Cees Waalwijk Ineke M de Vries Jrgen Khl Xiude Xu Theo A J van der Lee and Gert H J Kema

Abstract

We developed a multiplex PCR for the identification of the most frequently occurring species of Fusarium on wheat in Western Europe. Surveys suggest that Fusarium graminearum has replaced Fusarium culmorum as the dominant species on winter wheat in the Netherlands during the 1990s. Quantitative PCR was used to monitor Fusarium populations during the growing season. Populations on lower leaves consisted primarily of Microdochium nivale, but F. graminearum dominated in heads and on harvested grain, suggesting that the inoculum for the infection of the heads did not come from the leaves. A quantitative PCR recently developed for Fusarium verticillioides from maize may help to reduce the threat posed by fumonisin on large communities in Africa that rely on maize as a staple food.

Introduction

Fusarium diseases are a major cause of yield loss in many crops, including major staple foods, such as wheat (Bai and Shaner, 1994; Windels, 2000), rice (Abbas et al., 1998), maize (Fando-han et al., 2003) and banana (Ploetz, 1990; 2000). In some of these crops the losses due to reduced yield are increased since the causal agents also produce mycotoxins that reduce further the quality of the harvested crop. Mycotoxins have attracted considerable attention over the last years and regulatory limits have been established and enforced in the EU (European Commission, 2005) and several other countries, but not in many African countries (van Egmond, 2004).

Two major staple crops, wheat and maize are recurrently infected by various Fusarium species that can produce mycotoxins. In the United States, Fusarium head blight (FHB) of wheat is caused primarily by F. graminearum, but in other parts of the world a number of species may be involved (CWSCG, 1984; Parry et al., 1995), both toxigenic and non-toxigenic. In Northern and Western Europe, non-toxigenic species, e.g. Microdochium nivale var. majus, are commonly found on wheat particularly early in the season (Turner et al., 2002). The toxigenic species usually include F. graminearum, F. culmorum and Fusa-rium avenaceum and, depending on the region and the weather conditions, perhaps Fusa© CAB International 2008. Mycotoxins: Detection Methods, Management, Public Health - 195 -and Agricultural Trade (eds. J. F. Leslie et al.).

rium poae, Fusarium sporotrichioides, Fusarium tricinctum amongst others. Each of these toxigenic species has a unique secondary metabolite profile (Table 1). Multi-locus sequencing of six single-copy nuclear genes has identified a series of phylogenetic lineages within F. graminearum (O'Donnell et al., 2000) that have been proposed to have species status (O'Donnell et al., 2004). Trichothecene production is not correlated with phylogenetic lineage in F. graminearum (Ward et al., 2002). Toxins produced by F. graminearum include zearalenone (Desjardins, 2006; Lysoe et al., 2006) in addition to the type B trichothecenes nivalenol and deoxynivalenol. Other species found on wheat produce different toxins, e.g., F. poae produces the type-A trichothecenes T-2 and HT-2 (Desjardins, 2006) and F. ave-naceum produces moniliformin (Desjardins, 2006).

Fusarium infection of maize occurs as two distinct diseases that are caused by partially overlapping groups of species. Red ear rot, or Gibberella ear rot, occurs primarily in areas with high precipitation or lower temperature and usually is caused by F. graminearum, although other species also have been associated with the disease (Table 1). Pink ear rot, or Fusarium ear rot, occurs primarily on damaged kernels and is caused by a group of species including F. subglutinans and the fumonisin producers F. verticillioides and Fusarium pro-liferatum (Table 1). Toxigenic and non-toxigenic species can be found in the same field, in the same plant, on the same cob or even within the same kernel.

Qualitative detection

Traditionally the species occurring on cereals were characterized morphologically, but this is time-consuming and the results may be ambiguous, e.g., F. verticillioides and F. thapsinum

Table 1. Toxigenic species of Fusarium associated with Fusarium Head Blight (FHB) of wheat and, Pink Ear Rot (PER) and Red Ear Rot (RER) of maize (after Bottalico and Perrone, 2002, and Logrieco et al., 2002).

Species

Disease

Mycotoxina

F. acuminatum

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