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Evaluation of Peanut Genotypes for Resistance to Water Stress In Situ¹

Observations indicate that Spanish-type peanuts (Arachis hypogaea L.) 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 x Virginia selection (OK-FH15) were grown in situ under irrigated (IRR) and rainfed (RF) conditions. Leaf water potential (_w), osmotic potential (), turgor potential (_p), relative water content (RWC) and its apoplastic water fraction (A_w) 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) genotype _w, , and RWC showed significant differences among genotypes between 50 and 63 DAP, a critical period of peanut growth and development. The _w and RWC ratios were maximum for all genotypes at 63 and 70 DAP, respectively. The maximum ratio occurred on 56 DAP for Comet (1.25), 63 DAP for OK-FH15 (1.32), and 70 DAP for Florunner (1.18). Regression analysis of 1/_w vs. RWC showed a biphasic cubic polynomial function best fit the data for all genotypes. The data indicated that as RWC declined, Comet _w tended to decrease more rapidly than either OK-FH15 or Florunner. Conservative estimates of , changes between 95 and 55%R WC were highest for Comet, lowest for Florunner, and OK-FH15 was intermediate. A_w was calculated for each genotype and plotted against _p to determine its contribution to hydration maintenance. At high _p, maximum A_w, was 7.1, 12.1, and 25.2%f or Florunner, OK-FH15, and Comet, respectively. Florunner A_w, decreased to zero at 0.16 MPa _p, and the A_w of OK-FH15 decreased with _p to the origin. Comet had much greater A_w at low _p and was the only genotype with appreciable A_w at zero _p. These results indicate that A_w varies in peanuts and may be genotype specific. Comet showed significantly higher yield, grade, and dollar value than either Florunner or OK-FH15 under rainfed conditions. The lower _w, greater change in , and higher A_w and yield of RF Comet suggests greater resistance to dehydration when high soil moisture deficits and evaporative demand conditions occur.

Key Words: Arachis hypogaea L. • Dehydration resistance • Water relations • Osmotic adjustment • Apoplastic water • Hydration maintenance • Irrigation • Rainfed

² Formerly, research associate, present address: FMCC orporation, Princeton, NJ 08540; and plant physiologist, USDA-ARS, Plant Science Research Laboratory, Stillwater, OK 74076.

Received for publication September 13, 1984.