From June 2009 to November 2010, a disease was observed on peanut (Arachis hypogaea L.) in Ganzhou City, Jiangxi Province, China. Infected plants initially exhibited yellow leaves, then defoliated, and finally wilted and died. Basal stems, pegs, pods, and roots became black and rotted, with many orange-brown spherical fruiting bodies emerging on the lesions. Disease incidence reached as high as 30% in some plots, especially in those covered with plastic sheets after planting to control weeds. Isolations from 68 diseased plants were conducted on potato dextrose agar (PDA) amended with streptomycin sulfate and incubated at 25°C. A fungus was consistently isolated from the edge of the lesions. Mycelia grew at a linear rate of 3.9 mm per day on PDA at 25°C forming a pale buff, floccose colony with abundant orange-red perithecia. Perithecia were globose to pyriform, ostiolate and with a short neck, and measured 151 to 353 × 141 to 313 μm. Asci were narrowly cylindrical to clavate, thin walled with a short stalk, measured 100 to 160 μm high and 9 to 15 μm in diameter, and were eight spored. Ascospores were uniseriately arranged, globose to ellipsoid, nonseptate, thick walled, hyaline to pale yellow, and measured 7 to 16 × 7 to 12 μm. Scanning electron microscopy revealed that the wall of the ascospores had cerebriform ornamentation. Conidia were cylindrical to oblong-ellipsoidal, hyaline, most one celled, and measured 3 to 15 × 1 to 5 μm, aggregating in a gelatinous mass on the tip of the conidiogenous cell, which usually arose directly from the vegetative mycelium. The fungus was identified as Neocosmospora vasinfecta var. africana (anamorph Acremonium sp.) (1). The rDNA internal transcribed spacer (ITS) region of the fungus was amplified with universal primers ITS1/ITS4 and sequenced. The sequences of a representative isolate (No. N-JXLN02) were submitted to GenBank (Accession No. JF708085) and BLAST searches showed 99 to 100% similarity with sequences of N. vasinfecta deposited in GenBank (Accession Nos. HM461900, HM461901, and AY381142 ). Pathogenicity tests were conducted on 36 2-week-old peanut seedlings, cv. Yueyou No. 13, in plastic pots. Plants were inoculated by drenching the soil near the shoot with a mixed suspension of conidia and ascospores (105 spores per ml). Control plants were treated with sterile water. All plants were then incubated in a moist chamber at 25 ± 2°C. Fifteen days after inoculation, all inoculated plants showed lesions on basal stems and black root rot similar to that observed on naturally infected plants. No disease was observed on control plants. The pathogen was reisolated from infected tissues. To our knowledge, this is the first finding of Neocosmospora foot rot of peanut in Jiangxi Province, where outbreaks of this disease have been observed in several counties. The pathogen will pose a threat to peanut, which is a major oil crop in China. It has been previously reported in Taiwan (2) and recently in Guangdong Province, though the subspecies of the pathogen was not identified in the latter case (3).
References: (1) P. F. Cannon and D. L. Hawksworth. Trans. Br. Mycol. Soc. 82:673, 1984. (2) J. W. Huang et al. Plant Pathol. Bull. 1:203, 1992. (3) R. Pan et al. Plant Pathol. 59:1172, 2010.