Selection for Aluminum and Acid-Soil Resistance in White Clover

Abstract

Despite good resistance to acid-soil stresses, white clover (Trifolium repens L.) is not found on some acid soils. Our objectives were to develop a large-leafed white clover with acid-soil resistance, to relate seedling Al to mature plant acid-soil resistance, and to validate our soil-on-agar procedure. We used a two-stage selection procedure. In Stage 1 we used the soil-on-agar technique to select for seedling Al-resistance and Al-susceptibility in Brown Loam Synthetic No. 2 and ‘Grasslands Huia’ white clover. In Stage 2 we used conventional pot studies with two soil pH treatments, 4.2 and 5.2, and stem-tip cuttings of Al-resistant selections from Brown Loam to select for acid-soil resistance. The same Stage 1 and 2 techniques were used to evaluate 12 experimental populations and both parents for seedling Al resistance and mature plant acid-soil resistance. Across two cycles of selection, both Brown Loam and Huia Al-resistant and susceptible populations diverged. For Brown Loam, progress was made toward both increased Al resistance and susceptibility. For Huia, progress appeared more toward Al susceptibility than toward Al resistance. Populations developed from two-stage selection were more acid-soil resistant than their parent. However, populations selected only for seedling Al resistance or Al susceptibility were usually no more acid-soil resistant than their parent. We were able to increase the acid-soil resistance of Brown Loam white clover. But, the soil-on-agar procedure was not an effective technique for developing acid-soil-resistant white clover germplasm.