EVALUATION OF PEANUT GENOTYPES FOR RESISTANCE TO WATER-STRESS INSITU

Observations indicate that Spanish-type peanuts are more tolerant of dehydration than Virginia types under severe water stress. However, physiological reasons for differences in tolerance to water deficits among peanut genotypes have not been established. The objective of this study was to evaluate peanut genotypes for their response and relative resistance to severe water deficits. A Spanish type (''Comet), Virginia type (''Florunner'') and a Spanish .times. Virginia selection (OK-FH15) were grown in situ under irrigated (IRR) and rainfed (RF) conditions. Leaf water potential (.psi.w), osmotic potential (.psi..pi.), turgor potential (.psi..pi.), relative water content (RWC) and its apoplastic water fraction (Aw) were determined weekly between 1300 and 1500 h, and diurnally on selected days. Yields were determined at 149 days after planting (DAP). Ratios (RF/IRR) of genotype .psi.w, .psi..pi., and RWC showed significant differences among genotype between 50 and 63 DAP, a critical period of peanut growth and development. The .psi.w and RWC ratios were maximum for all genotypes at 63 and 70 DAP for Comet (1.25), 63 DAP for OK-FH15 (1.32), and 70 DAP, respectively. The maximum .psi..pi. ratio occurred on 56 DAP for Florunner (1.18). Regression analysis of 1/.psi.w vs. RWC showed a biphasic cubic polynomial function best fit the dat afor all genotypes. The data indicated that as RWC declined, Comet .psi.w tended to decrease more rapidly than either OK-FH15 decreased with .psi..pi. to the origin. Comet had much greater Aw at low .psi.p and was the only genotype with appreciable Aw at low .psi.p. These results indicate that Aw varies in peanuts and may be genotype specific. Comet showed significantly higher yiel, grade, and dollar value than either Florunner or OK-FH15 under rainfed conditions. The lower .psi.w, greater change in .psi..pi. and higher Aw and yield of RF Comet suggests greater resistance to dehydration when high soil moisture deficits and evaporative demand conditions occur.