Seasonal dynamics and prevalence of alfalfa fungal pathogens in Zanjan province, Iran

During 2000 and 2001, the prevalence of fungal diseases of alfalfa was surveyed under environmental conditions in Zanjan province, Iran. In total, 15 genera of fungal pathogens were isolated from plants sampled from the fields. All of these disease interactions had not been previously recorded in Zanjan and Colletotrichum truncatum, Leptotrochila medicaginis, Phoma medicaginis, Rhizoctonia crocorum on alfalfa were new disease reports for Iran. In 2000, the mean disease incidence of fungal pathogens of alfalfa varied by sampling time and field location. Decreases in the incidence of diseases occurred after cuttings. The incidence of diseases detected in 2000 was correlated negatively with mean monthly temperature and positively with monthly total rainfall, indicating that reductions in diseases were associated with higher temperature and less humidity, irrespective of fungal species. In 2001, Ph. medicaginis was the predominant fungus infected 42.8% of plants in the alfalfa fields followed by Pseudopeziza medicaginis (39.1%), Uromyces striatus (33.3%), Peronospora trifoliorum (29.8%), Sporonemaphacidioides (17.7%), and Leveillula taurica (10.1%), irrespective of sampling time and field location. There was no significant correlation between weather variables and disease incidence for Ph. medicaginis or L. taurica. However, the incidence of common leaf spot and downy mildew were significantly correlated with both monthly mean temperature and total rainfall. The incidence of rust was positively correlated with mean monthly temperature, whereas the incidence of yellow leaf blotch was negatively correlated with monthly total rainfall. This improved knowledge of diseases of alfalfa in Zanjan will assist in the future selection of management strategies and breeding of suitable cultivars for use in regions with similar climatic conditions.