Abstract:Phytophthora fragariae var. fragariae is the causal agent of red stele (red core) root rot in strawberry (Fragaria spp.). The inheritance of resistance to one isolate of this fungus was studied in 12 segregating
populations of F. *ananassa derived from crosses between four resistant cultivars (Climax, Redgauntlet,Siletz, and Sparkle) and three susceptible cultivars (Blakemore, Glasa, and Senga Sengana). The analysis clearly supports the hypothesis of a single segregating dominant resistance gene. It is proposed that this gene be designated Rpf2.
Abstract: The potential role of two pathogen-induced pepper genes, encoding basic pathogenesis-related protein 1(CABPR1) and ascorbate peroxidase-like 1 (CAPOA1), in tolerance against phytopathogens was examined in transgenic tomato (Lycopersicum esculentum cv. House Momotaro) plants. Polymerase chain reaction and reverse transcription-polymerase chain reaction analyses using gene-specific primers revealed that the pepper CABPR1 and CAPOA1 genes were integrated into the tomato genome. The constitutive expression of CABPR1 and CAPOA1 in the tomato did not exhibit any morphological abnormalities.
However, these transgenic tomato plants showed enhanced tolerance to the oomycete pathogen Phytophthora capsici, and very weak resistance to the bacterial pathogen Pseudomonas syringae pv. tomato. These results suggest that overexpression of CABPR1 and CAPOA1 in tomato plants altered their resistance responses to pathogenic attack.
Abstract:Phytophthora citrophthora is the most widely spread oomycete plant pathogen over all the citrus growing areas and represents one of the major causes of crop losses. Constitutive over-expression of genes encoding proteins involved in plant defence mechanisms to disease is one of the strategies proposed to increase plant tolerance to oomycete and fungal pathogens. P23 (PR-5), a 23-kDa pathogenesis-related protein similar to osmotins, is induced in tomato(Lycopersicon esculentum Mill. cv. Rutgers) plants when they are infected with citrus exocortis viroid, and its antifungal activity has been demonstrated in in vitro assays. We have successfully produced transgenic orange (Citrus sinensis L. Obs. cv. Pineapple) plants bearing a chimeric gene construct consisting of the cauliflower mosaic virus 35S promoter and the coding region of the tomato pathogenesis-related PR-5. Nine regenerated
transgenic lines constitutively expressed the PR protein. They were challenged with Phytophthora citrophthora using a detached bark assay. A significant reduction in lesion development was consistently observed in one transgenic line in comparison to the control plants. This same line achieved plant survival rates higher than control plants when transgenic trees were inoculated with oomycete cultures. These results provide evidence for the in vitro activity of the tomato PR-5 protein against a, and suggest that this may be employed as a strategy aimed at engineering Phytophthora disease resistance in citrus.
Abstract: Potato (cv. Bintje) was transformed with a gene encoding an oxalate oxidase from wheat under the control of the CaMV35S promoter. Transgenic potato plants produced high constitutive levels of H2O2 as visualized by 4-chloro-1-naphtol staining. The resistance of these plants was tested against Phytophthora infestans. An increased level of resistance to the disease was marked by a reduced number of lesions as well as by a decreased number of sporangia formed per lesion. In addition, oxalate oxidase overexpressing plants also exhibited improved resistance to Streptomyces reticuliscabiei, the causal agent of netted scab. Increased expression of oxalate oxidase had no effect on the interaction with Erwinia carotovora. These experiments show that overexpression of oxalate oxidase represents a potentially interesting approach for protection of potato to pathogens.
Abstract: Defense responses were investigated in the leaves of a cultivar of pepper, Capsicum annuum (cv. SCM334) resistant to Phytophthora blight.
Jasmonic acid (JA) increased in the resistant cultivar immediately after inoculation with the pathogen, Phytophthora capsici, but as the levels of
JA later decreased, levels of salicylic acid (SA) increased and were subsequently accompanied by hypersensitive response (HR)-mediated cell death in SCM334. Simultaneously, expression patterns of JA- and HR-related genes were analyzed. The mRNA of catalase and peroxidase (suppressing HR generation) disappeared, while the mRNA of OPR3 (encoding JA synthesis reductase) was detected in SCM334 specifically. JA-mediated defense appears to be crucial in the resistance of pepper plants against P. capsici.
Abstract: To elucidate the molecular events of potato quantitative resistance to Phytophthora infestans, we performed a comprehensive transcriptional analysis using cDNA microarrays, containing 1009 ESTs from a subtractive library. Leaves of a moderately resistant potato clone were inoculated with P. infestans and sampled at nine time points ranging from 2 to 72 h after inoculation. A total of 348 P. infestans-responsive genes were identified. These functional genes are mostly related to metabolism, plant defense, signaling and transcription regulation, involving the whole process of plant defense response to pathogens. Based on the general expression patterns of these genes at different time points, we discriminated distinct stages of potato defense against P. infestans and revealed genes participating in each stage. To further understand the dynamics of P. infestans-induced gene expression, hierarchical clustering was used to illustrate their various expression profiles during the time course, including early, mid and late gene induction as well as early gene repression. Interestingly, some genes involved in the hypersensitive response were also identified, suggesting that a same or similar defense system may exist in both race-specific and race-nonspecific resistances. In addition, 114 novel genes with unknown functions were isolated.
Abstract: Cocoa black pod rot, a disease caused by oomycetes of the genus Phytophthora, causes substantial yield losses throughout the world,
particularly in Africa with the very aggressive species Phytophthora megakarya. In order to reduce the impact of that pathogen, priority is
given to genetic control through more resistant cultivars, and breeders are seeking sources of resistance in wild cocoa trees. Wild cocoa trees were surveyed in French Guiana between 1985 and 1995, leading to the collection of abundant plant material from more than 200 mother trees originating from five river basins. We present here the results of tests to assess resistance to the species P. megakarya (a species only existing in Africa), conducted at CIRAD in Montpellier, France, on circa 40 genotypes collected in the Camopi river basin, along with approximately 20 genotypes from other populations (Ke rindioutou, Borne 7, Euleupousing, Pina and Oyapok). The strain used for artificial inoculation was NS269, isolated in Cameroon. Seven cacao clones were classified as highly resistant and 29 as resistant, some of which displayed greater resistance to P. megakarya than the reference resistant clone IMC 47. This study suggests that the wild material from French Guiana could play a significant role in controlling P. megakarya in Africa and also Phytophthora palmivora in all cocoa-producing zones.
Abstract: Previous studies have shown that suspension-cultured cells of Solanum genotypes with various polygenic resistances to Phytophthora infestans differed in activities of early oxidative processes in response to culture filtrate (CF) from this pathogen. These studies have now been extended by analysing production of reactive oxygen species (ROS), lipid peroxidation and lipoxygenase (LOX, E.C.1.13.11.12) activity induced by CF in detached leaves of S. tuberosum cv Bzura and clone H-8105, polygenically resistant and susceptible, respectively, as well as S. nigrum, nonhost, completely
resistant. The relative increase in the ROS production was higher in the susceptible clone H-8105 than in both resistant genotypes. Lipid peroxidation increased only in the nonhost S. nigrum. An increase in lipid peroxidation in S. nigrum leaves coincided with enhanced LOX activity. In both S. tuberosum genotypes, significant increases in LOX activity were delayed and unaccompanied by changes in the level of lipid peroxidation. LOX activity attained a higher level in both of the resistant genotypes than in the susceptible one. The present results suggest that the involvement of both ROS production and LOX activity in the defense strategy in Solanum species/P.infestans interactions.
Abstract: This study investigated the expression pattern of genes encoding for a basic PR-1 protein, a basic b-1,3-glucanase, a peroxidase, and a sesquiterpene cyclase involved in defense responses in three pepper cultivars with different levels of resistance to Phytophthora capsici. All genes were up-regulated in infected stems of the pepper cultivars, with expression being detected 8 h post-inoculation. mRNA levels of these genes increased markedly by 24 h post-inoculation, and maximal induction levels were observed for the PR-1 and sesquiterpene cyclase genes. PR-1, peroxidase, and sesquiterpene genes were always expressed at higher levels in resistant cultivars than in the susceptible cultivar, although up-regulation was observed in both, suggesting that the differences between these pepper genotypes in susceptibility and resistance are a matter of the timing and magnitude of the defense response.
Abstract: A doubled-haploid (DH) population (n = 176) obtained by anther culture of an F1 hybrid between a line susceptible to Phytophthora capsici K9-11 (Capsicum annuum L.) and a line resistant to P. capsici AC2258 (C. annuum L.) was inoculated with P. capsici. QTL analysis of the resistance was performed using a linkage map consisting of 16 linkage groups (LGs), covering a total distance of 1100.5 cM. Three QTLs were detected on LG1, LG6 and LG7. The QTL with the highest LOD score, detected on LG7, explained 82.7% of the phenotypic variance with a LOD score of 67.02. This QTL was designated as Phyt-1. The nearest marker was an AFLP marker, M10E3-6. The second QTL, designated as Phyt-2, was found on LG1. It explained 6.4% of the phenotypic variance with a LOD score of 2.54. The nearest RAPD marker was RP13-1. The other QTL, designated as Phyt-3, which was found on LG6, explained 5.6% of the phenotypic variance with a LOD score of 2.20. The nearest AFLP marker was M9E3-11. It was confirmed that the lines with a high resistance could be efficiently selected by using two markers, M10E3-6 and RP13-1, simultaneously. The presence of both Phyt-1 and Phyt-2 under homozygous conditions may enable to breed resistant cultivars of sweet pepper. The molecular markers identified in the present study could be useful for marker-assisted selection (MAS) in order to breed sweet pepper cultivars with a high resistance to P. capsici using AC2258 as a source of resistance genes.
Abstract