U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
April 1976
Abstract
Alfalfa (Medicago sativa L.) breeders are constantly striving to improve the productivity of alfalfa. Yields have been increased primarily through the selection of plant materials resistant to insects and diseases. The objective of this study was to evaluate physiological characteristics which might be used as selection criteria in alfalfa improvement. Alfalfa clones were grown under field conditions on a Mojave clay loam soil. Carbon dioxide flux was evaluated in a closed system using an infrared gas analyzer. The physiological variables measured in these studies did not account for the varialion in yield among the clones. Apparent photosynthetic rates, dark respiration rates, and postillumination CO2 burst rates expressed as mg CO2 dm-2 hour-1 were not correlated with dry matter production. However, when these physiological factors were multiplied by leaf area and expressed as total CO2 exchange per plant per hour, there was a significant relationship between yield and these calculated variables, in both studies. Regression analyses of more than 30 factors indicated that leaf area, leaf to stem-petiole ratio, and leaf weight per plant accounted for more than 95% of the variation in yield among alfalfa clones. The data from these studies suggest that morphological factors were more reliable indicators of alfalfa productivity than physiological factors.
Comments
Published in AGRONOMY JOURNAL, VOL. 68, JULY-AUGUST 1976.