Pyramiding wheat rust resistance genes using marker-assisted selection

[摘要] English: Wheat (Triticum aestivum L.) is widely cultivated over large areas and is an important food crop worldwide. Wheat is extensively used during the production of many different types of foods. Wheat rusts (leaf, stem and stripe rust) are important foliar diseases of wheat worldwide, causing large losses and damage to the wheat industry. The ability of these rust pathogens to change and be dispersed over long distances pose a continual global threat. Annually millions around the world are spent on fungicides in an attempt to control wheat rusts. Resistant cultivars have proven to be the most effective, economical and environmentally friendly form of rust control. Although many resistant cultivars have been developed historically, a need for more durable resistance exists. The application of molecular markers and marker-assisted selection (MAS) strategies in breeding programmes can support plant breeders in accomplishing pyramiding of several rust resistant genes into new cultivars. The aim of this study was to pyramid seven rust resistant genes/QTL (leaf, stripe and stem rust) into a single genotype using five SSR, three STS and two AFLP markers. The study focused on wheat genes applicable to the local wheat industry and markers used and/or developed in South African breeding programmes. In this study four bread wheat cultivars or lines (AvocetYrsp, Blade, CSLr19-149-299 and Kariega) were used as parental sources of five resistance genes (Sr2, Sr26, YrSp, Lr19 and Lr34) and two QTL (QYr.sgi-7D and QYr.sgi-2B). Selection after each cross was done using a MAS approach with SSR and STS markers linked to the different resistant genes/QTL. The study was conducted over a two year period, involving the development of two different sets of F1 offspring and one double cross generation from a series of directional crosses. Before crosses were made, the presence of the expected rust resistance genes was confirmed in the parental lines using specific SSR, STS and AFLP markers. The SSR and STS markers amplified the expected allele sizes in the parental lines, except for the unexpected detection of the Lr34 gene in AvocetYrSp. Results indicated that the Sr2 marker was not consistently present in Blade, suggesting the Blade cultivar was heterogeneous for Sr2. The AFLP markers linked to the YrSp resistance gene did not detect differences between the parental lines and were excluded from further experiments. The F1 generations were screened with one SSR or STS marker each to identify successful crosses. Genotyping of the F1 generations indicated than on average, 85.5% of the tested F1's were true hybrids. Phenotypic screening was done on the parental lines and F1 individuals for the three rust types and confirmed the presence of the expected genes in the parental lines as well as selected F1 individuals. A total of 900 individuals of the double cross generation were screened with five SSR and three STS markers associated with resistance genes and QTL to identify whether gene pyramiding within a single genotype was successful. The number of individual plants of the double cross population containing markers linked to the desired resistance gene(s)/QTL ranged from two individuals containing none of the markers to three individuals containing all eight markers. The three individuals containing eight markers confirmed the presence of markers associated to the presence of the four single genes (Sr2, Sr26, Lr19 and Lr34) and two QTL (QYr.sgi-7D and QYr.sgi-2B.1). Due to the inefficiency of the AFLP markers, the presence of the seventh gene (YrSp) could not be confirmed on genotypic level. The future uses of the developed rust resistance gene pyramided lines of this study are countless. The use of these lines in combating the continual threat of wheat rusts in some manner should be helpful in future.

[发布机构] University of the Free State