Physiological and Morphological Characteristics of Large and Small Leaflet Alfalfa Genotypes1

Abstract

AbstractA rapid test for identifying high‐yielding genotypes of all crop plants, including alfalfa (Medicago sativa L.), is needed. Because previous work indicated that alfalfa yield is closely associated with leaflet size, 15 alfalfa genotypes with large primary leaflets and 13 alfalfa genotypes with small primary leaflets were identified by visual selection in the field and compared for yield, leaflet size, specific leaf weight (SLW), and rate of carbon exchange in the spring of 1974. The large leaflet alfalfa genotypes had significantly higher yield, larger leaflets, and lower SLW than the small leaflet genotypes when the data were combined over the entire growing season. The large leaflet genotypes had significantly higher rates of total photosynthesis per plant, significantly lower rates of apparent photosynthesis per unit leaf area than the small leaflet genotypes, and equal rates of apparent photosynthesis per gram of leaves to those of the small leaflet genotypes.Correlation coefficients were calculated between the various morphological and physiological parameters measured on all genotypes. The best selection criteria for yield was total leaf area per plant (r=0.92, significant at 1% level). Dry matter production was positively and significantly associated with total CO2 uptake per plant (r=0.63, 1% level) and leaflet area of primary leaflets (r= 0.47, 1% level). Although apparent photosynthesis showed a significant but negative (r=−0.26, 570 level) association with yield, its predictive value was low. Carbon exchange, apparent photosynthesis, dark respiration, post‐illumination‐burst, and photorespiration were significantly and positively associated with each other. Further research is needed to determine if vegetatively propagated swards of large leaflet alfalfa would outyield swards of small leafet afalfa.