Fusarium cerealis, A New Pathogen Causing Ginseng (Panax ginseng) Root Rot in China.

Ginseng (Panax ginseng) is a perennial plant belonging to the genus Panax of the family Araliaceae, and it is a precious traditional Chinese medicine with immunity-enhancing, anti-tumor, anti-atherosclerosis, and other functions. Jilin Province, China, is the world's largest ginseng cultivation area, accounting for about 70% of global production. The root rots of ginseng caused by Fusarium spp. are one of the most serious threats to ginseng production. Seriously infected ginseng roots are not marketable, leading to enormous losses. The canopy of infected ginseng plants exhibit symptoms of red or yellow leaves from lower to upper during early plant development and growth, wither and wilt in the later stages, and lastly die. All parts of the root can be infected; brown or black lesions were mainly formed on surface and expanded gradually, and mature lesions are gray-brown. Samples of 208 Fusarium rotted roots (cv. landrace damaya) from Ji'an city (126°18' E, 41°12' N) and Dunhua city (128°23' E, 43°36' N) of Jilin Province were collected from April to September, 2012. Small tissue pieces were placed on potato dextrose agar (PDA), and all isolates were purified from single spore cultured at the condition of 25°C, 12-h/12-h light-dark cycle. Among the obtained purified 518 isolates, 10 isolates were different from the others. Colonies of the 10 isolates grew rapidly and produced profuse aerial mycelium with carmine red undersurface. When cultured on carnation leaf-piece agar (CLA), macroconidia were stout, thick-walled, apical and basal cells curved, usually 4 to 5 septa, 23.9 to 41.2 × 5.2 to 7.3 μm, but did not produce microconidia. Abundant chlamydospores were produced from mycelium or spores, singly or in chains. According to the morphological characteristics, all 10 isolates were consistent with the descriptions of F. cerealis (1). Further, identity of all isolates was confirmed by sequencing the partial rDNA internal transcribed spacer (ITS), translation elongation factor (TEF-1α) gene (3) and putative reductase (RED) gene (2). The sequences of all 10 isolates were homologous and BLAST analysis of the submitted sequences (KF530831, KF530830, and KF530829) showed 100% identity to the sequences (DQ459869, AF212464, and EF428900) of F. cerealis in the NCBI and the FUSARIUM-ID databases. As a result, 10 isolates of Fusarium spp. were identified as F. cerealis. Pathogenicity was tested by inoculating ginseng root in vitro and healthy plants in a greenhouse. The surface of healthy ginseng roots were washed with water and disinfested in 70% alcohol for 3 min and planted in flowerpots with sterilized soil and sorghum grain infested with each isolate and incubated in greenhouse (20 to 25°C). Five ginseng roots and five healthy plants were inoculated with agar cake and sterilized sorghum seed as controls. Root rots similar to the naturally symptoms were observed on inoculated ginseng roots in vitro and healthy plants after 3 days and 21 days, respectively, but no root rots developed on the controls. The pathogens were successfully re-isolated and were are identical to those of the originals. To our knowledge, this is the first report of F. cerealis causing root rot on ginseng in China. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (2) K. O'Donnell et al. Proc. Nat. Acad. Sci. 97:7905, 2000. (3) K. O'Donnell et al. Mycologia 92:919, 2000.