Differential nickel tolerance of mung bean (Vigna radiata L.) genotypes in nutrient culture

Eight cultivars of mung bean (Vigna radiata L.) were tested for their tolerance to different levels of nickel (Ni) (0, 6, 12, 18 and 24 mu M) in nutrient solution at pH 6.8. Seeds were germinated and grown in the presence of nickel under controlled environmental conditions. Standard growth parameters such as root length, shoot length, root/shoot dry biomass production and root/shoot tolerance index were used as markers of nickel toxicity. Measurements as early as 24 h after the beginning of treatment did not yield consistent results. However, root measurements 3, 6 and 9 days after the beginning of treatments yielded significant differences among cultivars which were similar to field performance in nickel-rich soils. The cultivars Dhauli and PDM-116 showed root growth while LGG-407, K-851, TARM-22 and TARM-1, TARM-21, TARM-26 exhibited a reverse trend in root growth in the presence of nickel (12 mu M). The root tolerance index (RTI) and the shoot tolerance index (STI) with respect to Dhauli and PDM-116 were high indicating their tolerance to nickel; TARM-21 and TARM-26, however, showed a low RTI and STI. Based on the growth parameters eight cultivars of mung bean were ranked with respect to their tolerance to nickel: Dhauli > PDM-116 > LGG-407 > K-851 > TARM-22 > TARM-1 > TARM-21 > TARM-26. Nickel induced greater G6PDH and GDH activity in Dhauli and PDM-116 as compared to LGG-407, K-851, TARM-22, TARM-1, TARM-21 and TARM-26. This method can be employed for quick screening of mung bean for nickel tolerance. (C) Inra/Elsevier, Paris.