Selection for resistance to Fusarium wilt in red clover

Abstract

In Wisconsin, Fusarium oxysporum, Schlect., a pathogen causing vascular wilt, is the most prevalent fungal pathogen recovered from diseased red clover (Trifolium pratense L.) plants. This study was conducted to determine the mode of inheritance for red clover resistance to this pathogen and to develop resistant germplasm. Virulent isolates of this pathogen, collected from red clover plants at the Ashland Research Station, Ashland, Wisconsin, were used to screen three populations, the red clover cultivars Arlington and Marathon and the C11 germplasm, for resistant plants. Plants were inoculated with the pathogen and evaluated for reaction, using a disease-severity index (DSI) score from 1 to 5 (1 = no reaction, 5 = plant dead). Selected plants from each cycle were intercrossed to produce subsequent generations. After two and three cycles of selection, the developed populations were simultaneously evaluated for gain from selection. The gain from selection for resistance in these populations (cycle 0 minus cycle 2) ranged from 0.31 to 0.48, 0.12 to 0.75, and 0.13 to 0.83 DSI units, respectively, for Arlington, Marathon, and C11. Estimated narrow-sense heritabilities, based on cycle-1 and cycle-2 progeny, were, respectively, 0.20 and 0.37 for Arlington, 0.15 and 0.13 for Marathon, and 0.06 and 0.17 for C11. These results indicate that resistance is a quantitative trait controlled by many loci, each contributing some portion to overall resistance in the host. Key words: Red clover, Trifolium pratense L., Fusarium oxysporum, vascular wilt, resistance