Wheat: Rust Resistance and Pollen Biology

Abstract

This study focuses on saving multi-million-dollar losses caused by rust diseases of wheat. Genetic diversity assessment in a panel of landraces through phenotypic assays and genotyping with markers linked with known adult plant stem rust resistance genes revealed the presence of Sr55 and Sr58 individually and in combination. Sr2 and Sr57 were present in two and five landraces, respectively. Genotypes carrying putatively new sources for adult plant stem rust resistance were identified. Two consistent QTL; QSr.sun-5BL and QSr.sun- 7BL were identified from a pre-Green Revolution winter wheat landrace Aus27959. Based on physical position of QSr.sun-5BL in Chinese Spring (NRG v1.0), this QTL was shown to be different from the chromosome 5B located stem rust resistance gene Sr56. Hence, this QTL represents a new source for stem rust resistance. The uniqueness of QSr.sun-7BL remains to be determined. Genetic analysis of stripe rust resistance at the 4th leaf stage in Australian wheat cultivar Axe indicated the involvement of a single locus. The underlying locus was mapped on chromosome 7A and named as Yr75. Fine mapping of the Yr75-carrying genomic region identified close linkage of kompetitive allele specific PCR (KASP) markers sunKASP_427 (0.4 cM) and sunKASP_430 (0.3 cM). These flanking markers are 1.24 Mb (physical disctance; IWGSC RefSeq v1.0 genome assembly) apart. Scanning electron microscopic (SEM) observations showed significant variation in pollen size. In vitro pollen germination medium was standardized to achieve 70-80% germination in 30-40 minutes. Pollen viability study among a set of 12 wheat genotypes showed the viability of wheat pollen up to five hours under controlled conditions. These experiments demonstrated the conditions for initiating pollen mediated gene editing in wheat.