Pontificia Universidad Católica del Ecuador, Ecuador
Stripe rust is the most important disease of wheat in Ecuador. Knowledge of race diversity of the pathogen population is limited. Here we present avirulence/virulence phenotypes found in Pst samples collected from wheat between 2001 and 2014. A total of 30 isolates from the Ecuadorian highlands were tested on 15 near-isogenic wheat lines carrying single resistance genes; 21 races were identified. Lines with Yr2, Yr3, Yr26 and Yr27 were not tested in some years. Virulences to Yr1, Yr6, Yr7 and Yr9 were the most frequent (over 70%) in all years, followed by virulence to Yr17 (67%) and Yr27 (53%). Virulence to Yr8 was not found in 2013 and 2014. Virulence to Yr24/Yr26 was present in each year except 2014, although at a low level. Virulence to Yr10 was low. There were some unconfirmed discrepancies from a perfect association of virulences to Yr24/Yr26 and Yr10. Virulence to YrSP increased up to 2013, but was absent in 2014. There was no virulence to Yr5 and Yr15. Despite limited sampling, a diverse population of Pst seems to be present in Ecuador, with virulence for most resistance genes being present. Based on these analyses resistance to Pst in Ecuador could be achieved with Yr5 and Yr15, together with Yr24Yr26, and perhaps YrSP. One possibility for the high pathogenic variation might be sexual recombination on one or more of the 32 Berberis species reported in Ecuador. This needs to be examined along with more intensive sampling from wheat and analysis of the actual resistance genes present in current cultivars.
State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, P.R. China
The appearance and spread of new Pst races are common consequences of the widespread use of single resistance genes in one or more widely grown cultivars, with epidemics occurring some time later. Based on the geographical situation in China, epidemiology of stripe rust can be divided into three major zones, namely autumn sources of inocula, spring sources of inocula, and the spring epidemic areas. About 67 stripe rust resistance genes (Yr1 – Yr67) and some temporarily designated genes have been catalogued in cultivated wheat varieties. Many of the genes have unique linked markers that enable their transfer by marker assisted selection (MAS). We recommend firstly that wheat breeders, rust geneticists and pathologists work in together in evaluating the effectiveness of resistance in multi-pathotype seedling tests in the greenhouse and in field trials at hot-spot locations to identify the genes conferring stable resistance across environments; and secondly to apportion the available resistance genes to the different epidemiological regions. We expect that such regional diversity of resistance genes will provide strong barriers to seasonal spread between regions.
The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Australia
Effective control of stripe rust (YR) requires deployment of resistant cultivars. Adult plant resistance (APR) is preferred over all-stage resistance because of its putatively durable nature. Discovery of new sources of resistance is a priority to combat rapidly evolving Pst races. Genebanks contain untapped genetic diversity that likely harbor novel resistance genes. We examined a diverse panel of 300 lines sourced from the Vavilov Institute, including landraces, cultivars and breeding lines from 28 countries. The most virulent Pst pathotype in Australia (134 E16 A+,Yr17+,Yr27) was used for all experiments, where YR reactions were determined on seedlings in a greenhouse and on adult plants in a field disease nursery. A total of 54% of accessions displayed all-stage resistance and 33% displayed moderate to high levels of APR. Accessions were genotyped using the DArTseq genotyping platform and using an association mapping approach we identified genomic regions associated with YR resistance. These were aligned with previously reported QTL and cataloged resistance genes on a consensus map. This enabled identification of novel genomic regions. Accessions carrying high levels of APR were screened using markers linked to well-known APR genes (i.e. Yr18, Yr29 and Yr46). Twenty two accessions carrying potentially novel sources of APR to YR were identified. Our current efforts are aimed at further characterizing and validating these genetic resources against a wide array of pathotypes and environments around Australia.
Department of Plant Pathology, University of Minnesota, USA
Our research objective is to identify new resistance genes in cultivated and wild tetraploid wheats that are effective against race TTKSK and other Pgt races, and could be utilized in durum breeding. We characterized 7,000 durum and 360 emmer accessions for field resistance at Debre Zeit, Ethiopia, and Saint Paul, Minnesota. Accessions with resistant to moderately resistant responses in multiple field evaluations were characterized at the seedling stage for resistance to races TTKSK, TRTTF, TTTTF, JRCQC, TKTTF, and an additional six representative U.S. races. We identified 208 durum and 28 emmer accessions resistant to moderately resistant in all field and seedling evaluations. A search for resistance through seedling evaluations was also conducted on wild emmer (840 accessions) and four cultivated tetraploids (Persian, Polish, Oriental, and Pollard wheats, 560 accessions). About 20% of the accessions were resistant to race TTKSK. Thirty-six resistant accessions of cultivated and wild tetraploids were selected to investigate the genetics of TTKSK and TRTTF resistance. Results from evaluating F2 and F2:3 generations from biparental crosses revealed that resistance to race TTKSK in various subspecies of T. turgidum was conferred mostly by one or two genes with dominant and recessive actions. Additional resistance genes were identified when populations were evaluated against race TRTTF. A bulk segregant analysis approach is being used to map the resistance genes in selected resistant parents using the 90K SNP platform.
Kashkadarya Branch of the Grain and Leguminous Research Institute, Uzbekistan
Winter wheat production in Uzbekistan is threatened by yellow rust and leaf rust. Both rusts are capable of causing substantial economic losses, but their incidence varies due to different ecological requirements. Yellow rust caused significant yield losses in 2009, 2010, 2013, and in some regions, also in 2014. Several stripe rust resistant lines with high grain yield and desirable agronomic characteristics are being introduced through the International Winter Wheat Improvement Program (IWWIP) and submitted to the State Varietal Testing Commission. A number of new yellow rust resistant varieties were released for specific epidemiological areas of Uzbekistan. These varieties planted on about 200,000 ha are helping to reduce inoculum buildup and spread of rust in farmers’ fields. The objective of the present work was to identify locally adapted yellow rust resistant wheat lines in international nurseries. In 2014 448 winter wheat lines were evaluated for response to the prevailing Pst population under controlled conditions at the Plant Industry Research Institute and field conditions at the Kashkadarya Branch of the Grain and Leguminous Research Institute. Eighty lines were immune and 73 lines showed moderate to high levels of resistance in the field. Following agronomic assessments 55 lines were promoted to advanced multi-site yield trials. A set of selected lines was also distributed to other wheat research institutions within the country. It is expected that this process will lead to the release and deployment of more resistant winter wheat varieties in Uzbekistan.