FIRST REPORT OF LEAF SPOT ON BUCKWHEAT CAUSED BY DIDYMELLA RHEI IN CHINA

Y. Wang, Q.G. Lian, M.Q. Zhu

Abstract


Leaf spot on buckwheat seriously occurred in Baoji, Shaanxi, China, in August 2015. The disease incidence ranged from 60 to 80%. Fungal isolates were isolated on potato-dextrose-agar media at 25±1°C (Sinclair and Dhingra, 1995). After 6 days of incubation, colonies developed dark pycnidia. The pycnidia were ostiolate and 100-125 µm in diameter. Conidia were elliptic, colorless, single cell, containing one or two lipid droplets, 4.2-5.8 ×2.7-3.7 µm. DNA was extracted from a representative monosporic culture and the internal transcribed spacer (ITS) and beta-tublin region of the nuclear ribosomal DNA (rDNA) was amplified and sequenced using primers ITS-1F/ITS4 and betatub3/betatub4r, respectively. The obtained sequences of 485 bp and 213 bp were deposited in the GenBank (accession No. LC198572.1 and LC198184.1). Phylogenetic tree based on ITS and beta-tublin showed 98% similarity to Didymella rhei. Pathogenicity tests were performed on four-leaf stage buckwheat seedlings ‘Xinong 9920’. Leaves of 20 plants were inoculated by either wounding or non-wounding. For the wounding test, 5 µl of 105 -106 spores/ml conidial suspension was dropped on the leaf sites with needle-prick wound. For the non-wounding test, the conidial suspension was sprayed on the leaf surface to runoff. Control plants were sprayed or dropped with sterilized water. Leaf lesions were observed after 2-3 weeks post-inoculation. The symptom development on wound-inoculated plants was faster than the non-wounding inoculation. The fungus was reisolated only from diseased leaves, fulfilling Koch’s postulates. Though many species of Didymella cause spot diseases in the world (Rothwell, 1982; Jellis and Punithalingam, 2007; Pearce et al., 2016), this is the first report of D. rhei infecting buckwheat.

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DOI: http://dx.doi.org/10.4454/jpp.v99i2.3907

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