Comparative pathogenicity of Fusarium graminearum isolates from China revealed by wheat coleoptile and floret inoculations

Abstract

Fusarium head blight (FHB) or scab caused by Fusarium species is an economically important disease on small grain cereal crops worldwide. Accurate assessments of the pathogenicity of fungal isolates is a key obstacle toward a better understanding of the Fusarium-wheat scab system. In this study, a new laboratory method for inoculation of wheat coleoptiles was developed, which consists of cutting off the coleoptile apex, covering the cut apex with a piece of filter paper soaked in conidial suspension, and measuring the lengths of brown lesions 7 days post inoculation. After coleoptile inoculation, distinct brown lesions in the diseased stems were observed, in which the presence of the fungus was verified by PCR amplification with F. graminearum Schwable-specific primers. Coleoptile inoculation of six wheat varieties indicated that a highly susceptible wheat variety was more suitable as a differentiating host for the pathogenicity assay. Analysis of the coleoptiles inoculated with a set of 58 different isolates of F. graminearum showed a significant difference in the lengths of the lesions, forming the basis by which pathogenicity of the isolates was assessed. Field inoculation of florets of three wheat varieties over 2 years revealed significant differences in pathogenicity among the 58 isolates, and that the highly resistant and highly susceptible wheat varieties were more appropriate and stable for pathogenicity assessment in field trials. Comparative analyses of eight inoculation experiments of wheat with 58 F. graminearum isolates showed significant direct linear correlations (P<0.001) between coleoptile and floret inoculations. These results indicate that the wheat coleoptile inoculation is a simple, rapid and reliable method for pathogenicity studies of F. graminearum in wheat.

In Planta Stage-Specific Fungal Gene Profiling Elucidates the Molecular Strategies of Fusarium graminearum Growing inside Wheat Coleoptiles

“…Three-day-old seedlings of wheat (Triticum aestivum) cultivar Zhongyuan 98-68 (susceptible to F. graminearum and widely cultured in Henan, China) were used for the coleoptile infection assay according to Wu et al (2005) with modifications. Three days after seed sowing, the top 2 to 3 mm of the coleoptiles were removed, and the seedlings were wrapped in 4 mm 3 1-cm cotton strips and incubated for 3 d (see Supplemental Figure 2A online).…”

Validation of a modified Petri-dish test to quantify aggressiveness of Fusarium graminearum in durum wheat

“…Pathogenicity is a qualitative measurement that reflects the ability of fungus to cause the disease, while aggressiveness is a quantitative measurement of the level of disease reached: more aggressive pathogens will reach a specific disease level faster (Shaner et al 1992). Aggressiveness assessment is a fundamental aspect that is considered crucial for understanding the interaction between host and pathogen in the FHBwheat system (Wu et al 2005).…”

“…This low specificity makes its aggressiveness and spread in plant tissues variable and greatly influenced by environmental conditions, thus a precise and accurate assay to quantify the levels of aggressiveness of F. graminearum is needed. Wu et al (2005) listed different methods that have been developed to quantify the aggressiveness, including inoculation of floral tissues, stems and seedlings (Bai et al 2001;Mesterhazy 1995;Snijders 1990;Hare et al 1999). The floret inoculation assay is a classical method, which has been used for several decades to assess the aggressiveness of fungal pathogen isolates.…”

“…This method is reliable and yields satisfactory results. However it is costly, time consuming, laborious and greatly influenced by growth stage and environmental factors (Wu et al 2005). The other inoculation methods (i.e.…”

“…The major problem is that there are very few experiments that really compare the aggressiveness of F. graminearum between each method and the single floret inoculation technique in controlled conditions and/or in the field. Wu et al (2005) published a new inoculation method for aggressiveness using wheat coleoptiles. This method was rapid, reliable and provided good correlation with floret field inoculation.…”