Basal Rachis Internode Injection (BRII): 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. Difficulties in reliably phenotyping of this disease, however, 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), which is implemented by injecting inoculum into the basal internode of a rachis instead of a floret as done in single floret inoculation (SFI). One of the prominent advantages of BRII over SFI and other traditional methods lies in its independence of moisture-maintaining system that is required for all existing methods, thus being insensitive to environmental humidity and cost-effective. Another unique feature for BRII is that this method produces nearly clear-cut reaction types, by which FHB resistance could be treated as a qualitative trait because generally no FHB symptom appeared on the spikelets of resistant genotypes. In addition, BRII outperformed SFI by higher infection rate and better goodness-of-fit with known FHB resistance and QTL components in a panel of 15 genotypes, as well as two populations of recombinant inbred lines (RILs) segregating in Fhb1. To be noteworthy, BRII and SFI methods are not mutually replaceable but rather complimentary to each other since each method has its own advantage in differentiating FHB resistance among genotypes. Combining these two methods would significantly improve the reliability and consistency of FHB phenotyping in wheat.