Archivio Journal of Plant Pathology

Abstract:

Mustard (Brassica compestris), one of the vegetables grown in Pakistan, is a highly valued crop also because of its edible oil-rich seeds, that have great medicinal potential. Mustard seeds stored in Lahore were found to be colonized by a previously undetected black powdery mold. Twenty infected seeds from three different wharehouses of Lahore were collected and spores present on the seeds were transferred aseptically to Czapek dox agar (CZA) and incubated at 25°C. A 7- day-old pure culture was used for the identification of the recovered fungus. Colonies were black, 4 cm in diameter and showed abundant radiatel heads bearing brown conidia 4-5.5 μm in diameter. Metulae were 13 x3.5 μm and phialides 10x3.5 μm in size. Identification of pathogen carried out by sequencing the ITS region of rDNA and part of the calmodulin gene (CAL) (White et al., 2000). BLAST results showed 99% similarity of the ITS sequence (GenBank accession No. KT277269) and 100% similarity of the calmodulin gene (LN890507) to strain DTO_178C2 and PW3050 of Aspergillus welwitschiae. To determine the pathogenicity of the fungus, 50 randomly selected seeds were surface-sterilized, soaked in a spore suspension (104 spores/ml) for 30 sec and, after drying, were transferred aseptically onto a layer of sterilized moist blotting papers. Control seeds were treated with sterilized water. All Petri dishes were incubated at 25oC. After 7 days of incubation, 75% of the seeds were colonized by the pathogen and failed to germinate while all control seeds germinated to produce healthy seedlings. To the best of our knowledge, this is the first report of A. welwitschiae from Pakistan causing postharvest rot of mustard seeds.