Inheritance of resistance to scab in two wheat cultivars from Brazil and China

One of the major diseases that reduces the quality of wheat is scab. Quality is reduced by the production of toxins in grain by the pathogen Fusarium graminearum. Various genetic sources of resistance have been identified, but the degree of resistance in most cultivars is insufficient. Although both South American and Chinese germ plasm are being used in breeding programs around the world, it is not known whether the resistance genes contributed by these sources are different. The purpose of this study was to determine the mode of inheritance and number of genes involved in the scab resistance of a wheat cultivar from Brazil and one from China, both known to possess intermediate to high resistance in regard to spread of the disease in the wheat head. The resistant Brazilian cultivar Frontana was compared to the highly resistant Chinese cultivar Ning 7840 in crosses with CNO79, a highly susceptible Mexican wheat, as the susceptible parent. Random F2-derived F7 lines from the six crosses possible (including reciprocals) among the parents were studied for their field response following inoculation with F. graminearum on two inoculation dates. Three methods of disease assessment were compared. The two resistant parents were shown to possess two unique dominant genes each, with all four genes being different. Combining their resistance genes may produce higher levels of resistance. The two inoculation dates provided the same gene postulations. The three disease assessment methods essentially measured the same basic process of disease spread within the head, based on the calculation of the genotypic correlations between the methods and the similarity in gene postulations. The easiest and most relevant method should therefore suffice for assessing the spread of scab through the wheat head.