Qfhi.nau-4B is a major quantitative trait locus (QTL) against Fusarium graminearum infection identified in the Fusarium head blight-resistant germplasm Wangshuibai. To fine map this QTL, a recombinant inbred line (RIL) population of 530 lines derived from Nanda2419 x Wangshuibai and the BC(3)F(2) population derived from the cross of a Qfhi.nau-4B near isogenic line (NIL) with susceptible cultivar Mianyang 99-323 as the recurrent parent were screened for recombinants occurred between microsatellite markers Xbarc20 and Xwmc349 that flank Qfhi.nau-4B. A total of 95 recombinants were obtained, including 45 RIL recombinants obtained through reverse-selection of Qfhi.nau-5A and 50 NIL recombinants from the BC(3)F(2) population. Genotyping these recombinant lines with 22 markers mapping to the Xbarc20 and Xwmc349 interval revealed fourteen genotypes of the RIL recombinants as well as of the NIL recombinants. Two-year field evaluation of their resistance to Fusarium infection showed that these lines could be clearly classified into two groups according to percentage of infected spikes. The more resistant class had over 60% less infection than the susceptible class and were common to have Wangshuibai chromatin in the 1.7-cM interval flanked by Xhbg226 and Xgwm149. None of the susceptible recombinants had this Wangshuibai chromatin. Qfhi.nau-4B was thus confined between Xhbg226 and Xgwm149 and named Fhb4. The interval harboring Fhb4 was mapped to 4BL5-0.86-1.00 bin using Chinese Spring deletion lines, a region with about 5.7 times higher recombination rate than the genome average. This study established the basis for map-based cloning of Fhb4.

Fine mapping Fhb4, a major QTL conditioning resistance to Fusarium infection in bread wheat (Triticum aestivum L.)

Stripe rust is best controlled by utilizing genetic resistance. Resistance to stripe rust has been studied for more than a century, but most progresses have been made during the last three decades. Two major types of resistance, all-stage resistance (ASR) and adult-plant resistance (APR) or high-temperature adult-plant (HTAP) resistance, have been characterized and used in breeding for resistant cultivars in both wheat and barley. So far, 78 permanently named, 67 temporarily designated and 327 quantitative trait loci (QTL) have been reported in various wheat varieties. The majority of these genes and QTL have been located to wheat chromosomes. Although some of the genes or QTL are the same, these numbers indicate that there are abundant resistance genes in wheat germplasm, which can be used for improving stripe rust resistance in commercially grown cultivars. Although the number is smaller, more than 50 resistance loci have been reported in barley for resistance to stripe rust, and about 30 loci have been mapped to barley chromosomes. Based on the characteristics of different types of resistance and the rich sources of resistance genes and molecular markers, we discuss different strategies for developing resistant cultivars and propose to use the combination of genes for durable APR or HTAP resistance and effective ASR to achieve more effective and sustainable control of stripe rust.

Stripe Rust Resistance

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici Erikss., is a severe foliar disease of common wheat (Triticum aestivum L.) worldwide. Use of adult-plant resistance (APR) is an efficient approach to provide long-term protection of crops from the disease. The German spring wheat cultivar Naxos showed a high level of APR to stripe rust in the field. To identify the APR genes in this cultivar, a mapping population of 166 recombinant inbred lines (RILs) was developed from a cross between Naxos and Shanghai 3/Catbird (SHA3/CBRD), a moderately susceptible line developed by CIMMYT. The RILs were evaluated for maximum disease severity (MDS) in Sichuan and Gansu in the 2009–2010 and 2010–2011 cropping seasons. Composite interval mapping (CIM) identified four QTL, QYr.caas-1BL.1RS, QYr.caas-1DS, QYr.caas-5BL.3 and QYr.caas-7BL.1, conferring stable resistance to stripe rust across all environments, each explaining 1.9–27.6, 2.1–5.8, 2.5–7.8 and 3.7–9.1 % of the phenotypic variance, respectively. QYr.caas-1DS flanked by molecular markers XUgwm353–Xgdm33b was likely a new QTL for APR to stripe rust. Because the interval between flanking markers for each QTL was less than 6.5 cM, these QTL and their closely linked markers are potentially useful for improving resistance to stripe rust in wheat breeding.

QTL mapping of adult-plant resistance to stripe rust in a population derived from common wheat cultivars Naxos and Shanghai 3/Catbird

https://www.scielo.cl/pdf/ejb/v14n3/a09.pdf

Identification of leaf rust resistance genes in selected Argentinean bread wheat cultivars by gene postulation and molecular markers

The genetic bottlenecks associated with plant domestication and subsequent selection in man-made agroecosystems have limited the genetic diversity of modern crops and increased their vulnerability to environmental stresses. Wild emmer wheat, the tetraploid progenitor of domesticated wheat, distributed along a wide range of ecogeographical conditions in the Fertile Crescent, has valuable “left behind” adaptive diversity to multiple diseases and environmental stresses. The biotic and abiotic stress responses are conferred by series of genes and quantitative trait loci (QTLs) that control complex resistance pathways. The study of genetic diversity, genomic organization, expression profiles, protein structure and function of biotic and abiotic stress-resistance genes, and QTLs could shed light on the evolutionary history and adaptation mechanisms of wild emmer populations for their natural habitats. The continuous evolution and adaptation of wild emmer to the changing environment provide novel solutions that ...

Evolution and Adaptation of Wild Emmer Wheat Populations to Biotic and Abiotic Stresses

The rust resistance genes Lr53 and Yr35, transferred to common wheat from Triticum dicoccoides, were reported previously to be completely linked on chromosome 6B. Four F3 families were produced from a cross between a line carrying Lr53 and Yr35 (98M71) and the leaf rust and stripe rust susceptible genotype Avocet “S” and were rust tested using Puccinina triticina pathotype 53-1,(6),(7),10,11 and Puccinia striiformis f. sp. tritici pathotype 110 E143 A+. The homozygous resistant lines produced infection types of “;1−” and “;N” to these pathotypes, respectively. The Chi-squared tests indicated goodness-of-fit of the data for one leaf rust gene and one stripe rust gene segregation. Linkage analysis using this population demonstrated recombination of 3% between the genes. Microsatellite markers located on the short arm of chromosome 6B were used to map the genes, with the markers cfd1 and gwm508 being mapped approximately 1.1 and 4.5 cM, respectively, proximal to Lr53. Additional studies of the relationship between Lr36, also located on the short arm of chromosome 6B, and Lr53 indicated that the two genes were independent.

H. Karaoglou

Papers

Mapping genes Lr53 and Yr35 on the short arm of chromosome 6B of common wheat with microsatellite markers and studies of their association with Lr36