TEMPERATURE-DEPENDENT REACTION AND SELECTION RESPONSE OF 2 RED-CLOVERPOPULATIONS TO FUSARIUM-WILT

Fusarium wilt (caused by Fusarium oxysporum Schlechtend,) has been ass ociated with stand reduction and decreased persistence in red clover ( Trifolium pratense L.), Previous research has also indicated that reac tion of red clover to isolates of F. oxysporum is temperature dependen t, The objectives of this study were to determine if temperature alter ed the interaction phenotype of two red clover populations inoculated with a single-conidium isolate of F. oxysporum and to determine if sel ection at divergent temperatures resulted in a different response for the two populations. Two populations of red clover, C11 and 'Arlington ', were inoculated in 1992 with a single-conidium isolate of F. oxyspo rum and grown in controlled environment chambers (16 and 28 degrees C) at Madison, WI. Resistant phenotypes were selected from each populati on at each temperature and recombined to form advanced populations for subsequent cycles of evaluation and selection. Three cycles of select ion (1992-1994) demonstrated that response to the pathogen was consist ently and significantly greater at 28 degrees C for both populations. However, the two red clover populations responded differently to the t emperature of the selection environment, Significant population x sele ction temperature interactions were found for Cycle 1 and Cycle 2 plan ts, Given the genetic homogeneity of the pathogen, the difference in p opulation response to selection temperature is probably due to the exi stence of distinct mechanisms of resistance in the host populations. T hese results have important implications for the development of durabl e red clover resistance to F. oxysporum.