First report of peanut foot rot caused by Neocosmospora vasinfecta in mainland China

In June 2009, disease symptoms on peanut (Arachis hypogaea) were observed in several fields in Huoping county, Guangdong Province. The characteristic symptoms were black rot of the basal stems and roots, with many orange-brown fruiting bodies on the diseasedparts (Figs. 1, 2). Entire vines eventually wilted and died. The disease incidence reached as much as 30% in some fields, causing severe yield losses. A fungus was consistently isolated from the edge of lesions and grown on potato dextrose agar at 25°C. Mycelia were white and floccose. Conidia were cylindrical to oblong-ellipsoidal, hyaline, one-celled, and measured 3-15 x 1-5 μm (Fig. 3). Perithecia were glabrous apart from a number of rhizoidal hyphae, ostiolate and with a neck (Fig. 4). The asci were cylindrical, thin-walled, stalk 5-27 μm long, 101-161 μm tall and 10-15 μm in diameter, without discernible apical structures, not evanescent, eight-spored (Fig. 5). Ascospores were uniseriately arranged, pale, globose to ellipsoidal, and 7-16 x 7-12 μm (Fig. 5). The fungus was identified as Neocosmospora vasinfecta (anamorph Acremonium sp.) (Cannon & Hawksworth, 1984). The ITS sequences of three isolates were obtained and a typical example deposited in GenBank (Accession No. GU213063). There was 98% similarity with published sequences of N. vasinfecta (FJ940902).

Pathogenicity was confirmed by dipping the roots of two-week-old peanut seedlings of cv. Yueyou 7 in a mixed suspension of conidia and ascospores for five minutes before transplanting in pots. All inoculated plants wilted, with a black rot at the base of the stem and in the roots after 15 days. N. vasinfecta was reisolated from inoculated plants. Control eedlings dipped in sterile water remained healthy. This is the first finding of peanut foot rot caused by N. vasinfecta in mainland China. Peanut is a major crop and this disease is a potentially serious threat to production. The pathogen has been reported in East Asia (Huang et al., 1992) and more recently in Australia (Fuhlbohm et al., 2007).  N. vasinfecta is also associated with corneal ulcers (Manikandan et al., 2008) though it is unclear whether the human isolates cause disease in peanut plants.