Use of SSR markers to determine the genetic purity of a popular Australian wheat variety and consequences for stripe rust reactions

Abstract

Sunvale is a popular bread wheat variety grown throughout central and northern New South Wales in Australia which has moderate resistance to the fungal leaf disease stripe rust. However, significant levels of stripe rust have been reported in Sunvale crops over the past few seasons. Sunvale is a 17-year-old variety so genetic purity may also be involved in the numerous reports of increased disease susceptibility in grower crops. Twelve SSR markers were used to determine the genetic purity of 23 grower-retained seed lots of cv. Sunvale. Sixteen of the 23 grower-retained Sunvale seed lots (70%) contained at least 5% contamination from a different genotype, while seven samples (30%) contained > 10% contamination. The SSR analysis was complemented by field observations of the various seed lots in a replicated small plot trial. In 17 of the 19 grower-retained Sunvale seed lots that had some level of contamination with another genotype(s), at least one contaminant was very susceptible to stripe rust. The pure Sunvale plants in the plots showed a moderately resistant reaction. This is the first report of seed impurity being definitively determined as the cause of unexpected stripe rust responses within a wheat variety.