Garlic Volatile Diallyl Disulfide Induced Cucumber Resistance to Downy Mildew.

Allicin compositions in garlic are used widely as fungicides in modern agriculture, in which diallyl disulfide (DADS) is a major compound. Downy mildew, caused by Pseudoperonospora cubensis (P. cubensis), is one of the most destructive diseases and causes severe yield losses in cucumbers. To explore the potential mechanism of DADS-induced cucumber resistance to downy mildew, cucumber seedlings were treated with DADS and then inoculated with P. cubensis at a 10-day interval. Symptom observation showed that DADS significantly induced cucumber resistance to downy mildew. Furthermore, both lignin and H2O2 were significantly increased by DADS treatment to responding P. cubensis infection. Simultaneously, the enzyme activities of peroxidase (POD) in DADS-treated seedlings were significantly promoted. Meanwhile, both the auxin (IAA) and salicylic acid (SA) contents were increased, and their related differentially expressed genes (DEGs) were up-regulated when treated with DADS. Transcriptome profiling showed that many DEGs were involved in the biological processes of defense responses, in which DEGs on the pathways of 'phenylpropanoid biosynthesis', 'phenylalanine metabolism', 'MAPK signaling', and 'plant hormone signal transduction' were significantly up-regulated in DADS-treated cucumbers uninoculated with the pathogen. Based on the results of several physiological indices and transcriptomes, a potential molecular mechanism of DADS-induced cucumber resistance to downy mildew was proposed and discussed. The results of this study might give new insight into the exploration of the induced resistance mechanism of cucumber to downy mildew and provide useful information for the subsequent mining of resistance genes in cucumber.

Effect of physio-chemical seed treatments on opium poppy downy mildews caused by Peronospora meconopsidis and P. somniferi.

Downy mildew of opium poppy is the single biggest disease constraint afflicting the Australian poppy industry. Within the pathosystem, the transmission of infections via infested seed is of major concern. Both downy mildew pathogens of poppy; Peronospora meconopsidis and P. somniferi, are known contaminants of commercial seed stocks. Using seed naturally infested with these pathogens, the effect of physio-chemical seed treatments on seedling health and disease transmission were evaluated. Individual seed treatments were tested to determine optimal treatment parameters for each; including incubation time, temperature and treatment concentration. Optimised physiochemical treatments were then compared. The most effective treatment methods were seed washes in acidified electrolytic water (400 ppm hypochlorous acid for 5 min) and hypochlorite solution (2% NaOCI for 5 min). In seed to seedling transmission assays, these two treatments reduced transmission of P. somniferi by 88.8% and 74.61%, and P. meconopsidis by 93.3% and 100%, respectively. These methods are recommended for seed treatment of commercial opium poppy seed to assist in the control of the downy mildew diseases.

Forecasting severe grape downy mildew attacks using machine learning.

Grape downy mildew (GDM) is a major disease of grapevine that has an impact on both the yields of the vines and the quality of the harvested fruits. The disease is currently controlled by repetitive fungicide treatments throughout the season, especially in the Bordeaux vineyards where the average number of fungicide treatments against GDM was equal to 10.1 in 2013. Reducing the number of treatments is a major issue from both an environmental and a public health point of view. One solution would be to identify vineyards that are likely to be heavily attacked in spring and then apply fungicidal treatments only to these situations. In this perspective, we use here a dataset including 9 years of GDM observations to develop and compare several generalized linear models and machine learning algorithms predicting the probability of high incidence and severity in the Bordeaux region. The algorithms tested use the date of disease onset and/or average monthly temperatures and precipitation as input variables. The accuracy of the tested models and algorithms is assessed by year-by-year cross validation. LASSO, random forest and gradient boosting algorithms show better performance than generalized linear models. The date of onset of the disease has a greater influence on the accuracy of forecasts than weather inputs and, among weather inputs, precipitation has a greater influence than temperature. The best performing algorithm was selected to evaluate the impact of contrasted climate scenarios on GDM risk levels. Results show that risk of GDM at bunch closure decreases with reduced rainfall and increased temperatures in April-May. Our results also show that the use of fungicide treatment decision rules that take into account local characteristics would reduce the number of treatments against GDM in the Bordeaux vineyards compared to current practices by at least 50%.

Root treatment with oxathiapiprolin, benthiavalicarb or their mixture provides prolonged systemic protection against oomycete foliar pathogens.

Oxathiapiprolin is a fungicide effective against downy mildews of cucumber (Pseudoperonospora cubensis) and basil (Peronospora belbahrii) and late blight of tomato (Phytophthora infestans). To avoid fungicide resistance, it is recommended to apply oxathiapiprolin as a mixture with a partner fungicide that have a different mode of action. Here it is shown that a single application of oxathiapiprolin, benthiavalicarb, or their mixture (3+7, w/w) to the root of nursery plants grown in multi-cell trays provided prolonged systemic protection against late blight and downy mildews in growth chambers and in field tests. Soil application of 1mg active ingredient per plant provided durable protection of up to four weeks in tomato against late blight, cucumber against downy mildew and basil against downy mildew. Not only did the mixture of oxathiapiprolin and benthiavalicarb provide excellent systemic control of these diseases but also mutual protection against resistance towards both oxathiapiprolin and benthiavalicarb.

Surfactin and fengycin contribute to the protection of a Bacillus subtilis strain against grape downy mildew by both direct effect and defence stimulation.

Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High-performance thin-layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew.

Downy Mildew: A Serious Disease Threat to Rose Health Worldwide.

Peronospora sparsa is a downy mildew-causing oomycete that can infect roses, blackberries, and other members of the rose family. During the last 70 years, this disease has become a serious problem for rose growers in the U.S. and worldwide. While much is known about the disease and its treatment, including significant research on molecular identification methods, as well as environmental conditions conducive to disease and the fungicides used to prevent it, significant knowledge gaps remain in our basic comprehension of the pathogen's biology. For example, the degree of genetic relatedness of pathogen isolates collected from rose, caneberries, and cherry laurel has never been examined, and the natural movement of genotypes from host to host is not known. Further work could be done to determine the differences in pathogen population structure over time (using herbarium specimens and fresh collections) or differences in pathogen population structure and pathogen environmental adaptation for specimens from different geographic regions. The oospore stage of the organism is poorly understood, both as to how it forms and whether it serves as an overwintering structure in nurseries and landscapes. In production greenhouses, the detection of the pathogen using infrared thermographic imaging and possible inhibition by ultraviolet light needs to be explored. Further work needs to be done on breeding using wild roses as new sources for resistance and using new methods such as marker assisted selection and RNAi technologies. As roses are one of the most economically important ornamental crops worldwide, a proper understanding of the disease cycle could allow for better use of cultural and chemical controls to manage rose downy mildew in landscapes and in greenhouse and nursery production areas.

Detection of Latent Peronospora effusa Infections in Spinach.

Downy mildew disease of spinach, caused by Peronospora effusa, is managed in conventional fields by a combination of host resistance and scheduled fungicide applications. Fungicides are currently applied to prevent downy mildew epidemics regardless of the infection status of spinach crops. A more streamlined approach would be to develop methods to target either latent infections for fungicide application in conventional production systems or to hasten harvest in organic production. In this study, conventional polymerase chain reaction (PCR) was applied to detect P. effusa DNA in symptomless spinach leaves in three spatially and temporally separated field plots, each containing four 2-m beds, 35 m in length. Spinach leaves were sampled weekly at 3-m intervals at 48 locations throughout each plot. Initial samples were asymptomatic and yet PCR enabled detection of P. effusa DNA extracted from sampled spinach leaves. Detection of latent downy mildew infection in spinach leaves was confirmed by PCR as early as 7 days prior to symptom development. The limit of pathogen DNA detection in spinach leaves was calculated at 10 pg using the conventional PCR approach. Quantitative PCR with TaqMan methodology revealed the presence of inhibitors from spinach leaf DNA extracts and affected amplification efficiencies, but not when diluted, enabling detection of P. effusa DNA at a concentration of <0.1 pg. In conclusion, detection of latent infections may enable management decisions for earlier-than-normal harvest of infected, symptomless organic crops, and for timing fungicide applications on symptomless plants in conventional production.

Pseudoperonospora cubensis in China: Its sensitivity to and control by oxathiapiprolin.

The novel fungicide oxathiapiprolin has potential for the control of downy mildew of cucumber, which is caused by Pseudoperonospora cubensis. In this study, an in vitro bioassay with detached leaves was used to determine the baseline sensitivity to oxathiapiprolin for 77 Ps. cubensis isolates from 11 provinces in China. The baseline sensitivity curve was continuous, and the average EC50 value was 2.23 × 10-4 µg ml-1. In field trials, the control of downy mildew of cucumber was greater with oxathiapiprolin at 20 or 30 g a.i. ha-1 than with dimethomorph at 262.5 g a.i. ha-1. Oxathiapiprolin was taken up by cucumber roots and transported upwards to stems and leaves. The full length of PscORP1, the gene that encodes the target protein of oxathiapiprolin in Ps. cubensis, was sequenced for the first time. Our results suggested that oxathiapiprolin will be an excellent alternative fungicide for control of cucumber downy mildew. However, as Ps. cubensis is a high-risk pathogen, resistance development to oxathiapiprolin should be monitored and managed.

Overexpression of VpPR10.1 by an efficient transformation method enhances downy mildew resistance in V. vinifera.

KEY MESSAGE: Putrescine and spermidine increase the transformation efficiency of Vitis vinifera L. cv. Thompson seedless. Accumulation of VpPR10.1 in transgenic V. vinifera Thompson seedless, likely increases its resistance to downy mildew. A more efficient method is described for facilitating Agrobacterium-mediated transformation of Vitis vinifera L. cv. Thompson Seedless somatic embryogenesis using polyamines (PAs). The efficacies of putrescine, spermidine and spermine are identified at a range of concentrations (10 µM, 100 µM and 1 mM) added to the culture medium during somatic embryo growth. Putrescine (PUT) and spermidine (SPD) promote the recovery of proembryonic masses (PEM) and the development of somatic embryos (SE) after co-cultivation. Judging from the importance of the time-frame in genetic transformation, PAs added at the co-cultivation stage have a stronger effect than delayed selection treatments, which are superior to antibiotic treatments in the selection stage. Best embryogenic responses are with 1 mM PUT and 100 µM SPD added to the co-culture medium. Using the above method, a pathogenesis-related gene (VpPR10.1) from Chinese wild Vitis pseudoreticulata was transferred into Thompson Seedless for functional evaluation. The transgenic line, confirmed by western blot analysis, was inoculated with Plasmopara viticola to test for downy mildew resistance. Based on observed restrictions of hyphal growth and increases in H2O2 accumulation in the transgenic plants, the accumulation of VpPR10.1 likely enhanced the transgenic plants resistance to downy mildew.

Kale BoRACK1 is involved in the plant response to salt stress and Peronospora brassicae Gaumann.

The receptor for activated C kinase 1 (RACK1) belongs to a protein subfamily containing a tryptophan-aspartic acid-domain (WD) repeat structure. Compelling evidence indicates that RACK1 can interact with many signal molecules and affect different signal transduction pathways. In this study, a kale (Brassica oleracea var. acephala f.tricolor) RACK1 gene (BoRACK1) was cloned by RT-PCR. The amino acid sequence of BoRACK1 had seven WD repeats in which there were typical GH (glycine-histidine) and WD dipeptides. Comparison with AtRACK1 from Arabidopsis revealed 87.1% identity at the amino acid level. Expression pattern analysis by RT-PCR showed that BoRACK1 was expressed in all analyzed tissues of kale and that its transcription in leaves was down-regulated by salt, abscisic acid, and H2O2 at a high concentration. Overexpression of BoRACK1 in kale led to a reduction in symptoms caused by Peronospora brassicae Gaumann on kale leaves. The expression levels of the pathogenesis-related protein genes, PR-1 and PRB-1, increased 2.5-4-fold in transgenic kale, and reactive oxygen species production was more active than in the wild-type. They also exhibited increased tolerance to salt stress in seed germination. H2O2 may also be involved in the regulation of BoRACK1 during seed germination under salt stress. Quantitative real-time PCR analyses showed that the transcript levels of BoRbohs genes were significantly higher in overexpression of BoRACK1 transgenic lines. Yeast two-hybrid assays showed that BoRACK1 could interact with WNK8, eIF6, RAR1, and SGT1. This study and previous work lead us to believe that BoRACK1 may form a complex with regulators of plant salt and disease resistance to coordinate kale reactions to pathogens.

Isolation and evaluation of proteolytic actinomycete isolates as novel inducers of pearl millet downy mildew disease protection.

Native endophytic actinomycetes isolated from pearl millet roots were examined for their efficacy to protect pearl millet against downy mildew. Nineteen of 39 isolates were found to be proteolytic, of which 7 strains could directly suppress the sporangium formation of Sclerospora graminicola, the pearl millet downy mildew pathogen. Thus, mycelial suspensions containing either spores or cell-free extract of these 7 isolates were used for seed-coating and -soaking treatments to test for their induction of downy mildew resistance. Results indicated that seed-coating overall provided better protection to downy mildew than seed-soaking. In both treatments, the tested isolates demonstrated differential abilities in downy mildew disease protection, with Streptomyces griseus SJ_UOM-07-09 and Streptosporangium roseum SJ_UOM-18-09 showing the highest protection rates. Additionally, the levels of disease protection conferred by the actinomycetes were just slightly lower than that of the systemic fungicide Apron, suggesting their effectiveness. Further studies revealed that the more rapid root colonization by SJ_UOM-18-09 resulted in faster and higher induced resistance in comparison with SJ_UOM-07-09 under greenhouse conditions, indicating that SJ_UOM-18-09 was superior than SJ_UOM-07-09 in inducing resistance. Results from this study provide comprehensive information on biocontrol functions of SJ_UOM- 18-09 with great potential to control downy mildew disease in pearl millet.

Enhancement of downy mildew disease resistance in pearl millet by the G_app7 bioactive compound produced by Ganoderma applanatum.

Pearl millet (Pennisetum glaucum) stands sixth among the most important cereal crops grown in the semi-arid and arid regions of the world. The downy mildew disease caused by Sclerospora graminicola, an oomycete pathogen, has been recognized as a major biotic constraint in pearl millet production. On the other hand, basidiomycetes are known to produce a large number of antimicrobial metabolites, providing a good source of anti-oomycete agrochemicals. Here, we report the discovery and efficacy of a compound, named G_app7, purified from Ganoderma applanatum on inhibition of growth and development of S. graminicola, as well as the effects of seed treatment with G_app7 on protection of pearl millet from downy mildew. G_app7 consistently demonstrated remarkable effects against S. graminicola by recording significant inhibition of sporangium formation (41.4%), zoospore release (77.5%) and zoospore motility (91%). Analyses of G_app7 compound using two-dimensional nuclear magnetic resonance spectroscopy and liquid chromatography-mass spectrometry revealed its close resemblance to metominostrobin, a derivative of strobilurin group of fungicides. Furthermore, the G_app7 was shown to stably maintain the inhibitory effects at different temperatures between 25 and 80 °C. In addition, the anti-oomycete activity of G_app7 was fairly stable for a period of at least 12 months at 4 °C and was only completely lost after being autoclaved. Seed treatment with G_app7 resulted in a significant increase in disease protection (63%) under greenhouse conditions compared with water control. The identification and isolation of this novel and functional anti-oomycete compound from G. applanatum provide a considerable agrochemical importance for plant protection against downy mildew in an environmentally safe and economical manner.

The Arabidopsis microtubule-associated protein MAP65-3 supports infection by filamentous biotrophic pathogens by down-regulating salicylic acid-dependent defenses.

The oomycete Hyaloperonospora arabidopsidis and the ascomycete Erysiphe cruciferarum are obligate biotrophic pathogens causing downy mildew and powdery mildew, respectively, on Arabidopsis. Upon infection, the filamentous pathogens induce the formation of intracellular bulbous structures called haustoria, which are required for the biotrophic lifestyle. We previously showed that the microtubule-associated protein AtMAP65-3 plays a critical role in organizing cytoskeleton microtubule arrays during mitosis and cytokinesis. This renders the protein essential for the development of giant cells, which are the feeding sites induced by root knot nematodes. Here, we show that AtMAP65-3 expression is also induced in leaves upon infection by the downy mildew oomycete and the powdery mildew fungus. Loss of AtMAP65-3 function in the map65-3 mutant dramatically reduced infection by both pathogens, predominantly at the stages of leaf penetration. Whole-transcriptome analysis showed an over-represented, constitutive activation of genes involved in salicylic acid (SA) biosynthesis, signaling, and defense execution in map65-3, whereas jasmonic acid (JA)-mediated signaling was down-regulated. Preventing SA synthesis and accumulation in map65-3 rescued plant susceptibility to pathogens, but not the developmental phenotype caused by cytoskeleton defaults. AtMAP65-3 thus has a dual role. It positively regulates cytokinesis, thus plant growth and development, and negatively interferes with plant defense against filamentous biotrophs. Our data suggest that downy mildew and powdery mildew stimulate AtMAP65-3 expression to down-regulate SA signaling for infection.

The Novel Oomycide Oxathiapiprolin Inhibits All Stages in the Asexual Life Cycle of Pseudoperonospora cubensis - Causal Agent of Cucurbit Downy Mildew.

Oxathiapiprolin is a new oomycide (piperidinyl thiazole isoxazoline class) discovered by DuPont which controls diseases caused by oomycete plant pathogens. It binds in the oxysterol-binding protein domain of Oomycetes. Growth chambers studies with detached leaves and potted plants showed remarkable activity of oxathiapiprolin against Pseudoperonospora cubensis in cucurbits. The compound affected all stages in the asexual life cycle of the pathogen. It inhibited zoospore release, cystospore germination, lesion formation, lesion expansion, sporangiophore development and sporangial production. When applied to the foliage as a preventive spray no lesions developed due to inhibition of zoospore release and cystospore germination, and when applied curatively, at one or two days after inoculation, small restricted lesions developed but no sporulation occurred. When applied later to mature lesions, sporulation was strongly inhibited. Oxathiapiprolin suppressed sporulation of P. cubensis in naturally-infected leaves. It exhibited trans-laminar activity, translocated acropetaly from older to younger leaves, and moved from the root system to the foliage. Seed coating was highly effective in protecting the developed cucumber plants against downy mildew. UV microscopy observations made with cucumber leaves infected with P. cubensis revealed that inhibition of mycelium growth and sporulation induced by oxathiapiprolin was associated with callose encasement of the haustoria.

Rhamnolipids elicit defense responses and induce disease resistance against biotrophic, hemibiotrophic, and necrotrophic pathogens that require different signaling pathways in Arabidopsis and highlight a central role for salicylic acid.

Plant resistance to phytopathogenic microorganisms mainly relies on the activation of an innate immune response usually launched after recognition by the plant cells of microbe-associated molecular patterns. The plant hormones, salicylic acid (SA), jasmonic acid, and ethylene have emerged as key players in the signaling networks involved in plant immunity. Rhamnolipids (RLs) are glycolipids produced by bacteria and are involved in surface motility and biofilm development. Here we report that RLs trigger an immune response in Arabidopsis (Arabidopsis thaliana) characterized by signaling molecules accumulation and defense gene activation. This immune response participates to resistance against the hemibiotrophic bacterium Pseudomonas syringae pv tomato, the biotrophic oomycete Hyaloperonospora arabidopsidis, and the necrotrophic fungus Botrytis cinerea. We show that RL-mediated resistance involves different signaling pathways that depend on the type of pathogen. Ethylene is involved in RL-induced resistance to H. arabidopsidis and to P. syringae pv tomato whereas jasmonic acid is essential for the resistance to B. cinerea. SA participates to the restriction of all pathogens. We also show evidence that SA-dependent plant defenses are potentiated by RLs following challenge by B. cinerea or P. syringae pv tomato. These results highlight a central role for SA in RL-mediated resistance. In addition to the activation of plant defense responses, antimicrobial properties of RLs are thought to participate in the protection against the fungus and the oomycete. Our data highlight the intricate mechanisms involved in plant protection triggered by a new type of molecule that can be perceived by plant cells and that can also act directly onto pathogens.

The pepper extracellular peroxidase CaPO2 is required for salt, drought and oxidative stress tolerance as well as resistance to fungal pathogens.

In plants, biotic and abiotic stresses regulate the expression and activity of various peroxidase isoforms. Capsicum annuum EXTRACELLULAR PEROXIDASE 2 (CaPO2) was previously shown to play a role in local and systemic reactive oxygen species bursts and disease resistance during bacterial pathogen infection. Here, we report CaPO2 expression patterns and functions during conditions of biotic and abiotic stress. In pepper plants, CaPO2 expression was strongly induced by abscisic acid, but not by defense-related plant hormones such as salicylic acid, ethylene and jasmonic acid. CaPO2 was also strongly induced by abiotic and biotic stress treatments, including drought, cold, high salinity and infection by the hemibiotrophic fungal pathogen Colletotrichum coccodes. Loss-of-function of CaPO2 in virus-induced gene silenced pepper plants led to increased susceptibility to salt- and osmotic-induced stress. In contrast, CaPO2 overexpression in transgenic Arabidopsis thaliana plants conferred enhanced tolerance to high salt, drought, and oxidative stress, while also enhancing resistance to infection by the necrotrophic fungal pathogen Alternaria brassicicola. Taken together, these results provide evidence for the involvement of pepper extracellular peroxidase CaPO2 in plant defense responses to various abiotic stresses and plant fungal pathogens.

Brush and spray: a high-throughput systemic acquired resistance assay suitable for large-scale genetic screening.

Systemic acquired resistance (SAR) is a defense mechanism induced in the distal parts of plants after primary infection. It confers long-lasting protection against a broad spectrum of microbial pathogens. Lack of high-throughput assays has hampered the forward genetic analysis of SAR. Here, we report the development of an easy and efficient assay for SAR and its application in a forward genetic screen for SAR-deficient mutants in Arabidopsis (Arabidopsis thaliana). Using the new assay for SAR, we identified six flavin-dependent monooxygenase1, four AGD2-like defense response protein1, three salicylic acid induction-deficient2, one phytoalexin deficient4, and one avrPphB-susceptible3 alleles as well as a gain-of-function mutant of CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR3 designated camta3-3D. Like transgenic plants overexpressing CAMTA3, camta3-3D mutant plants exhibit compromised SAR and enhanced susceptibility to virulent pathogens, suggesting that CAMTA3 is a critical regulator of both basal resistance and SAR.

Forward and reverse genetics to identify genes involved in the age-related resistance response in Arabidopsis thaliana.

SUMMARY Age-related resistance (ARR) occurs in numerous plant species, often resulting in increased disease resistance as plants mature. ARR in Arabidopsis to Pseudomonas syringae pv. tomato is associated with intercellular salicylic acid (SA) accumulation and the transition to flowering. Forward and reverse genetic screens were performed to identify genes required for ARR and to investigate the mechanism of the ARR response. Infiltration of SA into the intercellular space of the ARR-defective mutant iap1-1 (important for the ARR pathway) partially restored ARR function. Inter- and intracellular SA accumulation was reduced in the mutant iap1-1 compared with the wild-type, and the SA regulatory gene EDS1 was also required for ARR. Combining microarray analysis with reverse genetics using T-DNA insertion lines, four additional ARR genes were identified as contributing to ARR: two plant-specific transcription factors of the NAC family [ANAC055 (At3g15500) and ANAC092 (At5g39610)], a UDP-glucose glucosyltransferase [UGT85A1 (At1g22400)] and a cytidine deaminase [CDA1 (At2g19570)]. These four genes and IAP1 are also required for ARR to Hyaloperonospora parasitica. IAP1 encodes a key component of ARR that acts upstream of SA accumulation and possibly downstream of UGT85A1, CDA1 and the two NAC transcription factors (ANAC055, ANAC092).

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, fenamidone + fosetyl-Al and azoxystrobin. Two treatments were carried out at 8-12 day interval on lettuce and basil. The artificial inoculation of B. lactucae on lettuce (cv Cobham Green) and P. belbahrii. on basil (cv Genovese gigante) was carried out by using 1 x 10(5) CFU/ml 24 h after the first treatment. In the presence of a medium-high disease severity, all fungicides tested in these trials were effective against downy mildew on lettuce and basil as the other fungicides already available. The importance of the availability of a number of different chemicals to control downy mildews is discussed.

Expression of callose synthase genes and its connection with Npr1 signaling pathway during pathogen infection.

Callose synthesis occurs at specific stages of plant cell wall development in all cell types, and in response to pathogen attack, wounding and physiological stresses. We determined the expression pattern of "upstream regulatory sequence" of 12 Arabidopsis callose synthase genes (CalS1-12) genes and demonstrated that different callose synthases are expressed specifically in different tissues during plant development. That multiple CalS genes are expressed in the same cell type suggests the possibility that CalS complex may be constituted by heteromeric subunits. Five CalS genes were induced by pathogen (Hyaloperonospora arabidopsis, previously known as Peronospora parasitica, the causal agent of downy mildew) or salicylic acid (SA), while the other seven CalS genes were not affected by these treatments. Among the genes that are induced, CalS1 and CalS12 showed the highest responses. In Arabidopsis npr1 mutant, impaired in response of pathogenesis related (PR) genes to SA, the induction of CalS1 and CalS12 genes by the SA or pathogen treatments was significantly reduced. The patterns of expression of the other three CalS genes were not changed significantly in the npr1 mutant. These results suggest that the high induction observed of CalS1 and CalS12 is Npr1 dependent while the weak induction of five CalS genes is Npr1 independent. In a T-DNA knockout mutant of CalS12, callose encasement around the haustoria on the infected leaves was reduced and the mutant was found to be more resistant to downy mildew as compared to the wild type plants.