Characterization, pathogenicity and host range studies of Paecilomyces formosus associated with dieback of Christ's thorn trees (Paliurus spina-christi Mill.) in Iran

Christ's thorn (Paliurus spina-christi Mill.) tree is an important and valuable forestry species and has significant potential in afforestation and reforestation systems. In recent years, dieback symptoms were observed on Paliurus spina-christi trees in Gilan-e Gharb region of Kermanshah province, west Iran. During 2020 to 2021, Christ's thorn trees that exhibit branch dieback symptoms were sampled for fungal isolations. The pathogenicity tests, biochemical assay of growth, acid production on creatine sucrose agar (CREA) medium and morphological and molecular investigations (ITS and beta-tubulin regions) identified Paecilomyces formosus as a dieback causal agent. This is the first report of P. formosus pathogenicity on Paliurus spina-christi trees. Furthermore, disease severity was assayed on 11 tree species under three different temperatures 15, 25 and 35 degrees C. Disease severity caused by all isolates on detached branches was greater at 35 degrees C than at 15 and 25 degrees C. This study presents the host range of this pathogen and showed that these potential hosts are prone to this pathogen under high temperatures, which forest trees experienced in recent decades.

Automated summary

Dieback symptoms were observed on Paliurus spina-christi trees in Gilan-e Gharb region of Kermanshah province, west Iran. Paecilomyces formosus was identified as the causal agent, and it showed higher disease severity on various tree species under high temperatures. This study reveals the host range of the pathogen and highlights the vulnerability of potential hosts to this pathogen under recent decades' elevated temperatures.