GENETIC VARIATION AND INHERITANCE OF RESISTANCE FOR LEAF IRON-DEFICIENCY CHLOROSIS IN DRY BEANS (PHASEOLUS VULGARIS L.)

Iron (Fe)-deficiency chlorosis is common in plants grown on alkaline calcareous soils. Investigations were conducted to determine the extent of genetic variation, influence of environment and rootstock, and inheritance of iron-deficiency chlorosis in dry beans (Phaseolus vulgaris L.). One hundred dry bean cultivars/lines were evaluated for iron (Fe)-deficiency chlorosis on a calcareous soil. Twenty-four cultivars/lines, varying in resistance or susceptibility to Fe chlorosis, were grown in nutrient solutions in growth chambers and analyzed for total iron in leaves. Fifteen entries were subsequently screened for Fe chlorosis under field conditions on a calcareous soil. Five of the 15 entries were grown in nutrient solutions in growth chambers under low (21/15.5$\sp\circ$C) and high (32/26.5$\sp\circ$C) light/dark temperature regimes, and a photoperiod of 12 hrs. The cultivars/lines differed in Fe chlorosis severity ranging from high or intermediate resistance to susceptibility. No correlation was found between the degree of Fe chlorosis and total Fe in leaves. A genotype $\times$ environment interaction was noted. The rate of leaf-chlorosis development was more rapid and severity of symptoms greater under lower than under higher temperatures in growth chambers. A genotype $\times$ temperature interaction was also noted. Some of the dry bean cultivars/lines that differed in their response to iron-deficiency chlorosis in field trials were used to study the inheritance of this trait. Based on F$\sb{2}$ segregations, it was hypothesized that resistance was determined primarily by two complementary dominant genes. Segregation in the F$\sb{3}$ families confirmed the hypothesis. Environment influenced considerably the range in expression of the leaf chlorosis. Reciprocal graft combinations (2 methods) of two resistant and 2 susceptible dry bean cultivars/lines to Fe-deficiency chlorosis were used to determine the effect of rootstocks on Fe-deficiency chlorosis. The grafted plants were grown in pots in calcareous soil in a growth chamber under low (24/13$\sp\circ$C) and high (29.5/18.5$\sp\circ$) temperature regimes, with 15 and 9 hrs of light and dark periods, respectively. Rootstocks of dry beans controlled uptake or utilization of iron. The chlorosis was more severe on leaves of cleft-grafted scions than with approach-grafted scions and also under the lower than higher temperature regimes