| regulatory sequences for expressing genes in oomycete fungi. | promoter and terminator sequences from a range of species were tested for activity in the oomycetes, a group of lower fungi that bear an uncertain taxonomic affinity to other organisms and in which little is known of the sequences required for transcription. transient assays, using the reporter gene beta-glucuronidase (gus), were used to examine the function of these promoters and terminators in the plant pathogens phytophthora infestans and p. megasperma f. sp. glycinea, and in the saprophytic ... | 1992 | 1495476 |
| transformation of the oomycete pathogen, phytophthora infestans. | a stable transformation procedure has been developed for phytophthora infestans, an oomycete fungus that causes the late blight diseases of potato and tomato. this is the first description of reliable methods for transformation in an oomycete pathogen. drug-resistant transformants were obtained by using vectors that contained bacterial genes for resistance to hygromycin b or g418 fused to promoters and terminators from the hsp70 and ham34 genes of the oomycete, bremia lactucae. using polyethylen ... | 1991 | 1804404 |
| highly abundant and stage-specific mrnas in the obligate pathogen bremia lactucae. | germinating spores of the obligate pathogen bremia lactucae (lettuce downy mildew) contain several unusually abundant species of mrna. thirty-nine cdna clones corresponding to prevalent transcripts were isolated from a library synthesized using poly(a)+ rna from germinating spores; these clones represented only five distinct classes. each corresponding mrna accounted for from 0.4 to 9 percent by mass of poly(a)+ rna from germinating spores and together represented greater than 20 percent of the ... | 1990 | 2131094 |
| structure and expression of a gene encoding heat-shock protein hsp70 from the oomycete fungus bremia lactucae. | a gene encoding a protein homologous to a 70-kda heat-shock protein (hsp70) was isolated from bremia lactucae and its structure and pattern of expression were determined. this is the first report on the structure of a protein-coding gene from an oomycete fungus. the cloned gene is a member of a small multigene family. the level of hsp70 mrna in germlings increases from a low constitutive level in response to heat or cold treatment. a high level of the mrna is also detected in spores. the hsp70 g ... | 1989 | 2792764 |
| genetic analysis of the fungus, bremia lactucae, using restriction fragment length polymorphisms. | restriction fragment length polymorphisms (rflps) were developed as genetic markers for bremia lactucae, the biotrophic oomycete fungus which causes lettuce downy mildew. by using 55 genomic and cdna probes, a total of 61 rflp loci were identified among three heterothallic isolates of b. lactucae. of these 61 rflp loci, 53 were heterozygous in at least one of the three strains and thus were informative for linkage analysis in at least one of two f1 crosses that were performed. analysis of the co ... | 1988 | 2906309 |
| transfer of label from 3h-glucose in digitaria eriantha leaves to the rust fungus puccinia digitariae pole evans. | digitaria eriantha pentzii was fed 3h-glucose prior to inoculation with uredospores of puccinia digitariae pole evans. twenty-one hours after inoculation, uptake of label from 3h-glucose by the primary infection structures of p. digitariae was demonstrated employing autoradiography. these results indicate that an exchange of nutrients between host and pathogen occurs very early on in the infection process, during the formation of the primary infection structures. despite contrary reports that ob ... | 1985 | 4020098 |
| niaa, the structural nitrate reductase gene of phytophthora infestans: isolation, characterization and expression analysis in aspergillus nidulans. | the nitrate reductase (nr) gene niaa of the oomycete phytophthora infestans was selected from a gene library by heterologous hybridization. niaa occurs as a single-copy gene ant its expression is regulated by the nitrogen source. the nucleotide sequence of niaa was determined and comparison of the deduced amino-acid sequence of 902 residues with nrs of higher fungi and plants revealed a significant homology, particularly within the three cofactor-binding domains for molybdenum, heme and fad. the ... | 1995 | 7614559 |
| a lactuca universal hybridizer, and its use in creation of fertile interspecific somatic hybrids. | a lactuca sativa cv. ardente line heterozygous for a gene encoding resistance to kanamycin, a positive and dominant trait, was crossed with cv. girelle, which is heterozygous for a recessive albinism marker. the resulting seeds yielded 25% albino seedlings, of which 50% were also resistant to kanamycin. such plantlets (kr, a) grown in vitro were used for preparation of universal hybridizer protoplasts, since green buds that can develop on kanamycin containing-medium should result from fusion wit ... | 1994 | 7816020 |
| mutants of downy mildew resistance in lactuca sativa (lettuce). | as part of our investigation of disease resistance in lettuce, we generated mutants that have lost resistance to bremia lactucae, the casual fungus of downy mildew. using a rapid and reliable screen, we identified 16 distinct mutants of latuca sativa that have lost activity of one of four different downy mildew resistance genes (dm). in all mutants, only a single dm specificity was affected. genetic analysis indicated that the lesions segregated as single, recessive mutations at the dm loci. dm3 ... | 1994 | 8088530 |
| expression and antisense inhibition of transgenes in phytophthora infestans is modulated by choice of promoter and position effects. | procedures were identified for manipulating the expression of genes in the oomycete fungus, phytophthora infestans. the activities of five putative promoter sequences, derived from the 5' regions of oomycete genes, were measured in transient assays performed in protoplasts and in stable transformants. the sequences tested were from the ham34 and hsp70 genes of bremia lactucae, the actin-encoding genes of p. infestans and p. megasperma, and a polyubiquitin-encoding gene of p. infestans. experimen ... | 1993 | 8224895 |
| cloning and analysis of a constitutive heat shock (cognate) protein 70 gene inducible by l-glutamine. | an intronless gene encoding a protein of 652 amino acid residues with an m(r) of 71,266, showing between 79% and 59% identity in nucleotide sequence with heat shock protein 70 (hsp 70) genes of bremia lactucae (a parasitic oomycete of lettuce) and a wide range of organisms that include humans, was isolated from the nonparasitic oomycete achlya klebsiana. while the gene appears to be constitutively expressed, l-glutamine augmented its expression particularly under conditions of nutritional stress ... | 1994 | 8308021 |
| transformation of the oomycete pathogen phytophthora megasperma f. sp. glycinea occurs by dna integration into single or multiple chromosomes. | a procedure for stable transformation was developed for phytophthora megasperma f. sp. glycinea, an oomycete pathogen of soybean. transformants were obtained using a bacterial hygromycin resistance gene fused to a promoter and terminator from the ham34 gene of another oomycete, bremia lactucae. vector dna, alone or complexed to cationic liposomes, was introduced into protoplasts using polyethylene glycol and cacl2. dna and rna hybridization, and phosphotransferase assays, confirmed the presence ... | 1993 | 8382110 |
| a transgenic mutant of lactuca sativa (lettuce) with a t-dna tightly linked to loss of downy mildew resistance. | one hundred and ninety-two independent primary transformants of lettuce cv. diana were obtained by co-cultivation with agrobacterium tumefaciens carrying constructs containing maize ac transposase and ds. r2 families were screened for mutations at four genes (dm) for resistance to downy mildew. one family, designated dm3t524, had lost resistance to an isolate of bremia lactucae expressing the avirulence gene avr3. loss of resistance segregated as a single recessive allele of dm3. the mutation wa ... | 1997 | 9353944 |
| the major resistance gene cluster in lettuce is highly duplicated and spans several megabases. | at least 10 dm genes conferring resistance to the oomycete downy mildew fungus bremia lactucae map to the major resistance cluster in lettuce. we investigated the structure of this cluster in the lettuce cultivar diana, which contains dm3. a deletion breakpoint map of the chromosomal region flanking dm3 was saturated with a variety of molecular markers. several of these markers are components of a family of resistance gene candidates (rgc2) that encode a nucleotide binding site and a leucine-ric ... | 1998 | 9811791 |
| genome size determination in peronosporales (oomycota) by feulgen image analysis. | genome size was determined, by nuclear feulgen staining and image analysis, in 46 accessions of 31 species of peronosporales (oomycota), including important plant pathogens such as bremia lactucae, plasmopara viticola, pseudoperonospora cubensis, and pseudoperonospora humuli. the 1c dna contents ranged from 0.046 (45. 6 mb) to 0.163 pg (159.9 mb). this is 0.041- to 0.144-fold that of glycine max (soybean, 1c = 1.134 pg), which was used as an internal standard for genome size determination. the l ... | 1998 | 9917372 |
| a comparison of peronospora parasitica (downy mildew) isolates from arabidopsis thaliana and brassica oleracea using amplified fragment length polymorphism and internal transcribed spacer 1 sequence analyses. | amplified fragment length polymorphism (aflp) fingerprints and internal transcribed spacer 1 (its1) sequences from 27 peronospora parasitica isolates (collected from arabidopsis thaliana or brassica oleracea), 5 albugo candida isolates (from the same hosts and from capsella bursa-pastoris), and 1 bremia lactucae isolate (from lactuca sativa) were compared. the aflp analysis divided the isolates into five groups that correlated with taxonomic species and, in most cases, with host origin. the only ... | 2000 | 11017765 |
| cloning and expression of sesquiterpene synthase genes from lettuce (lactuca sativa l.). | sesquiterpenoid lactones (sls) from lettuce (lactuca sativa l.) include constitutive components of latex such as lactucin and the induced phytoalexin, lettucenin a. a redundant primer strategy was used to recover two full length cdna clones (ltc1 and ltc2) encoding sesquiterpene synthases from a cdna library derived from seedlings with the red spot disorder, which accumulate phytoalexins. recombinant enzymes produced from ltc1 and ltc2 in escherichia coli catalysed the cyclisation of farnesyl di ... | 2002 | 12031443 |
| lactuca saligna, a non-host for lettuce downy mildew ( bremia lactucae), harbors a new race-specific dm gene and three qtls for resistance. | lactuca sativa (lettuce) is susceptible to bremia lactucae (downy mildew). in cultivated and wild lactuca species, dm genes have been identified that confer race-specific resistance. however, these genes were soon rendered ineffective by adaptation of the pathogen. lactuca saligna (wild lettuce) is resistant to all downy mildew races and can be considered as a non-host. therefore, l. saligna might be an alternative source for a more-durable resistance to downy mildew in lettuce. in order to anal ... | 2002 | 12582542 |
| transformation of pythium aphanidermatum to geneticin resistance. | conditions for the production of protoplasts and gene transfer in pythium aphanidermatum were investigated. efficient protoplast generation was possible after culture of mycelium in potato dextrose broth followed by digestion with 0.5% (w/v) each of cellulase and beta- d-glucanase. plasmid phamt35n/sk encoding the nptii gene under control of the ham34 promoter from the oomycete bremia lactucae was used to define electroporation parameters for gene transfer. a square-wave electroporation pulse of ... | 2003 | 12612808 |
| a genetic map of the lettuce downy mildew pathogen, bremia lactucae, constructed from molecular markers and avirulence genes. | the genetic map of bremia lactucae was expanded utilizing 97 f(1) progeny derived from a cross between finnish and californian isolates (sf5xc82p24). genetic maps were constructed for each parent utilizing 7 avirulence genes, 83 rflp markers, and 347 aflp markers, and a consensus map was constructed from the complete data set. the framework map for sf5 contained 24 linkage groups distributed over 835cm; the map for c82p24 contained 21 linkage groups distributed over 606cm. the consensus map cont ... | 2003 | 12742060 |
| efficacy of salts against fungal diseases in glasshouse crops. | the constant input of chemical fungicides against foliar diseases in glasshouse crops has instigated research on alternative control substances. various salts have been mentioned in the literature and we have tested several bicarbonates, sulphates and phosphates against powdery mildew fungi in cucumber, tomato, sweet pepper and rose and against bremia lactucae in lettuce. the experiments were run according to eppo guidelines for efficacy in glasshouses of applied plant research (ppo). plants wer ... | 2003 | 15151280 |
| phylogenetic relationships of plasmopara, bremia and other genera of downy mildew pathogens with pyriform haustoria based on bayesian analysis of partial lsu rdna sequence data. | bayesian and maximum parsimony phylogenetic analyses of 92 collections of the genera basidiophora, bremia, paraperonospora, phytophthora and plasmopara were performed using nuclear large subunit ribosomal dna sequences containing the d1 and d2 regions. in the bayesian tree, two main clades were apparent: one clade containing plasmopara pygmaea s. lat., pl. sphaerosperma, basidiophora, bremia and paraperonospora, and a clade containing all other plasmopara species. plasmopara is shown to be polyp ... | 2004 | 15506014 |
| the disease resistance gene dm3 is infrequent in natural populations of lactuca serriola due to deletions and frequent gene conversions at the rgc2 locus. | resistance genes can exhibit heterogeneous patterns of variation. however, there are few data on their frequency and variation in natural populations. we analysed the frequency and variation of the resistance gene dm3, which confers resistance to bremia lactucae (downy mildew) in 1033 accessions of lactuca serriola (prickly lettuce) from 49 natural populations. inoculations with an isolate of bremia lactucae carrying avirulence gene avr3 indicated that the frequency of dm3 in natural populations ... | 2006 | 16762035 |
| extreme size and sequence variation in the its rdna of bremia lactucae. | bremia lactucae regel (chromista, peronosporaceae) is an economically destructive pathogen, which causes downy mildew disease on lettuce (lactuca sativa l.) worldwide. the ribosomal internal transcribed spacer (its) of bremia lactucae isolates was analyzed for the first time. the its region of lettuce downy mildew was observed to have a size of 2458 bp; thereby, having one of the longest its sizes recorded to date. the majority of the extremely large sized its2 length of 2086 was attributed to t ... | 2007 | 17286165 |
| silencing of the major family of nbs-lrr-encoding genes in lettuce results in the loss of multiple resistance specificities. | the rgc2 gene cluster in lettuce (lactuca sativa) is one of the largest known families of genes encoding nucleotide binding site-leucine-rich repeat (nbs-lrr) proteins. one of its members, rgc2b, encodes dm3 which determines resistance to downy mildew caused by the oomycete bremia lactucae carrying the cognate avirulence gene, avr3. we developed an efficient strategy for analysis of this large family of low expressed genes using post-transcriptional gene silencing (ptgs). we transformed lettuce ... | 2007 | 17587302 |
| localisation and metabolism of reactive oxygen species during bremia lactucae pathogenesis in lactuca sativa and wild lactuca spp. | a plant's physiology is modified simultaneously with oomycete pathogen penetration, starting with release and accumulation of reactive oxygen species (ros). localisation of superoxide, hydrogen peroxide, peroxidase and variation in their activity, and the isoenzyme profile of antioxidant enzymes peroxidase (1.11.1.7), catalase (ec 1.11.1.6), superoxide dismutase (ec 1.15.1.1) were studied in six genotypes of four lactuca spp. (l. sativa, l. serriola, l. saligna and l. virosa) challenged with bre ... | 2007 | 17629488 |
| basic compatibility of albugo candida in arabidopsis thaliana and brassica juncea causes broad-spectrum suppression of innate immunity. | a biotrophic parasite often depends on an intrinsic ability to suppress host defenses in a manner that will enable it to infect and successfully colonize a susceptible host. if the suppressed defenses otherwise would have been effective against alternative pathogens, it follows that primary infection by the "suppressive" biotroph potentially could enhance susceptibility of the host to secondary infection by avirulent pathogens. this phenomenon previously has been attributed to true fungi such as ... | 2008 | 18624639 |
| from breeding to cloning (and back again?): a case study with lettuce downy mildew. | | 1992 | 18647109 |
| impact of diurnal periodicity, temperature, and light on sporulation of bremia lactucae. | abstract we evaluated direct and interactive effects of light quality and intensity, temperature and light, diurnal rhythms, and timing of high relative humidity during long day lengths on sporulation of bremia lactucae, the causal agent of lettuce downy mildew, using inoculated lettuce seedlings and detached cotyledons. suppression of sporulation by light was strongly dependent upon temperature and there was little suppression at </=10 degrees c. the most suppressive waveband was in the range f ... | 2007 | 18943638 |
| sporulation of bremia lactucae affected by temperature, relative humidity, and wind in controlled conditions. | abstract the effects of temperature (5 to 25 degrees c), relative humidity (81 to 100%), wind speed (0 to 1.0 m s(-1)), and their interactions on sporulation of bremia lactucae on lettuce cotyledons were investigated in controlled conditions. sporulation was affected significantly (p < 0.0001) by temperature, with an optimum at 15 degrees c, and by relative humidity (rh), with sporulation increasing markedly at rh >/= 90%. there was a significant effect of exposure time in relation to temperatur ... | 2004 | 18944116 |
| incorporation of temperature and solar radiation thresholds to modify a lettuce downy mildew warning system. | abstract the effect of temperature on infection of lettuce by bremia lactucae was investigated in controlled environment studies and in the field. in controlled conditions, lettuce seedlings inoculated with b. lactucae were incubated at 15, 20, 25, or 30 degrees c during a 4-h wet period immediately after inoculation or at the same temperatures during an 8-h dry period after the 4-h postinoculation wet period at 15 degrees c. high temperatures during wet and dry periods reduced subsequent diseas ... | 2002 | 18944260 |
| spatial analysis of lettuce downy mildew using geostatistics and geographic information systems. | abstract the epidemiology of lettuce downy mildew has been investigated extensively in coastal california. however, the spatial patterns of the disease and the distance that bremia lactucae spores can be transported have not been determined. during 1995 to 1998, we conducted several field- and valley-scale surveys to determine spatial patterns of this disease in the salinas valley. geostatistical analyses of the survey data at both scales showed that the influence range of downy mildew incidence ... | 2001 | 18944386 |
| factors affecting the survival of bremia lactucae sporangia deposited on lettuce leaves. | abstract experiments to identify the factors affecting survival of bremia lactucae sporangia after deposition on lettuce leaves were conducted in growth chambers and outdoors under ambient conditions. lettuce seedlings at the four-leaf stage were inoculated with b. lactucae sporangia under dry conditions. sporangia deposited on lettuce seedlings were incubated at different temperature and relative humidity (rh) combinations, exposed to 100, 50, 25, and 0% sunlight in the second experiment, and e ... | 2000 | 18944503 |
| spore release of bremia lactucae on lettuce is affected by timing of light initiation and decrease in relative humidity. | abstract a suction-impaction mini-spore trap was developed to study the effect of light initiation and decreasing relative humidity (rh) on spore release of bremia lactucae in a controlled environment. three light periods (from 0400 to 1600, 0600 to 1800, and 0800 to 2000 h, circadian time) at a constant rh of 99 to 100% were used for studying the effect of light initiation on spore release. few spores were released during the dark periods. spore release increased sharply after the initiation of ... | 2000 | 18944573 |
| comparison of lettuce diseases and yield under subsurface drip and furrow irrigation. | abstract subsurface drip and furrow irrigation were compared on lettuce (lactuca sativa) cvs. salinas and misty day for yield and incidence and severity of three important diseases of lettuce in the salinas valley, ca. experiments were conducted between 1993 and 1995 during the spring and fall seasons. the diseases examined included lettuce drop (sclerotinia minor), downy mildew (bremia lactucae), and corky root (rhizomonas suberifaciens). replicated plots of subsurface drip and furrow irrigatio ... | 1997 | 18945057 |
| three combined quantitative trait loci from nonhost lactuca saligna are sufficient to provide complete resistance of lettuce against bremia lactucae. | the nonhost resistance of wild lettuce (lactuca saligna) to downy mildew (bremia lactucae) is based on at least 15 quantitative trait loci (qtl), each effective at one or more plant developmental stages. we used qtl pyramiding (stacking) to determine how many of these qtl from l. saligna are sufficient to impart complete resistance towards b. lactucae to cultivated lettuce, l. sativa. the alleles of four of the most promising qtl, rbq4, rbq5, rbq6+11, and rbq7 are effective at both the young and ... | 2009 | 19656050 |
| rin4 causes hybrid necrosis and race-specific resistance in an interspecific lettuce hybrid. | some inter- and intraspecific crosses may result in reduced viability or sterility in the offspring, often due to genetic incompatibilities resulting from interactions between two or more loci. hybrid necrosis is a postzygotic genetic incompatibility that is phenotypically manifested as necrotic lesions on the plant. we observed hybrid necrosis in interspecific lettuce (lactuca sativa and lactuca saligna) hybrids that correlated with resistance to downy mildew. segregation analysis revealed a sp ... | 2009 | 19855048 |
| cyazofamide: a fungicide against bremia lactucae on lettuce. | during 2007 and 2008 summers, experimentation was performed by the bioagritest test facility, according to eppo guidelines and principles of good experimental practice (gep), aiming at establishing the biological efficacy of cyazofamide 25sc (formulate mildicut, belchim) and cyazofamide 400sc + an organosilicone adjuvant containing polyalkyleneoxide modified heptamethyltrisiloxane (ranman 400 sc, belchim) on lettuce against bremia lactucae. the study was performed in nocera inferiore (salerno), ... | 2009 | 20222579 |
| chemical control of downy mildew on lettuce and basil under greenhouse. | eight experimental trials were carried out during 2007 and 2008 to evaluate the efficacy of different fungicides against downy mildew of lettuce (bremia lactucae) and basil (peronospora belbahrii) under greenhouse conditions, at temperatures ranging from 19 to 24 degrees c. the mixture fluopicolide (fungicide belonging to the + propamocarb hydrochloride (fungicide belonging to the new chemical class of acyl-picolides) was compared with metalaxyl m + copper, zoxamide + mancozeb, iprovalicarb + cu ... | 2009 | 20222581 |
| photosynthetic responses of lettuce to downy mildew infection and cytokinin treatment. | changes in primary metabolism of lettuce, lactuca sativa l. (cv. cobham green), induced by compatible interaction with the biotrophic oomycete pathogen bremia lactucae regel (race bl 16), under two intensities of illumination in the presence and absence of exogenous cytokinins were studied by chlorophyll fluorescence imaging. thirteen days post-inoculation leaf discs infected by b. lactucae exhibited impairments of photosynthesis associated with biotrophic infections, including: reductions in ph ... | 2010 | 20471849 |
| evidence for high degrees of specialisation, evolutionary diversity, and morphological distinctiveness in the genus bremia. | bremia lactucae is one of the most important pathogens in lettuce production. recent molecular studies revealed considerable genetic variation in this species complex. however, only few accessions from the same host have been examined for most species and no study investigating the morphological distinctiveness of phylogenetic lineages of bremia has so far been reported. thus it is believed that morphological species delimitation in bremia is not feasible. in the present study, multiple accessio ... | 2010 | 21315308 |
| vectors for fluorescent protein tagging in phytophthora: tools for functional genomics and cell biology. | fluorescent tagging has become the strategy of choice for examining the subcellular localisation of proteins. to develop a versatile community resource for this method in oomycetes, plasmids were constructed that allow the expression of either of four spectrally distinct proteins [cyan fluorescent protein (cfp), green fluorescent protein (gfp), yellow fluorescent protein (yfp), and mcherry], alone or fused at their n- or c-termini, to sequences of interest. equivalent sets of plasmids were made ... | 2011 | 21872185 |
| ecological responses to uv radiation: interactions between the biological effects of uv on plants and on associated organisms. | solar ultraviolet (uv)-b radiation (280-315 nm) has a wide range of effects on terrestrial ecosystems, yet our understanding of how uv-b influences the complex interactions of plants with pest, pathogen and related microorganisms remains limited. here, we report the results of a series of experiments in lactuca sativa which aimed to characterize not only key plant responses to uv radiation in a field environment but also consequential effects for plant interactions with a sap-feeding insect, two ... | 2011 | 22150399 |