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.
Bibliographical noteFunding Information:
The authors thank Mira Popovic, Ghassan Mardli, Tobi Malasiuk, Elaine Martineau, Taye Zegeye, Alison Morgan, Jessica Hyles, and Shideh Mojerlou for excellent technical assistance. The authors thank USDA-ARS Appropriated Project 5062-21220-021-00, USDA-ARS National Plant Disease Recovery System, the Durable Rust Resistance in Wheat project (MNR), Saskatchewan Agriculture Development Fund project #20080009 (CAM), Agriculture and Agri-Food Canada Growing Forward (CWH, TF, CAM), and as part of CTAG, a Genome Prairie project funded by Genome Canada, Saskatchewan Ministry of Agriculture, and Western Grain Research Foundation (CAM) for financial support. This project was also supported through a grant CIM/2007/084 provided by Australian Centre of International Agricultural Research. We also thank Dr Sridhar Bhavani for providing access to stem rust nursery at Njoro, Kenya.
© This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.