SCREENING CHICKPEA FOR IRON CHLOROSIS RESISTANCE USING BICARBONATE IN NUTRIENT SOLUTION TO SIMULATE CALCAREOUS SOILS

Chaney and Coulombe introduced an effective method to screen dicot genotypes for resistance to bicarbonate-induced Fe-deficiency chlorosis. Their method used low levels of FeEDDHA in a nutrient solution with high levels of Ca and Mg salts to mimic the soil solution of problem soils in Iowa and Minnesota. The combination of low Fe supply and high NaHCO3 induced Fe-stress. Only chlorosis-resistant soybean and bean cultivars were able to de-repress their Fe-stress-response enough to obtain adequate Fe and remain green. Susceptible genotypes became severely chlorotic. Although Fehr and Cianzio et al. found the method reliable, commercial breeders had poorer reproducibility. As more highly improved Fe-chlorosis resistance soybean genotypes were developed, lower FeEDDHA and/or higher bicarbonate were required in the screening solutions. With these very low FeEDDHA levels (1.5-2 muM), small amounts of soil or dust contamination of the solutions could markedly shift the screening results. With the development of chelator-buffered nutrient solutions which supplied adequate amounts of all required nutrients, it became possible to use DTPA-buffering of Fe rather than EDDHA. DTPA buffers Fe2+ much more strongly than EDDHA, so that 25 muM FeDTPA is used in normal screening rather than 1.5-2 muM FeEDDHA. In the present work, we tested FeDTPA levels required to screen chickpea and soybean cultivars for relative chlorosis resistance. Thirteen chickpea genotypes with a range of chlorosis-susceptibility demonstrated in the field, and 2 indicator genotypes of soybean and 1 tomato were screened at 60, 25, and 15 muM FeDTPA and 10 mM NaHCO, compared to a control. Highly chlorosis-susceptible chickpea genotypes were chlorotic at 60 muM, while only the most resistant were green at 15 muM FeDTPA. This indicates that bicarbonate is probably the soil factor which induces chlorosis in chickpea in the field. Soybean genotypes showed chlorosis severity similar to field ratings and FeEDDHA screening solution results, while tomato remained green at 15 muM Fe. Results indicate that dicots may be effectively screened using Fe-DTPA in DTPA-buffered solutions, and that the method is sufficiently robust for commercial breeders.