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Temperature Dependent Reaction and Selection Response of Two Red Clover Populations to Fusarium Wilt

Louisiana State Univ. Agricultural Center, Dep. of Agronomy, Baton Rouge, LA 70803-7511
U.S. Dairy Forage Res. Center, USDA-ARS, and Dep. of Agronomy, Univ. of Wisconsin-Madison
Dep. of Plant Pathology, Univ. of Wisconsin-Madison, Madison WI 53706

^* Corresponding author (venuto{at}lanmail.lsu.edu).

Fusarium wilt (caused by Fusarium oxysporum Schlechtend.) has been associated with stand reduction and decreased persistence in red clover (Trifolium pratense L.). Previous research has also indicated that reaction of red clover to isolates of F. oxysporum is temperature dependent. The objectives of this study were to determine if temperature altered the interaction phenotype of two red clover populations inoculated with a single-conidium isolate of F. oxysporum and to determine if selection 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. oxysporum and grown in controlled environment chambers (16 and 28°C) at Madison, WI. Resistant phenotypes were selected from each population at each temperature and recombined to form advanced populations for subsequent cycles of evaluation and selection. Three cycles of selection (1992–1994) demonstrated that response to the pathogen was consistently and significantly greater at 28°C for both populations. However, the two red clover populations responded differently to the temperature of the selection environment. Significant population x selection temperature interactions were found for Cycle 1 and Cycle 2 plants. Given the genetic homogeneity of the pathogen, the difference in population response to selection temperature is probably due to the existence of distinct mechanisms of resistance in the host populations. These results have important implications for the development of durable red clover resistance to F. oxysporum.

Received for publication July 31, 1995.