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Leaf Morphology, Shoot Growth, and Gas Exchange of Multifoliolate Alfalfa Phenotypes

Department of Agronomy, Purdue Univ., West Lafayette, IN 47907.

^* Corresponding author.

Herbage yield of alfalfa (Medicago sativa L.) is closely associated with leaf area. The objective of this study was to examine the relationships among leaf morphology, herbage growth, gas exchange, and root carbohydrate metabolism of alfalfa genotypes having trifoliolate or multifoliolate leaves. Plants selected for consistent production of five, seven, or nine leaflets per leaf were compared with genotypes having trifoliolate leaves that were selected for slow (SSER) or rapid (RSER) shoot elongation rate. Plants were grown in a controlled environment chamber at 23°C. In Exp. 1, multifoliolate selections averaged between 4.1 and 7.3 leaflets per leaf and had up to threefold greater area per leaf than trifoliolate phenotypes. Herbage regrowth of multifoliolate phenotypes was equal to phenotype RSER and greater than that of phenotype SSER. After Day 10 of regrowth, plant leaf area development was greater for phenotypes selected for seven or nine leaflets per leaf than trifoliolate phenotypes. Dark respiration rates of recently expanded leaves of plants were similar, while net photosynthetic rates of phenotypes selected for seven or nine leaflets per leaf were slightly lower than that of phenotype RSER. In Exp. 2, removal of lateral leaflets of multifoliolate leaves during early leaf expansion, converted them to trifoliolate leaves, increased net photosynthesis and dark respiration of trimmed leaves an average of 20% over that of intact multifoliolate leaves. Yield per shoot and herbage dry weight were reduced by removal of lateral leaflets, indicating that the multifoliolate leaf morphology was an important determinant of herbage yield of these multifoliolate phenotypes. In both experiments, selection for seven or more leaflets per leaf increased plant leaf area, a factor that may enhance herbage regrowth and forage yield of alfalfa.

Key Words: Medicago sativa L. • Regrowth • Phtosynthesis • Nonstructural carbohydrate • Dark respiration

Received for publication April 5, 1987.