Abstract

Disease resistance (R) gene cloning in wheat has been accelerated by the recent surge of genomic resources, facilitated by advancements in sequencing technologies and bioinformatics pipelines. However, with the population and climate challenges ahead of us, it is vital not only to clone a few handfuls of R genes and understand their function, but also to do so at a magnitude appropriate to current agri-ecological pressures. Pathogen populations are continually changing, and breeders must have the tools and resources available to respond to those changes as quickly as possible if we are to safeguard our daily bread. To meet this challenge, we propose the creation of a wheat resistance gene atlas by an international community of researchers and breeders. The atlas would take the form of an online directory from which sources of resistance could be identified and deployed to achieve durable resistance to wheat’s major pathogens (such as wheat rusts, fusarium head blight, blotch diseases, powdery mildew and wheat blast). We present a costed proposal detailing how the interacting molecular components governing disease resistance could be captured from both the host and pathogen through whole-genome association genetics. We explore options for the effective configuration and genotyping of diversity panels of hexaploid and tetraploid wheat as well as their wild relatives and major pathogens, and how the atlas could inform a dynamic, durable approach to R gene deployment. Set against the current magnitude of wheat yield losses worldwide (recently estimated at 209 million tonnes each year; Savary et al. 2019), this endeavour presents one route to bringing disease resistance genes from lab to field at a considerable speed and scale.

Abstract

Stem rust and yellow rust are major wheat production constraints in Ethiopia. The majority of Ethiopian varieties are susceptible to one or more new races of the stem rust pathogen Puccinia graminis f. sp. tritici, and very few newly released varieties are resistant to all P. graminis f. sp. tritici races. This project that involved the Ethiopian Institute of Agriculture Research (EIAR), the USDA-ARS Cereal Disease Laboratory and the University of Minnesota was designed to stack both stem rust and yellow rust resistance genes into four adapted varieties of bread wheat: Kubsa, Danda’a, Galama and Ogolcho. The selection of these varieties was completed in consultation with EIAR and CIMMYT wheat breeders and pathologists in Ethiopia. These varieties were backcrossed to four donor parents of resistant genes including Sr22, Sr26, Yr5-Yr53 and Yr15-Yr64. The backcrossing of these genes into Kubsa and Danda’a was completed at the Cereal Disease Laboratory while backcrossing the selected resistance genes into Galama and Ogolcho backgrounds is being conducted at the EIAR Kulumsa Agricultural Research Center. All genes were transferred individually to Kubsa and Danda’a, and marker-assisted background selection was employed to recover increased genetic content of the recurrent parents at every generation through the BC3 stage using amplicon sequencing. Crossing activities to stack all genes into one or more individuals of both Kubsa and Danda’a is in progress. The backcrossing into Galama and Ogolcho is at the BC1 stage, and hands-on training on the methods of identification of resistant progenies from backcrosses with molecular markers was provided for the wheat molecular breeding team at Holetta National Agricultural Biotechnology Research Center. We expect improved versions of the four adapted varieties with a pyramid of six stem rust or yellow rust resistance genes to soon be in the hands of wheat farmers in Ethiopia.

Abstract

Wheat, one of the major staple cereals in India, is largely prone to rusts infection. The incidence of stem and stripe rusts can result in yield loss upto 100 per cent, and leaf rust may lead to around 50 per cent loss (under severe epidemics) causing devastating decline in profit levels. Inter alia, farmers have been advocated to cultivate the recently released rust resistant wheat varieties to counter the significant yield loss. In the milieu, the present study investigates the demand for wheat varieties in terms of seed indent, adoption lag and seed production trend for 25 years’ period (1994-95 to 2018-19) followed by adoption constraints at farmers’ field. India’s National Agricultural Policy has a strong orientation towards high yielding varietal adoption and hence latest wheat varieties are taken to farmers’ field through the National Agricultural Research System (NARS). Seed multiplication and spread of rust resistant high yielding genotypes played a major role in quantum jump in wheat production. Our analysis indicated that, for the study period, the cumulative breeder seed indent was higher for varieties like Lok 1, PBW 343, HD 2967, PBW 502 and GW 322. Among these, HD 2967 is the newest and a mega variety of the decade. The seed indent and production for HD 2967 witnessed a consistent increase with an estimated acreage of about 40 per cent (~ 12 million hectares) of the national wheat area. Interestingly, the variety which was released (2011) initially for adoption in the north western plains zone of India, later outscaled to north eastern plains zones (2013) owing to its yield potential along with other traits including rust resistance. A similar case of upscaling and outscaling is witnessed for HD 3086. In the recent past five years, the top breeder seed indent and seed production of wheat varieties hasn’t witnessed a much change. HD 2967 still tops the chart having its peak indent and production, respectively at 307.99 tonnes and 431.98 tonnes during 2016-17. Approximately, a variety to reach its peak adoption takes about 5 years since its release. For the recent decade, the growth rate per annum in seed production was highest for GW 322, whereas for the recent quinquennial, it was for HD 2967 both in breeder seed production as well as seed indent. Rest of the varieties have exhibited a mixed trend. At the farmers’ level, recently released varieties have been upscaled though frontline demonstrations. For instance, hitherto,1511 demonstrations were given for HD 2967 which led to an average yield gain of 699 kg/ha in comparison to its check varieties. Despite the increasing trend in overall breeder seed production of wheat, and, upscaling and outscaling the recently released varieties through ‘cluster demonstrations’, the need and availability of the ‘farmer choice variety’ is still persisting which needs to be addressed. Establishing ‘seed banks’, strengthening public-private partnership, block-chain enabled seed tracker will strengthen the complete seed system in wheat.

Abstract

Lower yield and marginalized genetic gains across Nepal have been observed in the last decade mainly due to climatic variations, low adoption of improved varieties and a low SRR of 14%. Although in the Chitwan region more than 19% of the arable area is under wheat cultivation, the average yield witnessed in the region is around 1.7 MT/hectare, which is below the national average. Further, the seed systems in the region are challenged with sparingly equipped processing units. Agriculture and Forestry University (AFU), the first of its kind in Nepal based in Chitwan, under the aegis of DGGW set up a nationally recognized seed production facility to build the seed system towards quality seed production and enable adoption of improved varieties. The last three years have brought about a paradigm shift in the seed systems in the region for quality seed production by farmers, processing and distribution. The project encouraged the adoption of three new wheat varieties to the farmers.

With no seed production in 2016, today AFU has an established seed system capable of producing quality certified seeds meeting the national standards and is currently working towards producing and maintaining their own breeder seeds. The initiative now has scaled up the area under quality wheat seed production to almost ten-fold through AFU farms and engaging more than 200 farmers over the last three years. The quantum of seeds produced has been significantly increased by engaging farmers, building capacity in good agricultural practices, monitoring quality seed production and introduction of sophisticated seed processing. Frequent and timely interactions of farmers with experts and extension professionals on the adoption of newer techniques and technologies led to realizing higher yields in farmer fields. Within a year of implementation, the farmers acknowledge importance of the system and are benefited from doubling yields and higher incomes.

Abstract

Crop landraces and wild relatives are carriers of exotic diversity that was lost during domestication and intensive breeding. Considering the importance of this lost diversity in boosting the resilience of our cropping systems to fast-evolving pathogens, it is critical that we deploy the recent advances in plant genomics to identify the exotic resistance alleles and re-introduce them into cultivated varieties. One such technology that we recently developed is AgRenSeq, which combines association genetics with R gene enrichment sequencing, for rapid discovery and cloning of resistance genes. We have applied this genomic tool to genetically diverse panels of wild diploid wheat and hexaploid wheat landraces, leading to the identification of genes providing resistance to stripe and stem rust.

Abstract

Wheat blast is recognized as posing a serious threat to wheat production in many parts of the world. Wheat blast emerged in Brazil in 1985 following a host jump of the fungal pathogen Pyricularia oryzae from wild grasses onto bread wheat. The presence of RWT3 and RWT4 are believed to have provided non-host resistance towards isolates from wild grasses (Lolium) (PWT3, pwt4) and (Avenae) (PWT3, PWT4). While the host specificity determinants PWT3 and PWT4 have been characterised from the pathogen the corresponding host resistances have yet to be identified. We used map-based cloning, association mapping and mutational genomics combined with the use of Triticum isolates transformed to carry PWT3 or PWT4 to clone both RWT3 and RWT4 wheat blast resistance genes. We will discuss the characterization of these genes and their role in non-host resistance.