Population Structure of the Gibberella fujikuroi Species Complex Associated with Rice and Corn in Korea

Abstract

Microbial Safety Team, National Academy of Agricultural Science, RDA, Suwon 441-707, Korea(Received on September 1, 2012; Revised on September 20, 2012; Accepted on September 23, 2012)Several species belonging to the Gibberella fujikuroispecies ( Gf ) complex are commonly associated with riceand corn, not only causing serious diseases, but alsoproducing fumonisins, a group of mycotoxins harmfulto animals and humans. To characterize the populationstructure of the putative fumonisin-producing Gf complexin Korea, we obtained 276 candidate isolates from riceand corn harvested in 2009 and 2010 by diagnosticpolymerase chain reaction with several specific primersets. Phylogenetic trees were constructed using multilocussequences (combined RPB2 and EF1A, totaling 1.6 kb)from these isolates. Among the 135 isolates from rice,F. fujikuroi (teleomorph: G. fujikuroi; 59.3%) and F.proliferatum (G. intermedia; 13.3%) were predominant,followed by F. concentricum (5.9%). Additionally, twenty-five (18.5%) rice isolates belonged in a distinct sub-clade of F. commune, a non-member of the Gf complex.In contrast, F. verticillioides was the most predominantspecies (38.3%) among the 141 corn isolates, and followedby F. fujikuroi (27.7%), F. proliferatum (14.9%), F. sub-glutinans (7.1%), and F. concentricum (2.8%). A singlemating type ( MAT1-1) was found predominantly amongthe Gf complex isolates examined. Possible distinct sub-clades were detected within the populations of F. fujikuroiand F. proliferatum; however, this needs further confir-mation. This is the first reported population-level charac-terization of putative fumonisin-producing Gf complexassociated with rice and corn in Korea.Keywords : fumonisin, Gibberella fujikuroi species com-plex, mating-type distribution, population structure, speciescompositionThe genus Fusarium is one of the most important fungalisolates associated with rice and corn because some membersof this group, such as the F. graminearum species complexand Gibberella fujikuroi species complex, are mycotoxinproducers as well as plant pathogens. The G. fujikuroi speciescomplex, a monophyletic lineage, consists of at least ninebiological species, formerly designated as mating populations(MPs) (Britz et al., 1999; Leslie 1999; Leslie et al., 2004),and numerous additional Fusarium anamorphs that areassigned to phylogenetically distinct species (Nirenbergand O'Donnell 1998; O'Donnell et al., 1998; O'Donnell etal., 2000). The Fusarium species in the G. fujikuroi species complexare distributed worldwide and cause serious diseases in awide variety of agricultural crops (Leslie 1999). These speciesalso produce a variety of toxic secondary metabolites andmycotoxins, including gibberellic acid (Cerda-Olmedo etal., 1994), moniliformin (Marasas et al., 1986), and fumoni-sins (Rheeder et al., 2002). Among these, fumonisins, agroup of polyketide-derived mycotoxins, have gained con-siderable attention because they have been associated withesophageal and liver cancer (Desjardins, 2006).To date, at least 15 Fusarium species, most belonging tothe G. fujikuroi species complex, are known to producefumonisins using a biochemical pathway catalyzed by apolyketide synthase (FUM1) (Proctor et al., 1999). Only afew species outside the G. fujikuroi species complex, suchas F. oxysporum, have the capacity for fumonisin produc-tion (Rheeder et al., 2002).As both rice grains and corn kernels are capable ofharboring the toxigenic G. fujikuroi species complex duringthe growing season, monitoring the fumonisin-producingFusarium species on these substrates is important. Severalspecies within the G. fujikuroi species complex are knownto be frequently associated with rice and corn. Three fumonisin-producing species, F. fujikuroi (MP-C,teleomorph: G. fujikuroi), F. proliferatum (MP-D, G. inter-media), and F. verticillioides (MP-A, G. moniliformis ), havebeen isolated from rice plants showing bakanae symptomsin Asia, Africa, Europe, and the United States (Amatulli etal., 2010; Carter et al., 2008; Desjardins et al., 2000;Desjardins et al., 1997; Hsuan et al., 2011; Wulff et al.,2010; Zainudin et al., 2008). The incidence of the latter wasrelatively lower than the first two species. F. verticillioidesis the most prevalent species on corn worldwide (Chulze et