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 underenvironmental conditions in Zanjan province, Iran. In total, 15 genera of fungal pathogens wereisolated from plants sampled from the fields. All of these disease interactions had not been previouslyrecorded in Zanjan and Colletotrichum truncatum, Leptotrochila medicaginis, Phoma medicaginis,Rhizoctonia crocorum on alfalfa were new disease reports for Iran. In 2000, the mean diseaseincidence of fungal pathogens of alfalfa varied by sampling time and field location. Decreases in theincidence of diseases occurred after cuttings. The incidence of diseases detected in 2000 wascorrelated 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%), Sporonema phacidioides (17.7%), and Leveillula taurica(10.1%), irrespective of sampling time and field location. There was no significant correlationbetween weather variables and disease incidence for Ph. medicaginis or L. taurica. However, theincidence of common leaf spot and downy mildew were significantly correlated with both monthlymean temperature and total rainfall. The incidence of rust was positively correlated with meanmonthly temperature, whereas the incidence of yellow leaf blotch was negatively correlated withmonthly total rainfall. This improved knowledge of diseases of alfalfa in Zanjan will assist in thefuture selection of management strategies and breeding of suitable cultivars for use in regions withsimilar climatic conditions.