Search

Developing wheat varieties with durable resistance is a core objective of the InternationalMaize andWheat Improvement Center (CIMMYT) andmany other breeding programs worldwide. The CIMMYT advanced wheat line “Mucuy” displayed high levels of resistance to stripe rust (YR) and leaf rust (LR) in field evaluations in Mexico and several other countries. To determine the genetic basis of YR and LR resistance, 138 F5 recombinant inbred lines (RILs) derived from the cross of Apav#1× Mucuy were phenotyped for YR responses from 2015 to 2020 at field sites in India, Kenya, and Mexico, and LR in Mexico. Seedling phenotyping for YR and LR responses was conducted in the greenhouse in Mexico using the same predominant races as in field trials. Using 12,681 polymorphic molecular markers from the DArT, SNP, and SSR genotyping platforms, we constructed genetic linkage maps and QTL analyses that detected seven YR and four LR resistance loci. Among these, a co-located YR/LR resistance loci was identified as Yr29/Lr46, and a seedling stripe rust resistance gene YrMu was mapped on the 2AS/2NS translocation. This fragment also conferred moderate adult plant resistance (APR) under all Mexican field environments and in one season in Kenya. Field trial phenotyping with Lr37-virulent Puccinia triticina races indicated the presence of an APRQTL accounting for 18.3–25.5% of the LR severity variation, in addition to a novel YR resistance QTL, QYr.cim-3DS, derived fromMucuy.We developed breeder- friendly KASP and indelmolecularmarkers respectively for Yr29/Lr46 and YrMu. The current study validated the presence of known genes and identified new resistance loci, a QTL combination effect, and flanking markers to facilitate accelerated breeding for genetically complex, durable rust resistance. [ABSTRACT FROM AUTHOR]

Leaf rust on wheat caused by Puccinia triticina Eriks. is a disease widespread in all parts of the world where wheat is a main cereal crop. The race, pathotype and genetic variability of the pathogen's population in Bulgaria were investigated. The virulence of the pathogen population was studied on Thatcher near isogenic lines with genes Lr1, Lr2a, Lr2b, Lr2c, Lr3, Lr9, Lr11, Lr15, Lr17, Lr19, Lr21, Lr23, Lr24, Lr26 and Lr28. A total of 221 isolates were analyzed. Seventy-one phenotypically different pathotypes were identified. Pathotypes 63562, 63573 and 63762 had the highest frequency of occurrence. For the first time in this population 25 entirely new pathotypes were identified. The genetic variability was represented by 86 genetic formulae for virulence. The most common combination was 1, 9, 15, 19, 24, 28 / 2a, 2b, 2c, 3, 11, 17, 21, 23, 26 (37.9%). The genes for resistance demonstrated variable efficiency. During this period the immunity was conferred by the following genes: Lr22a, Lr22b and Lr43. Genes Lr1, Lr3ka, Lr9, Lr19, Lr25, Lr28, Lr40, Lr41, Lr42, Lr45, Lr47 and Lr50 demonstrated very good to high efficiency. During the investigated period, pathotypes were found which were overcoming the resistance of the two strong genes Lr9 and Lr19. [ABSTRACT FROM AUTHOR]

In Mitteleuropa sind auf Weizen (Triticum aestivum) drei Rostpilzarten (Pucciniales) bekannt, nämlich der Schwarzrost (Puccinia graminis), der Gelbrost (P. striiformis) und der Braunrost (P. triticina). Diese Arten sind ökonomisch bedeutend. Um sie zu überwachen, frühzeitig zu erkennen und Ernteeinbußen zu minimieren, ist eine schnelle und korrekte Bestimmung der Pilzarten nötig. Hier wurde eine einfache lichtmikroskopische Methode optimiert und getestet, bei der Keimporenmerkmale der Urediniosporen zur Artdifferenzierung herangezogen werden. Die Methode lässt eine eindeutige Bestimmung zu. Die Ergebnisse werden mit Sequenzanalysemethoden in Bezug auf Bestimmungssicherheit, Zeitaufwand und Material­kosten verglichen.

In Central Europe there are three wheat rusts (Pucciniales) all of which are economically important. These are the (black) stem rust or wheat stem rust (Puccinia graminis), the leaf rust (P. triticina) and the stripe rust (P. striiformis). In order to monitore or control them effectively, efficient and reliable identification methods are needed. Here, a simple light-microscopical (phase contrast) method using germ pore features of urediniospores for identification is presented. This method makes it possible to identify the rust species exactly. In the present study this method is compared with the ITS sequence analyses with respect to identification accuracy, time and material costs. [ABSTRACT FROM AUTHOR]

Marker-trait associations identified in diverse germplasm can be exploited in crop improvement programs. An attempt to establish such associations was made by evaluating 205 wheat landraces for stripe rust, leaf rust and stem rust responses in the field over three crop seasons. Diversity arrays technology was used to genotype the landraces and associations were identified using a single-marker scan. Sixty-eight markers were significantly associated with rust resistance. Several significantly associated loci coincided with the presence of known major genes or QTL for rust resistance. In contrast, many marker-rust response associations identified in this analysis for each of the three rust diseases uncovered new loci. Dual associations; stripe rust-leaf rust (1AL, 2BS, 2BL, 3DL, 5BS, 6BS and 7DL), leaf rust-stem rust (5BL) and stripe rust-stem rust (4BL and 6AS) resistance were also observed. These associations could enable a cost-effective targeted mapping of dual rust resistance. Some marker-trait associations identified in this study have been validated through genetic analyses and formal naming of resistance loci. [ABSTRACT FROM AUTHOR]

Developing wheat varieties with durable resistance is a core objective of the International Maize and Wheat Improvement Center (CIMMYT) and many other breeding programs worldwide. The CIMMYT advanced wheat line "Mucuy" displayed high levels of resistance to stripe rust (YR) and leaf rust (LR) in field evaluations in Mexico and several other countries. To determine the genetic basis of YR and LR resistance, 138 F 5 recombinant inbred lines (RILs) derived from the cross of Apav#1× Mucuy were phenotyped for YR responses from 2015 to 2020 at field sites in India, Kenya, and Mexico, and LR in Mexico. Seedling phenotyping for YR and LR responses was conducted in the greenhouse in Mexico using the same predominant races as in field trials. Using 12,681 polymorphic molecular markers from the DArT, SNP, and SSR genotyping platforms, we constructed genetic linkage maps and QTL analyses that detected seven YR and four LR resistance loci. Among these, a co-located YR/LR resistance loci was identified as Yr29/Lr46 , and a seedling stripe rust resistance gene YrMu was mapped on the 2AS/2NS translocation. This fragment also conferred moderate adult plant resistance (APR) under all Mexican field environments and in one season in Kenya. Field trial phenotyping with Lr37 -virulent Puccinia triticina races indicated the presence of an APR QTL accounting for 18.3-25.5% of the LR severity variation, in addition to a novel YR resistance QTL, QYr.cim-3DS , derived from Mucuy. We developed breeder-friendly KASP and indel molecular markers respectively for Yr29 / Lr46 and YrMu . The current study validated the presence of known genes and identified new resistance loci, a QTL combination effect, and flanking markers to facilitate accelerated breeding for genetically complex, durable rust resistance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Liu, Yuan, Singh, Randhawa, Bhavani, Kumar, Huerta-Espino, Lagudah and Lan.)

Cereal rust fungi are pathogens of major importance to agriculture, threatening cereal production worldwide. Targeted breeding for resistance, based on information from fungal surveys and population structure analyses of virulence, has been effective. Nevertheless, breakdown of resistance occurs frequently and continued efforts are needed to understand how these fungi overcome resistance and to determine the range of available resistance genes. The development of genomic resources for these fungi and their comparison has released a torrent of new ideas and approaches to use this information to assist pathologists and agriculture in general. The sequencing of gene transcripts and the analysis of proteins from haustoria has yielded candidate virulence factors among which could be defence-triggering avirulence genes. Genome-wide computational analyses, including genetic mapping and transcript analyses by RNA sequencing of many fungal isolates, will predict many more candidates. Functional assays, such as leaf infiltration using Agrobacterium for delivery of cloned fungal effectors, are being developed. This will allow the screening of wheat germplasm for novel resistance genes for breeding. Comparative analyses have also revealed fungal virulence genes, providing fungal targets for disease control in host-produced RNAi approaches. [ABSTRACT FROM AUTHOR]