Comparison of Spray and Point Inoculation To Assess Resistance to Fusarium Head Blight in a Multienvironment Wheat Trial

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Abstract
Fusarium head blight (FHB, scab), caused by Fusarium graminearum or F. culmorum, results in yield and quality reductions and accumulation of mycotoxins. Two inoculation methods are commonly used. Spraying a spore suspension on the head (spray inoculation) will detect resistance to initial infection (type I) and to disease spread within the spike (type II). Injecting a spore suspension into individual florets (point inoculation) will detect type II resistance only. To analyze the association of spray and point inoculation, 20 elite winter wheat cultivars from Romania, Germany, and Switzerland were inoculated in factorial field experiments in seven environments (location x year combinations) in Germany and Romania. Response to FHB was assessed by the percentage of visually infected spikelets and head weight relative to the noninoculated control. Point and spray inoculations resulted in a mean disease severity varying from 52 to 63%. Significant (P = 0.01) genotypic variation was found within and across the environments. Genotype-environment interaction was important also. Estimates of entry-mean heritability were higher for spray than for point inoculation as assessed by percent infected spikelets (0.81 versus 0.77) and relative head weight (0.77 versus 0.52). Significant (P = 0.01) interaction was found between inoculation methods. Consequently, coefficients of phenotypic correlation between both methods were low to medium for percent infected spikelets (0.40, P > 0.1) and relative head weight (0.52, P = 0.05). We conclude that the application of both inoculation methods should provide additional information for selection and scientific studies. Spray inoculation, however, is less laborious for large-scale routine screening of breeding materials.