Significance of the Stability of Fusarium Head Blight Resistance in the Variety Registration, Breeding, and Genetic Research of Winter Wheat Using Disease Index, Fusarium-Damaged Kernels, and Deoxynivalenol Contamination.

Fusarium head blight is one of the greatest threats to global wheat production. Despite the special attention paid by researchers to resistance genetics, the stability of resistance and the expression of its epidemiological relationships have not been tested in depth. As most studies only present data on visual symptoms, in this study, we present data from four experiments. Here, 15-40 genotypes were tested with four and eight isolates (inocula) in 3-4-year experiments, with 32, 24, 36, and 12 epidemic situations used to determine the disease index (DI), Fusarium-damaged kernels (FDKs), and DON. All genotypes were tested for stability by the variance across epidemics, and the b value of the linear function was considered. Both indices were suitable for measuring stability/instability, but the variance results were more closely correlated with the experimental data than the b value, known as the stability index (SI). The use of variance is recommended due to its simplicity and reliability. In the first test, the rate of maximum/minimum variance for DI, FDK, and DON differed 15-, 20-, and 120-fold, respectively. In the second test, the same rates were 200, 400, and over 4000, with the other tests exhibiting similar tendencies. The traits differ, the epidemics vary, and a dependence on resistance level can be proven. The genotype ranking varies strongly in different epidemics, with approximately 50% of the correlations between variety responses being insignificant. Therefore, many epidemics are needed to obtain a reliable picture of the adaptation ability of the resistance traits and their stability. Approximately 25% of the genotypes tested belong to the most stable group. About 35% were discarded, and in the 40% medium, we observed both highly unstable and moderately stable genotypes. Principal component analysis (PCA) of the three traits in the experiments showed a confirmatory, nearly uniform distribution of genotypes, with a different footprint or "identity card" present for each genotype. The genotypes for the traits belong to one or two groups, although sometimes individual genotypes seem to be independent. No strict rule was found. This underlines the necessity of considering the plant's traits (Di, FDK, and DON) in resistance testing. Highly resistant winter wheat lines could also be bred with very low variance and SI values and very high stability (SI values lower than 0.3). Of the traits, DON is the most important. With this methodology, variety registration also becomes possible. The epidemiological aspect has a decisive role in resistance studies, and without identifying stability in FHB resistance, no food safety estimates can be made.