Herbage Growth and Carbohydrate Metabolism of Diploid and Tetraploid Alfalfa

Abstract

Polyploidy influences growth of alfalfa (Medicago sativa L.), but its impact on shoot and root carbohydrate metabolism and subsequent herbage regrowth rate remains unclear. This study related differences in herbage growth between isogenic diploid (2x) and tetraploid (4x) alfalfa populations to concentrations of root total nonstructural carbohydrates (TNC) and nonstructaral carbohydrate pools and dark respiration rates (RD) of meristematic shoot tissues. Leaf area, herbage weight, and taproots of plants were obtained weekly during 4 wk of regrowth in a controlled environment. Leaf area per plant and relative leaf area growth rate were approximately 100 and 33% greater, respectively, in the 4x population than in the 2x population. Although more herbage accumulated on 4x plants, herbage relative growth rates of populations were similar between Days 7 and 14, averaging 0.27 kg kg−1 d−1. Differences in shoot growth were not related to RD of shoot tip tissues, which averaged 55.2 ümol O2 mkg−1 s−1, or concentrations of glucose, sucrose, and starch in shoot tips. Root TNC concentrations of 2x and 4x populations were similar, initially averaging 360 g kg−1 dry wt. Concentrations of TNC increased in a linear fashion in roots of both populations during regrowth. The greater amount of shoot tissue present in the crown immediately following defoliation, along with the larger mass of individual growing shoot tips, contributed to more rapid leaf area development and faster herbage regrowth of the 4x population than the 2x population.