Genetic variability of tolerance to Verticillium albo-atrum and Verticillium dahliae in Medicago truncatula

Verticillium wilt caused by Verticillium albo-atrum and Verticillium dahliae is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. In the present work, 25 Medicago truncatula genotypes from a core collection and six V. albo-atrum and V. dahliae strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant and the plant's susceptibility to the pathogens. The experiment was designed as factorial with randomised complete blocks and with three repetitions. The wilt symptoms caused by V. albo-atrum and V. dahliae were scored on a disease index scale from 0 to 4, during 30 days after inoculation of 10-day-old plantlets. Disease severity was quantified by maximum symptom scores (MSS) and areas under the disease progress curves (AUDPC), which integrate the time course of symptom development. Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86. The most severe symptoms were caused by the alfalfa strain V. albo-atrum V31-2 and the least severe by V. dahliae JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was the most susceptible genotype by mean values obtained with the six fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results can be used to choose parents for studying the genetics of resistance in Medicago truncatula to Verticillium strains with different levels of aggressiveness