The University of Sydney, Plant Breeding Institute, Australia
Genetic analysis of YrA resistance in Avocet R confirmed two complementary resistance genes. Marker-trait association analysis on a doubled haploid (DH) population derived from Teal/Avocet R mapped one of the genes to chromosome 5BL. A DArT-Seq genetic map for the population indicated the presence of a T5B-7B reciprocal translocation. Fluorescence in situ hybridization (FISH) confirmed the translocation in the susceptible parent Teal relative to Avocet R. Additional FISH examinations on Cappelle Desprez (CD), Chinese Spring (CS) and Avocet S as controls indicated that the translocation in Teal was similar to that in CD. FISH studies also revealed additional polymorphisms in both chromosome 7B arms of Avocet R and Avocet S relative to CS, and that chromosome 5B in Avocet S lacked about 32% of the long arm relative to Avocet R and CS. It was postulated that complementary gene Yr74 was deleted with the missing segment. Australian cultivars Banks, Condor and Egret are also polymorphic for stripe rust response, and intercrosses in earlier studies between the S selections failed to confirm complementary genes. FISH analyses are currently underway to test the hypothesis that the S selections carry the deletion. Results will be reported in the poster.
Tajik Agrarian University, 146, Tajikistan
The objective of this study was to characterize seedling and adult plant resistance to all three rusts in a set of 40 bread wheat varieties currently cultivated in Tajikistan. Gene postulation based on multi-pathotype seedling test data and adult plant responses identified Yr2, Yr9, Yr17 and Yr27; Lr10 and Lr26; and Sr5, Sr6, Sr10, Sr11, Sr31 and Sr38. The effects of slow rusting, adult plant, pleiotropic resistance genes Lr34/Yr18/Sr57 and Yr30/Lr27/Sr2 were observed in the field and confirmed with molecular markers. Furthermore, molecular markers diagnostic for Yr9/Lr26/Sr31 and Yr17/Lr37/Sr38 were assessed on all varieties. Genes Lr34/Yr18/Sr57, Yr9/Lr26/Sr31 and Yr27 were identified in varieties Sarvar, Vahdat, Oriyon, Isfara, Ormon, Alex, Sadokat, Ziroat-70, Iqbol, Shokiri, and Safedaki Ishkoshimi based on phenotypic and genotypic results. Some lines were highly resistant to stripe rust (4 varieties), leaf rust (5) and stem rust (9), but the genes responsible could not be identified. They may possess new resistance genes. We thus identified combinations of major and minor rust resistance genes in Tajik wheat varieties. These varieties can now be used by breeders in Tajikistan as crossing parents to develop new varieties with durable resistance to the rusts.
Research Institute of Crop Production, Czech Republic
farming because of lower demands for pesticide applications. Triticale as a hybrid of wheat and rye may possess disease resistances derived either or both from wheat and rye. In the Czech Republic the leaf rust pathogen isolated from triticale is Puccinia triticina. Triticale is usually resistant to the rye leaf rust pathogen (P. recondita). Limited information is available comparing P. triticina isolates collected from wheat and triticale. Manninger (2006, Acta Phytopathologica and Entomologica Hungarica 41: 93-100) pathotyped 82 isolates collected from wheat and triticale on 15 Thatcher NILs. More than 50% of isolates from wheat were virulent to Lr2b, Lr2c, Lr3, Lr11, Lr17, Lr21 and Lr26. Of 12 isolates from triticale 9 were virulent only to Lr2b and Lr2c and the other 3 isolates were virulent to Lr2b, Lr2c and Lr11. We inoculated 15 NILs and 7 triticale cultivars with 36 Pt isolates from wheat and 36 isolates from triticale. Characteristic differences between the reactions on NILs of isolates from triticale and wheat were not found except that virulence to Lr1 was much more frequent in isolates from wheat. Whereas isolates from triticale were virulent to all 7 tested triticale cultivars, isolates from wheat were virulent to only 3 triticales. In another experiment isolates from wheat and triticale were collected at four locations. Although paired isolates came from the same locations the responses of the NILs were different. Isolates from triticale for all four locations were virulent to a higher number of triticale cultivars than those from wheat. It seems that P. triticina races infecting triticale have changed over the last decade from having a narrow virulence range on bread wheat to the current situation of typical bread wheat races becoming specialized on triticale.
The University of Agriculture, Peshawar, Pakistan
The Himalayan and near Himalayan region of Pakistan, China and Nepal was recently identified as the center of diversity of Pst. The Pakistani Himalayan populations were shown to be recombinant and possibly maintained through sexual reproduction on the alternate host, Berberis spp. To examine the role of Berberis spp. in supporting Puccinia spp. in the Himalayan region of Pakistan, 274 pycnial/aecial-infected Berberis leaves and 16 grass samples with uredinial infections were collected in the region from 2012 to 2014. Amplification of infected grass and Berberis spp. samples with EF, ITS region, and β-tubulin primers and subsequent species identification based on comparisons of the sequences to sequences in GenBank identified at least five Puccinia spp. viz., P. brachypodii, putative P. coronata-loli and P. coronati-agrostis, P. striiformis f. sp. dactylis (P. striiformoides), and P. striiformis on Berberis and grasses. This infers a role of Berberis as alternate hosts to Puccinia spp. in the Himalayan region of Pakistan, and in contributing to the overall diversity of these species in the region. Microsatellite characterization of Pst samples collected on wheat in 2013 and 2014 indicated an overall high diversity and recombinant population structure in the region. However, the low frequency of wheat-infecting P. striiformis isolates obtained from Berberis spp. necessitates ongoing investigation.
Department of Plant Pathology, Kansas State University, USA
Puccinia triticina, the causal agent of wheat leaf rust, is a devastating disease that can cause up to 40% yield loss. During fungal infection the host plant recognizes pathogen effectors, which trigger a host defense response. Changes in the pathogen effectors due to host selection pressure are responsible for the rapid development of new rust races and make durable resistance hard to obtain. The objectives of this study are to identify and characterize wheat genes that are utilized by races differently throughout infection and to understand functions of these genes using gene silencing. Six races of leaf rust were inoculated on a susceptible wheat variety and tissue was collected at six days post inoculation. RNA was sequenced and 63 wheat genes were identified that showed varying expression in response to the six races. 54 of these genes were evaluated in a time course study from zero days to six days post inoculation with the same six races. Real-time PCR was then used to analyze the timing of expression during early infection. The characterized genes have proposed functions involved in plant defense and stress, energy and metabolism, protein transport, replication, and RNA binding. Majority of the candidate genes showed three main expression patterns. However, race specific expression was found in three wheat genes that are affected by race shifts on Lr2A, Lr2C, and Lr17A. Sixteen potential susceptibility genes were also identified. Host susceptibility genes could be altered to provide durable resistance. RNAi was used to silence seven wheat genes to further understand their roles in leaf rust infection. T0 and T1 plants have been obtained and confirmed for the gene of interest. T2 plants were inoculated and observed for changes in susceptibility.
The University of Sydney Plant Breeding Institute, Australia
Wild relatives, landraces and cultivars from different geographical regions are demonstrated sources of resistance to wheat rusts. Identification, characterisation and provision of diverse sources of rust resistance to Australian wheat breeding companies form a key component of the Australian Cereal Rust Control Program. This study was planned to assess diversity of resistance to the three rusts among a set of Nordic spring wheat cultivars. These cultivars were tested at the seedling stage with several pathotypes of each rust pathogen. Stem rust resistance genes Sr7b, Sr8a, Sr12, Sr15, Sr17, Sr23 and Sr30 and leaf rust resistance genes Lr1, Lr3a, Lr13, Lr14a, Lr16 and Lr20 were postulated either singly or in various combinations. A high proportion of cultivars were identified to carry Sr15/Lr20 presumably due to earlier selection, or fixation, of Pm1 in breeding populations. Seedling test data using five Pst pathotypes did not allow postulation of genes present in a many cultivars because of a widely effective single gene or overlapping effectiveness of two or more resistance genes. Stripe rust resistance gene Yr27 was postulated in five cultivars. The presence of Yr1 in one cultivar was predicted by amplification of the linked marker allele. Eighteen, 47 and 32 cultivars showing seedling susceptibility, respectively, to stem rust, leaf rust and stripe rust were tested under field conditions to identify sources of adult plant resistance (APR). Cultivars possessing APR to all three or to two rusts were identified. Molecular markers linked to APR genes Lr34/Yr18/Sr57, Lr68, and Sr2 detected the likely presence of these genes in some cultivars.