusa Bold, PCR-7 and BIO-902) of Indian mustard (Brassica juncea L.) grown under three levels of sodium adsorption ratio (SAR) of irrigation water (0.7, 15.0 and 30.0) were studied on plant growth, mineral composition, net photosynthetic rates and leaf metabolism at the flowering stage. Increasing SAR levels progressively reduced plant growth in terms of height, leaf area, shoot dry matter and seed yield in all the genotypes. However, cvs. Pusa Bold and BIO-902 displayed higher sodicity tolerance whereas genotypes CZM-2 and Varuna were most sensitive with 25% reduction in seed yield at SAR level of30. Genotype PCR-7 displayed an intermediate tolerance to sodicity. Concentrations of nitrogen and potassium in shoot declined while that of sodium increased with increasing SAR. Moreover sensitive genotypes CZM-2 and Varuna had higher concentration ofNa and consequently lower K:Na ratio at all levels ofSAR as compared to tolerant genotypes Pusa Bold and BIO-902. Increasing SAR, significantly decreased net photosynthetic rates and increased leaf diffusive resistance in all cultivars but genotypes BIO-902 and Pusa Bold experienced less alterations. Sodicity-induced changes in the levels of total chlorophyll, soluble protein, free amino acids, starch, total soluble sugars and nitrate reductase activity were consistently less in genotypes BIO-902 and Pusa Bold as compared to CZM-2 and Varuna. However, the response of cv. PCR-7 was variable and inconsistent. These differential genotypic responses have been discussed in the light of the present knowledge.