Leaf rust (caused by Puccinia triticina) continues to be the most important and widespread foliar disease of wheat in the Southern Cone. The P. triticina population of the region is extremely dynamic, leading to short-lived resistance in commercial cultivars. Some high yielding materials susceptible to leaf rust have been released and their increasing cultivation relies on fungicide applications to control leaf rust. The most important challenge of breeding programs in the Southern Cone is to incorporate durable leaf rust resistance in high yielding cultivars. These cultivars must also combine resistance to other relevant diseases and meet industrial quality standards demanded by the market. Leaf rust resistance in wheat varieties and lines lies mostly in combinations of seedling resistance genes or combinations of these with adult plant resistance (APR), including Lr34. Few recently released cultivars carry APR to leaf rust that might be expected to be durable. Since efforts to introduce slow rusting into high yielding adapted germplasm are increasing in most countries, more cultivars carrying this type of resistance will likely be released. If major genes are used, the introduction of effective genes not present in the regional germplasm will increase the diversity of resistance. Molecular markers are used in breeding in Argentina and are starting to be implemented in Brazil and Uruguay. Increased use of molecular tools could improve genetic progress in breeding programs, allow identification of APR genes present in current regional germplasm, and facilitate identification of new resistance genes.
Primary Author: Silvia German, National Institute of Agricultural Research [INIA], Uruguay
Approximately nine million ha of wheat (Triticum aestivum and T. durum) were sown annually in the Southern Cone of South America (Argentina, Brazil, Chile, Paraguay and Uruguay) during 2003-2007. Presently, leaf rust (caused by Puccinia triticina) is the most important rust of wheat throughout the region. The pathogen population is extremely dynamic leading to short-lived resistance in commercial cultivars. Leaf rust management relies on the use of resistant cultivars and fungicides. Sources of adult plant resistance conferred by minor additive genes have been increasingly used in breeding programs to obtain cultivars with more durable resistance. Stripe rust (P. striiformis f. sp. tritici) is endemic in central and southern Chile, where fungicides are required to control the disease on susceptible cultivars. Stem rust (P. graminis f. sp. tritici) has not caused widespread epidemics in the last 25 years due to the use of resistant cultivars. Virulence to Sr24 and Sr31, the most important genes conferring resistance to local races, has not been reported in the region. The areas sown with cultivars susceptible to local races in Argentina and Uruguay have increased in recent years. Since most varieties sown in the region are susceptible to Ug99 or derived races, testing and selection for resistance in Kenya, facilitated by the Borlaug Global Rust Initiative, is highly relevant for research aimed at preventing epidemics, which may occur if these races migrate, or are accidentally introduced to our region. The resistances identified in east Africa will also contribute to increasing the levels of resistance to current local races.
Primary Author: Silvia German, National Institute of Agricultural Research [INIA], Uruguay
Conservation agricultural practices have been found to be climate and labor smart, and sustainable, agricultural production technologies. The decline in productivity, increase in the cost of cultivation, labor intensive practice affected the cereal based farming system in Nepal particularly at the Indo-Gangetic plains. SRFSI has been working in response to concerns about the sustainability of the cereal based farming system at Sunsari and Dhanusha district of Nepal. This study was conducted to assess the adoption and scaling up of conservation agriculture in addition to input usage, production, net profit, B:C ratio, labour use, etc. of CA practice in Sunsari district, eastern Indo-Gangetic plains of Nepal. The study employed structured questionnaires survey and key informant survey as the main data collection tools. Project reports were taken as secondary data. The primary data related for the semi-annual report and annual report of the SRFSI project were collected jointly by the DADO, Sunsari and RARST, Tarahara. Study revealed that farmers had several tangible advantages and getting higher productivity through these practices. This study assessed the potential of CA based practices in Rice-Wheat and Rice-Maize farming system to improve the yields, net profit for sustainability of the cereal based farming system.
Primary Author: Simkhada, Nepal Agriculture Research Council, Nepal
Stripe rust and leaf rust are two most widely distributed diseases of wheat despite the fact that major emphasis has been made globally to develop rust resistant varieties. The wild tetraploid wheat Triticum araraticum (AAGG) evolved in the eastern part of Fertile Crescent is a source of useful traits for the improvement of wheat including resistance to disease. T. araraticum acc. pau4692 and a derived advanced backcross introgression line (IL) in susceptible T. durum cv. Malvi local background showed high level of seedling resistance against Indian pathotypes of leaf rust and stripe rust. The F5 Single seed descent (SSD) population developed from the crosses between T. araraticum IL with T. durum cultivar PBW114 was screened with commonly prevalent pathotypes of leaf rust and stripe rust in India at the seedling stage. The genetic analysis indicated that the leaf rust resistance is conditioned by two genes and stripe rust resistance by a single gene. The SSR markers mapped on A and B genome were used for parental polymorphism along with resistant and susceptible bulks for leaf rust and polymorphic markers between bulks were used on the whole population. The molecular marker data using single marker analysis showed that leaf rust resistance genes were mapped on chromosome 2A and 7A linked to SSR markers Xwmc149 and Xbarc49, respectively. The genes have been temporarily named as LrAr1 and LrAr2. Bulked segregant analysis (BSA) for mapping stripe rust resistance is in progress.
Primary Author: Singh, School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana-141004 India
Wheat breeding programs have successfully harnessed the potential of elite germplasm pool and have contributed significantly to global food security. However, to obtain additional genetic gain, useful diversity for key traits from landraces, synthetics and wild relatives should be incorporated in breeding germplasm pool. Maladaptation and linkage drags are the bottlenecks in utilizing these exotic genepools for pre-breeding. A systematic, focused, large scale effort has been pursued at CIMMYT through a three-way cross (exotic x elite1 x elite2) population development strategy. Population was advanced through selected-bulk scheme in way to select relevant genetic diversity while maintaining large population sizes. A total of 984 advanced pre-breeding lines (PBLs) were evaluated in multiple environments for grain yield related traits, micronutrient content and diseases resistance (yellow rust, stem rust, powdery mildew, and karnal bunt). Potential useful lines for these traits have been identified. High-density genomic characterization of PBLs, parental elites and exotics was conducted through a "haplotype map" based approach, which revealed 16% (58/361) exotic specific haplotype block (HB) introgression in PBLs. Out of 58 exotic specific HBs, 12 (12/361 = 3%) were found associated with traits evaluated in the study. Three HBs, H1.28 (1A), H18.1 (6D) and H5.23 (2B) were significantly important as they showed consistent effects across environments for grain yield (1A and 6D) and yellow rust (2B). This significant contribution of exotics into PBLs opens avenues to mine and utilize their useful alleles in wheat improvement. This research describes systematic large-scale pre-breeding efforts, as proof of concept of exotic germplasm deployment to the breeding pipelines simultaneously enriching genetic knowledge through high-density genomics analysis. Genetic knowledge coupled with breeding efforts should provide substantial gain required for next generation wheat varietal improvement.
Primary Author: Singh, CIMMYT
To monitor evolution and pathogenic variability of wheat stem rust pathogen (Puccina graminis f. sp. tritici) in Australia, the Australian Cereal Rust Control program regularly conducts national annual surveys. Recently, we detected a new pathotype 34-1,2,5,7 (culture # 661) virulent on stem rust resistance genes Sr5, Sr6, Sr7b, Sr9g, Sr11, Sr15 and Sr17. Although virulent on Sr11, this pathotype produced a low infection type (IT 22+C/X) on the Sr11-differential genotype Yalta, indicating that Yalta carries an uncharacterised resistance (SrY) in addition to Sr11. To characterize SrY, we screened a RIL population Yalta/W2691 (104 lines) with two pathotypes: 21-0 (avirulent on Sr11 or AA) and the newly identified 34-1,2,5,7 (virulent on Sr11 but avirulent on SrY or BB). Yalta produced low infection types, "1C" and "22+C/X" with pathotypes 21-0 and 34-1,2,5,7, respectively, whereas W2691 was susceptible to both pathotypes. The population segregated for AA/aa (35 Res: 69 Sus) and BB/bb (36 Res: 68 Sus) loci with pathotypes 21-0 and 34-1,2,5,7, respectively. The observed segregation (AA/aa and BB/bb) however failed to fit with predicted single gene 1:1 model (P<0.05) with both pathotypes. Joint segregation analysis (AA/aa vs BB/bb) also significantly deviated (P<0.01) from 1:1:1:1 (AABB:AAbb:aaBB:aabb) genetic model. It appears that population is skewed towards susceptibility in each case either by chance or differential gametic transmission as reported previously in progenies derived from crosses involving variety Yalta. The segregation pattern (AABB and aabb) with two pathotypes was, however, highly coupled apart from 13 lines, of which, 6 lines (AAbb) were susceptible with 21-0 and resistant with 34-1,2,5,7, and 7 lines (aaBB) resistant with 21-0 and susceptible with 34-1,2,5,7, showing that the two loci are linked (?2 linkage = 76.9; P<0.001) and located very close to each other. If that is the case, it may imply that SrY is common in wheats carrying Sr11. Cultivar Charter has been used in India to differentiate pathotypes virulent for Sr11, suggesting that Charter also carries a second stem rust locus (SrC) possibly corresponding with SrY. Further studies and mapping work are underway to determine the genetic relationship between SrY, SrC and Sr11.
Primary Author: Singh, University of Sydney
Yellow rust of wheat caused by Puccinia striiformis Westend. is one of the important diseases of wheat in India. In north Indian states it spreads quite fast due to favourable temperature and moisture prevailing in these states during major part of crop growth (November-mid March). In spite of favourable weather, proactive survey and surveillance and advisories issued in time resulted successful management of yellow rust in India during past four decades. Even large scale cultivation of varieties like HD 2967 in about 12 million ha past two years did not result any losses. Three spots of initial foci near foot hills in Punjab have been identified and are monitored regularly. Any sign of yellow rust is controlled effectively with the foliar sprays of fungicides like propiconazole @ 0.1%. Use of mobiles phones and internet services is regularly done for transfer of information on wheat crop health and suggestions for proper management. Strategic planting and sowing of wheat in which newly released high yielding yellow rust varieties helped in reducing the yellow rust inculum build up. Regular monitoring of wheat health via weather forecasts take place after every fortnight from December to March. During 2016-17 crop season, yellow rust was effectively managed and its occurrence was delayed in Punjab, Haryana and Uttarakhand states. Two new pathotypes, 110S 119 and 110S 84 developed recently were used for evaluation of entries of wheat yield trials during 2016-17 at hot spot locations. The new varieties in pipe line of identification and release are tested against yellow rust. The most critical period for yellow rust management remained from December till mid February.
Primary Author: Singh, ICAR-Indian Institute of Wheat and Barley Research
The changing climatic conditions are affecting wheat production in major agro-ecological zones in India, namely, north western plains(NWPZ), north eastern plains(NEPZ), central (CZ) and peninsular zone(PZ) where the reproductive phase has to endure higher temperatures. Also, the prevalence and virulence of rust pathotypes and other diseases are affected. To address such challenges, development of wheat for climate resilience was initiated following shuttle breeding approach for incorporating heat stress tolerance as well as resistance to wheat rusts. During 2010-16, a total of 583 elite lines were evaluated against prevalent pathotypes of stripe rust 78S84, 110S119, 110S84 and 46S119; leaf rust 12-2(1R5), 12-5(29R45), 77-2(109R31-1), 77-5(121R63-1), 77-9(121R60-1) and 104-2 (21R55) and stem rust 11(79G31), 40A(62G29), 42(19G35), 122(7G11) and 117-6(37G19) of which 108 promising entries were identified. These lines were evaluated for disease response in multilocational Initial Plant Pathological Screening Nursery (IPPSN) against prevalent races of all three rusts. Based on average coefficient of infection (15.0 ACI), 42 (39%), 104 (96%) and 90(83%) entries were found resistant to different races of stripe, leaf and stem rusts, respectively. Based on performance in multiplication yield trials, 29 entries were contributed in national coordinated evaluation system on Wheat & Barley which resulted in release of four wheat cultivars DBW71(Yr9+27+,Lr26+,Sr2+5+31+), DBW107(Yr9+,Lr26+3+,Sr31+), DBW110(Yr2+, Lr13+10+,Sr13+11+) and DBW93(Yr9+, Lr26+23+, Sr31+) for commercial cultivation in NWPZ, NEPZ, CZ and PZ, respectively. These cultivars are becoming popular among farmers due to their yield advantage, resistance to diseases, tolerance to high temperature and better quality traits. Also, DBW 129 was screened in multiple disease screening nursery (MDSN) and observed resistant to all rusts, leaf blight, powdery mildew, flag smut and shoot fly. The adoption of the newly developed cultivars for deployment of differential genes for resistance would lead to reduction in disease pressure and bring higher profitability to farmers in different agro-ecological zones in India.
Primary Author: Singh, ICAR- Indian Institute of Wheat & Barley Research, Karnal-132001, India
The identification of R-genes using traditional map-based approaches is a long, laborious process, not to mention the time required for subsequent development of cultivars incorporating the new resistances. Breeders seek to reduce the length of breeding cycles, and researchers require new tools to accelerate discovery and understanding of mechanisms associated with durable resistance, especially adult plant resistance (APR). A new method for rapid generation advancement, known as ‘speed breeding’, significantly reduces the length of breeding cycles, provide increased recombination during line development and enable selection in early generations. The speed breeding protocol uses controlled temperature regimes and 24h light to accelerate plant growth and development. Phenotyping methods adapted for use in the speed breeding system permit year-round evaluation of APR to rust pathogens within 5 weeks from time of sowing. RNA sequencing (RNA-Seq) technology has revolutionized gene expression profiling in plants. We previously used RNAseq to identify novel transcripts and miRNAs associated with seedling resistance (Lr28) leading to identification of transcription factors and miRNA families (e.g. miR36, miR37 and miR39) involved in signalling and defense response (Kumar et al. J. Nuc. Acids 2014:570176). In this study we report the application of speed breeding and RNAseq technologies for the purpose of rapidly identifying transcripts and miRNA associated with APR. Wheat landraces harbouring novel sources of resistance were grown under speed breeding conditions and sampled for RNA at key growth stages, before and after inoculation, which enabled discovery of differentially expressed miRNAs. Our next steps are aimed at validating these genetic factors associated with APR in order to better understand the signalling pathways and deliver tools to assist the assembly of robust wheat cultivars for the future.
Primary Author: Singh, The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Australia
The Lr34/Yr18/Sr57/Pm38/Ltn1 multi-resistance locus has been deployed and remained effective in wheat cultivars for more than 100 years. The durability and pleiotropic nature makes Lr34 a unique and highly valuable resource for rust resistance breeding. Despite its functional annotation as an ABC transporter, the mode of action is unknown. Considering this, we aimed to decipher molecular factors and signaling components essential for Lr34 function using RNA-seq of Chara resistant (Lr34) and Chara mutant (heavy ion irradiation, HII) susceptible wheat lines. Screening of Chara and Chara HII lines with Lr34-specific markers confirmed the integrity of Lr34 in both lines; however, phenotyping confirmed rust and powdery mildew susceptibility in the Chara HII lines. Plants were grown under controlled conditions and infected with Puccinia triticina pathotype 76-1,3,5,7,9,10,12,13+Lr37 at the flag leaf stage. Flag leaves were sampled at 0, 24, 48, 72, 96 and 168 hours post inoculation (hpi) from mock and infected plants. Based on real-time PCR analysis of basal defense genes and the Lr34 gene, we selected 72 hpi for RNA-seq with four biological replicates per condition. The samples were sequenced on an Illumina Hiseq 4000 at the Beijing Genomics Institute, China. A total of 9.0 Gb of sequence (2.25 Gb/library) from 16 libraries for four conditions was obtained. Differential expression analysis was performed using the Tuxedo analysis pipeline with standard parameters. Analysis revealed deletion of DNA fragments with collinear gene order on chromosomes 1A, 2D, 5A, 5B, 5D and 7D of Chara HII mutants. To determine the significance of the deletions we performed bulk segregant analyses on segregating F2 populations of Chara ? Chara HII crosses. Analyses revealed key genomic regions associated with Lr34-functional resistance and we are in the process of validating candidate genes using qPCR.
Primary Author: Singh, University of Queensland, St. Lucia