Basal Rachis Internode Injection: A Novel Inoculation Method to Evaluate Wheat Resistance to Fusarium Head Blight

Fusarium head blight (FHB) is one of the most destructive fungal diseases of wheat. However, difficulties in reliably phenotyping of this disease have greatly hindered the understanding of the mechanism of wheat-pathogen interaction and genetic improvement of FHB resistance. Here we report a novel inoculation method called basal rachis internode injection (BRII), in which inoculum is injected into the basal internode of a rachis instead of a floret, as is done in single floret inoculation (SFI). One of the prominent advantages of BRII over SFI and other traditional methods lies in its independence from the moisture-maintaining system that is necessary for all existing methods, making it insensitive to environmental humidity and hence cost-effective. Another unique feature of BRII is that this method produces nearly clear-cut reaction types, by which FHB resistance can be treated as a qualitative trait because generally no FHB symptoms appear on the spikelets of resistant genotypes. In addition, BRII outperformed SFI with a higher infection rate and better goodness of fit with known FHB resistance and quantitative trait locus components in a panel of 15 genotypes, as well as two populations of recombinant inbred lines segregating in Fhb1. Note that BRII and SFI methods are not mutually exclusive but rather complementary because each method has its own advantages in differentiating FHB resistance between genotypes. Combining these two methods would significantly improve the reliability and consistency of FHB phenotyping in wheat.