New Sources Of Resistance Research Articles

Behavior of Spanish durum wheat genotypes against Zymoseptoria tritici: resistance and susceptibility

Aim of study: Septoria tritici blotch (STB), caused by the fungus Zymoseptoria tritici, is one of the most important wheat diseases worldwide, affecting both bread and durum wheat. The lack of knowledge about the interaction of durum wheat with Z. tritici, together with limited resources of resistant durum wheat material, have both led to a rising threat for durum wheat cultivation, particularly in the Mediterranean Basin. In Spain, STB has increased its incidence in the last few years, leading to higher costs of fungicide applications to control the disease. Therefore, identification of new sources of resistance through wheat breeding stands out as an efficient method of facing STB.Area of study: The experimental study was conducted in growth chambers at the IFAPA facilities in Córdoba (Spain).Material and methods: The percentage of necrotic leaf area, the disease severity, and the pycnidium development through image analysis were evaluated from 48 durum wheat Spanish accessions (breeding lines and commercial cultivars) in growth chambers against an isolate of Z. tritici from Córdoba.Main results: Two breeding lines and six commercial cultivars showed resistant responses by limiting STB development through the leaf or its reproduction ability, while the other 40 accessions presented a susceptible response.Research highlights: Provided these resources of resistance in Spanish durum wheat genotypes, future breeding programs could be developed, incorporating both agronomic traits and resistance to STB.

Evaluation of Leaf Spot Resistance in Wild Arachis Species of Section Arachis

ABSTRACT Wild diploid Arachis species are potential sources of resistance to early (ELS) and late (LLS) leaf spot diseases caused by Passalora arachidicola (syn. Cercospora arachidicola Hori), and Nothopassalora personata (syn. Cercosporidium personatum (Berk. & Curt.) Deighton), respectively. Within section Arachis, limited information is available on the extent of genetic variation for resistance to these fungal pathogens. A collection of 78 accessions representing 15 wild species of Arachis section Arachis from the U.S peanut germplasm collection was evaluated for resistance to leaf spots. Screening was conducted under field (natural inoculum) conditions in Dawson, Georgia, during 2017 and 2018. Accessions differed significantly (P < 0.01) for all three disease variables evaluated, which included final defoliation rating, ELS lesion counts, and LLS lesion counts. Relatively high levels of resistance were identified for both diseases, with LLS being the predominant pathogen during the two years of evaluation. This research documents new sources of resistance to leaf spot diseases selected from an environment with high inoculum pressure. The presence of ELS and LLS enabled the selection of resistant germplasm for further introgression and pre-breeding.

Genome-wide association mapping of Pyrenophora teres f. maculata and Pyrenophora teres f. teres resistance loci utilizing natural Turkish wild and landrace barley populations.

Unimproved landraces and wild relatives of crops are sources of genetic diversity that were lost post domestication in modern breeding programs. To tap into this rich resource, genome-wide association studies in large plant genomes have enabled the rapid genetic characterization of desired traits from natural landrace and wild populations. Wild barley (Hordeum spontaneum), the progenitor of domesticated barley (Hordeum vulgare), is dispersed across Asia and North Africa, and has co-evolved with the ascomycetous fungal pathogens Pyrenophora teres f. teres and P. teres f. maculata, the causal agents of the diseases net form of net blotch and spot form of net blotch, respectively. Thus, these wild and local adapted barley landraces from the region of origin of both the host and pathogen represent a diverse gene pool to identify new sources of resistance, due to millions of years of co-evolution. The barley—P. teres pathosystem is governed by complex genetic interactions with dominant, recessive, and incomplete resistances and susceptibilities, with many isolate-specific interactions. Here, we provide the first genome-wide association study of wild and landrace barley from the Fertile Crescent for resistance to both forms of P. teres. A total of 14 loci, four against P. teres f. maculata and 10 against P. teres f. teres, were identified in both wild and landrace populations, showing that both are genetic reservoirs for novel sources of resistance. We also highlight the importance of using multiple algorithms to both identify and validate additional loci.

Cucumis melo L. Germplasm in Tunisia: Unexploited Sources of Resistance to Fusarium Wilt

Breeding for disease resistance has been one of the most important research objectives in melon for the last few decades. Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Fom) is among the most threatening melon fungal diseases along the Mediterranean coast, affecting yield and quality. Since genetic resistance is one of the best sustainable strategies that can be used to control this pathogen, 27 Tunisian melon accessions collected from local farmers have been tested using phenotypic and molecular approaches to identify new sources of resistance to be used directly as cultivars in affected areas or as resistance donors in breeding programs. The phenotypic evaluations, using artificial inoculations, showed several resistant accessions to the pathogenic races of Fom. Additionally, molecular analysis revealed that 13 out of 27 accessions carried the resistance Fom-1 gene (7 in homozygous state and 6 in heterozygous state), confirming their resistance to races 0 and 2. Two of them were also identified as heterozygous for the Fom-2 gene, being resistant to races 0 and 1. Furthermore, two accessions with a high level of resistance to the most virulent race 1.2 have been also reported. This melon germplasm should be explored as a potential source of resistance genes in breeding programs to develop new resistant melon cultivars.

Inheritance analysis and identification of SSR markers associated with fusarium wilt resistance in melon

ABSTRACT Fusarium wilt (FW), caused by Fusarium oxysporum Schlechtend f. sp. melonis (Leach & Currence) Snyd. & Hans (Fom) is a substantial threat to muskmelon (Cucumis meloL.) cultivation around the world. Identification of new sources of resistance and transfer of the resistance genes to elite cultivars is the effective breeding strategy to reduce the FW-associated crop losses in muskmelon. In the present study, inheritance studies and molecular mapping for FW resistance were conducted in a muskmelon inbred line KP4HM-15 with FW resistance introgressed from snapmelon. Inheritance studies in the F2 population derived from the cross Punjab Sunehri//KP4HM-15 indicated that FW resistance in KP4HM-15 is governed by a single dominant gene. Bulked segregant analysis was conducted to map the Fom-5(t) gene in KP4HM-15 using 527 SSR primers. Four primer pairs, CMCTN35, DM0096, CSWCTT02, and ECM181, were found to show differential polymorphism in the resistant and susceptible bulks and were analysed in the whole of the population. Two SSR markers, DM0096 and CSWCTT02, mapped close to the Fom-5(t) gene at a genetic distance of 1.4 and 2.5 cM, respectively. These markers can potentially be used to transfer Fom-5(t) in elite muskmelon genotypes through marker-assisted backcross breeding until more tightly linked markers are available.

Resistencia a lancha de papas nativas ecuatorianas: evaluación en campo y percepción de agricultores

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is one of the most devastating diseases of potato world-wide. A field experiment, in a location under high P. infestans pressure, was carried out in Ecuador to assess resistance or susceptibility to late blight of 31 potato landraces collected in Carchi, Chimborazo and Loja. Resistant commercial varieties (I-Fripapa) and a susceptible (Superchola) were included as references. Based on the Area Under the Disease Progress Curve (AUDPC) three categories were scored: resistant, intermediate and susceptible. The landraces under study showed different responses to late blight in the experimental field. Only, five landraces showed the best field resistance: Uva, Chaucha roja, Guata amarilla, Coneja and Chaucha ratona. Additionally, a survey to 150 farmers growing potato landraces in these three provinces identified the main diseases affecting their potatoes. Informal conversations with these farmers both during the collections and during farmer meetings provided additional information regarding late blight and their perception of landrace resistance. Similar to farmers growing commercial varieties also farmers currently cultivating landraces consider late blight as the main disease in their potatoes. Probably the broad crop diversity on their farms and the planting of potato landrace mixtures reduces the late blight severity effects within their potato fields. Possible strategies to improve late blight resistance in potato in Ecuador could include the identification of accessions with resistance among local landraces, wild potato relatives and/or the introduction of new sources of resistance from other origins.

New sources of powdery mildew resistance among winter bread wheat for adjusting the breeding immunological programs in the Agricultural Research Center “Donskoy”

Systematic work on the development of winter wheat varieties possessing resistance to a complex of the most harmful diseases has been carried out in the Agricultural Research Center “Donskoy” since the early 1970s. During this period, there has been created a large number of varieties that possess resistance to 3–4 diseases in conditions of infectious backgrounds of pathogens. Due to the analysis of varieties, there was identified a small number of varieties resistant to powdery mildew. Powdery mildew, caused by the fungus Blumeria graminis (DC) Speer, annually occurs on wheat, affecting all aboveground plant organs. Earlier the FSBSI “ARC “Donskoy” developed and widely cultivated the medium-resistant varieties ‘Tanais’ (2006), ‘Nakhodka’ (2015), ‘Etyud’, ‘Shef’, ‘Lilit’ (2016), ‘Volnitsa’ (2017), ‘Polina’, Yubiley Dona’ , ‘Podarok Krymu’ (2018), ‘Niva Dona’ (2019). In recent years, breeders have developed such varieties with high resistance to the pathogen as ‘Donskaya Step’ (2016), ‘Premiera’, ‘Univer’ (2018), ‘Priazovye’, ‘Zolotoy Kolos’ (2020). But the breeding process of varieties for resistance to powdery mildew is difficult, since it is explained by the small number of effective resistance genes and their sources. Therefore, the purpose of the current study was to identify new sources of resistance to the pathogen. Under the conditions of artificial infection, during last 10 years there was conducted a testing of 302 varieties and samples of winter wheat of domestic and foreign breeding. There have not been identified immune varieties. There was identified a small percentage (15.2) of varieties that were resistant to the pathogen. Among the Russian varieties they were ‘L 3191 k-5-8’, ‘Akhmat’, ‘Alievich’, ‘Barier’, ‘Ulyasha’, ‘Knyaginya Olga’, which were not attacked by the disease over the years of testing. Among foreign varieties, the varieties ‘Bombus’, ‘Sailor’ (France), ‘Etana’, ‘Rotax’, ‘KVS-Emil’ (Germany), ‘Fidelius’ (Austria), ‘MV 09-04’ (Hungary) were identified as the best ones in their resistance to powdery mildew. All identified sources of resistance have been recommended in breeding programs for immunity.

Genotypic Variation in Cultivated and Wild Sorghum Genotypes in Response to Striga hermonthica Infestation.

Striga hermonthica is the most important parasitic weed in sub-Saharan Africa and remains one of the most devastating biotic factors affecting sorghum production in the western regions of Kenya. Farmers have traditionally managed Striga using cultural methods, but the most effective and practical solution to poor smallholder farmers is to develop Striga-resistant varieties. This study was undertaken with the aim of identifying new sources of resistance to Striga in comparison with the conventional sources as standard checks. We evaluated 64 sorghum genotypes consisting of wild relatives, landraces, improved varieties, and fourth filial generation (F4) progenies in both a field trial and a pot trial. Data were collected for days to 50% flowering (DTF), dry panicle weight (DPW, g), plant height (PH, cm), yield (YLD, t ha−1), 100-grain weight (HGW, g), overall disease score (ODS), overall pest score (OPS), area under Striga number progress curve (ASNPC), maximum above-ground Striga (NSmax), and number of Striga-forming capsules (NSFC) at relevant stages. Genetic diversity and hybridity confirmation was determined using Diversity Arrays Technology sequencing (DArT-seq). Residual heterosis for HGW and NSmax was calculated as the percent increase or decrease in performance of F4 crossover midparent (MP). The top 10 best yielding genotypes were predominantly F4 crosses in both experiments, all of which yielded better than resistant checks, except FRAMIDA in the field trial and HAKIKA in the pot trial. Five F4 progenies (ICSVIII IN × E36-1, LANDIWHITE × B35, B35 × E36-1, F6YQ212 × B35, and ICSVIII IN × LODOKA) recorded some of the highest HGW in both trials revealing their stability in good performance. Three genotypes (F6YQ212, GBK045827, and F6YQ212xB35) and one check (SRN39) were among the most resistant to Striga in both trials. SNPs generated from DArT-seq grouped the genotypes into three major clusters, with all resistant checks grouping in the same cluster except N13. We identified more resistant and high-yielding genotypes than the conventional checks, especially among the F4 crosses, which should be promoted for adoption by farmers. Future studies will need to look for more diverse sources of Striga resistance and pyramid different mechanisms of resistance into farmer-preferred varieties to enhance the durability of Striga resistance in the fields of farmers.

New Sources of Eastern Filbert Blight Resistance and Simple Sequence Repeat Markers on Linkage Group 6 in Hazelnut (Corylus avellana L.).

Commercial production of hazelnut (Corylus avellana) in Oregon’s Willamette Valley is threatened by eastern filbert blight (EFB), a serious canker disease caused by the pyrenomycete Anisogramma anomala (Peck) E. Müller. The fungus also prevents the establishment of hazelnut orchards in eastern North America. Genetic resistance is considered the most effective way to control the disease. A high level of EFB resistance was first discovered in ’Gasaway’. This resistance is conferred by a dominant allele at a single locus on linkage group 6 (LG6). Resistance from several additional sources has been assigned to the same chromosomal region. In this study, new simple sequence repeat (SSR) markers were developed for the resistance region on LG6 and new sources of resistance were investigated. Forty-two new SSR markers were developed from four contigs in the genome sequence of ‘Jefferson’ hazelnut, characterized, and nine of them were placed on LG6 of the genetic map. Accessions representing 12 new sources of EFB resistance were crossed with susceptible selections resulting in 18 seedling populations. Segregation ratios in the seedling populations fit the expected 1:1 ratio for 10 sources, while one source showed an excess of resistant seedlings and another showed an excess of susceptible seedlings. Based on correlation of disease response and scores of SSR markers in the ‘Gasaway’ resistance region in the seedlings, eight resistance sources were assigned to LG6. Linkage maps were constructed for each progeny using SSR markers. The LG6 resistance sources include two selections (#23 and #26) from the Russian Research Institute of Forestry and Mechanization near Moscow, four selections from southern Russia, one selection (OSU 1185.126) from Crimea, one selection (OSU 533.129) from Michigan, Corylus heterophylla ‘Ogyoo’ from the South Korea, and the interspecific hybrid ’Estrella #1’. These new LG6 resistance sources and SSR markers should be useful in breeding new cultivars, including the pyramiding of resistance genes. For the other four resistance sources (Moscow #37, hybrid selection OSU 401.014, C. americana ‘Winkler’ and C. americana OSU 366.060), SSR marker scores on linkage groups 6, 7 and 2 were not correlated with disease response and merit further investigation.

Quantitative resistance linked to late effectors.

Quantitative resistance linked to late effectors.

Identifying potential novel resistance to the foliar disease \u2018Scald\u2019 (Rhynchosporium commune) in a population of Scottish Bere barley landrace (Hordeum vulgare L.)

Barley ‘Scald’ is an economically damaging fungal disease that is a global problem, causing significant yield and economical losses in the UK barley feed and malting industries. Presently, a limited number of Rhynchosporium resistance genes exist, but selective pressures on the fungi cause the demand for new sources of resistance. Landraces, such as the Scottish Bere barley, hold potential sources of resistance that can be utilised, with farmers providing anecdotal evidence of resistance in field populations of Bere. This study analysed 131 heritage cultivars and landrace lines, including 37 Bere lines, to screen for resistance using both detached leaf assays (DLAs) and field experiments. Results showed that Bere lines produced smaller, but more necrotic, lesions for the majority of isolates in the DLAs, as well as smaller scores when visually assessed in field conditions. Whilst the infection patterns of the lines differed between isolates and experimental conditions, three Bere lines were identified as consistently showing reduced levels of infection (45 A 23, 58 A 36 Eday, and 8-125). Using genome-wide association analysis, we were able to identify a number of genomic regions associated with reduced infection symptoms, four in regions associated with known resistance genes, but another four associated with new regions that contain promising candidate genes. Further analysis of these new regions and candidate genes should be undertaken to identify targets for future disease-resistance breeding.

Over 50 Years of Potato Parental Line Breeding Programme at the Plant Breeding and Acclimatization Institute in Poland

The paper describes the potato parental line breeding programme developed in Poland from the 1960s. The aim of the programme was to create parental forms useful for speeding up the breeding of new potato varieties and getting higher efficiency in directed selection for desired traits. The programme introduced new sources of resistance and quality traits into the Polish breeding pool by conducting research and breeding of tetraploid and diploid parental lines. The programme had significant impact on potato breeding, with 72 Polish potato varieties originating from crossings involving parental lines. These varieties show higher levels of resistance to major pathogens of potato crops, including resistance to Potato virus Y and late blight in starch group. Besides the direct impact on potato breeding, the programme was the stimulus for developing studies focused on potato genotype.

Fine mapping of a powdery mildew resistance gene MlIW39 derived from wild emmer wheat (Triticum turgidum ssp. dicoccoides).

Powdery mildew resistance gene MlIW39, originated from wild emmer wheat accession IW39, was mapped to a 460.3 kb genomic interval on wheat chromosome arm 2BS. Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is destructive disease and a significant threat to wheat production globally. The most effective way to control this disease is genetic resistance. However, when resistance genes become widely deployed in agriculture, their effectiveness is compromised by virulent variants that were previously minor components of the pathogen population or that arise from mutation. This necessitates continual search for new sources of resistance in both wheat and its near relatives. In this study, we produced a common wheat line 8D49 (87-1/IW39//2*87-1), which has all-stage immunity to Bgt isolate E09 and many other Chinese Bgt isolates, by transferring powdery mildew resistance from Israeli wild emmer wheat (WEW) accession IW39 to the susceptible common wheat line 87-1. Genetic analysis indicated that the powdery mildew resistance in 8D49 was controlled by a single dominant gene, temporarily designated MlIW39. Genetic linkage analyses with molecular markers showed that MlIW39 was located in a 0.7 cm genetic region between markers QB-3-16 and 7Seq546 on the short arm of chromosome 2B. Fine mapping using three large F2 populations delimited MlIW39 to a physical interval of approximately 460.3 kb region in the WEW reference genome (Zavitan v1.0) that contained six annotated protein-coding genes, four of which had gene structures similar to known disease resistance genes. This provides a foundation for map-based cloning of MlIW39. Markers 7Seq622 and 7Seq727 co-segregating with MlIW39 can be utilized for marker-assisted selection in further genetic studies and wheat breeding.

Validation of resistance to root‐knot nematode incorporated in peanut from the wild relative Arachis stenosperma

AbstractPeanut (Arachis hypogaea L.) root‐knot nematode (PRKN) Meloidogyne arenaria is a very destructive pathogen to which most peanut cultivars are highly susceptible. Current peanut cultivars rely on a single locus for PRKN resistance incorporated from the wild relative A. cardenasii Krapov. & W.C. Greg., that could be overcome as a result of the emergence of new nematode populations. Thus, new sources of resistance are continually needed. A new and strong resistance has been found in the wild diploid relative, A. stenosperma Krapov. & W.C. Greg. Arachis stenosperma‐derived quantitative trait loci (QTL) were described on chromosomes A02 and A09 and reduced nematode development by up to 98.2%. In order to validate these resistance segments, this study screened for PRKN resistance in BC2F1 lines and correlated with molecular genotypes. Here, six BC2F1s carrying chromosome introgressions in A02 and/or A09, showed strong resistance while one line was susceptible. Both phenotype and genotype data allowed us to validate and delineate the chromosomal segments in chromosomes A02 and A09 to ∼8.5Mbp and ∼6.5Mbp regions on the bottom of each, respectively. Within the QTL on A02 and top middle of both chromosomes A02 and A09 there are R‐gene clusters, often implicated in pathogen resistance. We have provided validation of these key resistance QTL that can be used to inform breeding via marker selection and insights into the functional basis of resistance provided by the wild peanut relative A. stenosperma.

Novel Disease Host Resistances in the World Core Collection of Trifolium subterraneum.

Glasshouse and field investigations of the phenotypic expressions of resistance of a 97-member World Core Collection of subterranean clover (Trifolium subterraneum) collected from its native Mediterranean habitat and representing approximately 80% of the total genetic diversity within the known 10,000 accessions of the species against the most important damping-off and root rot (Phytophthora clandestina, and Pythium irregulare) and foliar (Kabatiella caulivora, Uromyces trifolii-repentis, and Erysiphe trifoliorum) pathogens were performed. An additional 28 diverse cultivars were also included. Associations of these genotypes among 18 disease parameters and 17 morphological traits, and among these disease parameters and 24 climatic and eco-geographic variables from their collection sites, were examined. Many genotypes showed strong phenotypic expression of novel host disease resistance against one or more pathogens, enabling their potential deployment as disease-resistant parents in subterranean clover breeding programs. These new sources of resistance enable future "pyramiding" of different resistance genes to improve resistance against these pathogens. Of particular value were genotypes with multiple disease-resistance across soilborne and/or foliar diseases, because many of these pathogens co-occur. All diseases had some parameters significantly correlated with one or more morphological traits and with one or more sites of origin variables. In particular, there were significant negative correlations between damping-off (i.e., germination) and 8 of the 17 morphological characters. The outcomes of these studies provide crucial information to subterranean clover breeding programs, enabling them to simultaneously select genotypes with multiple resistance to co-occurring soilborne and foliar diseases and desirable traits to offer renewed hope for re-establishing a more productive subterranean clover livestock feedbase despite multiple diseases prevailing widely.

Using biotechnological approaches to develop crop resistance to root parasitic weeds.

New transgenic and biotechnological approaches may serve as a key component in achieving crop resistance to root parasitic weeds. Root parasitic weeds inflict severe damage to numerous crops, reducing yield quantity and quality. A lack of new sources of resistance limits our ability to manage newly developing, more virulent races. Having no effective means to control the parasites in most crops, innovative biotechnological solutions are needed. Several novel biotechnological strategies using regulatory RNA molecules, the CRISPR/Cas9 system, and T-DNA insertions have been acknowledged for engineering resistance against parasitic weeds. Significant breakthroughs have been made over the years in deciphering the plant genome and its functions, including the genomes of parasitic weeds. However, the basis of biotechnological strategies to generate host resistance to root parasitic weeds needs to be further developed. Gene-silencing and editing tools should be used to target key processes of host-parasite interactions, such as strigolactone biosynthesis and signaling, haustorium development, and degradation and penetration of the host cell wall. In this review, we summarize and discuss the main areas of research leading to the discovery and functional analysis of genes involved in host-induced gene silencing that target key parasite genes, transgenic host modification, and host gene editing to generate sustainable resistance to root parasitic weeds.

Genome-wide association mapping for resistance to bacterial blight and bacterial leaf streak in rice.

Using genome-wide SNP association mapping, a total of 77 and 7 loci were identified for rice bacterial blight and bacterial leaf streak resistance, respectively, which may facilitate rice resistanceimprovement. Bacterial blight (BB) and bacterial leaf streak (BLS) caused by Gram-negative bacteria Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), respectively, are two economically important diseases negatively affecting rice production. To mine new sources of resistance, a set of rice germplasm collection consisting of 895 re-sequenced accessions from the 3000 Rice Genomes Project (3K RGP) were screened for BB and BLS resistance under field conditions. Higher levels of BB resistance were observed in aus/boro subgroup, whereas the japonica, temperate japonica and tropical japonica subgroups possessed comparatively high levels of resistance to BLS. A genome-wide association study (GWAS) mined 77 genomic loci significantly associated with BB and 7 with BLS resistance. The phenotypic variance (R2) explained by these loci ranged from 0.4 to 30.2%. Among the loci, 7 for BB resistance were co-localized with known BB resistance genes and one for BLS resistance overlapped witha previously reportedBLS resistance QTL. A search for the candidates in other novel loci revealed several defense-related genes that may be involved in resistance to BB and BLS. High levels of phenotypic resistance to BB or BLS could be attributed to the accumulation of the resistance (R) alleles at the associated loci, indicating their potential value in rice resistance breeding via gene pyramiding. The GWAS analysis validated the known genes underlying BB and BLS resistance and identified novel loci that could enrich the current resistance gene pool. The resources with strong resistance and significant SNPs identified in this study are potentially useful in breeding for BB and BLS resistance.

A new source of resistance in rice against Brown planthopper, Nilaparvata lugens Stal (Homoptera: Delphacidae) and elucidation of its inheritance using phenotypic selections under artificial infestations at seedling and reproductive stages of the crop

Genetic resistance in rice through native traits is an important tactic to manage Brown planthopper (BPH), Nilaparvata lugens Staal (Homoptera: Delphacidae) which is one of the most dreaded pests in the farmer’s field causing serious crop losses. Many sources of resistance, both from cultivated and wild accessions, are known with almost 36 resistance genes mapped to different chromosomes through phenotypic and genotypic selections. A majority of resistance genes identified are effective for BPH biotypes prevailing in Southeast Asia and China. For South Asia, very few BPH resistance genes are effective but without their utilization for the development of commercial hybrids and varieties. A new source of resistance HSPP 6417 has been identified in the present paper, which displayed resistance to 11 populations of BPH collected from different rice ecologies of India. The new source HSPP 6417 had an adverse effect on the population dynamics of BPH by inhibiting the population build-up on the plants. The resistance of HSPP 6417 was equivalent to the only source of resistance in India, G7253 used to develop a commercial rice hybrid AZ8433 DT. On crossing HSPP 6417 with other prolific restorer lines of the commercial hybrids, the major genes were found to control its modes of inheritance. Field trials with F4 generation revealed that resistance was stable with good agronomic performance under infestations. The implications of using such a source of resistance for developing BPH resistant hybrids are discussed in the paper.

Characterization of the Resistance to Powdery Mildew and Leaf Rust Carried by the Bread Wheat Cultivar Victo.

Leaf rust and powdery mildew are two important foliar diseases in wheat. A recombinant inbred line (RIL) population, obtained by crossing two bread wheat cultivars (‘Victo’ and ‘Spada’), was evaluated for resistance to the two pathogens at seedling stage. Upon developing a genetic map of 8726 SNP loci, linkage analysis identified three resistance Quantitative Trait Loci (QTLs), with ‘Victo’ contributing the resistant alleles to all loci. One major QTL (QPm.gb-7A) was detected in response to Blumeria graminis on chromosome 7A, which explained 90% of phenotypic variation (PV). The co-positional relationship with known powdery mildew (Pm) resistance loci suggested that a new source of resistance was identified in T. aestivum. Two QTLs were detected in response to Puccinia triticina: a major gene on chromosome 5D (QLr.gb-5D), explaining a total PV of about 59%, and a minor QTL on chromosome 2B (QLr.gb-2B). A positional relationship was observed between the QLr.gb-5D with the known Lr1 gene, but polymorphisms were found between the cloned Lr1 and the corresponding ‘Victo’ allele, suggesting that QLr.gb-5D could represent a new functional Lr1 allele. Lastly, upon anchoring the QTL on the T. aestivum reference genome, candidate genes were hypothesized on the basis of gene annotation and in silico gene expression analysis.

BED domain-containing NLR from wild barley confers resistance to leaf rust.

SummaryLeaf rust, caused by Puccinia hordei, is a devastating fungal disease affecting barley (Hordeum vulgare subsp. vulgare) production globally. Despite the effectiveness of genetic resistance, the deployment of single genes often compromises durability due to the emergence of virulent P. hordei races, prompting the search for new sources of resistance. Here we report on the cloning of Rph15, a resistance gene derived from barley’s wild progenitor H. vulgare subsp. spontaneum. We demonstrate using introgression mapping, mutation and complementation that the Rph15 gene from the near‐isogenic line (NIL) Bowman + Rph15 (referred to as BW719) encodes a coiled‐coil nucleotide‐binding leucine‐rich repeat (NLR) protein with an integrated Zinc finger BED (ZF‐BED) domain. A predicted KASP marker was developed and validated across a collection of Australian cultivars and a series of introgression lines in the Bowman background known to carry the Rph15 resistance. Rph16 from HS‐680, another wild barley derived leaf rust resistance gene, was previously mapped to the same genomic region on chromosome 2H and was assumed to be allelic with Rph15 based on genetic studies. Both sequence analysis, race specificity and the identification of a knockout mutant in the HS‐680 background suggest that Rph15‐ and Rph16‐mediated resistances are in fact the same and not allelic as previously thought. The cloning of Rph15 now permits efficient gene deployment and the production of resistance gene cassettes for sustained leaf rust control.