TOLERANCE AND TOXICITY LEVELS OF BORON IN MUNG BEAN (VIGNA RADIATA (L.) WILCZEK) CULTIVARS AT EARLY GROWTH STAGES

Boron (B) toxicity has been recognized as a serious problem in arid and semi arid regions of the world. This study was aimed to determine critical levels of B by studying phenotypic variation for B-tolerance/toxicity at the germination and seedling stage in three mung bean (Vigna radiata) cultivars; M-6, M-8 & 96009. Boron levels ranging from 0-20 ppm were applied using Boric acid. Germination, growth and photosynthetic attributes were significantly (p<0.001) influenced by varying B levels. However, the cultivars were significantly invariable for germination, seedling height and leaf number. B levels (5-10 ppm) appeared to be nutritionally critical whereas, 15-20 ppm induced B toxicity. The toxicity was expressed in terms of reduction in plant's growth as well as by visible symptoms which included chlorosis and necrosis of the foliage. The present study also demonstrated variation in B tolerance at the seedling stage in these cultivars. Among the tested cultivars, M-6 and M-8 exhibited better growth responses as compared with 96009. Fresh biomass and shoot: root ratio appeared to serve as selection criteria for B tolerance. The study further suggested screening of cultivars/accessions on a large scale to explore more diversity of traits as well as the use of biochemical markers for mechanistic understanding of B tolerance.