FIRST REPORT OF MYCOSPHAERELLA CITRI, THE AGENT OF GREASY SPOT OF ORANGE IN EGYPT

Abstract

In winter 2011, extensive greasy spots was observed on about 36% of 12-year-old orange trees of cv. Navel in a commercial farm of Tahreer province (Bohara Governorate, Egypt). Symp- toms consisted of yellow spots on the leaves, which eventually turned dark acquiring a greasy appearance. Isolations from symp- tomatic leaves on potato dextrose agar yielded colonies with ver- ruculose, branched, septate, red-brown to medium brown hy- phae, 2-3 μm wide. Conidiophores are sparse, arising from extra- matricular hyphae, simple, deep olivaceous, paler towards the apex, septate, lightly rough walled, 12-40×2-3.5 μm. Conidio- genous cells are terminal, unbranched, thickened, darkened, 5- 10×2.8-4 μm. Pseudothecia immersed in decomposing leaves, subepidermal, amphigenous, up to 90 mm in diameter with a papillate ostiole. Asci obclavate, 8-spored, 25-35×8-10 μm. As- cospores hyaline, 1-septate, slightly curved, 6-14×2-4 mm. Based on these morphological and cultural features the fungus was identified as Mycosphaerella citri (Mondal et al., 2004). Identifica- tion was confirmed using comparisons of DNA sequences for the internal transcribed spacers (ITS1 and ITS2) of ribosomal DNA (Goodwin et al., 2001). A conidial suspension (6×105 conidia ml-1) prepared from single-conidial cultures was sprayed on 60 seedlings that were kept in the dark under plastic cover for 5 days. The first reactions appeared 25 days after inoculation and, within two months, all inoculated seedling but not the water- sprayed controls showed symptoms. M. citri was reisolated from symptomatic seedlings. This is the first record of M. citri in Egypt.