Barley rhynchosporium resistance research advanced by PhD

A glance along the rhynchosporium disease resistance rating lines in the Recommended Lists (RL) reveals plenty of room for improvement. Robert Saville, who manages disease research at AHDB, looks at a PhD project that has provided genetic leads in the quest to deliver more durable resistance to this major barley disease.

By the time irregular grey patches, ringed by dark-brown margins, develop on the leaves of barley, the opportunity to control rhynchosporium has passed. The earlier the disease is stopped in its tracks, the better.

Although several fungicides have good protectant activity against rhynchosporium, a more sustainable disease-management approach would be to let crop genetics take the strain. However, the lack of strong, durable resistance coupled with the economic importance of this disease mean barley breeders are hungry for new sources of resistance.

Based at James Hutton Institute, Jean-Noël Thauvin has recently completed a four-year (2017–21) AHDB PhD project on the topic. At the heart of his studies was a collection of 312 barley landraces that allowed him to tap into the worldwide genetic diversity for this crop.

He used a genetic technique (association mapping) to identify sections of the barley genome associated with changes to rhynchosporium levels. In all, 21 ‘quantitative trait loci’ (QTL) were identified and, in this mix, were the two main rhynchosporium resistance genes (Rrs1 and Rrs2). But they were not alone – he also identified several other areas associated with quantitative resistance. In particular, experiments showed the involvement of the HvADH-1 gene – which has recently been shown to be involved in powdery mildew resistance too.

Jean-Noël also crossed eight of the most interesting resistant landraces with a relatively susceptible elite malting spring barley cultivar (RGT Planet). Through a series of subsequent crosses, using a process known as backcrossing, genetic recombination events were fixed in 736 Recombinant Inbred Lines (RILs). These RILs were then assessed for disease symptoms (phenotypic data) in field trials.

The cross with a Syrian landrace (barley core collection 0187) resulted in the greatest distribution of disease symptoms in the subsequent population. This population was screened with single nucleotide polymorphism (SNP) markers to identify 50,000 genomic datapoints. Around one third (15,249) of these segregated between the two parents. He used information on the presence or absence of these genetic datapoints, alongside the disease data, to build a ‘linkage map’ to highlight genetic regions linked to rhynchosporium resistance.

The information, genetic markers/maps and lines produced are all amenable for the rapid introduction (introgression) of new resistance loci into elite breeding lines by the plant-breeding community. Although it will take many years for varieties based on this research to hit the RL, it has brought durable rhynchosporium resistance one step closer to the market.