FIRST REPORT OF RHIZOPUS ORYZAE CAUSING FRUIT ROT OF CITRUS MEDICA L IN PAKISTAN
H.S. Naz, S. Gul, H.J. Chaudhary, M.F.H. Munis
Citrus medica, commonly known as Otroj, is a member of the family Rutaceae that contains important nutrients (Al-Yahya et al., 2013). In a survey from September to October 2014, C. medica fruits showing brown, wrinkled, sunken and dark lesions and decayed tissues that extended into the center, were collected in Islamabad Capital Territory (Pakistan). As the disease progressed, the fruits rotted severely and collapsed. A fungus isolated from diseased fruits on Sabouraud dextrose agar (SDA) mediium had an initially white mycelium that, over time, turned grayish black with a net-like structure. The reverse of the colonies was light brown. This fungus resembled morphologically Rhizopus oryzae and was comprised of sporangia, apophysis, sporangiophores and rhizoids. It grew by extending the hyphae along the surface of the substrate and penetrated it with rhizoids. The ultimate identification as R. oryzae was achieved based on the comparative molecular analysis of the ITS1, ITS4 and 18SrRNA sequences. In particular, BLAST analysis revealed 100% similarity with R. oryzae strain LXM4 (GenBank accession No. GQ220706.1) and 99% similarity with R. oryzae isolate F750 (KM249084.1), respectively. To prove Koch’s postulates, mycelial plugs (5-mm diameter) were placed on superficially wounded surface-sterilized C. medica fruits, all of which developed lesions after seven days at 27°C. R oryzae was consistently re-isolated from symptomatic fruits. No infection was observed on wounded but non-inoculated controls. To our knowledge, this is the first report of R. oryzae causing fruit rot of C. medica in Pakistan.