Wheat stem base diseases and their causal agents

Abstract

Wheat stem base disease is an important disease complex, caused by various pathogens that are characterized by variable life cycles and ecological requirements. Wheat stem bases with symptoms of different stem diseases were collected in 2012-2018. Causal agents and other fungi were identified by mycological and molecular genetic methods. A total of 6787 isolates of fungi were obtained and identified to the genera/species level. Out of the total number of isolates, 50% belonged to causal agents of stem base diseases, 10% were causal agents of leaf spots, and 8% were different saprotrophs. Fungi from the genera Fusarium (51%) and Oculimacula (35%) were the most dominant causal agents of stem base diseases. An increasing occurrence of Microdochium nivale and M. bolleyi (totally 15%) was noticed. The dominant species of Fusarium were F. culmorum, F. avenaceum and F. tricinctum; other species were detected only in some cases. An unexpectedly high proportion (31%) of fungi from different ecological niches were isolated from wheat stems with stem base disease symptoms. Phaeosphaeria (most likely P. pontiformis) was the dominant fungus among non-pathogenic fungi. Further studies are required to clarify the interactions between this fungus, wheat, and causal agents of stem base diseases.