Investigation into components of partial disease resistance, determined in vitro, and the concept of types of resistance to Fusarium head blight (FHB) in wheat

Abstract

This work presents an analysis of the relationship between components of partial disease resistance (PDR) detected using in vitro detached leaf and seed germination assays, inoculated with Microdochium majus, and Fusarium head blight (FHB) resistance to Fusarium graminearum assessed using point inoculation, termed Type II resistance. Relationships between in vitro-determined PDR components and FHB resistance using techniques which inoculate the wheat spike uniformly, termed Type I resistance (incidence and severity), have been reported previously. In this study shorter incubation periods, longer latent periods and shorter lesion lengths in the detached leaf assay and higher germination rates in the seed germination assay were related to greater FHB resistance measured by single point inoculation (Type II), collectively explaining 54% of the variation. Overall the relationships observed for Type II FHB resistance were similar to previous findings for Type I resistances. However, the relative magnitude of effects of the individual PDR components determined in vitro varied between FHB disease resistance parameters. Resistance in seed germination and latent period in the detached leaf assay were more strongly related to resistance assessed by point inoculation (Type II) and severityType I as opposed to incubation period which was most strongly related to disease incidence-Type I. The results provide evidence that individual components of partial disease resistance differentially affect aspects of FHB disease progression in the wheat spike. This work supports the view that the current model of types of resistance is an oversimplification of the interacting mechanisms underlying expression of FHB resistance.Keywords Detached leaf assay . Microdochium majus . Seed germination assay Fusarium head blight (FHB) Type 1 resistance testing in plant breeding is predominantly conducted with inoculum evenly spread over the wheat head, assumed to be resistance to initial infection (Schroeder and Christensen 1963). A number of methods are utilised to achieve the even application of inoculum over the wheat head, typically spray inoculation, natural infection, or spreading infected corn or wheat during crop development. Resistance is subsequently measured as disease incidence and severity or a combination of both. Type II resistance was hypothesised as resistance to spread, determined by point inoculation of a single spikelet (Schroeder and Christensen 1963) conducted in the glasshouse. More recently, disease incidence in field-inoculated nurseries has been regarded as being more strongly related with resisEur J Plant Pathol (

A Simple Method for the Assessment of Fusarium Head Blight Resistance in Korean Wheat Seedlings Inoculated with Fusarium graminearum

“…The PDR component incubation period was highly related to FHB disease incidence while resistance detached in the seed germination assay related to a greater decline in the level of FDK and a smaller reduction in DON than would be expected from the reduction in FHB diseases on the wheat spike ( Browne, 2007 ). Browne (2009) showed that higher germination rates in the seed germination were greater FHB resistance measured by single point inoculation strongly related to resistance assessed in spike (Type II). In this report, FHB resistance determined by seed soaking or soak-dry methods did not predict Type I resistance or Type II resistance in adult plants.…”

“…Unfortunately, the evaluation of FHB resistance has been slow due to the necessity to avoid escapes by evaluating resistance in whole plants over several years and in environ- ment factors ( Browne and Cooke, 2004 ). Therefore, there has been interest in developing in vitro assays to provide methods for prescreening FHB resistance such as: detached leaf assay ( Browne et al, 2005 ; Browne and Cook, 2005b ; Browne, 2007 ; Diamond and Cooke, 1999 ), seedling resistance ( Mesterhazy, 1995 ; Snijders, 1990 ), seed germination assay ( Browne and Cook, 2005a ; Browne, 2007 , 2009 ), coleoptiles assay ( Li et al, 2010 ; Wu et al, 2005 ) and response to the Fusarium mycotoxin deoxynivalenol (DON) ( Buerstmayr et al, 1996 ). The detached leaf assay was successful in identification of an important component of the resistances of FHB in European wheat germplasm and may have utility as a mechanism for discrimination among different resistances in breeding program ( Browne et al, 2004 ).…”

“…in the in vitro assay ( Browne and Cooke, 2005a ). Browne (2009) reported that PDR components (incubation periods, longer latent periods and shorter lesion lengths) in the detached leaf assay and higher germination rates in the seed germination assay were related to greater FHB resistance (Type II). However, the exotic wheat germplasms which provide highly effective resistances to FHB resistance do not appear to be detected in the detached leaf ( Browne and Cook, 2004 ; Browne et al, 2005 ) or seed germination assays ( Browne and Cook, 2005a ).…”

Further characterization of the scab resistance of ‘Frontana’ spring wheat and the relationships between resistance mechanisms

“…1999, Steiner et al. 2004, Browne 2009). The correlation between disease severity and VFDK emphasizes the impact that disease severity has on kernel quality, and it highlights the interrelatedness of visual FHB metrics.…”

“…(2009) used spray and point inoculation to separately classify QTL associated with type I and type II resistance. Browne (2009) showed the relationship between various partial disease resistance components and FHB incidence and severity. He concluded that although type I and type II mechanisms generally relate to resistance, assuming that these two defense mechanisms function independently does not typically account for the full expression of resistance to FHB in wheat.…”