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During a survey in urban parks and gardens of eastern Sicily, bleeding trunk cankers and root rots were observed in scattered mature trees of Pistacia atlantica, Sterculia diversifolia and Morus alba. Isolations onto PARPNH V8-agar medium (Aloi et al. 2023) from stem bark and fine roots from four trees per each host-plant yielded consistently a homothallic Phytophthora species. Colonies of single-hypha isolates on potato dextrose agar (PDA) and V8 agar (V8A) were stellate and petaloid, respectively. On V8A, isolates produced semipapillate, persistent, ovoid to obpyriform sporangia (length/breadth ratio 1.7 ± 0.22), oogonia (diameter 25 to 31 μm), paragynous antheridia and plerotic oospores with a thick (2.6 ± 0.5 μm) wall. The identity of 15 randomly selected isolates (five per each host-plant) was confirmed by phylogenetic analysis of the ITS1-5.8 S-ITS2 and the cox1 gene regions according with Scott et al. (2009) (Figure S1). Sequences of isolates showed 99.4 to 100.0% identity with those of P. multivora ex-type MycoBank MB512497 (GenBank FJ237521 and FJ237508). Sequences of isolates selected for phylogenetic analysis were deposited in GenBank (Table S1). The pathogenicity of three isolates (one per each host-plant) was tested on 12-month-old saplings of P. atlantica, S. diversifolia and M. alba by soil infestation and stem wounding (Aloi et al. 2023), in two separate experiments. Within 20 days, all inoculated saplings exhibited leaf chlorosis and stem gummosis (size of stem lesion 13.5–18.3 mm), respectively, with no significant difference in virulence among the isolates. Control saplings remained asymptomatic. Re-isolation from bark and roots of symptomatic saplings yielded isolates morphologically and molecularly identical to those used for inoculations, Previously, P. multivora had been recovered from rhizosphere soil of P. atlantica and S. diversifolia (La Spada et al. 2022). However, this is the first report of P. multivora from M. alba and as a pathogen of P. atlantica and S. diversifolia worldwide. This report highlights the importance of surveys in urban green areas.
References
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Conti Taguali, S., Bua, C., Rovetto, E.I. et al. Bleeding stem cankers and root rot caused by Phytophthora multivora in Morus alba, Pistacia atlantica and Sterculia diversifolia trees in eastern Sicily. J Plant Pathol 106, 291 (2024). https://doi.org/10.1007/s42161-023-01547-2
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DOI: https://doi.org/10.1007/s42161-023-01547-2