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Variability and Selection for Characters Associated with Root Regeneration Capability in Alfalfa

Dep. of Plant Breeding and Biometry, Cornell Univ., Ithaca, NY 14853-1902.

^* Corresponding author.

Alfalfa (Medicago spp.) is capable of regenerating its root system to survive severe injury by biotic or a biotic stress factors. Four field experiments were conducted in Ithaca, NY to examine variability for characters associated with root regeneration capability and to determine if plant populations could be improved for root regeneration capability by phenotypic recurrent selection. Six-week old seedlings were dug from the greenhouse and their taproots artificially pruned 3 cm below the crown. These plants were transplanted to the field, and the regenerated plants dug 8 to 13 weeks later for root observations. Alfalfa populations ranged more than two-fold for secondary root number, secondary root size, and taproot diameter 1 cm below the crown after root regeneration. The range for fibrous root mass was 1.4-fold. All four root characters were positively associated with each other and with topgrowth vigor. Within a genetically broad-based population, secondary root number ranged from 3 to 23 per plant. Associations among plant characters suggested that more vigorous seedlings are better able to regenerate roots after pruning than are less vigorous seedlings. One to three cycles of phenotypic recurrent selection significantly improved regenerated secondary root number in three of five alfalfa populations. Significant increases in secondary root number ranged from 22 to 45%.

Key Words: Fibrous roots • Medicago spp. • Phenotypic recurrent selection • Plant survival • Secondary roots • Taproots

Received for publication February 13, 1987.