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Effect of alfalfa cultivars and ages on the occurrence of Verticillium wilt caused by Verticillium alfalfae.

In August 2019, Verticillium wilt was observed in commercial alfalfa fields in Jinta County, Jiuquan, located to the west of Gansu, China, where Verticillium wilt of alfalfa was first observed in this region. This study was conducted to evaluate the effect of alfalfa cultivars ('Galaxie Max', 'Liangmu No. 2', and 'Danon VNS' planted in 2017) and ages (cultivar 'Adrenalin' planted in 2014, 2015, and 2016) on the occurrence of Verticillium wilt caused by Verticillium alfalfae. The results showed that V. alfalfae was successfully isolated from both symptomatic and asymptomatic plants. The percentage of V. alfalfae colonization ranged from 22% to 83% in symptomatic plants and 19% to 31% in asymptomatic plants. Among the three cultivars tested, the lowest incidence of disease symptoms was observed in the plants of cultivar 'Galaxie Max', In addition, the plants of cultivar 'Galaxie Max' had a lower rate of infection with V. alfalfae in the field than the cultivar 'Danon VNS'. Moreover, the diseased plants of 'Galaxie Max' had a higher shoot dry weight and levels of nitrogen (N), phosphorus (P), starch, sucrose, and chlorophyll than the diseased plants of 'Liangmu No. 2' and 'Danon VNS'. This demonstrated the cultivar 'Galaxie max' has higher resistance/tolerance to Verticillium wilt than 'Danon VNS'. An examination of the different ages of 'Adrenalin' indicated that the plants in 2014 had a higher incidence of disease and rate of infection in the field than the plants in 2016. In addition, the diseased plants in 2016 had a higher shoot dry weight and contents of N, P, sucrose and starch than the diseased plants in 2014 and 2015. This result indicated an increase in the age of alfalfa plants contributes to the occurrence and development of Verticillium wilt. The infection of V. alfalfae significantly decreased the shoot dry weights and the contents of chlorophyll, N, P, and starch of alfalfa plants. These results provide a better understanding on the physiological mechanisms of the response of alfalfa plants to Verticillium wilt caused by V. alfalfae.