Selection for Resistance to Fusarium Root Rot, and Associations among Resistances to Six Diseases in Alfalfa

Abstract

Fusarium root and crown rot in New York, caused mostly by Fusarium avenaceum (Fr.:Fr.) Sacc., F. oxysporum Sehlechtend.:Fr., and F. solani (Mart.) Sacc., reduces longevity and productivity of alfalfa (Medicago saliva L.). The research objectives were to determine correlations among six alfalfa diseases and progress from recurrent phenotypic selection for resistance to fusarium root rot. From alfalfa half‐sib progenies, phenotypic and additive genetic correlation coetlicients were estimated among resistances to disease caused by the three Fusarium spp. and three common vascular diseases, bacterial wilt (BW) [caused by Clavibacter michiganense subsp, insidiosum (McCall.)], verticillium wilt [caused by Verticillium albo‐atrum (Reinke & Berthier)], and fusarium wilt [caused by F. oxysporum Seh. ex Fr. f. sp. medicaginis (J. L. Weimer)]. Resistances to fusarium wilt (FW) verticillium wilt (VW) were significantly correlated (additive genetic, r = 0.32). Correlations among resistances to the root and crown rot fusaria were moderately to highly positive. Resistances to root rot caused by F. avenaceum and F. solani were moderately and positively correlated with resistance to VW. In two plant populations, two cycles of recurrent phenotypic selection for resistance to root rot species increased levels of resistance by 15 to 44%. Selection for resistance to root rot caused by specific Fusarium species conferred a general resistance to rot caused by all three species, confirming the results of the correlation experiment. Alfalfa populations with resistance to disease caused by the Fusarium spp. can be developed by using an inoculum mixture of all three Fusarium spp., without negative effects on resistances to the vascular diseases.