PERSISTENCE AND SINGLE-PLANT PRODUCTIVITY IN NONDORMANT ALFALFA

Plant mortality is generally substantial in alfalfa (Medicago sativa L .) fields both at establishment and during the productive life of the stand, Most research has examined the effects of mortality on alfalfa yield per unit area, Consequences of mortality within a population on single-plant productivity have received relatively little attention, U nderstanding the basis for this mortality could affect management prac tices and the breeding and testing of alfalfa cultivars, The objective of this study was to describe agronomic, morphological, and physiolog ical traits associated with persistence in nondormant alfalfa, This wa s accomplished by comparing two populations of S-1 progenies derived f rom 60 surviving 6-yr-old plants from a commercial field of 'CUF-101' (=field-derived [FD] population) and 60 greenhouse-grown CUF-101 plant s (=greenhouse-derived [GHD] population) in field and greenhouse trial s at Tucson, AZ. In a field trial, crown mortality, as measured by the percent live stems, did not differ significantly between the populati ons, Total forage yield, yield in winter and spring, and stem elongati on rates were significantly greater in the GHD population, Root weight , total plant weight, root/shoot weight ratio, and concentration of to tal nonstructural carbohydrates in the root were Significantly greater in the FD population in a greenhouse trial, Differences observed betw een the two populations are consistent with the elimination of presuma bly less competitive plants with smaller root systems and plants intol erant of grazing in the winter and early spring, This research suggest s that mortality within stands of nondormant alfalfa is less likely fo r plants with larger roots and generally slower growth patterns that a re typically associated with increased fall dormancy.