Field Drought Tolerance of a Soybean Plant Introduction

Rainfall is seldom sufficient to meet the evaporative and transpirational demands of a soybean crop [Glycine max (L.) Merr.] in the southeastern USA. Development of new drought-tolerant cultivars would thus seem an effective way in which to address the problem of moisture stress. Unfortunately, few drought-tolerant genotypes have been identified for use as breeding stock. The objective of this study was to compare the relative droughtolerance of plant introduction PI 416937, a visually slow-wilting accession, with that of ‘Forrest’, a popular cultivar of similar maturity. Leaf water potential (Ψw), solute potential (Ψs), and relative water content (RWC) these genotypes were measured under two levels of soil water adjustment (well-watered and water-stressed at early pod-fill) during 2 yr in the field (on a Varina loamy sand, a clayey, kaolinitic, thermic Plinthic Paleudult). Although water stress reduced Ψw equally for both genotypes, PI 416937 maintained lower levels of Ψs and. higher levels of pressure potential and RWC than Forrest. A comparison of the relationship between RWC and Ψs for the two genotypes indicated that the PI may accumulate more solutes in leaf tissue under stress than Forrest. That is, at a normalized leaf pressure potential of zero, the Ψs of the PI was estimated to be 0.3 MPa lower than that of Forrest. Seed yields of Forrest and the unadapted PI were comparable under stress. However, stress reduced the yield of Forrest by more than half while reducing yield of the PI by only a third. The superior turgor maintenance and competitive yielding ability of the unadapted PI under stress indicated that the PI may be an important source of drought tolerance for breeding programs. Joint contribution of the USDA-ARS and North Carolina Agric. Res. Serv. Paper no. 11540 of the journal series of the North Carolina Agric. Res. Serv., Raleigh, NC 27695-7601.