Level of Endogenous Cytokinins and Abscisic and Salicylic Acids in the Leaves of Phlox paniculataand Ph. setaceaunder the Influence of Invasion by Conidia of Phytopathogens

We studied the effects of the invasion of Phlox paniculataL. and Ph. setaceaL. by causative agents of the phlox powdery mildew (compatible combination) and lupine powdery mildew (incompatible combination) on the level of endogenous cytokinins and abscisic and salicylic acids. In all experimental variants, the level of zeatin-riboside and abscisic and salicylic acids in the leaves of invaded plants increased within 48 h. The highest level of phytohormones and salicylic acid was recorded in the absolutely resistant species Ph. setacea.     

Influence of Phytohormones on Development of Conidial Inoculum of Causative Agents of the Phlox and Barley Powdery Mildew

We studied the role of phytohormones: zeatin, kinetin, and abscisic acid, in the regulation of development of the conidial inoculum of Erysiphe cichoracearumDC. f. phlogisJacz. and E. graminisDC. f. hordeiMarchal. When the pathogen conidia were in direct contact with phytohormones, the intensity of their germination significantly increased. In the presence of cytokinins, the amount of normal appressoria decreased and that of abnormal growth tubes increased. On the phlox leaves treated with cytokinins, the intensity of germination of the conidia increased, as compared to the control, while abscisic acid exerted the opposite effect. The treatment of barley leaves with cytokinins did not affect markedly the development of conidial inoculum, as compared to the control, while abscisic acid significantly decreased the intensity of germination of the conidia. On the leaves of different Phloxspecies, the degree of germination of the conidial negative correlated with their resistance against the powdery mildew. The role of cytokinins in pathogenesis of biotrophic fungi is discussed.     

A cDNA clone for a pathogenesis-related protein 1 from barley

A barley cDNA clone (PRb-1) corresponding to an mRNA differentially induced in resistant compared to susceptible barley cultivars by powdery mildew infection was isolated and characterised. The deduced amino acid sequence revealed 24 amino acids comprising the signal peptide and 140 amino acids of the mature peptide (15 kDa). This showed close homology to PR-1-like proteins, which have been isolated from maize, tobacco, tomato and Arabidopsis thaliana. Northern blot analysis showed accumulation of the corresponding mRNA 12 h after inoculation of resistant barley cultivars with Erysiphe graminis. Increased expression of the PRb-1 gene was also observed in resistant compared with near-isogenic susceptible barley plants following treatment with ethylene, salicylic acid, methyl jasmonate and 2,6-dichloro-isonicotinic acid.     

籽用美洲南瓜叶片对白粉病菌的抗逆生理响应

以籽用美洲南瓜(Cucurbita pepo L.)白粉病抗病品系F2和感病品系M3为试材,在人工气候箱内接种白粉病生理小种2US孢子悬浮液,考察在接种白粉病菌后南瓜幼苗植株与白粉病菌的互作、叶片活性氧代谢及保护酶活性的变化,探讨南瓜抵御白粉病的生理机制。结果表明：(1)与感病品系M3相比,接种白粉病菌后,抗病品系F2叶片上病原菌发育缓慢,较难侵染叶片。(2)抗病品系F2在感病初期叶片H₂O₂、O₂^-·含量迅速升高后逐渐下降,而感病品系在感病初期H₂O₂、O₂^-·含量上升缓慢,在达最大值后始终保持较高水平,且感病品系叶片MDA含量始终高于抗病品系;组织化学染色分析发现,抗病品系叶片着色比感病品系快,之后着色面积有所减少并趋于较低水平。(3)抗病品系F2和感病品系M3叶片抗氧化酶CAT、SOD、POD活性及PAL、PPO活性在接种白粉病菌后均显著增加,但抗病品系的活性及其增幅均高于感病品系。研究发现,籽用美洲南瓜抗病品系叶片上白粉病菌发育缓慢,较难受到侵染,生成菌丝体后叶片上粉状斑点较小;抗病品系在被白粉病菌侵染初期依靠活性氧的增加抵御病原菌的入侵,随着活性氧含量增加抗病品系通过迅速增加自身抗氧化酶活性来防止氧化胁迫;与感病品系相比,抗病品系在受病原菌侵染后能迅速增加PAL、PPO活性以抵御病原菌侵染。     

Artificial elevation of glutathione contents in salicylic acid‐deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) reduces susceptibility to the powdery mildew pathogen Euoidium longipes

• The effects of elevated glutathione levels on defence responses to powdery mildew (Euoidium longipes) were investigated in a salicylic acid‐deficient tobacco (Nicotiana tabacum cv. Xanthi NahG) and wild‐type cv. Xanthi plants, where salicylic acid (SA) contents are normal.
• Aqueous solutions of reduced glutathione (GSH) and its synthetic precursor R‐2‐oxothiazolidine‐4‐carboxylic acid (OTC) were injected into leaves of tobacco plants 3 h before powdery mildew inoculation.
• SA‐deficient NahG tobacco was hyper‐susceptible to E. longipes, as judged by significantly more severe powdery mildew symptoms and enhanced pathogen accumulation. Strikingly, elevation of GSH levels in SA‐deficient NahG tobacco restored susceptibility to E. longipes to the extent seen in wild‐type plants (i.e. enhanced basal resistance). However, expression of the SA‐mediated pathogenesis‐related gene (NtPR‐1a) did not increase significantly in GSH or OTC‐pretreated and powdery mildew‐inoculated NahG tobacco, suggesting that the induction of this PR gene may not be directly involved in the defence responses induced by GSH.
• Our results demonstrate that artificial elevation of glutathione content can significantly reduce susceptibility to powdery mildew in SA‐deficient tobacco.

     

The Dynamics of Abscisic Acid and Cytokinins Content in the Leaves of Wheat–Aegilops Lines and Their Parental Forms Affected by Powdery Mildew

We studied the dynamics of abscisic acid and cytokinins content in wheat–aegilops lines and their parental forms affected by powdery mildew. Lines 95/99 ⁱ and 56/99 ⁱ demonstrated the types of resistance untypical of the soft wheat Rodina and Aegilops speltoides k-389 but typical of Ae. speltoides Tausch from other natural habitats. A relative stability of the hormonal balance in the course of the infection was demonstrated for lines 95/99 ⁱ and Ae. speltoides k-389 highly resistant to the pathogen penetration. Line 56/99 ⁱ was sensitive to the penetration; however, a subsequent prolonged hypersensitive response eliminated pathogen colonies surrounded by necrotic areas. A correlation between disbalanced hormonal metabolism of cytokinins and low resistance to the infection has been revealed for 56/99 ⁱ line and Rodina cultivar. Free form of abscisic acid was revealed in the intact plants of the parental forms. Bound form of this hormone was revealed in the infected plants of lines 95/99 ⁱ and 56/99 ⁱ as well as of Ae. speltoides k-389, which seems to be a marker of their different stress resistance according to the phenotypic manifestation of powdery mildew.     

E3 ubiquitin ligase gene CMPG1–V from Haynaldia villosa L. contributes to powdery mildew resistance in common wheat (Triticum aestivum L.)

Powdery mildew is one of the most devastating wheat fungal diseases. A diploid wheat relative, Haynaldia villosa L., is highly resistant to powdery mildew, and its genetic resource of resistances, such as the Pm21 locus, is now widely used in wheat breeding. Here we report the cloning of a resistance gene from H. villosa, designated CMPG1–V, that encodes a U–box E3 ubiquitin ligase. Expression of the CMPG1–V gene was induced in the leaf and stem of H. villosa upon inoculation with Blumeria graminis f. sp. tritici (Bgt) fungus, and the presence of Pm21 is essential for its rapid induction of expression. CMPG1–V has conserved key residues for E3 ligase, and possesses E3 ligase activity in vitro and in vivo. CMPG1–V is localized in the nucleus, endoplasmic reticulum, plasma membrane and partially in trans‐Golgi network/early endosome vesicles. Transgenic wheat over‐expressing CMPG1–V showed improved broad‐spectrum powdery mildew resistance at seedling and adult stages, associated with an increase in expression of salicylic acid‐responsive genes, H₂O₂ accumulation, and cell‐wall protein cross‐linking at the Bgt infection sites, and the expression of CMPG1–V in H. villosa was increased when treated with salicylic acid, abscisic acid and H₂O₂. These results indicate the involvement of E3 ligase in defense responses to Bgt fungus in wheat, particularly in broad‐spectrum disease resistance, and suggest association of reactive oxidative species and the phytohormone pathway with CMPG1–V‐mediated powdery mildew resistance.     

TaRPP13-3, a CC-NBS-LRR-like gene located on chr 7D,promotes disease resistance to wheat powdery mildew in Brock

Disease resistance (R) gene, RPP13, plays an important role in the resistance of plants to pathogen infections; its function in resistance of wheat to powdery mildew remains unknown. In this study, a RNA-Seq technique was used to monitor expression of genes in susceptible wheat ‘Jing411’ and resistant near-isogenic line ‘BJ-1’ in response to powdery mildew infection. Overall, 413 differential expression genes were observed and identified as involved in disease resistance. RPP13 homologous gene on wheat chromosome 7D was preliminarily identified using the wheat 660K SNP chip. RPP13 was highly expressed in ‘BJ-1’ and encodes 1,027 amino acids, including CC, NB and LRR domain, termed TaRPP13-3. After inoculation with powdery mildew, expression of TaRPP13-3 in resistant wheat changed with time, but average expression was higher when compared to susceptible variety, thus indicating that TaRPP13-3 is involved in resistance to powdery mildew. Virus-induced gene silencing (VIGS) was used to inhibit expression of TaRPP13-3 in resistant parent ‘Brock’. Results indicated that silencing of TaRPP13-3 led to decreased disease resistance in ‘Brock’. Overall results of this study indicate that TaRPP13-3 gene is involved in the defence response of wheat to powdery mildew and plays a positive role in wheat powdery mildew interactions.     

Endogenous Abscisic Acid in Wheat Plants upon Inoculation with the Powdery Mildew Causative Agent (Erysiphe graminisf. sp. tritici)

We studied the dynamics of the abscisic acid content in above-ground parts of wheat cultivars with different resistance against powdery mildew. It was assayed by the HPLC method in healthy and diseased (inoculated by the powdery mildew causative agent) plants (from inoculation to the stage of pathogen spore formation). The results are discussed with special reference to the wheat resistance against the powdery mildew.     

Two new hosts of anamorphic Erysiphe quercicola: Cinnamomum camphora and Murraya paniculata

Based on collections of powdery mildews (Erysiphales) in Taiwan and combined molecular and morphological analyses, camphor tree (Cinnamomum camphora) and orange jasmine (Murraya paniculata) are recognized as new hosts of the anamorph of the powdery mildew Erysiphe quercicola. The anamorphic powdery mildew on C. camphora has been known as Pseudoidium cinnamomi, but its relationship to a teleomorph was unknown. For M. paniculata as substrate of powdery mildew, only an anamorphic Cystotheca species has been named. Morphological investigation of the fungus on this host shows that the specimens from Taiwan belong to another genus because of the lack of fibrosin bodies. Analysis of internal transcribed spacer sequences indicates that the anamorphic powdery mildews on camphor and orange jasmine belong to a clade representing E. quercicola, with the teleomorph found only on oak species (Quercus, Fagaceae), but with its anamorph reported from a broad host range, particularly in the tropics.     

Inheritance of powdery mildew (Erysiphe polygoni DC) resistance in mungbean (Vigna radiata L. Wilczek)

Detached mungbean (Vigna radiata L.Wilczek) leaves were inoculated with a conidial suspension of a local isolate (TI-1) of the powdery mildew pathogen (Erysiphe polygoni DC) under controlled environment conditions. Based on the latent period and severity of the infection, a rating scale of 0–5 was used to classify the host pathogen interactions. Reactions 0, 1 and 2 were considered resistant and referred to as R0, R1 and R2 while 3, 4 and 5 were classified as susceptible (S). RUM lines (resistant to powdery mildew) and their derivatives are crossed with several susceptible (reaction types 3–5) genotypes and the inheritance of the resistance was studied in the F₁, F₂ and F₃ generations. The results showed that powdery mildew resistance in mungbean is governed by two dominant genes designated as Pm-1 and Pm-2. When both Pm-1 and Pm-2 were present, an R0 reaction was observed after inoculation with TI-1. The resistant reaction was R1 when only Pm-1 was present and R2 in the presence of Pm-2. In the absence of both Pm-1 and Pm-2, susceptible reactions 3, 4 and 5 were observed.     

Sensibilité du Melon àSphaerotheca fuliginea en Fonction de L'Etage Foliaire

Effect of leaf position on the susceptibility of melon plants to artificial infection with powdery mildew, Sphaerotheca fuliginea The leaf position of melon plants seems to play a role on their susceptibility when they are artificially infected with powdery mildew Sphaerotheca fuliginea. The cotyledons are generally very susceptible, while the first leaf relatively resistant; the susceptibility again continues up to the 4th–5th leaf (but less susceptible than the cotyledons) and then after it decreases; these results can be obtained on plants in greenhouse or on detached leaves in Petri dishes. From this observation, we think that the screening of melon genotypes for resistance to powdery mildew can be evaluated neither on the cotyledons which are very susceptible nor on the first leaf which is resistant, but on the third leaf which is moderately susceptible. In fact, there is a good correlation between the reaction of the third leaf and the resistance or susceptibility of genotypes.     

Linkage of a RAPD marker with powdery mildew resistance <Emphasis Type="Italic">er-1</Emphasis> gene in <Emphasis Type="Italic">Pisum sativum</Emphasis> L.

The aim of this study was to investigate the inheritance of powdery mildew disease and to tag it with a DNA marker to utilize for the marker-assisted selection (MAS) breeding program. The powdery mildew resistant genotype Fallon ^er and susceptible genotype 11760-3 ^ER were selected from 177 genotypes by heavy infestation of germplasm with Erysiphe pisi through artificial inoculation The F₁ plants of the cross Fallon/11760-3 indicated the dominance of the susceptible allele, while F₂ plants segregated in 3: 1 ratio (susceptible: resistant) that fit for goodness of fitness by χ² (P > 0.07), indicating monogenic recessive inheritance for powdery mildew resistance in Pisum sativum. A novel RAPD marker OPB18 (5′-CCACAGCAGT-3′) was linked to the er-1 gene with 83% probability with a LOD score of 4.13, and was located at a distance of 11.2 cM from the er-1 gene.     

Genetic characterization of powdery mildew resistance in U.S. hard winter wheat

Powdery mildew significantly affects grain yield and end-use quality of winter wheat in the southern Great Plains. Employing resistance resources in locally adapted cultivars is the most effective means to control powdery mildew. Two types of powdery mildew resistance exist in wheat cultivars, i.e., qualitative and quantitative. Qualitative resistance is controlled by major genes, is race-specific, is not durable, and is effective in seedlings and in adult plants. Quantitative resistance is controlled by minor genes, is non-race-specific, is durable, and is predominantly effective in adult plants. In this study, we found that the segregation of powdery mildew resistance in a population of recombinant inbred lines developed from a cross between the susceptible cultivar Jagger and the resistant cultivar 2174 was controlled by a major QTL on the short arm of chromosome 1A and modified by four minor QTLs on chromosomes 1B, 3B, 4A, and 6D. The major QTL was mapped to the genomic region where the Pm3 gene resides. Using specific PCR markers for seven Pm3 alleles, 2174 was found to carry the Pm3a allele. Pm3a explained 61% of the total phenotypic variation in disease reaction observed among seedlings inoculated in the greenhouse and adult plants grown in the field and subjected to natural disease pressure. The resistant Pm3a allele was present among 4 of 31 cultivars currently being produced in the southern Great Plains. The genetic effects of several minor loci varied with different developmental stages and environments. Molecular markers associated with these genetic loci would facilitate incorporating genetic resistance to powdery mildew into improved winter wheat cultivars.     

Isolation of resistance gene analogues to powdery mildew resistance sequences in hexaploid wheat

This paper reports the characterization of the powdery mildew resistance homologous genes family of Triticum aestivum. Using degenerate primer pair for wheat resistance genes, we have cloned seven 3′ truncated powdery mildew resistance gene homologous fragments Tpc5a, Tp25a, Tp25b, Tp3a5a, Tp3a5b, Tp4b5a and Tp4b5b. These fragments were sequenced. The deduced amino acid sequences showed that six of them have premature stop codons. All these sequences had a very high level of similarity to known Pm resistance genes such as Pm3a, Pm3b, Pm3d and pm3f in hexaploid wheat. By ignoring the stop codons in the sequences, their deduced protein sequences were of coiled-coil (CC)-nucleotide binding site (NBS)-leucine repeat rich (LRR) structure. These results suggest that there are many powdery mildew resistance gene analogues in both resistant and susceptible wheat. Among them, small insertion/deletion events and point mutations can result in the diversity of wheat Pm resistance homologous genes.     

Genetic dissection of a TIR‐NB‐LRR locus from the wild North American grapevine species Muscadinia rotundifolia identifies paralogous genes conferring resistance to major fungal and oomycete pathogens in cultivated grapevine

The most economically important diseases of grapevine cultivation worldwide are caused by the fungal pathogen powdery mildew (Erysiphe necator syn. Uncinula necator) and the oomycete pathogen downy mildew (Plasmopara viticola). Currently, grapegrowers rely heavily on the use of agrochemicals to minimize the potentially devastating impact of these pathogens on grape yield and quality. The wild North American grapevine species Muscadinia rotundifolia was recognized as early as 1889 to be resistant to both powdery and downy mildew. We have now mapped resistance to these two mildew pathogens in M. rotundifolia to a single locus on chromosome 12 that contains a family of seven TIR‐NB‐LRR genes. We further demonstrate that two highly homologous (86% amino acid identity) members of this gene family confer strong resistance to these unrelated pathogens following genetic transformation into susceptible Vitis vinifera winegrape cultivars. These two genes, designated r esistance to P lasmopara v iticola (MrRPV1) are the first resistance genes to be cloned from a grapevine species. Both MrRUN1 and MrRPV1 were found to confer resistance to multiple powdery and downy mildew isolates from France, North America and Australia; however, a single powdery mildew isolate collected from the south‐eastern region of North America, to which M. rotundifolia is native, was capable of breaking MrRUN1‐mediated resistance. Comparisons of gene organization and coding sequences between M. rotundifolia and the cultivated grapevine V. vinifera at the MrRUN1/MrRPV1 locus revealed a high level of synteny, suggesting that the TIR‐NB‐LRR genes at this locus share a common ancestor.     

Identification and mapping of two powdery mildew resistance genes in <Emphasis Type="Italic">Triticum boeoticum</Emphasis> L.

Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt), is one of the important foliar diseases of wheat that can cause serious yield losses. Breeding for cultivars with diverse resources of resistance is the most promising approach for combating this disease. The diploid A genome progenitor species of wheat are an important resource for new variability for disease resistance genes. An accession of Triticum boeoticum (A^bA^b) showed resistance against a number of Bgt isolates, when tested using detached leaf segments. Inheritance studies in a recombinant inbred line population (RIL), developed from crosses of PM resistant T. boeoticum acc. pau5088 with a PM susceptible T. monococcum acc. pau14087, indicated the presence of two powdery mildew resistance genes in T. boeoticum acc. pau5088. Analysis of powdery mildew infection and molecular marker data of the RIL population revealed that both powdery mildew resistance genes are located on the long arm of chromosome 7A. Mapping was conducted using an integrated linkage map of 7A consisting of SSR, RFLP, STS, and DArT markers. These powdery mildew resistance genes are tentatively designated as PmTb7A.1 and PmTb7A.2. The PmTb7A.2 is closely linked to STS markers MAG2185 and MAG1759 derived from RFLP probes which are linked to powdery mildew resistance gene Pm1. This indicated that PmTb7A.2 might be allelic to Pm1. The PmTb7A.1, flanked by a DArT marker wPt4553 and an SSR marker Xcfa2019 in a 4.3 cM interval, maps proximal to PmT7A.2. PmTb7A.1 is putatively a new powdery mildew resistance gene. The powdery mildew resistance genes from T. boeoticum are currently being transferred to cultivated wheat background through marker-assisted backcrossing, using T. durum as bridging species.