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Response from Phenotypic Recurrent Selection for Root Regeneration after Taproot Severing in Alfalfa

Dep. of Plant Breeding and Biometry, 523 Bradfield Hall, Cornell Univ., Ithaca, NY 14853-1902

^* Corresponding author.

Alfalfa (Medicago sativa, S.) can regenerate secondary roots after taproot severing by biotic and abiotic factors. The research objectives were to: (i) determine progress from three or four cycles of selection of plants with many large secondary roots regenerated after taproot severing, (ii) compare techniques to evaluate plants for root regeneration capability, and (iii) determine whether alfalfa populations selected for higher root regeneration capability differed in stand and forage yield after frost heaving compared to nonselected populations. Six-wk-old plants, established in the greenhouse, were cut to taproot length of 3 cm and transplanted to two fields (artificial taproot severing). Over locations, four of five populations showed improvements for number of secondary roots regenerated per plant. The selected populations averaged 27% more regenerated secondary roots (P < 0.01), 25% larger taproots (P < 0.01), and 10% higher seedling weight (P < 0.05) than the original populations. Correlations were significant between field and greenhouse evaluations for secondary root number (r = 0.82, P < 0.01) and taproot size (r = 0.73, P < 0.01) after artificial taproot severing. Greenhouse experiments revealed that number of secondary roots regenerated after artificial taproot severing was positively correlated with that after severing by Phytophthora megasperma Drechs. f. sp. medicaginis (r = 0.85, P < 0.01). In the second production year of a yield trial severely injured by frost heaving, two selected populations averaged 50% higher stand during the spring and 13% (0.90 Mg ha^–1) more forage at the first harvest than did two unselected populations. Selection and evaluation for root regeneration capability in the greenhouse after taproot cutting is the most efficient method studied since the CV's and experimental resources were lowest.

Received for publication September 26, 1988.