First report of broccoli foot rot caused by Rhizoctonia solani AG-2-2 IV and pathogenicity comparison of the pathogen with related pathogens
Misawa, Tomoo | Kubota, Masaharu | Sasaki, Jun | Kuninaga, Shiro
Foot rot and wilt symptoms were found on mature broccoli plants in Hokkaido, Japan, in 2007. The causal fungus was identified as Rhizoctonia solani anastomosis group (AG)-2-2 IV based on a hyphal fusion test, cultural characteristics and DNA analysis. We compared the isolate with two reference isolates, the pathogen of broccoli damping-off, belonging to AG-1 IC and AG-2-2 IIIB, in terms of differences in virulence to broccoli plants at different growth stages under various conditions. All the isolates caused damping-off on all three broccoli cultivars tested. However, only the present isolate incited foot rot with wilt symptoms on mature plants, when temperature was optimum for plant growth (20–25 °C), indicating that the foot rot pathogen may be discriminated from the damping-off pathogen in terms of virulence to mature broccoli. We also compared the isolate with 10 reference isolates from various crops, belonging to AG-2-2 IV, AG-2-2 IIIB and AG-1 IC, in terms of virulence to broccoli. All the isolates caused damping-off on broccoli seedlings with one exception; however, only the present isolate and one of four AG-2-2 IV isolates tested caused foot rot with wilt symptoms on mature broccoli in all the replicates. These results suggest that a group of isolates among AG-2-2 IV population is capable of causing foot rot on mature broccoli plants. This is the first report of broccoli foot rot caused by R. solani AG-2-2 IV.
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