Varietal differences in spring and autumn sown maize (Zea mays) for tolerance against cadmium toxicity

Contamination of agricultural soils with heavy metals, including cadmium (Cd), is global threat to agricultural productivity. Maize is sensitive to Cd toxicity, although varietal differences exist. However, the responses of maize varieties to Cd toxicity across the growing seasons are not reported. With the objective to find variability for Cd tolerance across the seasons, in this study, nine maize (Zea mays L.) varieties were investigated for their comparative responses against Cd toxicity in sand medium during spring and autumn growing seasons, 2009. Data indicated significant varietal differences in all the growth attributes i.e., length and dry weight of shoot and root, number and area of green leaves and number of roots per plant. Although, tolerance of maize varieties were relatively better during autumn season, Pak-Afgoi, EV-79 and SWL-2002 were better tolerant whilst EV-20 was more sensitive to Cd toxicity during both the seasons. Application of Cd resulted in the appearance of visual toxicity symptoms on the leaves (overall leaf chlorosis & necrosis) and roots (constriction & browning) in all the varieties during both the seasons, but with great varietal differences. Correlations of visual toxicity symptoms with shoot growth data revealed that reduced leaf chlorosis, not the leaf necrosis, was positively related to shoot dry weight in both the seasons, while this was also the case for leaf area in autumn season. However, reduced root constriction and browning were positively related to increased root dry weight. Overall the results suggested that great varietal differences exist in maize for Cd tolerance, which provides room for improving and cultivating this species in marginally Cd contaminated soils. Leaf chlorosis, root constriction and browning can be taken as important determinants of tolerance against Cd in maize.