Morphological variation of Medicago sativa subsp falcata genotypes and their hybrid progeny

Semi-hybrid alfalfa cultivars offer the possibility of capturing non-additive genetic variation. Medicago sativa subsp. falcata and subsp. sativa have been shown to form a heterotic pattern for biomass yield. Objectives of this study were to examine morphological variation in a broad range of falcata germplasm and to determine how falcata morphological variation per se is related to the performance of falcata germplasm in hybrid crosses with subsp. sativa. Falcata genotypes from 40 populations spanning the subspecies native range were selected and biomass yield, plant width, plant height, growth angle, biomass density, plant maturity, and regrowth after cutting were measured on the genotypes and their hybrid progeny three times throughout the growing season. In addition weekly plant heights were measured and growth rates were determined with a Gompertz function. Falcata parental genotypes exhibited a full range of phenotypes for plant width, plant height, growth angle, density, and maturity. Heterosis was not only observed for biomass yield but also for plant width, plant height, and more erect growth habit. The top yielding sativa-falcata hybrids had increased plant width, plant height, and plant density. European germplasm was taller and had faster regrowth than Asian material. Sativa-falcata hybrids produced biomass yield superior to the mid-subspecies mean only after two to three weeks of growth prior to first and third harvests. Prior to second harvest, biomass production was inferior to the mid-subspecies mean for 30 days. Hybrids using falcata as one parent are not currently adapted to intensive harvest management due to their slower regrowth.