Archivio Journal of Plant Pathology

Abstract:

Mustard (Brassica juncea) plants grown on the premises of the Indian Agricultural Research Institute, New Delhi, showing wilting of leaves and twigs and necrosis of stem, crown and roots were observed in four consecutive years (2013 to 2016), with an incidence of up to 20%. To determine the causal agent of the disease, small pieces of stems and roots were surface-sterilized with 3% sodium hypochlorite washed in sterile distilled water, placed on potato dextrose agar (PDA) plates and incubated at 25°C for seven days. A dense white mycelium developed, that turned first beige, finally buff brown. Single-spore cultures produced falcate macroconidia with a pedicillate foot cell, and 4-7 distinct septa 21-58 x 3-6 µm in size, developing from lateral phialides. Chlamydospores were intercalary, in chains or solitary, brown-pigmented, 6-9 µm in diameter. The fungus was morphologically identified as Fusarium equiseti (Corda) Sacc. (Booth, 1977; Leslie and Summerell, 2004). To confirm the identity at the molecular level, the internal transcribed spacer (ITS) region and the translation elongation factor (tef-1) were amplified using the respective primers (White et al., 1990; Leslie and Summerell, 2004). The sequences (GenBank accession Nos. KT380024 for ITS and KY271154 for tef-1) matched those of F. equiseti in BLAST analysis. For pathogenicity tests mustard seedlings pot-grown in a glasshouse at 23±2°C with 75% relative humidity and 16 h light cycle/day were injected with 5 ml of a conidial suspension (104 conidia ml-1 ) at the root and collar region. Seedlings treated with sterile water served as control. The same symptoms seen in the field were shown within 30 days by inoculated plants only, from which F. equiseti was re-isolated. To the best of our knowledge, this is the first report of F. equiseti causing stem and root rot disease on mustard.