Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, Zurich

Restistance to southern anthracnose (Colletotrichum trifolii) in red colver (Trifolium pratense)

The degree of resistance to Colletotrichum trifolii was highly variable among red clover cultivars. Seven weeks after spray inoculation plant survival ranged from 3 % to 52 %. The new cultivars Pavo and Merula exhibited the highest level of resistance. The other Swiss cultivars of the persistent «Mattenklee» type showed an intermediate level of resistance. Cultivars of the short-lived type were generally the most susceptible among the cultivars tested, with the exception of cultivar Tedi, which exhibited a 31 % resistance. Of the cultivars of Medicago sativa L. evaluated, all five were very susceptible to a C. trifolii isolate, which had been found on diseased red clover plants in Switzerland. None of the red clover cultivars was severely affected by C. destructivum. Resistant and susceptible plants were selected and crossed reciprocally in a diallel design. Anthracnose resistance appeared to be highly heritable. Progeny of crosses between resistant plants exhibited a mean plant survival of 81 %. In the F1 populations from crosses between resistant and susceptible specimens, plants survived at a rate of 42 %. Crosses between susceptible plants produced F1 populations which were highly susceptible: only 8 % of the plants survived. The data suggest that in the populations tested, few partly dominant genes are involved in anthracnose resistance.

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