Leaf Area Expansion and Shoot Elongation of Diverse Alfalfa Germplasms1

Abstract

Rapid regrowth of alfalfa (Medicago sativa L.) following harvest is important to maximize use of solar radiation and obtain high herbage yields. The objectives of this study were to evaluate interrelationships among leaf area expansion rate (LAER), shoot elongation rate (SER), and several morphological and physiological characters. Leaf area per shoot and shoot length of four diverse germplasms were measured daily during 28 days of regrowth in the greenhouse. Leaf area per shoot and shoot length both increased in a nearly linear manner, and LAER and SER, calculated during the interval 8 to 21 days following harvest, were linearly related (R2 = 0.73**). In a second study, plant introductions selected for rapid regrowth following harvest had 37% greater SER and produced 32% more leaf area per shoot than plant introductions classified as having slow regrowth. This indicates that SER is an effective indicator of LAER. Averaged across experiments, plants with rapid SER had 55% higher specific stem weight with 26% more internodes and 80% longer internodes than plants with slow SER. This resulted in 74% higher yield per shoot of the rapid SER plants when compared to slow SER plants. The SER and LAER were not consistently associated with root total nonstructural carbohydrate concentrations or number of shoots per plant, and were negatively correlated with herbage N concentrations (r = −0.36 to −0.55). Additional work is underway to elucidate the biochemical and physiological basis for genetic differences in SER.