| Alfalfa roots are important because they are associated with persistence and productivity traits. The objectives of this research were: (1) to evaluate alfalfa plant introductions (PI's) and both historical and contemporary cultivars for seven root morphological traits, (2) to compare root development in direct seeded field grown plants with transplanted field grown plants and greenhouse grown plants, (3) to study rate of root development during the seedling year, (4) to determine the effect of plant spacing and location on root traits, (5) to correlate root traits with dormancy and forage yield, and (6) to determine the inheritance of seven root traits.;About 1200 PI's and cultivars were evaluated at the end of the seeding year for taproot diameter (TD), secondary root number (SN), secondary root diameter (SD), secondary root position (SP), fibrous root mass (FIB), determinate taproot percentage (PD), and determinate taproot position (DP). The effects of direct seeding in the field were compared to transplanting in the field and planting in two greenhouse environments. Inheritance studies were direct seeded at two field locations.;Extensive variability existed among both PI's and cultivars for all seven traits. Transplanted field grown plants and greenhouse grown plants did not emulate root development in the field. Rate of development during the seeding year plateaued at 14 to 17 weeks after planting for most traits. Plant spacing and location had large effects on root traits, but genotype by spacing and genotype by location interactions were generally nonsignificant. TD and SD were the root traits most correlated with forage yield. GCA effects were important for TD, SN, SD, SP, and FIB. Heritabilities of the traits were moderate to high. Genetic variances were not significant for PD and DP, and heritabilities were low. In conclusion, it should be possible to make gains from selection for TD, SN, SD, SP, and FIB using equally-spaced, field-grown plants at least 13 weeks old. |
