stripe rust resistance

In recent years new races of Puccinia striiformis f. sp. tritici, the causative agent of stripe rust, appeared in different world locations with a more aggressive virulence profile, and they rendered many resistance genes ineffective.

Grain protein content (GPC) is one of the most important quality factors for pasta and bread wheats. Breeding for an increase in GPC is difficult because the genetic variation for this character is small compared to variations caused by the environment, besides there is a negative correlation between GPC and grain yield.

In 2000 stripe rust became a threatening disease of soft red winter wheat in the eastern US when new races of stripe rust appeared in southeastern USA, which were virulent to the previously effective stripe rust resistance genes Yr8 from Aegilops comosa and Yr9from Secale cereale.

The hexaploid wheat line “Almop” showed moderate resistance to stripe rust in field test performed in México. The predigree of this line include a chromosome 1B monosomic line of “Lalbahadur” which was developed at CIMMYT for mapping the Lr46/Yr29 loci. Some of the lines produced for this mapping project lacked Lr46/Yr29 but carried a gene, later designated Yr60, which conferred moderate resistance to stripe rust.

The spring wheat germplasm 'PI 178759' originating from Iraq carries a locus for stripe rust resistance on chromosome arm 7B that was designated Yr59.

Quaiu 3 is a spring wheat line (Babax/Lr42//Babax*2/3/Vivitsi) with high yields and high levels of resistance against leaf and stripe rust. It has a good level of adult plant resistance against stripe rust, but it shows seedling stage susceptibility.

A wheat landrace collected in Pakistan, AUS27858, from the Watkins collection showed high levels of resistance against Australian pathotypes of Puccinia striiformis f. sp. tritici (1). The Watkins wheat collection is a set of landraces collected by A. Watkins in the 1920s (2).  The current collection has around 1200 accessions, and it is housed at the John Innes Centre Germplasm Resource Unit, in the UK, and at the Australian Winter Cereal Collection, in Tamworth, Australia.

Contributed by Josh Hegarty, Iago Hale and Jorge Dubcovsky

'PI 181434' is a spring wheat germplasm originating from Afghanistan that was resistant to of stripe rust in a series of screenings carried out in Washington from 2004 to 2009. The type of resistance was all-stage, and it was effective to races accounting for all types of virulence in that period.

Yr26 is a major resistance gene that has been widely deployed in China, especially in the Sichuan Basin since the 1990s, because of its effectiveness against the then predominant races, CYR32 and CYR33. However, new emerging races virulent against Yr26, designated V26/CM42 and V26/Gui22, were detected in the Sichuan Basin since 2008. These virulent strains have not been not reported yet in other wheat growing regions (1). In addition, it has been suggested that Yr26 and Yr24 are the same gene (2).