Rust Isolates Research Articles

Confirmation of oat crown rust disease in Taiwan.

Oat is a minor forage crop grown in Taiwan. Only a few historical records of oat rust disease have been reported in the country. Therefore, the pathogen population remains poorly characterized. A rust-like disease outbreak was detected at the Experimental Farm of National Taiwan University in 2019, which caused significant damage to field experiments. To determine the identity of the pathogen responsible for this disease outbreak, we collected infected foliar material. Disease signs suggested infection by the oat crown rust fungus. Hence, common procedures in rust pathology were applied to confirm the identity of the pathogen with phenotypic and molecular diagnostic techniques. A total of 50 field pathogen samples from infected oat cultivars were collected in 2019 and five single pustule rust isolates were obtained in 2020 and 2021. These isolates were initially identified as Puccinia coronata var. avenae f. sp. avenae (Pca) based on the phylogenetic analysis of nrITS sequence data. This identification was subsequently confirmed through whole-genome phylogeny, which showed that the representative Taiwanese isolate NTU1 clustered with other Pca representative strains in Basidiomycota. Phenotyping assays across 36 oat differential lines demonstrated that Taiwanese isolates are phenotypically similar with relatively low virulence. This study presents the first molecular confirmation of Pca in Taiwan and reports the virulence profiles of Taiwanese Pca population.

Virulence analysis of wheat stem rust isolates (Puccinia graminis f. sp. tritici) in Iran using differential lines

Virulence analysis of wheat stem rust isolates (Puccinia graminis f. sp. tritici) in Iran using differential lines

First Report of Rust Caused by Phakopsora nishidana on Creeping Fig, Ficus pumila, in South Africa.

Phakopsora nishidana has recently been reported as the causal organism of rust on edible fig, Ficus carica in South Africa (SA) (Boshoff et al. 2022). This contradicted reports by Doidge (1927, 1950) and Verwoerd (1929) who listed Cerotelium fici as the causal organism of the disease in SA. Similarities in urediniospore morphology and differing taxonomic interpretations most likely contributed to the use of both pathogen names as the causal agents for fig rust (Boshoff et al. 2022; Padamsee and McKenzie 2024). In January 2023 rust was commonly observed on nursery specimens of creeping fig, Ficus pumila, a popular evergreen and fast-growing garden plant in SA. Ficus pumila is native to southern China, Indochina, and eastern Asia but has been introduced to many countries worldwide (https://powo.science.kew.org/ accessed 20 March 2024). The F. pumila rust isolate collected in Somerset West (34°07'00.70"S, 18°52'41.75"E; Western Cape (WC) province) was identified using the sequenced 5.8S rRNA-ITS2-28S rRNA locus. When used in a BLAST analysis, this F. pumila isolate (GenBank accession number OR835538) shared the best homology with the Vermont P. nishidana isolate (34°24'33.37"S, 19°08'59.24"E) (MZ047090; e-value 0.0, 99.7% identity, 1400/1404 bp) reported on edible fig by Boshoff et al. (2022). Other P. nishidana isolates with excellent homology were KY764080 (e-value 0.0, 99.8% identity, 1012/1014 bp), KY764081 (e-value 0.0, 99% identity, 882/885 bp) and MF580676 (e-value 0.0, 99.3% identity, 981/988 bp). Accessions were used in a phylogenetic study that included four other rust samples collected from F. carica trees in Somerset West, WC (OR835534; 34°03'37.26"S, 18°51'02.18"E), Onrus River, WC (OR835535; 34°24'43.10"S, 19°09'57.99"E), Elgin, WC (OR835536; 34°14'31.37"S, 19°03'05.38"E), and Bloemfontein, Free State province (OR835537; 29°05'05.1"S 26°09'09.5"E). Reference sequences were as described in Boshoff et al. (2022). Despite limited variation, all six South African isolates, including the F. pumila isolate, grouped with the three P. nishidana reference isolates, but separate from the three P. myrtacearum isolates collected from eucalyptus trees (Maier et al. 2016). Uredinia on F. pumila leaves were mostly hypophyllous and surrounded by a halo of brown, necrotic tissue. On the upper leaf surface, the lesions appeared as small, dark leaf spots with infrequent sporulation. Urediniospores were echinulate, mostly obovoid or elliptical and their cell walls pale-yellow to yellowish-brown. The mean width and length of urediniospores were 16.7 x 21.3 µm. No telia were observed. Applying standard rust inoculation and incubation procedures (Boshoff et al. 2022), F. pumila plants inoculated with P. nishidana isolate PREM63073 produced sporulating uredinia on the abaxial surface of leaves. Likewise, inoculation of F. carica cv. Kadota leaves with the F. pumila isolate OR835538 yielded sporulating lesions containing urediniospores typical of P. nishidana, on the lower surface. Based on both the DNA sequence data and controlled infection studies, our study confirmed the host status of F. pumila for P. nishidana. The occurrence of rust on creeping fig plants in nurseries, the evergreen status of the creeper, and thus the potential to harbor the pathogen during winter, are likely to contribute to the spread of fig rust in SA.

Morphological and molecular characterization of the rust fungus, Phakopsora apoda causing leaf rust on Brachiaria grass in Rwanda

Brachiaria grass is one of the major forages that plays a key role in push pull technology. Different diseases including leaf rust caused by rust fungus, Phakopsora apoda have recently become an important challenge resulting in yield loss of Brachiaria grass in different countries including Rwanda. The objective of this study was to provide morphological and molecular characteristics of Phakopsora apoda causing Brachiaria leaf rust. Spores isolated from rusted Brachiaria leaves collected in five districts of Rwanda were analyzed. Samples were put in paper bags and left at room temperature for two days. Thereafter, spores were removed using brushes and put in eppendorf tubes, stored at 4oC in darkness for further characterization. For morphological characteristics, colour and measurements of spores were recorded using Optika B-350 microscope with installed camera and calibrated micrometer. Multigene analysis using rust specific primers and large subunit (LSU) of nuclear ribosomal RNA was performed for molecular characterization. The results indicated that the colour of spores was yellowish or brownish while the shape was ellipsoidal or circular with average measurements of 25.1µm and 16.8µm for length and width respectively. Primers amplified the size of DNA between 1291bp and 1381bp and the size between 874bp to 882bp for rust specific primers and LSU respectively. The identity of the sequence was 96% with e-value of 0, sequence coverage of 60% for rust primer and the sequence identity was 94.97% to 95.37%, sequence coverage of 99% to 100% and e-value of 0 for LSU primer. All sequences recovered from five isolates of leaf rust matched to the genebank accession number MG461668.1 for both rust specific and LSU sequences. The results of this study provide useful information to develop effective options for leaf rust disease management in Rwanda. Key words: Internal transcribed spacer, large subunit, nuclear ribosomal RNA, Phakopsora apoda, sequence, spore.

Single amino acid change alters specificity of the multi-allelic wheat stem rust resistance locus SR9

Most rust resistance genes thus far isolated from wheat have a very limited number of functional alleles. Here, we report the isolation of most of the alleles at wheat stem rust resistance gene locus SR9. The seven previously reported resistance alleles (Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, Sr9g, and Sr9h) are characterised using a synergistic strategy. Loss-of-function mutants and/or transgenic complementation are used to confirm Sr9b, two haplotypes of Sr9e (Sr9e_h1 and Sr9e_h2), Sr9g, and Sr9h. Each allele encodes a highly related nucleotide-binding site leucine-rich repeat (NB-LRR) type immune receptor, containing an unusual long LRR domain, that confers resistance to a unique spectrum of isolates of the wheat stem rust pathogen. The only SR9 protein effective against stem rust pathogen race TTKSK (Ug99), SR9H, differs from SR9B by a single amino acid. SR9B and SR9G resistance proteins are also distinguished by only a single amino acid. The SR9 allelic series found in the B subgenome are orthologs of wheat stem rust resistance gene Sr21 located in the A subgenome with around 85% identity in protein sequences. Together, our results show that functional diversification of allelic variants at the SR9 locus involves single and multiple amino acid changes that recognize isolates of wheat stem rust.

Genetic diversity and structure of the coffee leaf rust fungus Hemileia vastatrix across different coffee management systems in Ethiopia.

Although coffee leaf rust (CLR), caused by Hemileia vastatrix, poses an increasing threat to coffee production in Ethiopia, little is known regarding its genetic diversity and structure and how these are affected by coffee management. Here, we used genetic fingerprinting based on sequence-related amplified polymorphism (SRAP) markers to genotype H. vastatrix samples from different coffee shrubs, across 40 sites, covering four coffee production systems (forest coffee, semi plantation coffee, home garden coffee, and plantation coffee) and different altitudes in Ethiopia. In total, 96 H. vastatrix samples were successfully genotyped with three primer combinations, producing a total of 79 scorable bands. We found 35.44% of amplified bands to be polymorphic, and the polymorphic information content (PIC) was 0.45, suggesting high genetic diversity among our CLR isolates. We also found significant isolation-by-distance across the samples investigated and detected significant differences in fungal genetic composition among plantation coffee and home garden coffee and a marginally significant difference among plantation coffee and forest coffee. Furthermore, we found a significant effect of altitude on CLR genetic composition in the forest coffee and plantation systems. Our results suggest that both spore dispersal and different selection pressures in the different coffee management systems are likely responsible for the observed high genetic diversity and genetic structure of CLR isolates in Ethiopia. When selecting Ethiopian coffee genotypes for crop improvement, it is important that these genotypes carry some resistance against CLR. Because our study shows large variation in genetic composition across relatively short geographical distances, a broad selection of rust isolates must be used for coffee resistance screening.

Seeing red: a modified RUBY reporter assay for visualizing inplanta protein-protein interactions.

Seeing red: a modified RUBY reporter assay for visualizing inplanta protein-protein interactions.

Mapping of leaf rust resistance genes in common wheat ‘Guinong08-6’

Wheat leaf rust (Puccinia triticina Eriks.), a devastating disease of wheat in the world, causes severe yield losses and therefore the development of resistant cultivars is very important. Here, a Chinese wheat line (Guinong08-6) showed adult-plant resistance against mixed fungal isolates of leaf rust, which is common in Guiyang region. It was crossed with a susceptible wheat line (Guinong19) to develop F1, F2, and F3 hybrids. Combined SSR and STS markers were used to map leaf rust resistance genes in Guinong08-6, and the resistance phenotype of Guinong08-6 was co-regulated by two complementary dominant genes, named LrGn08-6A and LrGn08-6B. LrGn08-6A was mapped to chromosome 2AS with markers URIC-LN2 and Xgpw2204, which flanked the gene at distances of 1.8 centimorgan (cM) and 14.83 cM, respectively. LrGn08-6B was mapped to chromosome 4DL with markers Xgpw342 and Xbarc93, which both flanked the gene at a distance of 26.57 cM. Genetic and molecular marker analyses demonstrated that LrGn08-6A, which was inherited from Aegilops ventricosa may be the resistance gene Lr37, while LrGn08-6B may be a newly discovered leaf rust resistance gene.

Virulence of Puccinia triticina and Puccinia tritici-duri on durum wheat in southern Spain, from 2020 to 2022

Leaf rust is a major wheat disease in southern Spain, where durum wheat is an important crop. Until the 2019/2020 season, this disease was effectively managed, as the most widely planted cultivars in southern Spain had effective resistance genes. A problem arose in the spring of 2020, when every farm field and durum wheat trial examined displayed leaf rust symptoms. Leaves had few but large uredinial pustules, different from those of the normal leaf rust caused by Puccinia triticina, and telia developed rapidly after only a few days. The symptoms clearly fitted with P. tritici-duri, another wheat leaf rust species already reported in the western Mediterranean Basin. This species is not new in southern Spain but has never been observed at such high severity on almost every durum wheat cultivar grown in that region. Leaf rust severity was assessed in durum wheat field trials in the 2020, 2021 and 2022 growing seasons in four provinces of southern Spain. During 2020 and 2021, 13 single pustule isolates of leaf rust were also collected from different cultivars of durum wheat. Inoculation of the isolates on a differential host set showed that four different races were present, two being of P. tritici-duri. Only cultivar Calero showed consistent resistance to the races of P. tritici-duri employed in this study.

Identification and Characterization of Resistance to Rust in Lentil and Its Wild Relatives.

Lentil rust is a major disease worldwide caused by Uromyces viciae-fabae. In this study, we screened a large germplasm collection of cultivated lentils (Lens culinaris ssp. culinaris) and its wild relatives, both in adult plants in the field with a local rust isolate during 2 seasons and in seedlings under controlled conditions with four fungal isolates of worldwide origin. The main results from our study were the following: (1) a significant number of accessions with resistance based on hypersensitive reaction (reduced Infection Type (IT)) were identified in cultivated lentil and in L. ervoides, L. nigricans and L.c. orientalis. The IT scores showed a clear isolate-specific response suggesting race-specificity, so each fungal isolate might be considered a different race. Resistance was identified against all isolates what might be the basis to develop a standard differential set that should be a priority for rust definition and monitoring. (2) Interestingly, although at lower frequency than in L. ervoides and L. nigricans, the hypersensitive response was also observed within cultivated lentil, with accession 1561 (L.c. culinaris) displaying resistance to the four isolates making this accession a valuable ready-to-use resource for lentil resistance breeding. Resistance to all other rust isolates was also available within L.c. culinaris in an isolate-specific manner. Accession 1308 (L. ervoides) showed resistance against all isolates tested, as well as a reduced number of accessions belonging to other wild Lens species. (3) In addition, our screenings allowed the identification of several accessions with partial resistance (reduced Disease Severity (DS) despite high IT). Adult Plant Resistance resulting in reduced severity in adult plants in the field, despite high susceptibility in seedlings, was more frequently identified in L.c. culinaris, but also in L. nigricans and L.c. orientalis.

Molecular and cytogenetic dissection of stripe rust resistance gene Yr83 from rye 6R and generation of resistant germplasm in wheat breeding.

Rye 6R-derived stripe rust resistance gene Yr83 in wheat background was physically mapped to fraction length (FL) 0.87-1.00 on the long arm by non-denaturing-fluorescence in situ hybridization (ND-FISH), Oligo-FISH painting and 6R-specific PCR markers.Stripe rust resistance gene Yr83 derived from chromosome 6R of rye (Secale cereale) “Merced” has displayed high resistance to both Australian and Chinese wheat stripe rust isolates. With the aim to physically map Yr83 to a more precise region, new wheat- 6R deletion and translocation lines were produced from derived progenies of the 6R(6D) substitution line. The non-denaturing fluorescence in situ hybridization (ND-FISH) patterns of 6R were established to precisely characterize the variations of 6R in different wheat backgrounds. Comparative ND-FISH analysis localized the breakpoints of 6RL chromosomes relative to Oligo-pSc200 and Oligo-pSc119.2 rich sites in deletion lines. Molecular marker and resistance analyses confirmed that Yr83 is physically located at the fraction length (FL) 0.87-1.00 of 6RL and covers the corresponding region of 806-881 Mb in the reference genome of Lo7. Oligo-FISH painting demonstrated that the region carrying Yr83 is syntenic to the distal end of long arm of homoeologous group 7 of the Triticeae genome. The developed wheat-6R lines carrying the Yr83 gene will be useful for breeding for rust resistance.

Stem rust on barberry species in Europe: Host specificities and genetic diversity.

The increased emergence of cereal stem rust in southern and western Europe, caused by the pathogen Puccinia graminis, and the prevalence of alternate (sexual) host, Berberis species, have regained attention as the sexual host may serve as source of novel pathogen variability that may pose a threat to cereal supply. The main objective of the present study was to investigate the functional role of Berberis species in the current epidemiological situation of cereal stem rust in Europe. Surveys in 11 European countries were carried out from 2018 to 2020, where aecial infections from five barberry species were collected. Phylogenetic analysis of 121 single aecial clusters of diverse origin using the elongation factor 1-α gene indicated the presence of different special forms (aka formae speciales) of P. graminis adapted to different cereal and grass species. Inoculation studies using aecial clusters from Spain, United Kingdom, and Switzerland resulted in 533 stem rust isolates sampled from wheat, barley, rye, and oat, which confirmed the presence of multiple special forms of P. graminis. Microsatellite marker analysis of a subset of 192 sexually-derived isolates recovered on wheat, barley and rye from the three populations confirmed the generation of novel genetic diversity revealed by the detection of 135 multilocus genotypes. Discriminant analysis of principal components resulted in four genetic clusters, which grouped at both local and country level. Here, we demonstrated that a variety of Berberis species may serve as functional alternate hosts for cereal stem rust fungi and highlights the increased risks that the sexual cycle may pose to cereal production in Europe, which calls for new initiatives within rust surveillance, epidemiological research and resistance breeding.

Biochemical profiling of Brassica juncea doubled haploid mutant genotypes under white rust disease stress

White rust, caused by oomycete pathogen Albugo candida, is a serious disease for the crops of Brassicaceae family. It is an obligate pathogen responsible for up to 60% yield loss with combined infection of leaves and inflorescence across the globe. Biochemical variations in host plants can alter the content of proteins, sugars, phenols, iron content etc. enables to understand the biochemistry of host-pathogen interaction. Therefore, the present study was conducted during 2017-2019 at Amity University, Noida, Uttar Pradesh to evaluate the biochemical response of Brassica juncea var. Varuna and its doubled haploid (DH) mutant genotypes infected with A. candida causing white rust at cotyledonary leaf stage. The seven mutant genotypes were tested for pathogenic response against five white rust isolates (WRI). In the challenge assay, mutant genotypes C66 and C69 showed resistance response as compared to susceptible host B. juncea var. Varuna against different isolates on the basis of disease severity. The biochemical parameters were found to be high in the uninoculated genotypes in comparison to infected cotyledons of B. juncea genotypes. The biochemical profile emphasizes significant increase in content of protein, sugar, and phenol from highest in genotype C66 positively correlating with resistance response against pathogen in comparison to other mutant genotype C69 and susceptible check Varuna. The results suggest that factors conditioning the response of mutant genotypes to WRI may differ or control in different ways and triggers novel defense signaling.

Discovery of stripe rust resistance with incomplete dominance in wild emmer wheat using bulked segregant analysis sequencing

Durable crop disease resistance is an essential component of global food security. Continuous pathogen evolution leads to a breakdown of resistance and there is a pressing need to characterize new resistance genes for use in plant breeding. Here we identified an accession of wild emmer wheat (Triticum turgidum ssp. dicoccoides), PI 487260, that is highly resistant to multiple stripe rust isolates. Genetic analysis revealed resistance was conferred by a single, incompletely dominant gene designated as Yr84. Through bulked segregant analysis sequencing (BSA-Seq) we identified a 52.7 Mb resistance-associated interval on chromosome 1BS. Detected variants were used to design genetic markers for recombinant screening, further refining the interval of Yr84 to a 2.3–3.3 Mb in tetraploid wheat genomes. This interval contains 34 candidate genes encoding for protein domains involved in disease resistance responses. Furthermore, KASP markers closely-linked to Yr84 were developed to facilitate marker-assisted selection for rust resistance breeding.

Establishment and identification of six wheat-Thinopyrum ponticum disomic addition lines derived from partial amphiploid Xiaoyan 7430.

Six wheat-Thinopyrum ponticum disomic addition lines derived from partial amphiploid Xiaoyan 7430 were identified using in situ hybridization and SNP microarray, the homoeologous group and stripe rust resistance of each alien chromosome were determined, and Th. ponticum chromosome-specific markers were developed. Xiaoyan 7430 is a significant partial amphiploid, which is used to set up a bridge for transferring valuable genes from Thinopyrum ponticum (Podp.) Barkworth & D.R. Dewey into common wheat. To accelerate the application of these useful genes in enriching the genetic variability of cultivated wheat by chromosome engineering, a complete set of derived addition lines has been created from Xiaoyan 7430. The chromosome composition of each line was characterized by the combination of genomic in situ hybridization and multicolor fluorescence in situ hybridization (mc-FISH), and the homoeology of each alien chromosome was determined by wheat SNP microarray analysis. Addition line WTA55 with alien group-6 chromosome was evaluated resistant to stripe rust isolates at both the seedling and grain-filling stages (Zadoks scale at z.11 and z.73). Diagnostic marker analysis proved that it could carry a novel stripe rust resistance gene derived from Th. ponticum. Furthermore, a FISH probe and 45 molecular markers specific for alien chromosomes were developed based on specific-locus amplified fragment sequencing (SLAF-seq). Of which 27 markers were separately located on single alien chromosome, and some of them could be used to identify the derived translocation lines. This set of addition lines as well as the molecular markers and the FISH probe will promote the introgression of abundant variation from Th. ponticum into wheat in wheat improvement programs.

Fig rust caused by Phakopsora nishidana in South Africa

Fig rust, caused by Cerotelium fici, was first recorded in South Africa in 1927. Recent observations have revealed high incidence of rust and untimely defoliation of fig trees (Ficus carica) in residential gardens and commercial orchards. Using phylogenetic analysis, the causal organism of a fig rust isolate (PREM63073) collected in 2020 was confirmed as Phakopsora nishidana. Inoculation and microscope studies showed that mulberry plants were immune to P. nishidana isolate PREM63073. Infection of fig leaves occurred through stomata on the abaxial leaf surfaces. Very long germ tubes were observed for P. nishidana, often with no clear contact with the leaf surfaces and an apparent lack of directional growth towards stomata. Inoculated plants from 15 fig cultivars varied in their severity of leaf infection, whereas fruit of the cultivar Kadota developed reddish-brown blemishes without sporulation. Currently, C. fici and P. nishidana are recognised as occurring on F. carica in South Africa. This suggests a need to resolve the worldwide distribution and identity of the rust species involved.

Identification and Characterization of Resistance Loci to Wheat Leaf Rust and Stripe Rust in Afghan Landrace "KU3067".

Leaf rust and stripe rust are important wheat diseases worldwide causing significant losses where susceptible varieties are grown. Resistant cultivars offer long-term control and reduce the use of hazardous chemicals, which can be detrimental to both human health and the environment. Land races have been a valuable resource for mining new genes for various abiotic and biotic stresses including wheat rusts. Afghan wheat landrace “KU3067” displayed high seedling infection type (IT) for leaf rust and low IT for stripe rust; however, it displayed high levels of field resistance for both rusts when tested for multiple seasons against the Mexican rust isolates. This study focused on identifying loci-conferring seedling resistance to stripe rust, and also loci-conferring adult plant resistance (APR) against the Mexican races of leaf rust and stripe rust. A backcrossed inbred line (BIL) population advanced to the BC1F5 generation derived from the cross of KU3067 and Apav (triple rust susceptible line) was used for both, inheritance and QTL mapping studies. The population and parents were genotyped with Diversity Arrays Technology-genotyping-by-sequencing (DArT-Seq) and phenotyped for leaf rust and stripe rust response at both seedling and adult plant stages during multiple seasons in Mexico with relevant pathotypes. Mapping results identified an all-stage resistance gene for stripe rust, temporarily designated as YrKU, on chromosome 7BL. In total, six QTL-conferring APR to leaf rust on 1AS, 2AL, 4DL, 6BL, 7AL, and 7BL, and four QTL for stripe rust resistance on 1BS, 2AL, 4DL, and 7BL were detected in the analyses. Among these, pleiotropic gene Lr67/Yr46 on 4DL with a significantly large effect is the first report in an Afghan landrace-conferring resistance to both leaf and stripe rusts. QLr.cim-7BL/YrKU showed pleiotropic resistance to both rusts and explained 7.5–17.2 and 12.6–19.3% of the phenotypic variance for leaf and stripe rusts, respectively. QYr.cim-1BS and QYr.cim-2AL detected in all stripe environments with phenotypic variance explained (PVE) 12.9–20.5 and 5.4–12.5%, and QLr.cim-6BL are likely to be new. These QTL and their closely linked markers will be useful for fine mapping and marker-assisted selection (MAS) in breeding for durable resistance to multiple rust diseases.

Biochemical aspects of pathogenic variability in white rust infected Indian mustard

ABSTRACT White rust caused by Albugo candida, an oomycete pathogen, is a devastating disease of Brassica juncea (Indian mustard) worldwide. There is a need to screen virulent white rust isolates to challenge the developed white rust–resistant B. juncea cultivars to screen their resistance potential. The current study explores pathogenic and biochemical response of Indian mustard to white rust isolates collected from three different geographic locations of India. The observations refine our understanding of the disease severity in India. Disease progression and biochemical responses were studied in the cotyledonary as well as true leaf stage of the B. juncea cultivar Varuna at different time points. The biochemical findings highlight the fluctuation of significant biochemical parameters such as total proteins, sugars, and phenols, superoxide dismutase, and hydrogen peroxide during the A. candida infection in B. juncea.

Evaluation of Advanced Kenyan Barley (Hordeum vulgare L.) Genotypes for Resistance to Stem Rust (Puccinia graminis Pers:.Pers. f.sp tritici Eriks. & E. Henn.) Race Ttksk and Its Variants

Stem rust caused by Puccinia graminis Pers:.Pers. f.sp tritici affects all the aerial parts of wheat and barley plants leading to yield losses. The objective of this study was to determine the level of resistance in advanced Kenyan barley lines to stem rust race TTKSK and its variants. The greenhouse and field experiments were laid in complete block design and randomized complete block design respectively with all experiments replicated three times. The experiments were conducted at Kenya Agricultural and Livestock Research Organization- Njoro. In the greenhouse experiment, forty genotypes were sown in perforated plastic pots and when the seedlings attained two-leaf stage, stem rust isolate collected from wheat variety, KS Mwamba was used to inoculate the genotypes. In the field, forty genotypes were sown in a one meter twin rows of each genotype were planted and all agronomic practices implement except management of stem rust disease. Infection types (IT) on the seedlings were observed and data collected following a scale described by Stakman et al. 1962. Disease severity data was collected according to modified Cobbs scale and then subjected to Area Under Disease Progress Curve (AUDPC). All genotypes showed immunity to moderate resistance at seedling level ranging from 0 to 2+. Adult plant reactions to race TTKSK and its variants ranged from an overlap of moderately resistant (MR) to susceptible (S). In all genotypes AUDPC ranged from 225.83 to 887.92 for under this study and the Coefficient of Infection ranged from 13 to 47. High levels of slow rusting were observed in only 12.5% of the genotypes tested while 10% of the genotypes had low levels. 77.5% of the genotypes had moderate levels of slow rusting. The genotypes with high levels of slow rusting can be advanced for release as varieties or be included in barley breeding.

Contribution of the life‐history traits of a plant pathogen to the development of field epidemics

AbstractThe pathogenicity‐related traits of biotrophic plant pathogens are usually measured on the individual host plant, at the scale of a single pathogen life cycle, whereas epidemic development in the field encompasses a succession of cycles. It remains unclear which traits make the greatest contribution to pathogen fitness in the field and to epidemic severity. The objective of this study was to determine the contributions of elementary pathogenicity traits to epidemic development in field conditions. We challenged a set of wheat cultivars with three different leaf rust isolates, under both controlled and field conditions, in 3 consecutive years. Infection efficiency, latent period, lesion size, spore production per lesion and spore production capacity were measured in the greenhouse, whereas disease severity was measured in the field. Most, but not all, of the pathogenicity traits were related to each other. All traits contributed to epidemic development in the field, but to different extents. Surprisingly, lesion size and spore production per lesion were inversely correlated with epidemic severity. Conversely, there was a strong positive correlation between spore production capacity and pathogen fitness in the field, in accordance with the concept of propagule pressure as a strong determinant of invasion success. Severe epidemics were mostly associated with small lesions with a high spore production capacity, high infection efficiency and a short latent period.