Infection of wheat spikes by Fusarium avenaceum and alterations of cell wall components in the infected tissue

Abstract

The infection process of Fusarium avenaceum on wheat spikes and the alteration of cell wall components in the infected host tissue were examined by means of electron microscopy and cytochemical labelling techniques following spray inoculation at growth stage (GS) 65 (mid-flowering). Macroconidia of the pathogen germinated with one to several germ-tubes 6-12 h after inoculation (hai) on host surfaces. The germ-tubes did not penetrate host tissues immediately, but extended and branched on the host surfaces. Hyphal growth on abaxial surfaces of the glume, lemma and palea was scanty 3-4 days after inoculation (dai) and no direct penetration of the outer surfaces of the spikelet was observed. Dense mycelial networks formed on the inner surfaces of the glume, lemma, palea and ovary 36-48 hai. Penetration of the host tissue occurred 36 hai by infection hyphae only on the adaxial surfaces of the glume, lemma, palea and upper part of ovary. The fungus penetrated the cuticle and hyphae extended subcuticularly or between the epidermal wall layers. The subcuticular growth phase was followed by penetration of the epidermal wall, and hyphae spread rapidly inter-and intracellularly in the glume, lemma, palea and ovary. During this necrotrophic colonization phase of the wheat spike, a series of alterations occurred in the host tissues, such as degeneration of cytoplasm and cell organelles, collapse of host cells and disintegration of host cell walls. Immunogold labelling techniques showed that cell walls of spike tissues contained reduced amounts of cellulose, xylan and pectin near intercellular hyphae or infection pegs compared to walls of healthy host tissues. These studies suggest that cell wall degrading enzymes produced by F. avenaceum facilitated rapid colonization of wheat spikes. The different penetration properties of abaxial and adaxial surfaces of the spikelet tissues as well as the two distinct colonization strategies of host tissues by F. avenaceum are discussed. The penetration and colonization behaviour of F. avenaceum in wheat spikelets resembled that of F. culmorum and F. graminearum, although mycotoxins produced by F. avenaceum differed from those of the latter two Fusarium species.

Fusarium species associated with plants in Australia

“…Outside of Australia, strains of this fungus causes head blight of wheat (Golinski et al 2002;Kang et al 2005) and frequently are recovered from the grain and field stubble of a number of cereals (Hall and Sutton 1998;Turkington et al 2002). Fusarium avenaceum has been isolated from winter cereals in south-eastern Australia .…”

In vitro sensitivity of Fusarium graminearum, F. avenaceum and F. verticillioides to carbendazim, tebuconazole, flutriafol, metconazole and prochloraz

“…Among these species, F. graminearum is the main causal agent of FHB (McMullen et al, 1997;Lević, 2008). F. avenaceum is regarded as a saprotroph on cereals by some authors (Summerell et al, 2003), but several studies confirmed the pathogenicity of this species on wheat (Jenkinson and Parry, 1994;Kang et al, 2005). F. verticillioides is an important pathogen of maize, but it does not cause FHB (Leslie and Summerell, 2006).…”

Cytological and immunocytochemical studies on responses of wheat spikes of the resistant Chinese cv. Sumai 3 and the susceptible cv. Xiaoyan 22 to infection by Fusarium graminearum

“…Wheat heads are most susceptible to F. graminearum infection for a short time period from flowering to the soft dough stage of kernel development. More recently, we elucidated in detail the infection process and pathway of spread of F. culmorum, F. graminearum, F. avenaceum and M. nivale in wheat spikes by means of light microscopy and scanning and transmission electron microscopy, and found that these pathogens exhibited a similar behaviour regarding infection and colonization of wheat spikes (Kang and Buchenauer 2000a;Kang et al 2004Kang et al , 2005. Furthermore, using enzyme-gold and immuno-gold labelling techniques, it has been demonstrated that these pathogens produced cell wall degrading enzymes such as cellulases, xylanases and pectinases at early stages of infection in wheat spikes (Kang and Buchenauer 2000b;Wanyoike et al 2002;Kang et al 2004Kang et al , 2005.…”

“…More recently, we elucidated in detail the infection process and pathway of spread of F. culmorum, F. graminearum, F. avenaceum and M. nivale in wheat spikes by means of light microscopy and scanning and transmission electron microscopy, and found that these pathogens exhibited a similar behaviour regarding infection and colonization of wheat spikes (Kang and Buchenauer 2000a;Kang et al 2004Kang et al , 2005. Furthermore, using enzyme-gold and immuno-gold labelling techniques, it has been demonstrated that these pathogens produced cell wall degrading enzymes such as cellulases, xylanases and pectinases at early stages of infection in wheat spikes (Kang and Buchenauer 2000b;Wanyoike et al 2002;Kang et al 2004Kang et al , 2005. In addition, immunogold labelling studies revealed a close relationship between the accumulation of Fusarium toxins in infected wheat spikes and the pathogenic changes in the host cells, colonization of the pathogen in the host tissues and symptom appearance (Kang and Buchenauer 1999).…”