TEMPERATURE AND PHOTOPERIOD EFFECTS ON MULTIFOLIOLATE EXPRESSION AND MORPHOLOGY OF ALFALFA

Alfalfa (Medicago sativa L.) cultivars with multifoliolate (MF) leaves are being promoted as a source of high quality forage, but informatio n is lacking about the effect of environment on MF expression. We stud ied the influence of air temperature and photoperiod on the MF trait a nd its association with leaf and stem morphology. We grouped plants fr om four cultivars into four MF expression classes (very low, < 10%; lo w, 10-29%; medium, 30-60%; and high, > 60% MF leaves). These plants we re grown in four growth chamber environments combining cool (20/11-deg rees-C day/night) and warm (29/17-degrees-C) air temperatures with sho rt (13 h) and long (16 h) photoperiods. Photoperiod had a greater infl uence than temperature on MF expression (MF%, number of MF leaves tota l leaf number-1). Under long-days, MF expression of plants in very low , low, and medium MF expression classes declined linearly with increas ed maturity. Under short-days, MF% of these classes declined until bud , but then increased until maturity. Multifoliolate expression of plan ts in the high expression class decreased in the cool-long day environ ment, but maintained or increased MF% in other environments. At harves t, MF%, leafiness, and leaflet number per MF leaf were greater for sho rt vs. long photoperiods, but were not affected by air temperature. Mu ltifoliolate expression was positively correlated (r = 0.43) with leaf iness and number of leaflets per MF leaf (r = 0.96), but was not corre lated with stem characteristics. Individual MF leaves had larger leaf area but similar specific leaf weight as trifoliolate leaves in all en vironments. In evaluation of MF expression, stage of maturity, and env ironmental conditions should be standardized.