Abstract
The rootstock Myrobalan 29C (Prunus cerasifera Ehrh.) is largely used as rootstocks of plum and apricot planting material. In May 2020, symptoms of powdery mildew were observed on leaves and young stems of Myrobalan 29C rootstocks. On the adaxial and abaxial leaf surface white colonies with white superficial mycelium and conidia were present. Chasmothecia appeared in some injured leaf tissues. Microscopic examination showed globose chasmothecia with appendages arising from the upper half of the fruiting bodies. Usually, the appendages were one to four times longer than the chasmothecial diameter and had two to four dichotomous branches. A single ascus observed in chasmothecium was broadly ellipsoid-ovoid and contained six to eight ascospores. The shape of the ascospores was ellipsoid-ovoid, too. Conidia formed in true chains on erect conidiophores, which were ellipsoid, hyaline and measured 24.6-33.6 × 10.8-20.8 µm (average 29.6 × 15.8 µm). Pathogenicity was confirmed by inoculation of healthy Myrobalan 29C, apricot (P. armeniaca L.) and cherry (P. avium L.) plants. Disease signs on all of the inoculated experimental species appeared as white powdery coating very similar to the powdery coating on natural infected Myrobalan 29C. Based on the morphological characteristics of the conidia, chasmothecia and results of the pathogenicity tests, the causative agent of the symptoms observed was presumed to belong to Podosphaera sp. (Ascomycetes). To the best of our knowledge, previously no detailed characterization of Podosphaera sp. in P. cerasifera was made in Bulgaria.
Keywords: Prunus cerasifera, powdery mildew, Podosphaera sp.