Major gene for field stem rust resistance co-locates with resistance gene sr12 in 'thatcher' wheat

Citation

Hiebert, C.W., Kolmer, J.A., McCartney, C.A., Briggs, J., Fetch, T., Bariana, H., Choulet, F., Rouse, M.N., Spielmeyer, W.S. (2016). Major gene for field stem rust resistance co-locates with resistance gene sr12 in 'thatcher' wheat. PLoS ONE, [online] 11(6), http://dx.doi.org/10.1371/journal.pone.0157029

Plain language summary

Stem rust is a disease of wheat that is caused by a fungus that cause large yield losses when epidemics occur. ‘Thatcher’ is an old wheat cultivar that was widely grown in Canada from the 1930s to the 1960s and is an important parent in many wheat varieties grown in Canada presently. Thatcher has very good resistance to stem rust in the field, even when races (strains) of the stem rust fungus are present that can infect seedlings of Thatcher in lab tests. The objective of this study was to determine which genes are responsible for the field resistance to stem rust observed in Thatcher. Since Thatcher is found in the pedigrees of many Canadian wheat varieties, the outcomes from this research could be directly applied to wheat breeding programs. A population was produced by crossing Thatcher to a susceptible wheat line in order to study the genes involved in stem rust resistance observed in field trials. We determined that there was one gene that had a large effect on stem rust resistance in the field trials. This gene was co-inherited with a known stem rust resistance gene called Sr12. Sr12 does not provide resistance to most of the stem races used in the field trials when tested in the lab at the seedling stage. It is unknown if Sr12 is responsible for the field resistance at the adult-plant stage or if a second gene is located near Sr12. A DNA marker was developed for the resistance and is useful for selecting the stem rust resistance in breeding programs. A study is underway to determine if Sr12 or a neighbouring gene is responsible for the field resistance.

Abstract

Stem rust, caused by Puccinia graminis (Pgt), is a damaging disease of wheat that can be controlled by utilizing effective stem rust resistance genes. 'Thatcher' wheat carries complex resistance to stem rust that is enhanced in the presence of the resistance gene Lr34.The purpose of this study was to examine APR in 'Thatcher' and look for genetic interactions with Lr34. A RIL population was tested for stem rust resistance in field nurseries in Canada, USA, and Kenya. BSA was used to find SNP markers associated with reduced stem rust severity. A major QTL was identified on chromosome 3BL near the centromere in all environments. Seedling testing showed that Sr12 mapped to the same region as the QTL for APR. The SNP markers were physically mapped and the region carrying the resistance was searched for sequences with homology to members of the NB-LRR resistance gene family. SNP marker from one NB-LRR-like sequence, NB-LRR3 co-segregated with Sr12.Two additional populations, including one that lacked Lr34, were tested in field nurseries. NB-LRR3 mapped near the maximum LOD for reduction in stem rust severity in both populations. Lines from a population that segregated for Sr12 and Lr34 were tested for seedling Pgt biomass and infection type, as well as APR to field stem rust which showed an interaction between the genes. We concluded that Sr12, or a gene closely linked to Sr12, was responsible for 'Thatcher'-derived APR in several environments and this resistance was enhanced in the presence of Lr34.

Publication date

2016-06-01