Identification of Transposable Element Markers for a Rust (Puccinia arachidis Speg.) Resistance Gene in Cultivated Peanut

Peanut rust (Puccinia arachidis Speg.) affects pod yield and quality up to an extent of 10–50%. Efforts have been made on transferring the rust resistance gene to cultivated peanut species through interspecific hybridization. But, in most of the cases, it failed due to linkage drag of undesirable plant and pod features. Identification of tightly linked molecular markers will help to identify the desirable recombinants more efficiently. A recombinant inbred line population comprising 164 lines was developed from a cross between a rust‐resistant parent VG 9514 and a rust susceptible parent TAG 24. Using a modified bulk segregant analysis, 243 transposable element (TE) primer pairs were screened for putative linkage with rust resistance. Of the 243, 40 TE primer pairs were found polymorphic between parents and two transposable element markers, and TE 360 and TE 498 were found associated with rust resistance gene. Based on genetic mapping, TE 360 was found linked to the rust resistance gene at 4.5 cM distance. Identification of such markers could be applied for marker‐assisted selection of rust resistance plants in peanut.     

Short Note: Effect of Acremonium obclavatum glucan on groundnut leaf rust disease caused by Puccinia arachidis Speg.

A water soluble glucan purified from the culture filtrate of Acremonium obclavatum, an antagonist to the groundnut rust, Puccinia arachidis, inhibited germination of uredospores of P. arachidis. Prior treatment of groundnut leaves with glucan prolonged the incubation period between inoculation and development of rust disease, and caused a decrease in the number of pustules and uredospores/sorus. Treated groundnut leaves showed an increase in endogenous salicylic acid, intercellular chitinase and -1,3 glucanase activities.     

Genetic control of resistance to crown rust (Puccinia coronato Corda) in Lolium perenne L. and its implications in breeding

Summary A genetic analysis of resistance to crown rust in a series of natural populations of Lolium perenne by means of the diallel cross has revealed that heritability is high (58%) and that the genes concerned show complete but ambi-directional dominance for resistance. An environmental correlation was established between the degree of infection and productivity but no genetic correlation was present. The implications of this mode of control for resistance breeding procedures are briefly considered.     

Exome association analysis sheds light onto leaf rust (Puccinia triticina) resistance genes currently used in wheat breeding (Triticum aestivum L.)

Resistance breeding is crucial for a sustainable control of leaf rust (Puccinia triticina) in wheat (Triticum aestivum L.) while directly targeting functional variants is the Holy Grail for efficient marker‐assisted selection and map‐based cloning. We assessed the limits and prospects of exome association analysis for severity of leaf rust in a large hybrid wheat population of 1574 single‐crosses plus their 133 parents. After imputation and quality control, exome sequencing revealed 202 875 single‐nucleotide polymorphisms (SNPs) covering 19.7% of the high‐confidence annotated gene space. We performed intensive data mining and found significant associations for 2171 SNPs corresponding to 50 different loci. Some of these associations mapped in the proximity of the already known resistance genes Lr21, Lr34‐B, Lr1 and Lr10, while other associated genomic regions, such as those on chromosomes 1A and 3D, harboured several annotated genes putatively involved in resistance. Validation with an independent population helped to narrow down the list of putative resistance genes that should be targeted by fine‐mapping. We expect that the proposed strategy of intensive data mining coupled with validation will significantly influence research in plant genetics and breeding.     

Identification and characterisation of resistance against rust (Puccinia allii) in garlic (Allium sp.) germplasm

In this work we studied the resistance response against Puccinia allii of 533 Allium sp. germplasm accessions under field conditions. Ten resistant accessions were selected to further characterise the defence mechanisms operative. Histological studies showed a range of defence mechanisms, acting alone or combined, that impeded fungal development at different stages. Some accessions showed prehaustorial resistance. In other accessions, mesophyll cells were penetrated by the fungus, but then hypersensitive response leading to cell death hampered fungal development. In some cases, cell death was very fast and early colony abortion was obvious already by 2 days after inoculation (DAI), whereas in others it was slow being marked only by 6 DAI. The fact that resistant accessions studied showed both pre‐ and posthaustorial resistance offers breeding opportunities for these traits.     

Sources of resistance to Exserohilum turcicum (Pass.) and Puccinia polysora (Underw.) incitant of Turcicum leaf blight and polysora rust of maize

A study was carried out to identify the sources of resistance to Turcicum leaf blight (TLB) and polysora rust in maize. Sixty indigenous and exotic inbred lines were evaluated under artificial epiphytotic conditions at two identified hot spot locations, Almora and Nagenahalli. After two years continuous screening, a total of 20 inbred lines were identified as a sources of resistance at both the locations for TLB, whereas 10 inbred lines were identified resistant against Polysora rust at Nagenahalli. A clear cut variation in virulence pattern in case of E. turcicum was observed. Some of the inbred inbred lines, i.e CM 138, CM 212, IML 235, NAI 135, showed resistant reaction in both the locations in the year 2005, whereas they acted as susceptible in 2006 at both locations. It was also observed that the Nagenahalli isolate of E. turcicum was more virulent than the Almora isolate.     

A review of white rust (Puccinia horiana Henn.) disease on chrysanthemum and the potential for its biological control with Verticillium lecanii (Zimm.) Viégas

The biology, aetiology and epidemiology of Puccinia horiana, the cause of white rust disease of chrysanthemum (Chrysanthemum spp.) is reviewed in relation to current environmental, cultural and chemical methods for its control. Importantly, basidiospore release, germination and infection can take as little as 5 h at optimum r.h. (96%) and temperature (between 17–24°C). Recent developments using the fungus Verticillium lecanii for the control of insects on glasshouse-grown all-year-round chrysanthemums rely upon the maintenance of r.h. during night periods in excess of 95%, thus predisposing plants to white rust attack. However, V. lecanii is unusual in that it can also parasitise spores and fruiting structures of a range of rust fungi including P. horiana. This mycoparasitic ability is also reviewed, and against this background, the potential for an integrated insect and white rust control programme on all-year-round chrysanthemums is assessed.     

Selection of parents for crossing based on genotyping and phenotyping for stripe rust (Puccinia striiformis) resistance and agronomic traits in bread wheat breeding

Bread wheat (Triticum aestivum L.) germplasm consisting of 45 genotypes were clustered phenotypically using ten morphological traits and Area Under Disease Progress Curve (AUDPC) as measure of stripe rust resistance. The clustering was ratified by using twenty three molecular markers (SSR, EST and STS) linked to stripe rust (Puccinia striiformis f. sp. tritici) resistant QTLs. The aim was to asses the extent of genetic variability among the genotypes in order to select the parents for crossing between the resistant and susceptible genotypes with respect to stripe rust. The Euclidian dissimilarity values resulted from phenotypic data regarding morphological traits and AUDPC were used to construct a dendrogram for clustering the accessions. Using un-weighted pair group method with arithmetic means, another dendrogram resulted from the similarity coefficient values was used to distinguish the genotypes with respect to stripe rust. Clustering based on phenotypic data produced two major groups and five clusters (with Euclidian dissimilarity ranging from 244 to 16.16) whereas genotypic data yielded two major groups and four clusters (with percent similarity coefficient values ranging from 0.1 to 46.0) to separate the gene pool into highly resistant, resistant, moderately resistant, moderately susceptible and susceptible genotypes. With few exceptions, the outcome of both type of clustering was almost similar and resistant as well as susceptible genotypes came in the same clusters of molecular genotyping as yielded by phenotypic clustering. As a result seven genotypes (Bakhtawar-92, Frontana, Saleem 2000, Tatara, Inqilab-91, Fakhre Sarhad and Karwan) of diverse genetic background were selected for pyramiding stripe rust resistant genes as well as some other agronomic traits after hybridization.     

A QTL study on late leaf spot and rust revealed one major QTL for molecular breeding for rust resistance in groundnut (Arachis hypogaea L.)

Late leaf spot (LLS) and rust are two major foliar diseases of groundnut (Arachis hypogaea L.) that often occur together leading to 50–70% yield loss in the crop. A total of 268 recombinant inbred lines of a mapping population TAG 24 × GPBD 4 segregating for LLS and rust were used to undertake quantitative trait locus (QTL) analysis. Phenotyping of the population was carried out under artificial disease epiphytotics. Positive correlations between different stages, high to very high heritability and independent nature of inheritance between both the diseases were observed. Parental genotypes were screened with 1,089 simple sequence repeat (SSR) markers, of which 67 (6.15%) were found polymorphic. Segregation data obtained for these markers facilitated development of partial linkage map (14 linkage groups) with 56 SSR loci. Composite interval mapping (CIM) undertaken on genotyping and phenotyping data yielded 11 QTLs for LLS (explaining 1.70–6.50% phenotypic variation) in three environments and 12 QTLs for rust (explaining 1.70–55.20% phenotypic variation). Interestingly a major QTL associated with rust (QTL_rust01), contributing 6.90–55.20% variation, was identified by both CIM and single marker analysis (SMA). A candidate SSR marker (IPAHM 103) linked with this QTL was validated using a wide range of resistant/susceptible breeding lines as well as progeny lines of another mapping population (TG 26 × GPBD 4). Therefore, this marker should be useful for introgressing the major QTL for rust in desired lines/varieties of groundnut through marker-assisted backcrossing.     

Epidermal cell response to rust hyphae and the resistance mode of tropical maize to southern corn rust (Puccinia polysora underwood)

Southern Corn Rust (SCR), caused byPuccinia polysora Underwood, is found primarily in the tropics, occurring especially during wet and cool winters in Hawaii. Whereas Hi38-71, a tropical Hawaiian super sweet corn, is resistant to SCR, the G24 inbred is susceptible. Anatomical traits are distinct in these two lines, with differences evident in their epidermal cell shapes, cell types, epidermal cell walls, hairs, and bulliform cells. Trichomes are found on the leaves of Hi38-71 plants and their epidermal surface cells are flat. In contrast, the epidermal surfaces of G24 leaves are circular, rough, and woolly, and are uniform in their size and pattern. These woolly epidermal leaf surfaces on the susceptible G24 provide access for disease infection while the trichomes and smooth leaves may confer more resistance in Hi38-71. Our genetic study utilized Generation Mean Analysis (GMA) of progenies derived from crosses of these two inbred lines. Resistance to SCR was scaled from 1 (resistant) to 9 (susceptible) in the winter and spring in Hawaii. Average scores for Hi38-71 and G24 were 3.1 and 6.9 respectively, while the F₁ and F₂ hybrids were both highly resistant to the rust. Both additive and dominant effects for SCR resistance were highly significant, as were their epistatic interactions [aa] and [dd]. However, the additive x dominance interaction was not. Therefore, a single dominant gene in inbred line Hi38-71 might be involved in determining its high resistance to SCR.     

The detection and molecular mapping of a major gene for non-specific adult-plant disease resistance against stripe rust (Puccinia striiformis) in wheat

A major gene determining non-specific adult-plant disease resistance against stripe rust (Puccinia striiformis) designated Yrns-B1 was mapped by using a cross between ’Lgst.79–74’ (resistant) and ’Winzi’ (susceptible). Analyzing F₃ lines of two consecutive experimental years contrary modes of inheritance were observed due to the intermediate character of the gene and the difference in the disease pressure during the seasons. Using the disease scoring data of both experimental years independently two maps were constructed detecting Yrns-B1 20.5 and 21.7 cM, respectively, proximal to the wheat microsatellite (WMS) marker Xgwm493 on the short arm of chromosome 3BS. The genetic relationships to other major genes or to quantitative trait loci controlling adult plant disease resistance against rusts in wheat are discussed. Received: 27 May 1999 / Accepted: 28 September 1999     

Partial resistance to rust (Puccinia allii) in cultivated leek (Allium ampeloprasum ssp.porrum): estimation and improvement

The extent to which resistance to leek rust (Puccinia allii) in commercially useful cultivars of leek (Allium ampeloprasum) could be developed by selection within current commercial cultivars or their recent predecessors was investigated. Differences in resistance among commercial cultivars was not great. However, a wide range of resistance levels was found in both half‐sib and inbred progeny derived from these cultivars. In a crop simulation, one of the breeding lines showed a reduction in the rate of new pustule appearance of 44% compared to cv. Wintra. It is concluded that selection within modern cultivar level material is a potentially productive strategy for the commercial development of leek rust resistance in the short to medium term.     

Response to stripe rust (Puccinia striiformis Westend. f. sp.tritici) and its coincidence with leaf rust resistance in hexaploid introgressive triticale lines withTriticum monococcum genes

Triticale introgressive lines were developed by incorporating diploid wheat (Triticum monococcum [TM16]) genes into the hexaploid triticale genotype LT522/6. The synthetic allotetraploidT. monococcum cereale (A^mA^mRR) was used as a bridging form to introduce the genes. A group of 43 introgressive lines, parental stocks and a check cultivar were inoculated at the seedling stage (in the greenhouse) and at the adult plant stage (in the field) with four pathotypes ofPuccinia striiformis f. sp.tritici to determine if the stripe rust resistance was derived from TM16 and to analyze the expression of the diploid wheat gene(s) at the hexaploid level. At the seedling stage, 14 triticale introgressive lines expressed resistance to some of the used pathotypes, showing introduction of a genetic material from theT. monococcum genome. Among them, 7 lines were resistant to all four stripe rust pathotypes applied at this stage. In the field, adult plant resistance and percentage of infected leaf area were scored and transformed into the coefficient of infection. Plant response to stripe rust was compatible at these two developmental stages with a high statistical probability showing the genetic dependence on the same genetic background. Also observed was a full concordance of the adult plant resistance to stripe rust with previously assessed resistance to leaf rust, as well as the highly significant linkage of the resistance to the both diseases at the seedling stage in the set of the tested introgression lines. This result strongly suggests thatT. monococcum genes responsible for these characters are located in proximity.     

多基因抗性的QTL作图及其在作物持久性抗病育种上的应用

QTL作图已成为解析生物复杂性状遗传基础和基因座之间互作机制的一种有效的研究工具。多基因抗性没有明显的生理小种特异性,一般表现为数量性状。多基因抗性的QTL作图在植物持久性抗病育种中有重要的应用价值,有助于分离到广谱性抗病基因。从作图群体(F1、F2、DH、RIL、BIL和NIL)构建、抗性表型测定和标记辅助育种等方面论述了多基因抗性QTL作图的最新研究进展。     

Correction to: Genetic dissection of maize disease resistance and its applications in molecular breeding

Molecular Breeding - The ‘Honeycrisp’ apple, an economically important cultivar and breeding parent, is prone to soft scald and soggy breakdown postharvest physiological disorders....     

Identification and molecular tagging of a gene from PI 289824 conferring resistance to leaf rust (Puccinia triticina) in wheat

Host-plant resistance is the most economically viable and environmentally responsible method of control for Puccinia triticina, the causal agent of leaf rust in wheat (Triticum aestivum L.). The identification and utilization of new resistance sources is critical to the continued development of improved cultivars as shifts in pathogen races cause the effectiveness of widely deployed genes to be short lived. The objectives of this research were to identify and tag new leaf rust resistance genes. Forty landraces from Afghanistan and Iran were obtained from the National Plant Germplasm System and evaluated under field conditions at two locations in Texas. PI 289824, a landrace from Iran, was highly resistant under field infection. Further evaluation revealed that PI 289824 is highly resistant to a broad spectrum of leaf rust races, including the currently prevalent races of leaf rust in the Great Plains area of the USA. Eight F₁ plants, 176 F₂ individuals and 139 F_2:3 families of a cross between PI 289824 and T112 (susceptible) were evaluated for resistance to leaf rust at the seedling stage. Genetic analysis indicated resistance in PI 289824 is controlled by a single dominant gene. The AFLP analyses resulted in the identification of a marker (P39 M48-367) linked to resistance. The diagnostic AFLP band was sequenced and that sequence information was used to develop an STS marker (TXW₂₀₀) linked to the gene at a distance of 2.3 cM. The addition of microsatellite markers allowed the gene to be mapped to the short arm of Chromosome 5B. The only resistance gene to be assigned to Chr 5BS is Lr52. The Lr52 gene was reported to be 16.5 cM distal to Xgwm443 while the gene in PI 289824 mapped 16.7 cM proximal to Xgwm443. Allelism tests are needed to determine the relationship between the gene in PI 289824 and Lr52. If the reported map positions are correct, the gene in PI 289824 is unique.     

Plant disease resistance genes: recent insights and potential applications

Plant disease resistance genes (R genes) encode proteins that detect pathogens. R genes have been used in resistance breeding programs for decades, with varying degrees of success. Recent molecular research on R proteins and downstream signal transduction networks has provided exciting insights, which will enhance the use of R genes for disease control. Definition of conserved structural motifs in R proteins has facilitated the cloning of useful R genes, including several that are functional in multiple crop species and/or provide resistance to a relatively wide range of pathogens. Numerous signal transduction components in the defense network have been defined, and several are being exploited as switches by which resistance can be activated against diverse pathogens.