Growth Analysis of Tall Fescue Genotypes Differing in Yield and Leaf Photosynthesis

Relationships between leaf photosynthesis and yield have not been well defined in forage grasses. Therefore, leaf growth, dry matter distribution, carbohydrate concentration, and growth analysis of four genotypes of tall fescue (Festuca mundinacea Schreb.) were examined. Genotypes, selected in the field for high and low CO2 exchange rate (CER) in combination with high and low yield, were compared in an attempt to study the relationship between photosynthesis and yield. In the vegetative growth stage, high yielding genotypes produced greater amounts of all plant parts (leaves, stem bases, and roots) than did low yielding genotypes; however, low yielding genotypes produced more leaf tissue relative to total increase in plant dry weight than did high yielding genotypes. Water-soluble carbohydrate (WSC) concentrations of plant parts were significantly different among genotypes, with high-CER genotypes having highest levels during early stages of regrowth. High yielding genotypes had highest WSC concentrations at later stages regardless of CER rating. Mean relative growth rates of the four genotypes were similar. Mean net assimilation rates and mean relative leaf area growth rates tended to be greater for the high yielding genotypes than for the low yielding genotypes. Results indicated the greater yields exhibited by the high yielding genotypes regardless of CER rating resulted from (1) greater carbohydrate reserves to initiate new leaf growth, (2) more rapid leaf area development, and (3) partitioning a greater amount of newly assimilated dry matter into leaf tissue during the first 16 to 19 days of regrowth