Archivio Journal of Plant Pathology

Abstract:

During August-September 2013, a new leaf spot disease was observed on pearl millet (Pennisetum americanum) in the Birjand district of South Khorasan province of Iran. Nearly 20% of plants showed irregularly shaped yellow to brown lesions that with time turned dark brown and caused leaf shredding. A fungus was consistently isolated from symptomatic tissues on potato dextrose agar (PDA) which formed one-celled, smooth, black, spherical to subspherical conidia (5-10 μm in diameter). Each conidium was born on a hyaline vesicle at the tip of each conidiophore. Fungal colonies were initially white, then became grayish-brown. The fungus was identified as Nigrospora oryzae (Berk. et Br.) Petch. The internal transcribed spacer (ITS) region of ribosomal DNA was amplified using ITS4/ ITS5 primer pair and the PCR product was sequenced. Comparison of the sequence revealed 99-100% similarity to N. oryzae (GenBank accession Nos. Fj496318 and GQ22186). Thus, morphological and molecular data supported the identification of this fungus as N. oryzae. Pathogenicity tests were performed by placing 5-mm diameter mycelial plugs from 7-day-old colonies onto pearl millet leaves. While the inoculated isolates caused symptoms similar to those in the field within 7-10 days, no infection was observed on control leaves. N. oryzae has been reported on Pennisetum purpureum and P. typhoides in Africa and Asia (Farr and Rossman, 2014) but this is the first report of this fungus causing a disease on P. americanum.