Breeding Birdsfoot Trefoil for Resistance to Fusarium Wilt in New York.

Fusarium wilt (FW) (caused by Fusarium oxysporum f.sp. loti) has long been a disease problem of birdsfoot trefoil, Lotus corniculatus L. in New York (NY) and Vermont, affecting seeding year stands, thus reducing forage and seed yield in the first production year.  Acreage of birdsfoot trefoil in the Northeast USA could be increased significantly if FW-resistant cultivars were available.  Previous efforts to improve birdsfoot trefoil for resistance to FW have been successful in the greenhouse, but field-testing of FW-resistant populatins has not been reported.  The objectives were to determine progress from selection in the greenhouse for resistance to FW, and to compare forage yield and persistence of a FW-resistant cultivar to those of susceptible cultivars in a field with a history of FW on birdsfoot trefoil, and in fields that were inoculated.  In all six birdsfoot trefoil populations tested, recurrent phenotypic selection was highly effective for improving resistance in the greenhouse, with mean improvement of 35% across all populations after three cycles of selection.  In a NY field with a history of FW on birdsfoot trefoil, a population developed after two cycles of selection for FW-resistance had lower levels of disease incidence and yielded 0.84 Mg ha^-1 more than the mean of nine FW-susceptible cultivars at harvest 1 and 0.38 Mg ha^-1 more at harvest 2 in the seeding year (1999).  It also maintained at least 50% stand through September of the first production year while stands of all other cultivars decreased to a mean of 14%.  In three inoculated field trials, the population developed after two cycles of selection had greater plant stands than the variety 'Norcen', a susceptible check.  Birdsfoot trefoil with improved resistance to FW yielded more and persisted longer than did FW-susceptible cultivars under FW-infested field conditions.