Influence of Different Host Plants on the Sporulation of Thanatephorus cucumeris Anastomosis Group 3 (AG-3)

Thanatephorus cucumeris anastomosis subgroup 3-TB (AG-3-TB) is the primary pathogen causing tobacco target spot disease, which has resulted in substantial economic losses in tobacco production worldwide. Traditionally, soilborne sclerotia has been considered to be the main primary infection source, while the role of airborne basidiospores has long been underestimated, particularly they serve as inoculum of primary and secondary infection developing on the hymenia of infected alternate host plants. This study investigated the influence of different host plants on T. cucumeris AG-3 sporulation. The results showed that in the natural environment, T. cucumeris AG-3-TB could develop hymenia on Solanaceae (tobacco, tomato, eggplant, pepper, potato), Gramineae (rice), Cruciferae (cabbage), weeds (shamrock, dandelion, tartary buckwheat) and the soil surface surrounding tomato stems, and the capacity of these fungal hymenium formation differed among plant host species. Furthermore, this sporulation phenomenon was widely prevalent across the AG-3-TB subgroup, as well as urea as a nitrogen fertilizer and 18% albendazole-moroxydine hydrochloride wettable powder as a virucide significantly promoted AG-3-TB strains sporulation on tomato hosts. Our findings indicate that host plant species, strain differences, urea, and fungistatic stress significantly influence the fungal sporulation, revealing the pivotal role of spore production in the disease development.