VARIETAL TOLERANCE OF ZINC TOXICITY IN PEANUTS

Peanuts (Arachishypogaea) are more susceptible to zinc (Zn) toxicity t han other crops. However, there is potential for rapid evolution of Zn tolerance in many species. The objectives of this study were to test a nutrient solution screening procedure for identifying Zn tolerant cu ltivars and to identify plant characteristics and cultivars which have potential for Zn tolerance. Florunner was used as the test cultivar t o determine the optimum Zn and pH levels for the nutrient solution cul tivar screening test. The screening test showed that VA 81B and NC 6 ( both virginia-type peanuts) were more Zn sensitive than Florunner and that N. M. Valencia C and McRan (both valencia-type peanuts) were more tolerant than Florunner. Field tests were carried out at three locati ons in Tift County, Georgia: Gibbs Farm (1986-87), Richards Farm (1991 ), and Stephens Farm (1992). Two out of four field tests did not have adequate soil Zn levels to test Zn tolerance; soil pH between 5.0 and 5.5 and Mehlich 1 soil Zn level ranging from 15-20 mg/kg should be ade quate for cultivar screening in the field. Spanish-type cultivars (Pro nto, Spanco, and Starr) had the lowest toxicity ratings and highest yi elds (Gibbs, 1987), but yields were not economically viable for any cu ltivars. Aboveground plant Zn or calcium (Ca):Zn ratio were not good i ndicators of cultivar tolerance. However, low hull Zn concentration, h igh hull Ca:Zn ratio, and high plant Zn:root Zn ratio correlated well with high yield and low toxicity rating. Minimization of Zn uptake by the hulls would evidently be beneficial in aiding peanut plants in tol erating high soil Zn levels while producing economic yields.