Developing aluminum‐tolerant strains of tall fescue for acid soils

Abstract

Tall fescue (Festuca arundinacea Schreb.) is an important cool season perennial grass used for forage and turf. It is reportedly more tolerant to acid soils than Kentucky bluegrass (Poa pratensis L.) but less tolerant than the fine leafed fescues. In previous studies, Kentucky 31 was the most acid soil tolerant cultivar tested on aluminum (Al)‐toxic Tatum subsoil at pH 4.3. However, a few plants within several cultivars showed high tolerance to this acid soil. This suggested the potential for increasing acid soil (Al) tolerance by selection within established cultivars. Aluminum‐tolerant cultivars are needed for use on marginal soils having acid (pH <5.0), Al‐toxic surface and/or subsoil horizons. Such soils are often involved in low level management systems of forage production or turf maintenance. To exploit this genetic variability, populations of tall fescue, obtained by recurrent selection from three parents (Ky‐31, Alta, and a turf‐type fescue), on acid, Al‐toxic Tatum subsoil, were tested for Al tolerance on the same acid soil and in nutrient solutions, in comparison with their parents. In general, recurrent selections were more tolerant to the acid subsoil at pH 4.2 (compared with pH 5.7) than were their parents. They also produced more absolute green and dry shoot weights on unlimed soil at pH 4.2 than parents. Based on relative green shoot weight (wt at pH 4.2 / wt at pH 5.7 × 100), two cycles of recurrent selection on acid Tatum subsoil increased tolerance to the same soil by 75,33, and 107% for Ky‐31, Alta, and turf‐type fescues, respectively. Based on relative dry shoot weight, acid soil tolerance was increased by 50, 18, and 70% for Ky‐31, Alta, and turf‐type fescues, respectively. In the turf‐type fescue, recurrent selection increased acid soil tolerance to a greater degree in the first cycle than in the second. In this selection (TT₀), relative dry weights were increased by 99% for shoots and 111% for roots. Increases in acid soil tolerance were more pronounced in derivatives of Ky‐31 and turf‐type than in those of Alta fescue. When plants were grown in nutrient solutions, recurrent acid soil selections of Ky‐31 and turf‐type fescues showed increased overall plant vigor and Al tolerance, but those of Alta fescue did not. Recurrent acid soil selection was more effective in increasing acid soil tolerance per se than in increasing Al tolerance in nutrient solutions. Increased acid soil (Al) tolerance in the first and second cycle selections in the Ky‐31 cultivar was associated with greater plant‐induced pH increases in nutrient solutions than those produced by the parent cultivar. A lower pH in solution means that the parent Ky‐31 cultivar was exposed to higher concentrations of soluble Al than were its derivatives. Results indicated that established cultivars of tall fescue contain considerable genetic variation with respect to acid soil tolerance and that recurrent selection can be used to identify genotypes that are better adapted to acid marginal soils that are frequently used in low level management systems for forage or turf. During a severe drought, a field plot of KpH₂ remained green 10 days longer than that of the parent cultivar Ky‐31. Hence, acid soil (Al) tolerance coincided with drought tolerance.

Notes

Deceased. Formerly, Field Crops Laboratory, Plant Genetics and Germplasm Institute, ARS, USDA, Beltsville, MD 20705.