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First Report of Peanut Pod Rot Caused by Neocosmospora vasinfecta in Northern China

From 2006 to 2010, peanut (Arachis hypogaea) pod rot became more prevalent in northern China, especially in the Sha River drainage area. The incidence of pod rot ranged from 30 to 100%. Typical symptoms were black rot of the pods, but no obvious morphological abnormality of the aboveground parts of infected plants was observed. Brown or black spots appeared on many pods when initially infected and then all peanut pods became black and rotten. The same fungus was isolated from 54 surface-disinfested lesions (85.2% of all lesions) on potato dextrose agar (PDA) media. One isolate, designated as HBXLb, was chosen for further characterization. In culture, both anamorph and teleomorph were present. Mycelia of the fungus grew quickly (colonies were 3.2 cm in diameter in 3 days) and became white and floccose on PDA at 28°C. The hyaline, elongated-to-cylindrical conidia aggregated on the slimy heads of conidiogenous cells that developed on undifferentiated hyphae after incubation for 3 to 4 days. Conidial sizes varied from 5 to 10 × 1.5 to 3 μm (n = 50) and were mostly single celled. Some conidia appeared slightly curved. The morphology was consistent with Acremonium spp. Numerous ascomata (perithecia) formed within 10 to 14 days when incubated at 28°C under light and dark conditions. Perithecia were orange-brown, strawberry shaped (300 to 400 μm in diameter), and ostiolate on the top. Cylindrical asci, with an average size of 90 to 110 × 7.5 to 9 μm, were present inside the ascomata with each containing eight ascospores in a row. The ascospores were brownish, spherical to ellipsoidal, and 10 to 15 × 8 to 12 μm. The cultural and morphological characteristics of isolate HBXLb matched the description of N. vasinfecta (2). The internal transcribed spacer (ITS) region of rDNA was amplified by the primer pairs ITS4/ITS5. A 525-bp amplicon (ITS4-5.8s-ITS5) was obtained and sequenced (GenBank Accession No. HM461901). The ITS sequence was a 100% match to N. vasinfecta strain N-JXLN01 (GenBank Accession No. GU213063) by BLASTn in GenBank. Pathogenicity tests were conducted on detached pods of peanut cultivar Jihua 4. Forty surface-disinfested peanut pods were soaked in a conidial suspension (10⁵ conidia per ml) for 2 min and 40 pods were soaked in sterile water as a control. Then all peanut pods were maintained in moist petri dishes under darkness for 14 days at 28°C. Brown or black spots appeared on all pods inoculated with the fungus within 10 days, while the controls remained healthy. Symptoms were similar to those originally observed in the field, and N. vasinfecta could be reisolated from all infected pods. This fungus previously has been reported as the pathogen of foot rot of peanut in South Africa (1), Taiwan (4), and Australia (3). To our knowledge, this is the first report of peanut pod rot caused by N. vasinfecta in China.

References: (1) S. W. Baard et al. Phytophylactica 17:49, 1985. (2) O. A. Cornely et al. Emerg. Infect. Dis. 7:149, 2001. (3) M. F. Fuhlbohm et al. Australas. Plant Dis. Notes 2:3, 2007. (4) J. W. Huang et al. Plant Pathol. Bull. 1:203, 1992.