Ambo Plant Protection Research Center, Ethiopia
During the 2014/15 main crop season 831 wheat fields and experimental plots were assessed for diseases; 66.2% were in the Oromiya, 20.3% in Tigray and 13.4% in SNNP regions. The major diseases encountered include rusts, septoria leaf blotches, foot and root diseases, Fusarium head blight and smuts. The overall mean prevalence of stem rust was 61%, yellow rust 22%, leaf rust 18.8% and Septoria leaf blotches 52.9%. The incidence of the important diseases was highest in SNNP region. The mean incidence of yellow rust ranged from 5.7% in Oromiya to 39.2% in SNNP. The lowest incidence of stem rust, 15.9%, was noted in Tigray and the highest, 64.4%, in SNNP. The minimum mean Septoria incidence was 23% in Oromiya, and maximum was 66.7% in SNNP. Stem rust severities varied from 7 MR-MSS in Tigray to 36 MR-MSS in SNNP. Furthermore, the widely grown varieties Digelu and Danda’a were resistant to yellow rust, but susceptible to stem rust. Varieties Meda Wolbu, Hogona and Ogolcho were not affected by any of the rusts in Oromiya. Variety Hidase was susceptible in SNNP. Out of 115 Pgt cultures established from stem rust samples collected from the three regions, races TKTTF, RRTTF, TTKSK, TRTTF and JRCQC were identified. Stem rust samples were collected from varieties Digelu, Danda’a, Kakaba, and Hidase. Race TKTTF, virulent on Digalu and first identified in Oromiya region in 2013, is now present in all areas. Adapted varieties with durable stem rust resistance in Ethiopia remains an urgent requirement.
Crop Diseases Research Institute, Pakistan Agricultural Research Council, Pakistan
Detailed rust surveillance of wheat growing areas in Pakistan was conducted from 2011 to 2014. Information about varietal distribution, growth stage, and rust incidence and severity was collected at 950 locations, and rust samples collected from these locations were subjected to race analysis. Yellow rust showed increasing incidence of high to moderate severity. Commercial cultivars released during 1991 to 2011 showed MS to S reactions. Twenty eight races were identified, most with wide virulence ranges. The frequencies of virulence to Yr1, Yr6, Yr7, Yr8, Yr9, Yr17, Yr27, Yr43, Yr44 and YrExp2 all exceeded 50%. Leaf rust also showed increasing incidence, mainly due to cultivation of the susceptible cv. Sehr-06. Fourteen races were identified. The frequencies of virulence to Lr1, Lr2c, Lr3a, Lr16, Lr26, Lr3c, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr14b and Lr21 exceeded 50%. Virulences to Lr2, Lr9, Lr24, Lr18 and Lr19 were not detected and frequencies of virulence to Lr11 and Lr20 were low. Current and old commercial cultivars showed MS to S reactions. In 2011 and 2014 stem rust incidence was sporadic, but in 2013 it was present at 33 of 232 locations in Sindh, Punjab, Khyber Pakhtunkhwa and Baluchistan. Race RRTTF was identified in all samples.
Campo Experimental Valle de México INIFAP, México
Yellow (stripe) rust continues to be an important disease of wheat in the irrigated EL Bajio region and northwestern Mexico, and in the High Plateau of Central Mexico. Isolate MEX 96.11, virulent to race-specific resistance genes Yr2, Yr3, Yr6, Yr7, Yr9 and Yr27, represented the most prevalent Pst race until 2001 and evolution of new virulences was slow. Several additional R-genes, including a gene in Pollmer triticale, are now defeated. The aggressive Pst race with Yr8 virulence, first detected in the United States in 2000, not only became widespread in Mexico by 2003 but continued to evolve at a more rapid rate with virulence to Yr1 occurring in 2003. However these races did not cause crop losses other than increased levels of head infections in some cultivars. Variants with virulences to Yr17 and Yr31 were detected in 2007 and 2008, respectively. These resistance genes are known to occur in some wheat varieties and breeding materials. 2010 disease data from trap nurseries that included the Avocet isolines and other varieties indicated the existence of virulence for Yr1, 2 (Siete Cerros), 3 (Tatara), 6, 7, 8, 9, 17, 27 and 31 (Rebeca F2000) in different Pst isolates. During the 2014 crop season, an epidemic occurred in farm fields and samples were collected and analyzed in greenhouse tests. Virulence combination V2, 3, 6, 7, 8, 9, 17, 27 and 31 first identified and represented in isolates CEVAMEX14.25 and MEX 14.141, and a similar isolate MEX14.146 virulent to Yr1 were the most frequent. These new virulence combinations caused yield losses in cultivar Nana F2007 grown in the Mexican highlands and Luminaria F2012, released for the irrigated areas of Bajio. Our results indicate a continuing evolution and accumulation of virulences in the aggressive Pst lineage. Determination of the defeated genes in Nana F2007 and Luminaria F2012 is underway.
Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, Canada
Most of the current stem rust resistance genes (Sr) in Canadian wheat varieties are ineffective against the Pgt race Ug99 lineage, which pose a major threat to wheat production worldwide. Several stem rust resistance genes, including Sr33, Sr35, Sr36, SrCad/Sr42 and Sr43, are effective against race TTKSK. Although Sr36 is ineffective against Ug99 race TTTSK, it is still potentially useful for pyramiding genes to develop germplasm with durable stem rust resistance. For this purpose, we made crosses among RL5405 (Sr33), RL6099 (Sr35), Lang (Sr36), AC Cadillac (SrCad/Sr42), and RWG34 (Sr43) containing the respective Sr genes. A total of 54 doubled haploid (DH) lines were produced from the F1 from AC Cadillac/Lang//RWG34/RL5405, and 82 DH lines were obtained from RWG34/RL5405//RL6099. The DH progeny were tested at the seedling stage with race TTKSK and susceptible lines were discarded. We putatively developed 12 genotypes with multiple Sr gene combinations, including Sr33+Sr36+SrCad/Sr42+Sr43, Sr33+Sr36+SrCad/Sr42, Sr33+Sr36+Sr43, Sr33+SrCad/Sr42+Sr43, Sr36+SrCad/Sr42+Sr43, Sr35+Sr33+Sr43, Sr33+Sr36, Sr33+Sr43, Sr36+SrCad/Sr42, Sr36+Sr43, Sr35+Sr33, and Sr35+Sr43, based on positive association with linked PCR markers. Another population with 63 DH lines was derived from (Hoffman*2/RL6099)//(Hoffman*2/Lang) to combine the Fusarium head blight (FHB) resistance of Hoffman (Fhb1) with Sr35 and Sr36. We found 17 of 63 DH lines containing both Sr35 and Sr36 based also on linked PCR markers. This indicated that the combination Sr35+Sr36 was pyramided into the Canadian cultivar Hoffman; this derivative will be useful for development of cultivars resistant to Ug99 and FHB in Canada.
National Research Council of Canada, Canada
Leaf rust is the most widely occurring disease of wheat worldwide. Resistance is the most practical and effective way to control the disease. Most leaf rust resistance genes are race-specific (“R”, qualitative resistance) and a relatively few are adult plant resistance genes, some of which have been described as slow rusting (“APR”, quantitative resistance). Due to limited knowledge, most resistance genes have been deployed in cultivars by an inefficient “blind” approach. This results in the well known “boom and bust cycle” (resistance followed by susceptibility) because the pathogen evolves rapidly and migrates over long distances. Therefore, a breeding-by-design approach is needed to achieve durable resistance. Pyramiding multiple R, APR or APR+R genes has been used successfully over many years to achieve durable resistance to leaf rust in Canada and some other countries. To further enhance this strategy we seek to understand the molecular mechanisms underlying key resistance genes. To identify the molecular mechanisms underlying rust resistance conferred by major R and APR genes, we performed an integrated systemic transcriptome analysis via RNA-seq on the Thatcher NILs with Lr16, Lr22a, Lr21, Lr34, Lr34+Lr16, and Lr67 challenged with Pt race BBBD. Sampling was conducted over a time series during the infection process of both seedlings and adult plants. Through RNA-seq we were able to capture the dynamic interactome of host-pathogen interactions conferred by these R and APR genes. Preliminary results revealed that resistance reactions conferred by R gene Lr21 and APR gene Lr67 were significantly different compared to other R and APR genes. Significantly, the Thatcher NIL line with Lr34+Lr16 showed the combines defense reactions of Lr16 and Lr34.
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.
Institute of Phytopathology and Biodiversity, Batumi Shota Rustaveli State University,Georgia
Stripe rust is a worldwide constraint to wheat production. The rust pathogens are assumed to have originated in the Caucasus, from which they disseminated into Western Europe and Asia (Zhukovsky 1965, Euphytica, 14; Stubbs 1985, The Cereal Rusts II). Rust surveys are a useful means to provide information on distribution. More than 400 wheat fields were monitored for rust incidence and severity and for collection of samples at 20 locations in Georgia during 2010-2013. The majority of wheat fields were occupied by Russian cultivars and Bezostaya-1 was the most common, followed by Copper and American cv. Jagger. Yellow rust was the most widely distributed rust, with>65% of fields showing its presence. In 2009 yellow rust incidence was moderate to high. Abundant overwintering inoculum, susceptible cultivars and favorable conditions resulted in severe epidemics in late May and early June 2010. Mean field incidence and severities were 74.8 and 84.6% in the Kakheti zone, and 70 and 68.2% in Kvemo Kartli. Incidence was lower in the following years due to drought and high late spring temperatures. Bezostaya 1 and Jagger showed moderately susceptible reactions to all three rust, but Copper was moderately resistant. Accessions of Georgian endemic species T. carthlicum, T. timopheevi, T. macha, T. georgicum and T. monococcum were resistant to all three rusts.
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.