DIFFERENCES IN RESPONSES TO IRON-DEFICIENCY AMONG VARIOUS CULTIVARS OF MUNGBEAN (VIGNA-RADIATA (L.) WILCZEK)

Ten mungbean cultivars were evaluated for their resistance to iron def iciency in view of chlorosis symptoms, plant growth and seed yield und er field conditions on a calcareous soil in Thailand. The KPS2 cultiva r was highly susceptible; the KPS1, PSU1 and Pag-asa 1 cultivars were somewhat susceptible; the VC1163B cultivar was moderately tolerant; th e CN36, CN60, UT1 and CNM-I cultivars were tolerant, and the CNM8509B cultivar was very tolerant to iron deficiency. Foliar application of a solution of 5 g L-1 ferrous sulphate was effective in correcting chlo rosis that was induced by iron deficiency, and it enhanced both the gr owth and the yield of susceptible cultivars. Compared with the suscept ible cultivar KPS2, the tolerant cultivar UT1 had a greater ability to lower the pH of the nutrient solution in response to iron deficiency. The root-associated Fe3+-reduction activity of UT 1 that had been gro wn in -Fe medium was similar to that of the plants grown in +Fe medium when the acidification of the medium occurred. Acidification of the m edium in response to iron deficiency might contribute to the efficient solubilization of iron from calcareous soils, and it related more clo sely to the resistance to iron deficiency than Fe3+ reduction by roots in mungbean cultivars.