Bogale Nigir, Cherinet Alem, Yosef G. Kidane, Mario Enrico Pè, Matteo Dell'Acqua
Septoria tritici blotch (STB) is a devastating fungal disease affecting durum and bread wheat cultivation worldwide. The search for resistance sources in untapped genetic resources may speed up breeding for STB resistance. Ethiopian durum wheat landraces represent a valuable source of allelic diversity for several traits, including disease resistance. In this study, we measure STB phenotypes under natural infection on two interconnected populations: i) a diversity panel comprising 318 Ethiopian durum wheat lines, mostly farmer varieties, and ii) a nested association mapping (NAM) population developed from a subset of the diversity panel. Phenology, yield and yield component traits were concurrently measured in the populations. We evaluated the distribution of STB resistance in Ethiopian genetic materials and the relationship existing between STB resistance and agronomic traits. STB resistance sources were found in landraces as well as in NAM lines. The genetic material was genotyped with more than 13 thousand genome-wide SNP markers to describe the linkage disequilibrium and genetic structure existing within the panels. The genotyping information was combined with phenotypes to identify marker-trait associations and loci involved in STB resistance. We identified several loci, each explaining up to 10% of the phenotypic variance for disease resistance. We developed KASP markers tagging the most interesting loci to allow the uptake of our results in a breeding perspective. Our results showed that the Ethiopian untapped allelic diversity bears a great value for studying the molecular basis of STB resistance and for breeding for resistance in local and international material.
State Key Laboratory of Crop Stress Biology for Arid Areas and College of Plant Protection, Northwest A&F University
Yuan Tian, Yan Meng, Hengbo Ma, Lili Huang, Zhensheng Kang
Stripe rust, caused by Puccinia striiformis Westend f.sp. tritici, is currently one of the most prevalent and damaging disease on wheat. Up to now, some genes in wheat which are resistant to wheat stripe rust have been cloned, but little is known about the corresponding avirulence gene according to the gene-for-gene hypothesis. A population containing 118 progeny isolates population acquired by selfing an isolate, PL17-7, with virulence to Yr26 was derived. Seventy-two progeny isolates were different in genotype depending on 92 simple sequence repeat (SSR) markers. The progeny population segregated for avirulence to Yr6 at one locus (3 avirulent :1 virulent ratio). The parental isolate and 72 of 118 progeny isolates were resequenced to find candidate avirulence genes corresponding to Yr6. Overall, 7.6 million reads per sample were obtained and mapped to the draft genome of a Chinese Pst isolate CY32. The median depth of coverage was 63.6 fold. For each isolate, between 97.6% and 98.1% of the sequence reads were mapped to the race CY32 genome, which covered between 87.3% and 95.4% of the reference genome bases. An average of 97357 single nucleotide polymorphisms (SNP) per isolate was found, which covered 8.1% of the reference genome. Different SNPs and Indels were found when isolates virulent and avirulent to wheat cultivar containing Yr6 were grouped into two groups. Though screening discrepant SNP and indel in these two groups, candidate avirulence genes corresponding to Yr6 may be found.
Plant Pathology Division, Nepal Agricultural Research Council
Baidya Nath Mahto, Durba Bahadur, Thapa Roshan, Basnet Nautan Raj, Gautam Sesh, Raman Upadhyaya
Disease surveillance is very important in establishing the status of disease response in crops. During the 2014 to 2016 wheat seasons, foliar blight (spot blotch caused by Bipolaris sorokiniana and tan spot caused by Pyrenophora tritici-repentis) was recorded as severe across the entire whole plains region. Foliar blight was moderate in the mid hills, especially the Kathmandu valley. Leaf rust was severe (10MS - 100S) at several places in the mid hills. This could be due either to climatic conditions or varieties susceptible to the prevailing pathotypes. Yellow rust was also recorded up to 100S in the Kathmandu valley. Newly released varieties Gaura and Dhaulagiri showed yellow rust incidence of 20MS to 40S. Stem rust was sporadic and light and was observed very late in the season (tR - 10MR) in far western districts and the Kathmandu valley. Powdery mildew was moderate and localized. Loose smut was found at low levels throughout the mid hills. In 2014, Karnal bunt (caused by Tilletia indica) was also recorded in far western regions. Five different pathotypes of P. triticina (121R63-1, 21R55, 21R63 and 0R9) and one Pst pathotype (110S119) have prevailed during the last few years. Wheat genotypes were evaluated at Khumaltar and those reputed to have Yr27, Yr27+, Yr27+Yr18, Yr31+APR, Yr9, Yr10 and Yr15 were resistant. Similarly, genotypes containing Lr34+ had lower leaf rust severities than others.
Ayub Agricultural Research Institute, Faisalabad
Different biotic and abiotic stresses are hampering wheat yield across different geographic regions. Among biotic stresses, wheat rusts are principal cause of yield reduction. Whereas among abiotic stresses, drought is the principle cause of reduction in growth and lowering yield potential. So developing rust resistance and drought tolerance in wheat germplasm is needed, which requires assessment of genetic potential of current cultivars against these stresses to identify variation among existing germplasm. Screening of genotypes under naturally prevailing races of rust species is the better and inexpensive approach. In the present study 65 genotypes including five checks (AARI-11, Chakwal- 50, Aas- 11, Morocco and Galaxy-13) were evaluated for adult plant response to wheat rusts and water deficit conditions. Experimental material was planted in four blocks each having new entries along with repetition of five checks in augmented design. Data was recorded on morphological traits including plant height, peduncle length, spike length, productive tillers per meter, flag leaf area, number of spikelet per spike, grains per spike, single head weight, 1000 grain weight, days to maturity and grain yield per acre. Significant variation was observed among genotypes for all the studied traits. On the basis of performance G39 and G36 were better than commercial drought check Chakwal-50 in almost all the traits. However rust screening under natural rust infestation revealed that although Morocco showed susceptible (S) response yet only six genotypes were susceptible to yellow rust whereas all others were resistant. In case of leaf rust 29 were completely resistance, 25 were moderately resistant, seven were moderately susceptible and only four were completely susceptible to currently active races of leaf rust. However, in the case of stem rust, 61 genotypes showed complete resistance to stem rust, two showed moderately resistance and two were moderately susceptible. Information obtained from this study would be favorable for breeding rust resistant and drought tolerant cultivars.
Ebrahiem Babiker, Tyler Gordon, Sam Stoxen, Matthew Rouse, Yue Jin, Shiaoman Chao, John Bonman
Stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a threat to wheat production worldwide. To manage this important disease, new sources of genetic resistance are needed and common wheat landraces are a potential source of such resistance. Landrace accessions from the USDA-ARS National Small Grains Collection were evaluated for seedling resistance to the Ug99 race group. To identify accessions most likely to carry novel resistance genes, a bulked segregant analysis (BSA) approach was used. Seven resistant accessions were crossed to a susceptible parent line and F3 families were tested against Pgt race TTKSK. The resistant plants were identified and grouped into two bulks per population. The bulks, along with the parents and F1 progeny, were genotyped with the 90K wheat iSelect SNP genotyping platform. Four of the populations appeared to segregate in a 1:1 phenotypic resistant/susceptible ratio, one in a 1:2 ratio, and two in 1:3 ratios. However, chi squared tests indicated the ratios were statistically the best fit for only two of the 1:1 segregating populations and one of the 1:3 segregating populations. Initial BSA results indicate the markers associated with reduced stem rust infection are located on wheat chromosomes 1DL and 2B. These mapping populations are being advanced for further evaluation to ascertain if novel resistance to the Ug99 stem rust race group is present.
Barani Agricultural Research Station, Kohat
Fida Mohammad, Muhammad Imtiaz
Stripe rust is one of the major limiting factors in wheat production. An objective-based breeding program was initiated at Barani Agricultural Research Station (BARS), Kohat in 2013/14 to transfer APR genes from CIMMYT and ICARDA spring wheat lines into wheat germplasm well adapted in Khyber Pakhtunkhwa (KPK). Nine high yielding but stripe rust susceptible KPK wheat varieties were crossed in various combination with 17 CIMMYT and ICARDA wheat lines carrying resistance genes. The resultant 79 F1s were backcrossed with respective susceptible parents followed by single plant selection in F2 generation. During 2015/16, 367 segregating populations/lines were screened in multi-environment stripe rust tests within Khyber Pakhtunkhwa. Sixty-nine out of 367 lines showing adequate resistance were again screened for strip rust resistance at hot spot and in yield trial at BARS, Kohat during 2016/17. Seventeen lines showed considerable resistance and were higher yielding than check cultivars. Lines exhibiting adequate resistance will be further tested in advanced yield trial at provincial and national level for possible release of new varieties in wheat.
1,3 Colegio de Postgraduados-Fitosanidad, Campus Montecillo, Texcoco, 56230, Estado de M?xico, M?xico
Julio Huerta-Espino, Ravi P. Singh, Caixia Lan, Sridhar Bhavani, Reyna I. Rojas-Martínez, Ignacio Benitez-Riquelme, Cristian Nava-Díaz, Mandeep Singh Randhawa
Leaf rust and stripe rust caused by the fungi Puccinia triticina and P. striiformis f. sp. tritici, respectively, are important diseases of wheat and represent a significant threat in most wheat producing regions worldwide. Growing resistant varieties and the identification and characterization of new sources of resistance are necessary to combat the threat from the evolving pathogen population. Bread wheat (Triticum aestivum L.) line 'Kijil' developed at CIMMYT showed adult plant resistance (APR) to leaf rust (LR) and stripe rust (YR). The genetic basis of the resistance was investigated using 198 recombinant inbred lines (RILs) derived from the cross of susceptible Apav#1 and resistant Kijil. Field phenotyping of parents and RILs were conducted at El Batón, Toluca and Ciudad Obregon, Mexico during 2016 and 2017. Pearson correlation coeffcients (P< 0.0001) were high for disease severities between two years of evaluations: LR (r= 0.90) and YR (r= 0.83). Correlations (r= 0.30-0.76) were also significant between LR and YR in all environments. Genetic analyses indicated that 3 to 5 genes of additive effects governed resistance to both rusts. RILs carrying the pleiotropic APR gene Lr46/Yr29/Sr58 showed 23 and 41% of disease severity for LR and YR respectively, whereas lines lacking it had 55 and 78% severities. RILs positive for Sr2/Yr30 showed 66% YR severity, whereas those negative displayed 78%. In addition, lines carrying the race-specific gene Yr17/Sr38 showed 28% YR severity in contrast to non-carriers that displayed 78% severity. We conclude that Kijil possesses a complex nature of resistance.
Wheat Research Centre, Bangladesh Agricultural Research Institute
Kishwar-E-,Mustarin, Md Mostofa Ali, Reza, Krishna Kanto, Roy, Md. Ashraful, Alam, Md. Rezaul, Kabir, MD Abdil, Hakim, Md Monwar, Hossain, Md Rabiul, Islam, Tim, Krupnik, Md Forhad, Amin, Md. Mosharraf, Hossain, Nure Alam, Siddque, Paritosh Kumar, Malaker, Maricellis, Acevedo, Noresh Chandra Deb, Barma
Disease surveillance and monitoring has been regularly organized by Wheat Research Centre (WRC), in major wheat growing areas of Bangladesh since 2010-11 to track the current status of common diseases, first outbreak of new disease(s), the pathogen hotspot and identify new virulent races. Besides the paper based traditional survey, scientists of WRC are now using different tools like Smartphone/Tablet with supporting applications. Several trainings were arranged under DGGW project on rust tool box in Bangladesh. Among all smartphone applications, RustSurvey is the easiest and handy application which integrates with the SAARC Surveillance Toolbox.
A disease surveillance program on wheat blast was organized in Mid February 2017 followed by hands on training in collaboration with CIMMYT and CU, USA. Out of 103 sites surveyed, 33 sites were found infected with wheat blast. Overall disease incidence was comparatively lower than the previous season with low disease severity (5-10%). Surveillance program on rust diseases was also conducted in early March 2016. Among 102 rust survey sites stem rust and yellow rust was not found, but leaf rust occurred with varying levels of severity depending on field locations, sowing times and cultivars grown. About 52% of the 102 fields investigated had leaf rust, and almost 73% of the infected fields showed low (<20%), 21% moderate (20-40%) and only 6% showed high (more than 40%) disease severity. Timely (15-30 November) planted crops largely escaped or had less disease compared to those planted late in the season. The predominant cultivar Prodip as well as BARI Gom 25 and 26 showed zero to high disease levels with MSS type reactions. BARI Gom 21, 28, 29 and 30 were free from leaf rust infection. Furthermore, Spot blotch was found in most of the region with low to high level field incidence depending on crop growth stage.
CSIRO Agriculture and Food, Australia
Timothy Hewitt, Peng Zhang, Zacharias A. Pretorius, Narayana Upadhyaya, Rohit Mago, Sambasivam Periyannan, Xiuying Kong, Burkhard Steuernagel, Brande H. Wulff, Evans S. Lagudah
Multiple rust resistance gene combinations are considered as a practical solution for providing durable rust resistance and preventing resistance breakdown arising from single gene deployment. The stem rust resistance locus Sr26, originally derived from Thinopyrum ponticum and introgressed into wheat as a chromosome translocation, is one of the very few genes conferring durable resistance for almost 40 years to all known races of stem rust, including the highly virulent stem rust race Ug99 (TTKSK) and its derivatives (Dundas et al. 2015). To understand the underlying mechanisms of its unusual long-term effectiveness and to explore allelic diversity in different Th. ponticum accessions for other functional alleles that may offer new sources of resistance, we used comparative genomics and gene capture techniques (Resistance gene enrichment sequencing, RenSeq) as complementary strategies for isolating the target gene (Steuernage et al. 2016). Sr26 region was first mapped using NB-LRR (Nucleotide-binding site and leucine-rich repeat) sequences from the orthologous gene members located on the long arm of chromosome 6D from Aegilops tauschii (the D-genome donor of wheat) reference genome. Subsequently, we revealed a cluster of NB-LRR sequences located at the distal end of the Th. ponticum introgression segment that were absent in the smallest interstitial Sr26 deletion mutant. Therefore, we substantially narrowed down the genetic interval for Sr26. In addition to this approach, we subjected the mutant population to RenSeq pipeline. A candidate gene of Sr26 has been successfully identified to be a NBS-LRR type resistance gene. Validation of the gene candidate by complementation studies is currently in progress. In order to enhance durable resistance, genetic stocks of Sr26 from different backgrounds as well as a panel of Sr26-APR (Adult Plant Resistance) gene combinations have been generated to further investigate the resistance response of Sr26 in combination with different multi-pathogen APR genes.
University of Sydney Plant Breeding Institute
Naeela Qureshi, Vallence Nsaiyera, Pakeer Kandiah, Mesfin Gesesse, Mandeep Randhawa, Mumta Chhetri, Bosco Chenayek, James Kolmer, Miroslav Valarik, Zaroslav Dolezel, Beat Keller, Matthew Hayden, Justin Faris, Harbans Bariana, Vanessa Wells
Dr. Norman Borlaug stated that rust never sleeps and this enables rust pathogens to produce new strains capable of putting rust resistance genes to rest. These pathogens continue to pose threats to global wheat production. Wheat breeders have made significant progress to control rust outbreaks using conventional selection technologies; however, some critical shifts in pathogen populations have let them down. Rapid evolution in molecular marker technologies in the last 15 years and refinement of phenomic facilities have expedited the process of discovery and characterisation of rust resistance genes to underpin the development and validation of markers closely linked with genetically diverse sources of resistance. A high proportion of the formally named rust resistance genes were characterized in the 21st century and markers closely linked with these genes have been developed and validated. The marker tagged sources of resistance to three rust diseases have equipped the wheat breeding community with tools to deploy combinations of all stage and adult plant resistance genes in future wheat cultivars. The question that whether we have enough resistance genes discovered to compete against the ever-awake rust pathogens. In our opinion, we cannot be complacent and discovery needs to continue to ensure food security. This presentation will discuss the role of advances in phenomic and genomic technologies to achieve durable rust control in wheat.