FIRST REPORT OF FUSARIUM ROT CAUSED BY FUSARIUM OXYSPORUM ON GRAPEFRUIT IN PAKISTAN

Abstract

During year 2014-2015, severe infection was observed on grapefruit plants in Rawalpindi and Islamabad Capital Territory (ICT), Pakistan. Symptoms appeared as brown, oval or round spots, with varying sizes ranging from small spot (5 mm) to decay of the entire fruit. Twenty-five infected fruits were collected, surface-sterilized and 3-mm-diameter sections were placed on potato dextrose agar (PDA) medium at 26°C. After 4 days, the mycelia of the isolates were delicate, creamy white and pink or purple tinge, and their margins slightly lobed or smooth. Microconidia were single, oval to reniform and monophialides type. Moon crest shape macroconidia were produced in sporodochium with multiseptum. Short aerial conidiophores were unbranched, producing one-cell conidia in false head (Hussain et al., 2012). The microscopic structure was similar to that of Fusarium oxysporum. Molecular identification of pathogen was achieved by its rDNA sequence analysis. Genomic DNA was extracted from a single pure colony of fungus and its 18S rDNA region was amplified (White et al., 1990). Sequence analysis showed 99% similarity with Fusarium oxysporum strain NSF2 18S ribosomal RNA gene, partial sequence (KR611565.1). This sequence was deposited in NCBI database (KX384665). To prove Koch’s postulates, ten fruit were spray inoculated with isolated fungal conidial suspension (1 × 105 spores/ml of water). All inoculated fruit showed similar symptoms. No spots or lesions were observed on controlled fruits. F. oxysporum was re-isolated from the diseased fruits. To our knowledge this is the first report of F. oxysporum causing fruit rot on grapefruit.