Relations between photoperiod, temperature, abscisic acid, and fall dormancy in alfalfa (Medicago sativa)

Abstract

Three alfalfa (Medicago sativa L.) cultivars differing in fall dormancy were examined for endogenous abscisic acid content in relation to fall dormancy. The alfalfa cultivars studied were 'Beaver' (dormant type), 'Lahonton' (semidormant type), and 'Moapa 69' (nondormant type). Alfalfa seedlings were grown in controlled-environment chambers set at a 16-h photoperiod (16 h light: 8 h dark) and 20:15 °C (light:dark) for 55 days. They were cut and then regrown under environmental conditions simulating summer and fall in western Canada. In leaf samples, the ABA level increased from about 200 in 3-week-old plants to more than 1200 ng/g fresh weight in 8-week-old plants. After cutting, abscisic acid levels dropped abruptly and then increased gradually, reaching a peak level at the stage of the appearance of flower buds. The peak of abscisic acid content was highest in 'Beaver', next highest in 'Lahontan', and lowest in the nondormant type, 'Moapa 69'. At the 6th week of regrowth, abscisic acid content in 'Beaver' was found to be 2200 ng/g fresh weight, which is the highest reported level in nonstressed plants of any species. The analysis of variance suggests photoperiod, temperature, and photoperiod × temperature interaction all have a significant effect on alfalfa regrowth and on abscisic acid content. Under long days and cool temperatures, the amount of foliage regrowth and the characteristic of fall dormancy are manifestly correlated. There is no apparent link between endogenous abscisic acid content and fall dormancy.