Boron induced modulation in growth, photosynthesis and antioxidant system in two varieties of Brassica juncea

Boron toxicity is an environmental constraint that limits crop productivity worldwide. The aim of the present study was to explore the boron-induced modulation in growth, photosynthesis, antioxidant system under varied levels of boron in two varieties of Brassica juncea L. Czern & Coss var. Varuna and Chapka rohini. The surface-sterilized seeds of these varieties were sown in soil amended with different levels (0, 10, 20, 30, 40, 50 or 60 mg kg-1) of boron and were sampled at 45 d stage of growth. The boron treatment (20, 30, 40, 50 or 60 mg kg-1) significantly decreased growth, net photosynthetic rate and its related attributes, chlorophyll fluorescence, SPAD value of chlorophyll, and leaf carbonic anhydrase and nitrate reductase activities whereas, the proline content and the level of various antioxidant enzymes (catalase, peroxidase and superoxide dismutase) increased in both the varieties. Out of the graded concentrations of boron, 20 mg kg-1 was least toxic and 60 mg kg-1 B generated maximum toxicity. However, the application of 10 mg kg-1 B did not generate any significant effect in almost all the parameters. Furthermore, the variety Varuna was found more tolerant than Chapka rohini to the boron stress and possessed higher values for growth, photosynthetic attributes and antioxidant enzymes. The variation in the responses of these two varieties to boron toxicity is attributed to their differential photosynthetic traits, SPAD chlorophyll value and antioxidant capacity, which could be used as potential markers for screening mustard plants for boron tolerance.