Metabolomics and plant physiology during the wheat-stripe rust interaction
BGRI 2015 Plenary Abstract Veronica Roman-Reyna
Australian National University
Stripe rust is one of the major diseases of wheat worldwide. The causative fungus, Puccinia striiformis f.sp. tritici (Pst), keeps the infected tissue alive even after sporulation phase, a strategy that is referred to as biotrophy. The compatible interaction is divided into three phases; colonization, growth, and sporulation, the last occurring ~14 days after germination of spores. During the growth phase plant apoplast is completely occupied by hyphae, and the fungus develops special invasive structures called haustoria within plant cell. Both hyphae and haustoria are thought to take up nutrients from the host, but haustoria are specialized for this role. However, it is still unknown how the fungus obtains nutrients; perhaps by direct manipulation of host metabolic pathways related to photosynthesis or by changes in whole plant metabolite fluxes by acting as a sink. Also, it is unclear why wheat plants do not detect either the fungus itself, or the consequent loss of nutrients. The aim of this study is to understand the changes during the three phases of infection, comparing metabolites and plant photosynthetic efficiency in healthy and infected tissue, and correlating this with fungal growth. The results show that CO2 assimilation rates decreased only at the sporulation phase, which correlates with a reduction in transitory starch accumulation. However, glucose and fructose levels were lower only during colonization phase. Interestingly, although the infection alters the nutrient balance, this did not seem to affect the development of young leaves. In addition to these results, we found that stripe rust grows faster in younger leaves, which might be related to their morphology and the nutrient availability and fluxes within the leaf. This research suggests that the fungus is undetected until sporulation, and will aid future studies to understand the mechanisms of adult plant resistance conferred by transporter proteins. The research will aid future studies to understand the dynamic of adult plant resistance conferred by transporter proteins. The knowledge in wheat physiology and metabolism during rust infection could help to explain the role of transporter proteins during wheat-stripe interaction in different plant growth stages.
Training agricultural scientists for a more globalized world: Monsanto’s Beachell-Borlaug International Scholars Program after 7 years
BGRI 2015 Plenary Abstract Edward Runge
Texas A&M University
Monsanto’s Beachell-Borlaug International Scholars (MBBIScholars) Program was established on March 25, 2009, on Dr. Norman Borlaug’s 95th birthday. Monsanto initially funded the MBBIScholars program for $10 MM ($2 MM per year for 5 years) and extended the program with a second grant for $3 MM ($1 MM per year for 3 years). As of February 2015 (6 Years of funding) the program has supported 70 students. The 70 MBBIScholars were selected from 359 applications. MBBIScholars are from 25 countries with India having 20 scholars. MBBIScholars from other countries are – Argentina 3, Bangladesh 2, Brazil 2, China 4, Columbia 4, Ecuador 1, Egypt 1, England 1, Ethiopia 4, Kenya 2, Korea 2, Iran 3, Italy 1, Mali 1, Nepal 2, Pakistan 1, Philippines 1, Syria 2, Tajikistan 1, Thailand 1, Tunisia 1, USA 4, and Uruguay 2. Forty scholars studied wheat breeding and 30 studied rice breeding. Twenty seven scholars were young ladies. Applications for the 7th round were due on or before February 1, 2015. A unique feature of the MBBIScholars Program is the requirement that scholars must complete part of their PhD program in both developed and developing/transition countries. Scholars have worked with developed country scientists as follows – Australia 4, Canada 3, USA 43, and Western Europe 20. The program pays for the MBBIScholars to participate in a 3 day Leadership course prior to attending the World Food Prize during their first 2 years. It has been a good experience to see MBBIScholars gain self-confidence after attending the Leadership Course and World Food Prize, and as they study and conduct research in developed and developing/transition countries. They also gain many lifelong contacts in the plant breeding community. Based on the current funding agreement with Monsanto, the final round of MBBIScholars will be selected from applications due February 1, 2016. In view of the great success of this model of training international plant breeders, it would be highly desirable for donors to support and extend this PhD training program to include additional crops of interest in developed and developing countries.
Wheat stripe (Puccinia striiformis f. sp. tritici,=Pst) and stem (Puccinia graminis f. sp. tritici =Pgt) rusts are the most important wheat disease in Egypt as well as present in all wheat growing areas. This study to evaluate a set of tester lines of wheat carrying stripe Yr's, stem Sr's rust genes and selected Egyptian varieties have been studied for their response to Pst and Pgt at adult plant stage under field conditions in Sakha Agriculture Research Station, during the 2011 to 2014 growing seasons. The results revealed that stripe rust, it has been observed that the new race Yr27-virulence to Pst. In addition pathotypes were virulent for Yr2, Yr6, Yr7, Yr8, Yr9, Yr27, while Yr18 showed moderate susceptibility. On the other hand, Yr1, Yr5, Yr10, Yr15, Yr17, Yr32 and YrSP exhibited high levels of resistance. Regarding, evaluation of resistance genes sources of stem rust on ICARDA, CIMMYT wheat germplasm, and Egyptian wheat varieties released i.e. Misr1 and Misr2 which having Ug99_resistance genes Sr2 and Sr25 were found susceptible to Pgt, also Sr31 recorded infection moderately susceptible to susceptible at adult stage. Genes Sr2 complex, Sr24, Sr26, Sr27, and Sr32 were resistant at adult plant stages. The combination of Sr26 with Sr2 and Sr25 provided stem rust resistance in some CIMMYT wheat germplasm. The objectives of this work are: race analysis of wheat stem and stripe rust disease, evaluation the level and distribution of wheat stripe and stem rust in Egypt, and identification the resistance genes in commercial varieties or new promising lines using standard and molecular genetic markers. Egyptian germplasm such as Misr1, and Misr2 and others tester lines of wheat carrying stem rust Sr's were evaluative under field condition at adult stage in Egypt during 2014 growing season, Egyptian cultivars Misr1 and Misr2 were susceptible rated 10S-20S and Sr31 rated MSS. that results clearly presence a new Sr31-virulence. On other hand, genes Sr2 complex, Sr24, Sr26, Sr27 and Sr32 were resistant and combination of Sr26 with (Sr2 and Sr25) produced stem rust resistance in some CIMMYT wheat germplasm. Shahin et al., 2015, in APS Annual Meeting, Aug. 1-5, Pasadena, CA, US, (In Press).
A key objective of BGRI is to breed high yielding, stem rust resistant spring wheat germplasm suitable for releases as successful varieties in wheat growing countries of Africa, Middle East, Asia and Latin America. High emphasis was given to select adult plant resistance (APR) to stem rust in achieving this goal that is especially important in East African highlands where various variants belonging to the Ug99 race group and other lineages of stem rust fungus are now known, disease is endemic and present throughout the year on wheat crops. Recent molecular mapping studies show that combinations of partially effective APR gene Sr2 with 3 to 4 additional APR genes such as Sr55, Sr56, Sr57, Sr58 and other undesignated quantitative trait loci confer adequate to high levels of resistance to stem rust. A ‘Mexico-Kenya shuttle breeding scheme’ was initiated in 2008 to select APR to stem rust under high disease pressures at Njoro, Kenya while selecting for resistance to other rusts, yield, agronomic and quality traits in Mexico. This selection scheme, combined with phenotyping of advanced lines for multiple seasons in Kenya has resulted in identifying a small frequency of high yielding lines that possess a high level of resistance with a stable and low stem rust severity performance over seasons/locations under high disease pressures. These near-immune wheat lines are the best candidates for release in East Africa to achieve durable disease control and simultaneously curtail, or reduce, further selection of new virulences. A significantly higher proportion of wheat lines were also developed with moderate levels of resistance that is considered suitable for deployment in wheat growing areas where rust builds up later in the season. The worldwide distribution of the wheat lines derived from Mexico-Kenya shuttle breeding initiated in 2012 through the international yield trials and nurseries from CIMMYT. Potential releases and cultivation of these lines in different countries together with a reduction in area sown to susceptible varieties are expected to reduce the threat from stem rust.
Recent events in worldwide populations of the fungal pathogen Puccinnia striiformis, which causes the yellow rust disease on wheat and other cereals, have suggested that other factors than shifts in virulence can lead to epidemic events. For instance, the spread of two strains across four continents that has occurred within the last 10-15 years seems to be a result of high temperature adaptation combined with a relatively short latent period (Hovmøller et al. 2008; Milus et al. 2009). Variation for quantitative traits like latent period has often been hypothesized to play a significant role in population shift but only very few experimental data have been generated. Here we report difference for components of aggressiveness which included latent period and lesion growth for 17 isolates derived from a selfing of an aggressive isolate using Berberis vulgaris. A group of offspring isolates had a significantly longer latent period and higher lesion growth than the parental isolate. Interestingly, the two traits were found to be positively correlated where a long latent period was correlated with a higher lesion growth rate. This may suggest a trade-off between latent period and lesion growth. All isolates were assessed on seedlings of two highly susceptible host varieties and the two hosts gave similar results. In a previous study the progeny isolates showed segregation for virulence/avirulence and SSR markers (Rodriguez-Algaba et al. 2014). In conclusion, this study demonstrates genetically inheritable variability for latent period and lesion growth in P. striiformis, even within a single parental isolate. The results contribute to a better understanding of the ability of P. striiformis to adapt to new host varieties and changing environments at the quantitative level.
We will present an update on the BBSRC-funded SCPRID project “Maximizing the potential for sustainable and durable resistance to the wheat yellow rust pathogen”. This aims to understand the molecular basis of Puccinia striiformis f. sp. tritici (PST) pathogenicity and exploit this information to design effective breeding strategies that maximize the potential for durable disease resistance in the field. We have established a PST genomics platform through sequencing of PST genomes (UK, European, African, and Indian races) and analysis of expression time courses during infection (Cantu et al 2013). Using this platform we have characterised the PST effector complement, identified putative candidates and have begun their validation. The latest results of this will be presented. We have also evaluated a collection of hexaploid wheat landraces for resistance to PST across continents and have initiated single seed descent mapping populations and initial characterisation in F2:3 populations. We will exemplify the use of new genomic technologies to develop closely linked markers to enable deployment of resistance loci in breeding programmes (Ramirez-Gonzalez et al 2014). We will also provide an update of a new technique, called Field Pathogenomics (Hubbard et al 2015). This method uses transcriptome sequencing of PST-infected wheat leaves to describe pathogen diversity and also identify the host variety. This analysis uncovered a dramatic shift in the PST population in the UK and suggests a recent introduction of a diverse set of exotic PST lineages that may have displaced previous PST populations.
Placement of South African stripe rust in a global context and development of diagnostic tools for genotyping field samples
BGRI 2015 Plenary Abstract Hester van Schalkwyk
Department of Plant Sciences, University of the Free State, South Africa
Stripe (yellow) rust, caused by the fungus Puccinia striiformis f. sp. tritici (PST), is a major global wheat disease. New PST strains that show higher infection rates and rapid adaptation to less favourable environmental conditions have been observed over the last 15 years. It has also continued to spread to areas where it was not previously recorded. In South Africa, stripe rust was first detected in 1996. In subsequent years three more PST races were observed, with what seemed to be a step-wise virulence gain. A better understanding of the South African PST pathotypes and how they fit in the global context is needed. We aimed to address this by sequencing the genomes of four historical PST isolates displaying the four distinct virulence profiles. This allowed us to characterise the genetic diversity between these stripe rust races and develop diagnostic markers to easily genotype current detections. We also placed the South African PST isolates in context with global PST isolates where sequence data was available. This analysis illustrates that the South African PST races are more closely related to PST from other African countries when compared to isolates from Africa, Europe and Asia. Through pairwise comparison of isolates, we identified 27 candidate effector genes showing specific polymorphisms between the four isolates that could be related to their distinct virulence profiles. We are currently undertaking gene expression profiling of these candidates to determine if these effectors are specifically upregulated during infection–a key characteristic of effector genes. This study has shed new light on the potential origin and adaptation of stripe rust in South Africa and provides tools for rapid genotypic classification of infections in the field.
The Green Revolution involved the deployment of reduced height (Rht) genes to generate shorter wheat varieties with increased grain yields. It also contributed to a reduction in genetic diversity in the modern gene pool. Therefore, the pre- Green Revolution tall wheat landraces may provide a reservoir of genetic variation for economic traits such as rust resistance. Considering the breakdown of a suite of rust resistance genes through the emergence of currently predominant pathotypes (e.g. Ug99 and high temperature adapted isolates of the stripe rust pathogen) after three decades of Green Revolution, the discovery, characterisation and deployment of diverse sources of resistance remains a high priority. We have screened the Watkins wheat landrace collection and discovered, characterised and formally named a suite of new rust resistance genes including Yr47, Yr51, Yr57, Yr63 and Sr49. In addition, genotypes carrying potentially new genes for resistance to three rust pathogens are currently being investigated by students from seven nations representing three continents (Australia, Asia and Africa). Yr47, Yr51, Yr57 and Lr52 have been backcrossed into modern cultivars including the widely adapted cultivar PBW343 (Atilla) using markers developed in our research program. Development of triple rust resistant derivatives in modern wheat backgrounds is in progress. Stocks carrying Yr47, Yr51, Yr57 and Lr52 have been mutated to facilitate cloning of these loci for their eventual use in development of multi-gene cassettes for transformation.
Wheat stem rust is one of the major wheat yield limiting factors in Ethiopia. A stem rust epidemic occurred in the wheat belts of Arsi and Bale zones in the 2013-2014 crop season caused by Pgt race TKTTF that is virulent to the widely grown Ug99-resistant variety Digelu. This epidemic highlighted the need for wheat varieties with resistance to multiple Pgt races. This study was therefore, carried out to evaluate the reaction of the major Ethiopian varieties and advanced breeding lines against the dominant Pgt races in Ethiopia. Races TKTTF, TTKSK, TRTTF and JRCQC were isolated from field samples and multiplied on the susceptible cultivar McNair starting in May 2014. Four wheat stem rust nurseries, each inoculated with a single Pgt race, were established at Kulumsa and monitored from July through October, 2014. Each nursery included 34 entries in two replicates and 137 entries in a single replicate, augmented with six sets of five repeating checks. An additional nursery established at Debre Zeit, containing 551 entries in an augmented design, was evaluated with the epidemic Pgt race TKTTF. These entries included the most relevant Ethiopian bread and durum wheat breeding lines and cultivars, and 34 seedling-susceptible lines to evaluate the race-specificity of adult plant resistance. Stem rust severities for the four races ranged from trace to 80 %. Out of all entries evaluated, 10 were resistant to all four Pgt races, while 11 entries were effective to three of the four races. At Debre Zeit, 31.4% of the entries were resistant to Pgt race TKTTF. This study showed that rapid isolation and increase of Pgt races in Ethiopia is possible to facilitate field screening of breeding lines to select for candidate cultivars with resistance to multiple virulent races of Pgt.
Using ‘speed breeding’ to harness rust resistance: faster, cheaper and easier
BGRI 2015 Plenary Abstract Lee Hickey
The University of Queensland, Queensland Alliance for Agriculture and Food Innovation, Australia
Watch presentation (YouTube)
A new method for rapid generation advance, called ‘speed breeding’, has considerable advantages over DH technology for spring wheat because it provides increased recombination during line development and enables selection in early generations for some traits. The system has been refined over the past 8 years at The University of Queensland, utilizing controlled temperature regimes and 24-hour light to accelerate plant growth and development. The low-cost management system enables up to 6 plant generations of wheat annually – just like Arabidopsis. Currently, three of the six wheat breeding companies in Australia are exploiting speed breeding, and elite lines developed using the technology are in the final stages of yield evaluation. Recently, we developed methods adapted for use in the speed breeding system, which permit year-round high-throughput screening for adult plant resistance (APR) to rust pathogens that attack wheat. In this presentation, we describe the protocols, explain how phenotypes are related to field-based measures and highlight how the system can even handle diverse germplasm, such as winter types and landraces. Our ‘triple rust’ screening methodology enables selection for APR to all three rust pathogens and crossing of selected plants within a single plant generation. We applied the technique to rapidly introgress rust resistance into several Australian cereal cultivars. The technology is also a useful tool to accelerate rust research efforts. RIL populations designed for mapping novel APR genes can be developed within 12–18 months. Experiments to understand gene function in terms of temperature stability and onset of resistance can be performed year-round and if combined with sequencing technologies, such as RNAseq, transcripts involved in rust defence can be rapidly identified and harnessed via the speed breeding system. We will also reveal our current activities aiming to integrate the system with other plant breeding technologies to maximise genetic gain for wheat.