The causal agents of sainfoin fungal diseases and disease dynamics in Gansu Province.
To classify the fungal diseases on sainfoin in Gansu Province, pathogens were isolated and purified for analyses including morphological and molecular identification and pathogenicity test. Disease dynamics was determined by investigation of disease incidence in Tongwei, Weiyuan, Yuzhong, and Luqu counties from June to September in 2012 and 2013. The significance of each disease was evaluated based on disease characteristics occurred in field and data obtained from the investigation. The results showed that there were 12 diseases, including leaf spot caused by Macrophoma sp., leaf spot caused by Septoria orobina, anthracnose caused by Colletotrichum spaethianum, black stem caused by Ascochyta onobrychis, C. spinaciae and Alternaria alternata, Ascochyta leaf spot, Phoma leaf spot, Cercospora leaf spot, Ramularia white leaf spot, Stemphylium leaf spot, Alternaria black leaf spot, rust and powdery mildew. Three fungi pathogenic to sainfoin, Macrophoma sp., C. spaethianum and C. spinaciae were firstly recorded. Macrophoma leaf spot was the new disease in the world. Septoria leaf spot and Cercospora leaf spot were new records in Gansu Province. Powdery mildew, rust and Alternaria black spot occurred at late growing stage, and other diseases occurred from June each year. Generally, disease incidence of black stem and Ramularia white leaf spot increased, and Phoma leaf spot, Ascochyta leaf spot and Septoria leaf spot decreased from June to September, of which the incidences were up to 89.7%, 96.0%, 88.7%, 57.4% and 45.1%, respectively. Black stem and Phoma leaf spot were the most severe diseases in Gansu Province.