Wheat stripe rust, caused by basidiomycete fungus Puccinia striiformis f. sp. tritici (Pst), is a damaging disease worldwide. The recent discovery demonstrated the fungus depends on living wheat and aecial hosts, mainly barberry (Berberis) species, to complete its life cycle. In China, we determined that, under natural conditions, the sexual cycle of Pst occurs based on collections of Pst isolates from the diseased barberry in the past three years. However, no direct evidence to support whether barberry plays a role in spreading inoculums to wheat field to cause stripe rust was detected. In the present study, we recovered 103 Pst samples from natural-infected B. shensiana in the western Shaanxi in spring 2016, and also collected 107 Pst isolates from neighboring wheat fields. Phenotype and genotype of the two Pst populations were tested using a set of Chinese differential hosts for Pst and SSR markers, respectively. The phenotype tests showed that 57 race types produced from the barberry-derived Pst populations, consisting of 58 known races, such as CYR 34, CYR32, G22-14, and Su11-14-3, and 45 new races. Many of the two Pst populations shared the same race types. The genotype tests indicated the barberry-derived Pst population produced a rich genotype, obviously higher than the wheat-derived Pst populations. The seven same genotypes were found on 40 isolates of the former and 26 of the latter. Our results provide evidence to support that sexual cycle of Pst occurs regularly in nature in China and that barberry provides inoculums to neighboring wheat fields, triggering stripe rust infections in the spring. This could be a reason why the Chinese Pst populations represent extreme genetic diversity.
Primary Author: Zhao, College of Plant Protection, Northwest A&F University, China
In China, wheat is grown on approximately 24 million hectares with an annual yield of 100 million tonnes. Stem rust, caused by Puccinia graminis f. sp. tritici, is a threat mainly to spring wheat in northeastern China. Leaf rust, caused by P. triticina, occurs on crops in the late growth stages in the Yellow-Huai-Hai River regions. Stripe rust, caused by P. striiformis f. sp. tritici (Pst), is destructive in all winter wheat regions and is considered the most important disease of wheat in China. During the last 20 years, widespread stripe rust epidemics occurred in 2002, 2003, and 2009, and localized epidemics occurred in many other years. In recent years, major yield losses were prevented by widespread and timely applications of fungicides based on accurate monitoring and prediction of disease epidemics. A total of 68 Pst races or pathotypes have been identified using a set of 19 differential wheat genotypes. At present, races CYR32 and CYR33 virulent to resistance genes Yr9, Yr3b, Yr4b, YrSu and some other resistance genes are predominant. Moreover, these races are virulent on many cultivars grown in recent years. Of 501 recent cultivars and breeding lines 71.9% were susceptible, 7.0% had effective all-stage resistance, mostly Yr26 (= Yr24), and 21.2% had adult-plant resistance. Several resistance genes, including Yr5, Yr10, Yr15, Yr24/Yr26, YrZH84 and some unnamed genes, are still effective against the current Pst population. All have been widely used in breeding programs. Lines with one or more of Yr1, Yr2, Yr3, Yr4, Yr6, Yr7, Yr8, Yr9 and other unnamed resistance genes are susceptible to currently predominant races. Durable adult plant resistance sources are being increasingly used as parents in breeding programs. Progress has been made in genomics and population genetics of Pst, molecular mapping of resistance genes, and cytological and molecular mechanisms of the host-pathogen interactions involved in stripe rust.
Primary Author: Zhensheng Kang, 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.
Primary Author: Zhou, State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University, P.R. China
Elite barley breeding lines from the Australian Northern Region Barley Breeding Program were evaluated at the seedling and adult growth stages for resistance to leaf rust (LR) caused by Puccinia hordei. F3:5 lines derived from parental germplasm of different geographic origins were screened in the glasshouse and field spanning four years of trials. The 2009 and 2011 breeding populations (BP1 and BP2) comprised 360 lines and were genotyped with 3,244 polymorphic diversity arrays technology (DArT) markers. The 2012 and 2013 breeding populations (BP3 and BP4) comprised 320 lines genotyped with the DArT GBS array (DArTseq), providing 15,400 high quality polymorphic markers. Association mapping (AM) using the DArT/DArT-seq datasets and phenotypic data from 15 independent LR response assays identified a number of genomic regions associated with resistance. The BP1 and BP2 study detected a total of 15 QTL; 5 QTL co-located with catalogued LR resistance genes (Rph1, Rph3/19, Rph8/14/15, Rph20, and Rph21), 6 QTL aligned with previously reported genomic regions and 4 QTL (3 on chromosome 1H and 1 on 7H) were novel. Markers in common between the DArT and DArTseq datasets enabled integration of mapping results for LR response across the four breeding populations and all QTL detected were visualised on a single map for validation. The adult plant resistance (APR) locus Rph20 was the only region detected in all field environments. Markers and their associated sequences identified in this study will be useful for building QTL combinations involving Rph20, thereby providing stable LR resistance in improved barley cultivars. We will also highlight the advantages of AM using breeding germplasm over traditional bi-parental mapping approaches that underutilise genetic diversity and divert valuable resources into populations of low breeding value.
Primary Author: Ziems, The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Australia
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.
Primary Author: Ziyaev, Kashkadarya Branch of the Grain and Leguminous Research Institute, Uzbekistan