Erysiphe azerbaijanica

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Erysiphe azerbaijanica is a species of powdery mildew found in Azerbaijan on the leaves of sweet chestnut trees. It was described in 2018 by Lamiya Abasova, Dilzara Aghayeva, and Susumu Takamatsu. The type specimen came from Baş Küngüt village in the Shaki District, where it grows on Castanea sativa.

This fungus belongs to the genus Erysiphe in the family Erysiphaceae and sits in the Microsphaera lineage. On infected leaves it forms thin, white, irregular patches on both surfaces. The mycelium is amphigenous (on both sides), white and thin. Hyphae are straight to slightly curved and about 4–6 μm wide. Conidiophores are up to about 125 μm long. Basal foot cells are cylindrical, about 28–64 × 4–7 μm. Conidia (asexual spores) are produced singly, mostly cylindrical to oblong, about 33–54 × 12–18 μm, with a length/width ratio of 2–3.6. The sexual form has not been observed.

Erysiphe azerbaijanica differs from similar species such as E. alphitoides, E. castaneae, and E. castaneigena by its larger, predominantly cylindrical conidia and longer conidiophores and foot cells. It is known from Azerbaijan on sweet chestnut, with confirmed records from the Shaki (Baş Küngüt) and Qabala (Zaraghan) districts based on 2015 collections. Prior to this work, powdery mildew on C. sativa in Azerbaijan had been recorded as E. alphitoides.