Growth Potential of the Axis as a Determinant of Seedling Vigor in Birdsfoot Trefoil1

Abstract

Seedlings which developed from large seeds of birdsfoot trefoil (Lotus corniculatus L.) cv. Leo elongated faster than seedlings from small seeds, and this has been associated in previous experiments with improved field emergence and forage yield in the year of establishment. The physiological basis for the difference in seedling elongation between large and small seeds and between the cultivars Leo and Empire was investigated. The increased rate of axis elongation in large seeds was associated with an increased rate of dry weight (DW) accumulation. Both endosperm and cotyledon reserves contributed to this growth. When grown on an agar medium, supplemented with nutrients but without hormones, the axes from large seeds accumulated more DW than axes from small seeds suggesting that differences in sink size are primarily responsible for the differences in growth rates. Seedlings of Leo elongated faster than those of Empire and this was associated with a greater increase in axis DW. Endosperm reserves were depleted similarly in both cultivars, but Leo had a greater quantity of cotyledon reserves and translocared more to the axis than Empire. When grown on agar medium, the Leo axes accumulated more DW than Empire. The data are interpreted as indicating that differences in the ability of the axis to accumulate DW (sink size) account for differences in seedling vigor between seed sizes and contribute to the differences in vigor between the cultivars Leo and Empire.