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Breeding for Resistance to Alfalfa Root Rot Caused by Fusarium Species

1180 Lark Hill Drive, Vista, CA 92084
Dep. of Plant Breeding and Biometry, 252 Emerson Hall, Cornell Univ., Ithaca, NY 14853-1902

^* Corresponding author (DON_VIANDS{at}QMRELAY.MAIL.CORNELL.EDU).

Fusarium root and crown rot is a significant factor in stand and yield reduction of alfalfa (Medicago sativa L.). The objectives of this study were to develop a greenhouse inoculation procedure for screening alfalfa germplasm for resistance to root rot caused by Fusarium species, collect virulent isolates of Fusarium species from New York, and determine progress from two cycles of recurrent phenotypic selection. Fusarium avenaceum (Fr.: Fr.) Sacc., F. oxysporum Schlechtend.:Fr., and F. solani (Mart.) Sacc. were isolated from rotted alfalfa roots and crowns in each of four regions of New York. At least one of the three species was present in every field sampled, but not all species were found in every field. The V-V8 inoculation method was developed by culturing the Fusarium species in vermiculite saturated with V8 juice; the inoculum was placed in contact with severed alfalfa root balls in pots. This method was as effective as the application technique for inciting infection of alfalfa roots; however, the Y-Y8 method was more efficient for mass inoculation of plants. Using the V-V8 method in the greenhouse, we subjected two alfalfa populations to two cycles of recurrent phenotypic selection for resistance to root rot caused by each of the three Fusarium species. Mean lesion length (vertical discoloration) within taproots was the selection criterion. Only selection for resistance to disease caused by F. solani was effective; mean lesion length decreased by 34% from Cycle 0 to Cycle 2 in Oneida, and by 48% in (Flamande x SaranacAR-2)AN. Future selection should account for lateral spread as well as vertical length of lesions.

Received for publication August 23, 1993.