CSIRO Agriculture Flagship, Australia
The Lr34 resistance gene from Triticum aestivum encodes a putative ABC transporter protein that confers broad spectrum, partial adult plant resistance to all three rusts species and powdery mildew. It has remained a durable source of resistance for over 100 years in which time no increased virulence towards Lr34 has been observed. This gene is located on chromosome 7D and consequently cannot be readily transferred to durum wheat by traditional breeding. A transgenic approach was used to transfer Lr34 to durum wheat cultivar Stewart by Agrobacterium transformation. Homozygous progeny from a number of independent Stewart lines expressing Lr34 under regulatory control of its endogenous promoter showed high levels of rust resistance at the seedling stage. A correlation between seedling resistance and transgene expression levels was observed in these plants. In contrast seedlings from a near isogenic line of hexaploid wheat cultivar Thatcher containing Lr34 showed only a minor difference in rust growth when compared with Thatcher seedlings, typical of this adult plant resistance gene in hexaploid wheat. Little is known about how the Lr34 gene product functions; however, the seedling resistance of these durum transgenics enables functional assays to be readily undertaken without the need for adult plant material. By infecting seedlings we have shown that day length has an effect on Lr34 resistance to leaf rust, with higher levels of resistance observed under long days (16 h light) compared with short days (8 h light). This study demonstrates that Lr34 provides strong and presumably durable seedling resistance to rust in durum plants that can be used to further understand how this gene confers resistance.
Universidad de las Américas, Ecuador
Identifying and tracking new races of wheat rust pathogens in a timely manner is important for early warning of disease potential in wheat-growing regions. Ecuador, located in northwestern South America, serves as a strategic monitoring location for rust fungi between the wheat production areas of North and South America. New races are likely to occur more often when the fungus is in the proximity of the alternate Berberis species host. More than 30 Berberis species have been reported in Ecuador, most of them endemic. However, most herbarium collections correspond to types, have only been found once, and/or date back 20 years or more. Therefore, the current status of diversity in Berberis spp. in Ecuador is largely unknown. Our goal is to collect Berberis species in Ecuador, document their distribution, prepare herbarium specimens, and identify the species morphologically and genetically. We will use this information to establish the relationships of neotropical Berberis species with Berberis in other parts of the world, and determine the pathogenicities of various rust fungi associated with them. Preliminary results show that the Ecuadorian Berberis spp. are phylogenetically distinct from those of Argentina and Brazil. To date, the rust fungi on Ecuadorean Berberis do not infect wheat. We have identified three potentially new rust fungal species based on DNA analysis.
Institute of Phytopathology and Biodiversity, Batumi Shota Rustaveli State University, Georgia
Stem rust is a major threat to wheat production in Georgia. Breeding for resistance to the rusts is a major strategy for wheat improvement programs. Our objective was determination of the stem rust resistance levels in entries of the 4nd International Winter Wheat Stem Rust Resistance Nursery. Responses of 85 varieties/lines were evaluated in an inoculated field nursery. A coefficient of infection (CI) and area under the disease progress curve (AUDPC) were estimated for each entry. Fifteen entries (T03/17, TAM-107/T21, SD92107-2/SD99W042, KS95U522/TX95VA0011/F1/JAGGER, AR800-1-3-1/NW97S320, FL9547/NC00-14622, FL9547/TX00D1626, TAM302/KS93U450, MCCORMİCK/TREGO, NC00-14622/2137, TAM200/KAUZ//GOLDMARK/3/BETTY, KS920709-B-5-1-1/BURBOT-4, AFINA SOMNEZ, TAM200/KAUZ/4/BEZ/NAD//KZM(ES85.24/3/F900K) were resistant; 39 showed moderate resistance; 15 were scored MR-MS and 17 were moderately susceptible. Most of entries had very low CI (0.2 - 0.5) and AUPDC (less than 10.0); the best including T07/08, T07/09, T08/02, T08/01, T08/02, T08/04, CAKET/PEHLIVAN, ID800994.W/VEE//PIOPIO/3/MNCH/4/FDL4/KAUZ, PBI1013.13.3/3233.35 /3/STAR//KAUZ/STAR, DULGER-1//VORONA/BAU, ZANDER-17/3/YE2453/KA//1D13.1/MLT, 55-1744/7C//SU/RDL/3/CROW/4/MILAN/5/ITOR, 1D13.1/MLT//TUI/3/S?NMEZ/4/ATAY/GALVEZ87, TAM107//ATAY/GALVEZ87, HBF0290/X84W063-9-39-2//ARH/3/LE2301, STAR/BWD/3/PRL/VEE#6//CLMS, FRTL//AGRI/NAC/3/KALYOZ-17, CV. RODİNA/AE.SPELTOİDES10 KR, TAM 107//ATAY/ GALVEZ87, and 06393GP1. The severities for susceptible entries varied from 20 to 70%, with checks Morocco and Bezostaya 1 at 80% and 60%, respectively. However, the majority of entries (94%) had average CI of 0.2 - 20 and five entries with CI 21 - 40 had high to moderate levels of resistance.
Cereal Pathology Unit, Department of Cereal Research, Seed and Plant Improvement Institute (SPII), Iran
Resistance is an effective and economic method of controlling wheat stem rust provided the resistance gene(s) remains effective. We studied the stem rust responses of 372 synthetic hexaploid wheats (SHW) originally from CIMMYT under natural field infection conditions at Kelardasht, a stem rust hotspot. Stem rust severities were recorded using the modified Cobb scale prior to harvest ripeness. Seventy six and 17% of the genotypes (93% in total) were scored susceptible or moderately susceptible, whereas only 5 and 2% (7% in total) were moderately resistant or resistant, respectively. Based on our results, 26% of the genotypes were considered to have resistance, displaying field responses of 40MS to 20MSS. Those SHWs resistant to local Pgt races at Kelardasht could be used as sources of resistance in Iranian wheat breeding programs. Race analysis of Pgt isolates from the trials and seedling response tests on the entire SHW set are in progress.
Department of Plant Pathology, University of Minnesota, USA
The durability of stem rust resistance in wheat varieties is strengthened by the use of polygenic, and broad-spectrum sources of resistance. Adult plant resistance (APR) was observed in the mid-20th century Ecuadorian bread wheat cv. Morocho Blanco (PI 286545) in field tests at Njoro, Kenya, and at St. Paul. Morocho Blanco was susceptible to races TTKSK, RCRSC and TPMKC at the seedling stage. A doubled haploid (DH) mapping population was created from a cross between Morocho Blanco and the susceptible line LMPG-6 to identify loci associated with APR phenotypes. Eighty-eight DH lines were genotyped with approximately 90,000 SNPs using a custom Infinium assay from Illumina. Sixty-seven additional DH lines were used to verify SNPs associated with reduced stem rust levels. Severity and infection type were assessed on adult plants at the stem rust screening facility in Kenya in 2013 and 2014, and in two single race nurseries inoculated with races RCRSC and TPMKC at St. Paul in 2014. Two identified and verified QTL reducing stem rust severity were located on chromosome arms 2BS and 6AS. The QTL on 6AS also reduced infection type at Njoro, but a similar reduction was not observed at St. Paul suggesting a genotype x environment or genotype x race interaction. The QTL on 2BS was associated with reduced stem rust severity at both Njoro and St. Paul. It is a strong candidate for use in breeding for APR to stem rust.