Resistance of the Wheat Cultivar ‘Renan’ to Septoria Leaf Blotch Explained by a Combination of Strain Specific and Strain Non-Specific QTL Mapped on an Ultra-Dense Genetic Map

Quantitative resistance is considered more durable than qualitative resistance as it does not involve major resistance genes that can be easily overcome by pathogen populations, but rather a combination of genes with a lower individual effect. This durability means that quantitative resistance could be an interesting tool for breeding crops that would not systematically require phytosanitary products. Quantitative resistance has yet to reveal all of its intricacies. Here, we delve into the case of the wheat/Septoria tritici blotch (STB) pathosystem. Using a population resulting from a cross between French cultivar Renan, generally resistant to STB, and Chinese Spring, a cultivar susceptible to the disease, we built an ultra-dense genetic map that carries 148,820 single nucleotide polymorphism (SNP) markers. Phenotyping the interaction was done with two different Zymoseptoria tritici strains with contrasted pathogenicities on Renan. A linkage analysis led to the detection of three quantitative trait loci (QTL) related to resistance in Renan. These QTL, on chromosomes 7B, 1D, and 5D, present with an interesting diversity as that on 7B was detected with both fungal strains, while those on 1D and 5D were strain-specific. The resistance on 7B was located in the region of Stb8 and the resistance on 1D colocalized with Stb19. However, the resistance on 5D was new, so further designated Stb20q. Several wall-associated kinases (WAK), nucleotide-binding and leucine-rich repeats (NB-LRR) type, and kinase domain carrying genes were present in the QTL regions, and some of them were expressed during the infection. These results advocate for a role of Stb genes in quantitative resistance and for resistance in the wheat/STB pathosystem being as a whole quantitative and polygenic.

Winter wheat septoria blotch (Zymoseptoria tritici) (literature review)

In the Southern Federal District, winter wheat is a main food crop. One of the most important factors that can destabilize gross grain yields and reduce grain crop productivity are parasitic organisms. One of the most common wheat diseases is septoria blotch (Zymoseptoria tritici). The purpose of the current study was to analyze the biological cycle of distribution, harmfulness, measures to combat septoria blotch on winter wheat. The paper has considered the importance of winter wheat septoria disease in various countries and in Russia. There was noted a leading position in distribution and harmfulness of the disease, and according to the results of study conducted by Russian and foreign researchers, it was found that this pathogen was inferior in importance only to wheat rust. There were presented three types of septoria blotch pathogens and there was established a dominant type in the Southern Federal District. Yield losses caused by septoria blotch can reach upto 30-40%, and the optimal temperature for its development and spread is from 5 to 20°C, with frequent precipitation. There have been given the technological methods under which the crop damage by pathogens increased. There have been presented the measures to combat septoria blotch and there has been described the most effective, economical and environmentally friendly method, namely the development of resistant varieties and their introduction into production. There has been considered qualitative and quantitative resistance of varieties. Currently there have been identified 21 major septoria blotch resistance genes. There has been considered longevity of stb-genes and the reasons for its loss. It has been established that the development of winter wheat varieties resistant to septoria blotch is a priority issue of breeding, since this control measure reduces yield losses and potential reserve of the pathogen in the agrocenosis.

Selection of Diploid and Tetraploid Banana Hybrids Resistant to Pseudocercospora fijiensis

Black Sigatoka, a disease caused by the fungus Pseudocercospora fijiensis, can lead to the complete loss of banana and plantain production in the absence of chemical control. The development of resistant cultivars is the focus of many banana breeding programs and is an alternative to the use of fungicides. In order to define a refined method of selection in genetic breeding programs, this study evaluated 23 improved diploids, seven tetraploids, and two commercial cultivars in the presence of P. fijiensis. Four selection criteria were considered: means of the disease severity index (ID) and area under the disease progress curve (AUDPC) estimated over the total period of the experiment, only in summer, only in winter, and the emission and harvesting of bunches. The selection of genotypes was more effective in the winter, and the evaluation of four leaves no. 3 emitted after six months of growth was efficient at differentiating the resistant and susceptible genotypes. For the improved diploids and tetraploid hybrids, DI varied from 0.0 to 48.8 and from 15.1 to 63.5, respectively, and the AACPD for the improved hybrids and tetraploid hybrids varied from 0.0 to 2439.5 and 1000.2 to 3717.7, respectively. The tetraploid hybrid of the Prata-type CNPMF0906 and the commercial cultivar, which is a hybrid of the BRS Princesa Silk type, showed quantitative resistance and can be used by banana producers. Results suggest that the guidelines adopted for the selection of genotypes resistant to black Sigatoka may include methodologies that reduce the evaluation time. In addition, new sources of resistance to the disease and the influence of its genetic inheritance in future crosses were found.

Comparison of non-subjective relative fungal biomass measurements to quantify the Leptosphaeria maculans—Brassica napus interaction

Background Blackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is a serious threat to canola (Brassica napus) production worldwide. Quantitative resistance to this disease is a highly desirable trait but is difficult to precisely phenotype. Visual scores can be subjective and are prone to assessor bias. Methods to assess variation in quantitative resistance more accurately were developed based on quantifying in planta fungal biomass, including the Wheat Germ Agglutinin Chitin Assay (WAC), qPCR and ddPCR assays. Results Disease assays were conducted by inoculating a range of canola cultivars with L. maculans isolates in glasshouse experiments and assessing fungal biomass in cotyledons, petioles and stem tissue harvested at different timepoints post-inoculation. PCR and WAC assay results were well correlated, repeatable across experiments and host tissues, and able to differentiate fungal biomass in different host-isolate treatments. In addition, the ddPCR assay was shown to differentiate between L. maculans isolates. Conclusions The ddPCR assay is more sensitive in detecting pathogens and more adaptable to high-throughput methods by using robotic systems than the WAC assay. Overall, these methods proved accurate and non-subjective, providing alternatives to visual assessments to quantify the L. maculans-B. napus interaction in all plant tissues throughout the progression of the disease in seedlings and mature plants and have potential for fine-scale blackleg resistance phenotyping in canola.

Identity of genes of resistance to broomrape race G in sunflower lines of different origin

Broomrape is an obligate parasite and one of the most significant biotic factors reducing sunflower yield. The main means of controlling broomrape is breeding for sunflower resistance to it. New strategies are required to develop parasite resistant breeding germplasm, such as a stacking of key genes or a combination of qualitative and quantitative resistance mechanisms. In this regard, it is necessary to keep searching for new sources of resistance and to combine existing genes in case they are not identical. Thus, it is necessary to determine whether the genes of resistance to race G of broomrape are identical in the sunflower lines bred at the V.S. Pustovoit All-Russian Research Institute of Oil Crops. The research material was the previously developed sunflower lines RG, RGP1, RGP2, RGВ, RGL1, RGL2, and RGM – donors of resistance to race G of broomrape. The F1 hybrids from pair crossbreeding of these lines were obtained in a greenhouse. The F2 hybrids were obtained in the field by self-pollination of F1 hybrid plants. Plants were tested in a greenhouse for resistance and susceptibility to broomrape using the method of early diagnosis. Mathematical processing was performed by using the χ 2 -test. 13 combinations of crossbreeding were received to complete the test for allelism. In each F1 combination 11–33 plants were evaluated for resistance to race G of broomrape. Among the tested combinations, there was no one resistant to broomrape. Despite the differences in the number of affected plants, the affection degree was small in all hybrid combinations – from 1.0 to 1.8. All F2 hybrid combinations were also affected by broomrape. For eight combinations of F2, two phenotypic classes were found. There was no segregation in three combinations. The number of plants of two combinations was too small to perform χ 2 -test. In general, the χ 2 values were higher than the acceptable ones with a probability of 0.05, which indicates that the genes of resistance to race G of broomrape in these lines are identical.

In vitro variation in pathogenicity of Fusarium species causing head blight in relation to their isolation from barley head

Till now, no published study is available on the variation in pathogenicity of Fusarium head blight (FHB) pathogens in relation to their isolation origin in barley head. To end this, two barley cultivars of contrasting quantitative resistance were artificially infected by four FHB species under field conditions over two consecutive growing seasons. Then, pathogenicity tests were conducted under in vitro conditions on single-spore cultures originated from both kernels and glumes in the heads. Different pathogenicity was detected among Fusarium species originated from both kernels and glumes, indicating that the same isolate from glumes and kernels differs in pathogenicity on leaves/seedlings. Isolates of Fusarium culmorum and Fusarium verticillioides originated from infected kernels had shorter latent periods and higher area under disease progress curves compared to isolates originated from glumes, and the reverse was observed for the Fusarium equiseti isolate. In the case of Fusarium solani, isolates originated from kernels or from glumes were equally pathogenic. Primarily findings in this first in-depth study have implications for breeding programs relied principally on actual quantification of pathogenicity in Fusarium species present in a given environment. The sampling of fungi should take into account the presence of Fusarium species of interest on kernels or glumes.

Comparative association mapping reveals conservation of major gene resistance to white pine blister rust in southwestern white pine (Pinus strobiformis) and limber pine (P. flexilis)

All native North American white pines are highly susceptible to white pine blister rust (WPBR) caused by Cronartium ribicola. Understanding genomic diversity and molecular mechanisms underlying genetic resistance to WPBR remains one of the great challenges in improvement of white pines. To compare major gene resistance (MGR) present in two species, southwestern white pine (Pinus strobiformis) Cr3 and limber pine (P. flexilis) Cr4, we performed association analyses of Cr3-controlled resistant traits using SNP assays designed with Cr4-linked polymorphic genes. We found that ~ 70% of P. flexilis SNPs were transferable to P. strobiformis. Furthermore, several Cr4-linked SNPs were significantly associated with the Cr3-controlled traits in P. strobiformis families. The most significantly associated SNP (M326511_1126R) almost co-localized with Cr4 on the Pinus consensus linkage group 8 (LG-8), suggesting that Cr3 and Cr4 might be the same R locus, or have localizations very close to each other in the syntenic region of the P. strobiformis and P. flexilis genomes. M326511_1126R was identified as a non-synonymous SNP, causing amino acid change (Val376Ile) in a putative pectin acetylesterase (PAE), with coding sequences identical between the two species. Moreover, top Cr3-associated SNPs were further developed as TaqMan genotyping assays, suggesting their usefulness as marker-assisted selection (MAS) tools to distinguish genotypes between quantitative resistance (QR) and MGR. This work demonstrates the successful transferability of SNP markers between two closely related white pine species in the hybrid zone, and the possibility for deployment of MAS tools to facilitate long-term WPBR management in P. strobiformis breeding and conservation.

Spatiotemporal Changes in Varietal Resistance to Wheat Yellow Rust in France Reveal an Increase in Field Resistance Level During the Period 1985–2018

Monitoring spatiotemporal changes in varietal resistance and understanding its drivers seem essential to managing plant diseases but require having access to the genetic basis of disease resistance and to its deployment. In this study, we focused on yellow rust (Puccinia striiformis f. sp. tritici ) for three decades in France, by using field adult plant resistance levels, Yr race-specific resistance genes of varieties, presence of Puccinia striiformis f. sp. tritici pathotypes and their virulence profiles, and systematic surveys of the acreages of bread wheat varieties available at a yearly survey time and at a district level. Based on these data, we studied spatiotemporal changes in varietal resistance over the period from 1985 to 2018 in 54 French administrative districts (hereafter “departments”) by using a set of relevant indicators weighted by the relative acreage proportion of the varieties sown at the department level. Our analyses revealed an increase in varietal resistance over decades that would be due to the accumulation of both quantitative resistance and different race-specific resistance genes. We suggest that, beyond breeders, several actors, including examination offices, agricultural advisory services, and farmers, may have had a substantial influence on these spatiotemporal changes, promoting more resistant varieties and the rapid replacement of newly susceptible varieties by still resistant ones at the beginning of each epidemic.