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Constant climatic change and rapid evolution of diseases and pests have created challenges for plant breeders to find novel sources of resistance within cultivated gene pool. However wild (alien) relatives of crops still carries many promising resistance genes to biotic and abiotic stresses. Plant breeders around the world have successfully attempted to recover some of the beneficial genetic diversity lost (or never included) during the domestication and crop improvement process by crossing cultivated varieties with wild species to introgressed many valuable genes into crops like wheat and barley. This pre-breeding attempt to regain the genetic diversity of crops based on crop wild relatives (CWR) had been started at ICARDA 1994. Furthermore, The Global Crop Diversity Trust (GCDT) recently provided a grant to ICARDA within the Crop Wild Relatives (CWR) project to strengthen the research on use of genetic resources in pre-breeding of barley and grass pea. The pre-breeding activity in barley is focused on transferring genes of resistance to complex diseases and pests (scald, spot blotch and barley gall midge), improving tolerance to drought, heat and salinity, and enhancing the nutritional value through improving Iron and Zinc concentrations and amylases activity. Crosses were made between wild barely H. Vulgare X cultivated barley H. Vulgare subsp. H. spontaneum. The main objective of pre-breeding in Grasspea is transferring genes of low or no ?-ODAP from crossable species L. cicera and L. amphicarpus, L. tingitanus, L. aphaca, L. odoratus, L. sphaericus, L. nissolia, and L. aureus. Interspecific crosses were made between L. sativus x L.cicera followed by embryo rescue. Currently all the pre-breeding lines with targeted traits are under screening against the respective selection pressures using precision phenotyping..
Primary Author: Patokar, International Center for Agriculture Research in Dry Areas (ICARDA)
In 2016, severe epidemics of yellow (stripe) rust were observed on durum and bread wheat in European regions where the diseases in the past were insignificant or absent. Stem rust was also observed at epidemic levels for the first time in more than 50 years in Europe. On Sicily, both yellow and stem rust caused epidemics on cultivated durum and bread wheat and numerous breeding lines. In 2017, surveys in farmer fields and trial monitoring were carried out in Southern Italy during April-June. A total of 61 farmer fields and 9 experimental plots were inspected and rust samples collected. Despite unfavourable weather conditions for rust development, stem rust, yellow rust and leaf rust were detected on 86%, 50% and 14% of the surveyed sites, respectively. The surveys on Sicily covered approximately 70% of the durum wheat area, and data uploaded and visualised on the Wheat Rust Toolbox. On mainland Italy and Sardinia, yellow rust was observed, and sampled from nine fields in Sardinia and two in Puglia, whereas stem rust was detected and sampled in experimental plots in Sicily, Sardinia, Puglia, Lazio and Emilia Romagna. A total of 94 samples of stem rust, 30 samples of yellow rust, and 3 rust samples from Berberis aetnensis were sent to GRRC. Preliminary results of yellow rust genotyping and race phenotyping showed prevalence of race Triticale2015. Warrior(-) and a new race (Pst'New'- First detected in 2016) were also detected. For stem rust, TTTTF and TTRTF were detected in Sicily and mainland Italy and TKTTF was identified in Sardinia. Susceptibility of major commercial durum cultivars and breeding lines suggests the need for both durable resistance breeding and systematic surveys coupled to an early warning system.
Primary Author: Patpour, Global Rust Reference Center (GRRC), Aarhus University, Denmark
Rust fungi can cause devastating diseases in agriculture and are particularly important pathogens of wheat. We have been using the flax (Linum usitatissimum) and flax rust (Melampsora lini) model system to study disease resistance mechanisms to this important class of pathogens. Rust resistance in flax and other plants is mediated by the plant innate immunity system in which highly polymorphic resistance (R) proteins act as receptors that recognize specific avirulence (Avr) proteins produced by the pathogen. This race-specific resistance is characterised by Flor’s “gene-for-gene” model, first proposed based on the flax rust system. In gene-for-gene resistance, recognition between the R and Avr proteins initiates defense responses leading to host resistance to infection, including a localised necrosis or hypersensitive response. Nineteen different rust resistance genes have been cloned from flax, including 11 allelic variants of the L locus, which all encode cytosolic proteins with conserved nucleotide-binding (NB) and Leucine-rich repeat (LRR) domains. Four families of Avr genes, AvrL567, AvrM, AvrP123 and AvrP4, have been identified in the flax rust pathogen and all encode small secreted proteins. Rust Avr proteins are secreted from haustoria, specialized infection structures that penetrate the host cell wall, and are translocated across the host plasma membrane and into the host cytoplasm. These proteins are probably members of a suite of disease ‘effectors’ involved in manipulating host cell biology to facilitate infection, but have become targeted for recognition by the host immune system. As yet the mechanism of Avr protein transport is unknown, but could prove to be a useful target for novel disease control strategies. Recognition of at least two of these Avr proteins is based on direct interaction with the cytoplasmic NB-LRR R proteins. One interesting observation from the flax rust system is that all of the virulent rust strains retain intact copies of the Avr genes, but have altered their sequences sufficiently to escape recognition. Thus it may be possible to re-engineer R genes to recognise new Avr gene variants. We are currently identifying haustorially expressed secreted proteins from wheat stem rust as candidate Avr/effector proteins.
Primary Author: Peter Dodds, CSIRO Plant Industry, Australia
Stem rust caused by Puccinia graminis tritici (Pgt) is one of the most serious diseases in wheat and is combated mainly through the use of resistant varieties. Because the fungus evolves virulence towards previously resistant varieties, continuous breeding and identification of new sources of resistance are necessary to combat the threat of rust epidemics. Our work on the flax rust model system has provided insights into how the plant immune system recognises and responds to rust pathogens. We have been extending this work to wheat stem rust by targeted cloning of resistance (R) genes in wheat and corresponding Avr genes in Pgt. Plant R genes encode immune receptors that recognise and respond to pathogen effector proteins delivered into host cells from haustoria. We recently isolated the Sr33 and Sr50 resistance genes from wheat and have begun functional analyses to determine how they trigger defense responses. We are also targeting effectors from Pgt that are recognised by wheat R genes. We used genome and transcriptome sequencing to predict ~400 candidate effector genes from Australian Pgt race 21- 0. To screen for recognition of these proteins by wheat R genes, we developed a bacterial Type III Secretion System delivery assay using Pseudomonas fluorescens to inject the effector candidates into wheat leaf cells. We are screening candidate effectors on a set of 18 wheat cultivars carrying 22 different R genes and have so far identified one effector that induces a cell death response specifically on a wheat genotype carrying Sr22. Understanding the nature of wheat R genes and the Avr proteins that they recognize will allow better prediction of R gene durability and enable the possibility of rational design of novel R genes. We are also developing techniques for stacking R genes in cassettes for deployment of multiple genes at a single locus in wheat.
Primary Author: Peter Dodds, CSIRO Plant Industry, Australia
There is emerging evidence that the geographical footprint of stripe rust is expanding, opening up prospects for an increase in economic losses attributable to this disease worldwide. Drawing on newly compiled data, along with insights obtained from a survey initiated at the BGRI meeting in New Delhi in August 2013, this talk will report on efforts to model the global occurrence and persistence of stripe rust in a geo-spatially sensitive fashion. Using the available data in conjunction with these newly developed climate suitability maps, I will present probabilistic crop production losses associated with the disease and place an economic value on the prospective losses. Given changes in the geographical spread of this disease, and the associated uncertainties about its likely wheat yield and economic effects, various scenarios will be assessed to inform and thereby help shape the research investment decisions regarding crop breeding and other options for ameliorating these prospective losses over the longer term.
Primary Author: Phillip Pardey, Department of Applied Economics, University of Minnesota
Wheat (Triticum aestivum L.) is one of the major cereal crops vital for global food supply. Most of the wheat crop in developing world including that of Nepal is either grown with limited irrigation or under rainfed conditions and thus face moisture stress at one or more growth stages limiting grain yield. An experiment was carried out at the Institute of Agriculture and Animal Science, Rampur to evaluate the genetic variability of selected drought adaptive traits in Nepalese wheat germplasm. The wheat genotypes evaluated comprised of Nepalese landraces and commercial cultivars, CIMMYT (International Center for Maize and Wheat Improvement) derived advanced introduction lines and three checks with differential drought adaptability. The wheat genotypes were grown in pots (single plant) arranged in a replicated split plot design in greenhouse under two contrasting moisture regimes, optimum and moisture stressed. The genotypes were evaluated for water use, water use efficiency, relative leaf water content and biomass production. The ANOVA (Analysis of Variance) revealed significant variation between environments and among the wheat genotypes for most of the traits studied. A wide range of variability was observed for water use, water use efficiency, biomass yield and relative leaf water content in moisture stressed and non-stressed environments. Nepalese cultivar Gautam showed a number of favorable drought adaptive traits, whereas, Bhrikuti was average in this respect. Based on the scores of drought adaptive traits recently released Cultivar (cv). Vijay was characterized as drought sensitive. A number of landraces and advanced breeding lines showed high level of water use efficiency and other positive traits for drought adaptation.
Primary Author: Pokharel, Department of Agriculture, Sunsari, Nepal
Urediniospores of rust fungi can be applied to cereal plants in several ways. Depending on the objective and available infrastructure, plants can be inoculated with a suspension of spores in either water, light mineral oil (e.g. Soltrol 130®) or engineered fluid (e.g. Novec 7100®). Alternatively, dry spores can be allowed to settle on plant surfaces by dusting or directly applied with a spatula or small brush. Several rust laboratories employ a system where a spore-oil suspension, contained in a gelatin capsule, is sprayed onto seedling leaves by means of a dedicated atomizer connected to an air pressure source. Although this approach is easy to use and highly efficient, the devices are not commercially available in South Africa. Locally, these inoculation appliances need to be manufactured by a conventional milling process that requires a specialized workshop and skilled personnel. This subtractive process is labour intensive and greatly prohibitive in terms of costs. Using a process called Additive Manufacturing (AM), also known as "3D printing", the body of an inoculator was digitally designed and then laser sintered in nylon. Loose powder was removed from flow channels by compressed air. A copper tube fitted afterwards connected the nylon body with the spore suspension in the capsule. Replicated inoculation tests of wheat seedlings with urediniospore bulks or single pustule collections of Puccinia triticina and P. graminis f. sp. tritici resulted in consistent levels of rust severity and infection frequency. Cleaning of inoculators in acetone for 1 min followed by a 1 h heat treatment at 60°C produced no contaminant infection in follow-up tests. The design has been registered in South Africa, the USA and Europe.
Primary Author: Pretorius, University of the Free State
Wheat plays a vital role in multifaceted farming system of Pakistan. Like other many other countries, Pakistan's sustainable wheat production is also continuously threatened by a number of biotic and abiotic stresses. Among the biotic stresses, three rust diseases of wheat have been the most devastating. Stem rust was effectively controlled with adoption of the semi-dwarf spring wheats of the Green Revolution. However, the threat of the evolution of Ug99 race of stem rust in East Africa and its migration to Iran cannot be neglected. The Chance of of Ug99 migrating from Iran into Pakistan, coupled with the presence of dangerous new races of stripe and leaf rusts invites enormous efforts for development of rust resistant varieties for sustainable production of the wheat in the country. In this regard the Wheat Program, NARC, Pakistan initiated an intensive breeding program with financial and technical support of USDA and CIMMYT. Diverse sources of resistance to the three rusts particularly to the stem rust race Ug99 were introduced from CIMMYT. Through the rigorous selection procedure, four rusts resistant wheat varieties (NARC 2011, Pakistan 2013, Zincol 2016 and Borlaug 2016) have been released. These varieties are also resistant to Ug99. The varieties i.e. NARC 2011, Borlaug 2016 and Zincol 2016 are performing well in irrigated areas whereas Pakistan 2013 is suitable for rainfed conditions. The variety Zincol 2016 has high Zn content (35 ppm) in grain as compared to national standard check variety (25 ppm). These varieties are not only higher yielding but also possess good grain quality and other desirable traits. A considerable quantity of seed of the varieties is already present in the national seed system and will reduce the risk of Ug99 threat.
Primary Author: Qamar, Wheat Program, National Agricultural Research Center (NARC) Islamabad
Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is a major threat to global food security. Although stripe rust was detected for the first time in Eastern Australia in 1979, Western Australia (WA) remained free from stripe rust until 2002. The Pst incursion in WA was pathotyped as 134 E16A+ and differed from the most widely virulent pre-2002 group by combined virulence to Yr8 and Yr9 and avirulence for Yr3 and Yr4. An advanced breeding line, WAWHT2046, expressed resistant to moderately resistant (R-MR) response to 134 E16A+ under field conditions, and infection type (IT) 23C - 3C at the seedling stage. The resistance gene Yr34 that controlled stripe rust in WAWHT2046 was 12.2 cM distal to the awn inhibitor B1 in chromosome 5AL (Bariana et al. 2006; Theor Appl Genet 112:1143-1148) based on a Carnamah/WAWHT2046 doubled haploid (DH) population. The present investigation was planned to identify SNP markers closely linked with Yr34. Eight homozygous resistant and eight homozygous susceptible lines from the Carnamah/WAWHT2046 DH population were used for selective genotyping using SNP markers. Twenty four SNP markers were associated with resistance. Kompetitive allele-specific primers (KASP) were designed and SNP markers were genotyped on the DH population. SNP marker IWB80451 mapped 1.7 cM proximal to Yr34.
Primary Author: Qureshi, The University of Sydney Plant Breeding Institute, Australia
Seed is a basic, vital and central input in agriculture and in all farming systems. Timely availability of quality seeds of varieties/hybrids adapted to to different agro-climatic conditions and in sufficient quantity at affordable prices is a measure of the strength and health of an agricultural economy. Sustained increase in agricultural production requires a continuous development of improved crop varieties/hybrids, an efficient system of production, and a means of distribution to farmers. India is one of the few countries where the seed sector has advanced in parallel with the agricultural production. However, the availability of quality seed of improved varieties and hybrids is grossly inadequate and is a major constraint to enhanced production. Studies made by several workers (Gadwal 2003, Patil et al 2004, Hanchinal et al. 2007) clearly indicate that with high-volume low-value seeds, such as wheat, groundnut, soybean and chickpea, 80% of the cropping area is sown with farm-saved seeds of old and obsolete varieties During last few decades, a number of high yielding disease and pest resistant varieties/hybrids in different crops had 10 to 40% yield superiority over local cultivars. With the exception of high-value low-volume seeds, seed production of low-value high-volume crops is generally left to public sector agencies. The bulky nature of most self pollinated crops, and lack of adequate investment on infrastructure means low remuneration. Although there is enough breeder seed production in most of the high volume crops, further seed multiplication through the foundation and certified seed stages are major constraints to the availability of quality seed. The present rate of seed replacement (SRR) for such crops is 6 to 8%. There is a need to increase SRR to 25 to 30% in varieties and obviously 100% for hybrids. To increase the productivity of low-value high-volume crops farmers need to have access to improved seeds of the right type, at the right time, at the right place and at a reasonable price. For supply of such seeds, both the informal seed sector (farmer managed seed systems) and the formal seed system (seed enterprises) need to be engaged. The informal seed sector is often highly effective in reaching isolated, inaccessible, small holder areas and is a sound opportunity for entrepreneurs to gradually evolve into the formal enterprises Wheat, the most important food crop of world and backbone of global food security, belongs to the highvolume low-value seed group. Of the total area sown to both hexaploid bread wheat and tetraploid durum and emmer wheat worldwide, 44% (95 m ha) is in Asia. Of this,62 m ha are located in just three countries viz. China, India, and Pakistan (Table 1 and Figure 1). Food security and production stability are of paramount importance in most Asian countries, given that the majority of farmers are poor. The wheat rusts have historically been major biotic constraints both in Asia and the rest of the world. Stem rust has been under control since the beginning of the green revolution in South and West Asia in the 1960s. Leaf rust and stripe rust continue to be major threats to production over approximately 60 (63%) and 43 (46%) m ha, respectively, in Asia. Although, the timely application of fungicides can provide adequate control, their use adds to production costs and they are considered environmentally unsafe. Growing resistant cultivars is thus the most effective and efficient control strategy, as it has no cost to farmers and is environmentally safe. Rapid evolution of races with new virulences, or combinations of virulences, dictate a need for discovery and deployment of new resistance genes and/or resistance gene combinations.
Primary Author: R.R. Hanchinal, University of Agricultural Services, India
