Understanding hybrid disease susceptibility to net blotch in barley
By Dr. Shaun Clare, postdoctoral researcher with Dr. Bob Brueggeman, Washington State University barley breeder and Associate Professor and Robert. A. Nilan Endowed Chair of Barley Research and Education
As a barley pathologist, previously at North Dakota State University, Dr. Brueggeman focused his research on two main disease systems, stem rust (barley-Puccinia graminis) and net blotch (barley-Pyrenophora teres). Picking up that work at Washington State University is postdoctoral researcher, Dr. Shaun Clare, who was tasked with working on a unique phenomenon with net blotch in barley, first identified by another of Brueggeman’s PhD students and now professor at King Saud University, Dr. Abdullah Al-Hashel. This phenomenon of a phenotype outside of the parental range and which does not remain stable in future generations is called non-transgressive hybrid susceptibility. In barley, genes are named based on their function that are abbreviated into a three letter acronym followed by a number. This led to the identification of a section or locus of the barley genome containing a single candidate gene that is hypothesized to be responsible for this non-transgressive hybrid susceptibility and was named Susceptibility to Pyrenophora teres 2 (Spt2). Spt1 had previously been documented.
Typically, breeders across agriculture make use of hybrid vigor or heterosis to create offspring that outperform either of their parents, with corn being one of the most famous examples. Hybrid crops often have yield boosts or other impactful traits to benefit the grower. Nearly all research into heterosis has been conducted on the positive impact of this phenomenon. However, negative impacts also exist such as hybrid necrosis where hybrids spontaneously exhibit disease lesions like necrotic spots in the absence of the pathogen. While generating hybrids between CI5791 (an Ethiopian landrace) and Tifang (a Chinese landrace), or Golden Promise (a Scottish malting variety) that were all resistant to moderately resistant to an isolate of net blotch, all resulting first-generation progeny were found to be hyper susceptible. When investigating the second-generation between these crosses, only half of the progeny were hyper susceptible suggesting that plants containing two copies from either parent at the Spt2 locus were resistant. However, plants heterozygous, or containing one copy of the locus from each parent, were hyper susceptible. Utilizing high-resolution mapping with 715 F2 (second generation) plants, a single Spt2 candidate gene responsible for this phenomenon was identified on chromosome 5H. This locus has been described as non-transgressive, meaning that the trait does not remain stable when plants only have DNA from one of the parents in later generations. The locus is also distinct from hybrid necrosis mentioned earlier as plants appear perfectly healthy until challenged by the pathogen.
Since barley is primarily grown as a stable inbred crop, not as a hybrid crop, this may appear to be insignificant research that does not affect barley production. However, this basic research helps to understand pitfalls that may exist if barley is converted to a hybrid crop, which is becoming increasingly common in European feed barley. More significantly, it provides an excellent model system to begin understanding how the complex genetics surrounding heterosis may control hybrid vigor as well. The team at WSU is actively pursuing research to further understand the mechanisms underlying this hybrid susceptibility.
You can learn more about this research in the following manuscript recently published in the BMC Plant Biology:
Clare, S. J., Alhashel, A. F., Li, M., Effertz, K. M., Sharma Poudel, R., Zhang, J., Brueggeman, R. S. 2024. High resolution mapping of a novel non-transgressive hybrid susceptibility locus in barley exploited by P. teres f. maculata. BMC Plant Biol. 24, 622. DOI: 10.1186/s12870-024-05303-1
