Age-related resistance to Pseudomonas syringae pv. tomato is associated with the transition to flowering in Arabidopsis and is effective against Peronospora parasitica

As plants mature it has been observed that some become more resistant to normally virulent pathogens. The ability to manifest the Age-Related Resistance (ARR) response in Arabidopsis to Pseudomonas syringae pathovars tomato (Pst) coincided with the transition to flowering in plants both delayed and accelerated in the transition to flowering. ARR was also associated with a change in PR-1 gene expression, such that young plants expressed PR-1 abundantly at 3 days post inoculation (dpi) while mature plants expressed much less. The Arabidopsis ARR response requires SA accumulation via isochorismate synthase (ICS1) [24]. ICS1 was expressed one dpi with virulent and avirulent Pst in both young and mature plants. The ARR response was also effective versus avirulent Pst providing an additional 4-fold limitation in bacterial growth. Arabidopsis ARR was found to be ineffective against two necrotrophs, Erwinia carotovora subspecies carotovora (bacterium) and Botrytis cinerea (fungus) and one obligate biotroph, Erysiphe cichoracearum (fungus). However, mature wild type, SA-deficient sid2 and NahG plants supported little growth of the obligate biotrophic oomycete, Peronospora parasitica. Therefore ARR to P. parasitica appears to be SA-independent, however the level of ARR resistance was somewhat reduced in these mutants in some experiments. Thus, there may be numerous defence pathways that contribute to adult plant resistance in Arabidopsis.     

瓜类白粉病抗性育种研究进展

文章概述了引起瓜类白粉病病原菌的种类与其分布,S.fuliginea和E.cichoracearum的致病力类型和生理小种的分化,分子标记在瓜类白粉病病原菌群体遗传差异检验中的应用及瓜类抗白粉病的遗传基础。     

Understanding pathogen population structure and virulence variation for efficient resistance breeding to control cucurbit powdery mildews

Cucurbit powdery mildew (CPM) is caused most frequently by well-differentiated obligate erysiphaceous ectoparasites Golovinomyces orontii and Podosphaera xanthii, which vary in their ecology and virulence. All economically important cucurbit crops host both of these CPM species. Breeding of cucurbits for CPM resistance is highly important worldwide, but adequate knowledge of CPM species determination, as well as virulence structure, population dynamics, and spatiotemporal variation of these pathogens, has not yet been achieved. New tools have been developed to enhance research on CPM virulence variation for more efficient breeding and seed and crop production. A set of differential genotypes of Cucumis melo, with high differentiation capacity, may contribute substantially to understanding of variation in CPM virulence at both individual and population levels. Long-term observations (2001–2012) of CPM pathogens in the Czech Republic were used to analyse virulence variation within and among annual CPM populations and demonstrate the utility of recently developed tools for studying species variability and virulence variation of CPM pathogens worldwide. Detailed analyses of diversity and spatiotemporal fluctuations in the composition of CPM populations provide crucial information for shaping breeding programmes and predicting the most effective sources of race-specific resistance. The primary aim of this work was to create a uniform framework for determination of CPM species structure and diversity, virulence phenotypes, virulence and phenotype frequencies, phenotype complexity, dynamics, and variation within and among CPM populations. In addition, practical advice is presented on how to select the most relevant data and interpret them for use in cucurbit resistance breeding.     

Morphological and molecular characterization of <Emphasis Type="Italic">Oidium</Emphasis> subgenus <Emphasis Type="Italic">Reticuloidium</Emphasis> (powdery mildew) newly occurred on cucumber in Japan

In 2002, a powdery mildew with catenate conidia lacking fibrosin bodies was found on cucumber in a greenhouse in Kanagawa Prefecture, Japan. Morphological observation revealed that the fungus belongs to Oidium subgenus Reticuloidium, anamorph of the genus Golovinomyces. Molecular phylogenetic analyses of the nucleotide sequences of the rDNA ITS regions and D1/D2 domains of the 28S rDNA indicated that the fungus belongs to the clade of G. orontii with other Golovinomyces fungi from a wide range of host plants, suggesting that the fungus was newly transported from abroad. Because there has been no prior report of cucumber powdery mildew caused by Reticuloidium, further research on the physiology, epidemiology, control and resistant cucumber varieties is required.     

Hydroxyproline-rich glycoprotein accumulation in tobacco leaves protected against Erysiphe cichoracearum by potato virus Y infection

Tobacco cv. Havana 425 acquired resistance to a compatible isolate of Erysiphe cichoracearum after infection by a strain of potato virus Y (PVY^N) that causes veinal necrosis; another common strain (PVY^O) that does not cause necrosis gave less protection. Hydroxyproline-rich glycoproteins (HRGPs), believed to be involved in resistance, were determined by analysing hydroxyproline (Hyp) in purified cell walls. Hyp content increased significantly in PVY^N-protected leaves, compared with untreated controls, 2–4 days after necrotic lesion symptoms developed. No further increase in Hyp was noted in PVY^N-protected leaves after E. cichoracearum challenge. Hyp increases were significantly higher in protected leaves of plants showing symptoms on day 7 than on day 10. Infection with the PVY^O strain caused significant decrease in Hyp content, compared with uninoculated controls. Inoculation of virus-free plants with E. cichoracearum induced moderate and transitory Hyp increases on day 2 or 3, followed by a quick decrease associated with a weak response by the compatible host. It is suggested that HRGP accumulation induced by PVY^N (but not by PVY^O) causes changes in the host cell wall that result in resistance to E. cichoracearum .     

Evaluation and QTL mapping of resistance to powdery mildew in lettuce

Lettuce (Lactuca sativa) is the major leafy vegetable that is susceptible to powdery mildew disease under greenhouse and field conditions. Quantitative trait loci (QTLs) for resistance to powdery mildew under greenhouse conditions were mapped in an interspecific population derived from a cross between susceptible L. sativa cultivar Salinas and the highly susceptible L. serriola accession UC96US23. Four significant QTLs were detected on linkage groups LG 1 (pm‐1.1), LG 2 (pm‐2.1 and pm‐2.2) and LG 7 (pm‐7.1), each explaining between 35 to 42% of the phenotypic variation. The four QTLs are not located in the documented hotspots of lettuce resistance genes. Alleles for the disease resistance at the four QTLs originated from both parents (two from each), demonstrating that even highly susceptible accessions may provide alleles for resistance to powdery mildew. These QTLs appeared to operate during limited periods of time. Results of the field trials with F_2:3 and F_3:4 families derived from a Soraya (moderately resistant) × Salinas cross demonstrated effective transfer of resistance to powdery mildew in this material. An integrated rating approach was used to estimate relative levels of resistance in 80 cultivars and accessions tested in a total of 23 field and greenhouse experiments. Generally, very low resistance was observed in crisphead‐type lettuces, while the highest relative resistance was recorded in leaf and butterhead types. Comparison of two disease assessment methods (percentage rating and the area under the disease progress steps, AUDPS) for detection of QTLs shows that the two approaches complement each other.     

A new resistance gene to powdery mildew identified in <Emphasis Type="Italic">Solanum neorossii</Emphasis> has been localized on the short arm of potato chromosome 6

A new resistance (R) gene to powdery mildew has been identified and characterized in a population derived from the wild potato species, Solanum neorossii under natural infection in the greenhouse. The segregation of resistance has revealed that this R gene is controlled by a single monogenic and dominant gene designated Rpm-nrs1. Analysis of the DNA sequence on an internal transcribed spacer (ITS) region of the pathogen genome suggests that the pathogen causing the powdery mildew disease is either Golovinomyces orontii or G. cichoracearum. The resistance locus was localized to the short arm of chromosome 6 where several disease R genes already identified in potato and tomato are known to reside. The resistance locus cosegregated in 96 progeny with three AFLP markers and one PCR marker. The sequences of the two cosegregating AFLP markers are highly homologous to Mi-1 conferring resistance to nematode, potato aphid and whitefly and Rpi-blb2 conferring resistance to late blight. The results in this study will facilitate the cloning of this gene conferring resistance to powdery mildew.     

Genetic differentiation in the French population of Erysiphe cichoracearum, a causal agent of powdery mildew of cucurbits

The relative incidence of Erysiphe cichoracearum and Sphaerotheca fuliginea , both agents of powdery mildew of cucurbits, was determined from 275 samples of mildewed leaves of cucurbits collected in 1994 from five regions of France. E. cichoracearum was identified in 9 to 39% of the mildewed leaf samples from four of the regions but was not detected in samples from the Mediterranean island of Corsica. The genetic structure of the French population of E. cichoracearum was examined using RFLPs of the ribosomal internal transcribed spacers amplified by PCR, random amplified polymorphic DNA (RAPD) markers, pathogenicity and mating-type tests. Forty-one isolates, including one from England, were analysed. Cluster analysis from 147 RAPD fragments using 16 primers revealed the existence of three distinct genetic lineages corresponding to three rDNA haplotypes (designated groups A, B and C). Bootstrap, genetic diversity, gametic disequilibrium and private allele analyses supported this differentiation. The genetic differentiation observed in the French population was not related to the geographical origin of the isolates. Group A isolates may be more specialized on melon as, with one exception, they were of race 1 (growth on four of the five melon cultivars tested) in comparison with group B and C isolates, which were of race 0 (growth on IranH only). Thus, the genetic differentiation observed may indicate a host-specialized subdivision within the French population of E. cichoracearum from cucurbits. Gametic disequilibrium analysis among RAPD loci and biological observations suggest that the sexual stage is of minor importance for epidemics of E. cichoracearum on cucurbits.     

不同黄瓜品种(材料)抗白粉病性研究

对市场上常见的44个品种和育种部门提供的10份材料进行了抗白粉病性研究.结果表明,供试的54份黄瓜品种(材料)在抗病性水平上可分为高抗、抗病、中抗、中感、感病和高感6大类群,其中40.74 %的黄瓜品种(材料)属于高抗,病情指数均小于6.5,为生产上合理布局和育种提供抗源.