Evidence for selective pathogenicity of Globisporangium coniferarum in coniferous urban trees

Urban trees are vital to sustainable cities but are increasingly affected by abiotic stressors that increase their susceptibility to biotic factors. Among these, oomycetes of the genus Globisporangium are important agents of root diseases that manifest symptoms in both root and foliar systems, particularly under poorly drained and intensively irrigated conditions. This study evaluated the pathogenicity of Globisporangium coniferarum, a recently described species from Iran, on seedlings of Acer sp., Cupressus sempervirens, Eucalyptus obliqua, Morus alba, Pinus eldarica, and Salix alba under greenhouse conditions. Inoculations were performed using a vermiculite-based inoculum applied to the crown region, and disease development was assessed over eight weeks based on disease symptom expression, plant growth traits, tissue colonization frequency, and pathogen re-isolation. Clear decline symptoms developed only in inoculated P. eldarica and C. sempervirens, which showed reduced vigor, foliar discoloration, crown thinning, and root necrosis. These species also exhibited significant reductions in most measured growth traits compared with non-inoculated controls. In contrast, Acer sp., E. obliqua, M. alba, and S. alba remained symptomless and showed no significant growth reduction compared with control treatments. Colonization assays revealed significant host-dependent differences, with the highest root and crown colonization in P. eldarica, C. sempervirens, and Acer sp., intermediate colonization in E. obliqua, and minimal colonization in M. alba and S. alba. Koch’s postulates were fulfilled by re-isolation and molecular confirmation of the pathogen using the cox۱ gene. These findings demonstrate marked host-dependent pathogenicity in G. coniferarum and identify coniferous potential hosts, particularly P. eldarica and C. sempervirens, as the most susceptible.

کلیدواژه ها:

Globisporangium coniferarum ، host specificity ، oomycete pathogenicity ، root and crown rot ، urban forestry