Agronomic and breeding value of genes for resistance to leaf scald (Rhynchosporium secalis) in barley (Hordeum vulgare)

Abstract

Scald (Rhynchosporium secalis) is one of the most damaging leaf and stem diseases of barley grown in southern Australia. The development of resistant cultivars is the most effective means of controlling scald. However, the highly variable nature of the scald pathogen has often resulted in resistance conferred by single major genes being rendered ineffective. Breeding and selection for non-race specific, durable resistance, or the adoption of major gene deployment strategies such as gene pyramiding, could largely overcome this problem. Four cultivars of barley (Guardian, Halcyon, Sultan, Waveney) were evaluated as potential sources of scald resistance, suitable for gene introgression and pyramiding programs in southern Australia. Each of these prospective donor parents was backcrossed to the susceptible recurrent parent Sloop through one cycle of backcrossing. All 4 cultivars were resistant to scald isolates common in southern Australia. No factors, either deleterious or beneficial to grain yield, were associated with scald resistance genes from Guardian, Halcyon, and Waveney. Scald resistance genes carried by Sultan were found to be associated with lower grain yield. Both resistant and susceptible first backcross lines derived from Guardian produced a lower proportion of plump grain than the recurrent parent Sloop. A greater number of backcrosses and large population size may be required to successfully introgress scald resistance genes from Sultan and Guardian into germplasm adapted to southern Australian conditions. The development of molecular markers linked to resistance genes in these parents will allow efficient introgression and pyramiding of scald resistance genes from Waveney, Halcyon, and Sultan.