Journal of Plant Pathology (2014), 96 (1), 133-142
Edizioni ETS Pisa, 2014
Ferrigo et al.
133
TRICHODERMA HARZIANUM T22 INDUCES IN MAIZE SYSTEMIC RESISTANCE AGAINST FUSARIUM VERTICILLIOIDES D. Ferrigo, A. Raiola, E. Piccolo, C. Scopel and R. Causin Dipartimento Territorio e Sistemi Agro-forestali, Sezione di Patologia Vegetale, Università degli Studi di Padova, Viale dell’Università 16, 35020 Legnaro (PD), Italy
SUMMARY
Fusarium verticillioides is one of the most common plant pathogenic fungi affecting maize causing ear and kernel rot. Nearly the totality of the fungal strains are able to produce mycotoxins known as fumonisins at very different levels. However, information on the ability of the biocontrol fungus Trichoderma harzianum to induce systemic resistance in maize against F. verticillioides is still lacking. We now show that, upon root colonization by T. harzianum, F. verticillioides consistently reduces maize disease symptoms. The enhanced activation of SA- and JA/ ET-dependent defence responses indicates that resistance in maize is caused by a better perception of the fungal pathogen due to the effect of Trichoderma inocula. Seed biopriming with T. harzianum could be a useful strategy to control F. verticillioides infection and fumonisin accumulation under field conditions. Key words: Trichoderma harzianum, Fusarium verticillioides, maize, fumonisin, induced systemic resistance.
INTRODUCTION
Fusarium verticillioides (Saccardo) Nirenberg (teleomorph: Gibberella moniliformis Wineland = G. fujikuroi mating population A, sect. Liseola) is one of the most common plant pathogenic fungi affecting maize (Leslie, 1991; Nelson, 1992) and is the prevailing maize pathogen in Italy (Rossi et al., 2004). It attacks roots, stems and ears causing crop yield reductions ranging from 10% to 30%. Inoculum come from infected maize seeds (Bacon and Hinton, 1996), root colonization (Kedera et al., 1992; Lumsden et al., 1995), environmental damage (Wicklow et al., 1988), corn borer lesions (Sobek and Munkvold, 1999; Miller, 2001) and silks (Munkvold et al., 1997). Regardless of the inoculation pathways, the pathogen spreads to the whole plant and kernels colonization results in fumonisin B1 (FB1) and B2 (FB2) contamination. Fumonisins are the most common mycotoxins in maize kernels (Placinta et al., 1999), occurring at biologically significant levels in Corresponding author: R. Causin Fax: +39.049.8272890 E-mail:
[email protected]
grains and in a variety of maize-based human foodstuffs and animal feed (Marasas, 1995). FB1 and FB2 have a notable impact on human and animal health (Logrieco et al., 2002). They are toxic and known (Rossi et al., 2004) to cause pulmonary oedema in swine, encephalomalacia in horses (Prelusky et al., 1994) and immunological disorders in ducks (Bennet and Klich, 2003). Human consumption of F. verticillioides-contaminated maize has been associated with elevated rates of oesophageal cancer and FB1 has been classified by the International Agency for Research on Cancer (IARC) in Group 2B as “possibly carcinogenic to humans” (Vainio et al., 1993). Detection, prevention and control of maize infection by F. verticillioides are difficult, especially when the fungus remains at the endophytic stage and kernels appear to be uninfected (Bacon and Hinton, 1996). The main current strategies for an effective control of F. verticillioides infection to maize are indirect measures based on “good agricultural practices” or on reduction of European corn borer attacks in the field. Little is known on the possible role of direct control of infections through chemicals or biological agents. The possible use of fungicides against F. verticillioides has been investigated (Folcher et al., 2009; Mazzoni et al., 2011), whereas the usefulness of biological control is poorly studied and requires further attention (Cavaglieri et al., 2005; Chandra Nayaka et al., 2010). Biological control agents (BCAs) represent a promising strategy for managing seed-borne, soil-borne and foliar diseases in a wide range of crops and could also be applied to control F. verticillioides infections and the consequent fumonisin contamination. Trichoderma harzianum appears one of the most promising BCAs: it can colonize roots and compete for space and nutrients with plant pathogenic fungi (Elad, 1996). It produces antifungal substances (Vinale et al., 2008) and enhances plant growth by improving nutrient uptake and nitrogen use efficiency (Harman, 2000; Yedidia et al., 2001). Moreover, both the ethylene and jasmonate signalling pathways (Shoresh et al., 2005; Djonovic et al., 2007) induced by release of fungal elicitors (Woo et al., 2006) and auxin-like metabolites (Vinale et al., 2008) can activate an avirulent symbiotic interaction (Harman et al., 2004a). Induction of systemic resistance by Trichoderma spp. occurs towards different pathogens, including fungi (Rhizoctonia solani, Botrytis cinerea, Colletotrichum spp.,
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Magnaporthe grisea, Phytophthora spp., Alternaria spp., etc.), bacteria (Xanthomonas spp., Pseudomonas syringae, etc.) and viruses [Cucumber mosaic virus (CMV)] in more than ten different dicots and monocots, including Graminaceae, Solanaceae and Cucurbitaceae (Zimand et al., 1996; Howell, 2002; Yedidia et al., 2003; Harman et al., 2004a). T22 is an effective T. harzianum strain commercially available, characterized by good rhizosphere competence and able to colonize plant roots in different types of soil and pH ranges (Harman and Björkman, 1998). Several studies have already been published on the interaction between T. harzianum, maize and a variety of pathogens (Harman et al., 2004b; Chen et al., 2005; Shoresh and Harman, 2008) except for F. verticillioides, and the protective effect of a wide range of BCAs (except for T. harzianum) against F. verticillioides, has also been reported (Bacon et al., 2001; Cavaglieri et al., 2005; Chandra Nayaka et al., 2010). Thus, very little is known on F. verticillioidesmaize-T. harzianum interactions (Sobowale et al., 2007). As reported in this paper, we have now shown the ability of T. harzianum strain T22 to induce systemic resistance against F. verticillioides in maize.
MATERIALS AND METHODS
Plant and fungal material. T. harzianum Rifai strain T22 and F. verticillioides strain 19 (FvS19) were used in this study. Uncoated seeds of hybrid maize Kermess (FAO 600 KWS) were used in all experiments. Root plant treatment with T. harzianum T22 was done using a commercial formulation (Rootshield, Intrachem Bio, Italy) containing 107 CFU g−1 propagules and conidia. Control plants were treated with the autoclaved Rootshield formulation. Thirty F. verticillioides strains were isolated from maize kernels grown in the north-eastern Italy and monoconidial cultures were obtained from these fungal isolates as reported by Tuite (1969). Molecular identification of the species was done by PCR using VER1 and VER2 primers (Mulè et al., 2004). Stalks of greenhouse-grown 30-dayold maize plants were inoculated with the monoconidial F. verticillioides strains. Fifteen days post inoculation the pathogenicity of the strains was tested twice on five plants per strain by measuring the extension of the necrotic area after image digitalization and graphic analysis with Autocad Autodesk software. Statistical analysis of pathogenicity tests was performed by one-way ANOVA followed by Tukey’s test (p
