Cucumber downy mildew and the mechanisms of host resistance: a review / 生物工程学报

The cultivation and production of cucumber are seriously affected by downy mildew caused by Pseudoperonospora cubensis. Downy mildew damages leaves, stems and inflorescences, and then reduces the yield and quality of cucumber. This review summarized the research advances in cucumber downy mildew, including pathogen detection and defense pathways, regulatory factors, mining of pathogens-resistant candidate genes, proteomic and genomic analysis, and development of QTL remarks. This review may facilitate clarifying the resistance mechanisms of cucumber to downy mildew.

QTL identification for downy mildew resistance in cucumber using genetic linkage map based on SSR markers

Fourteen cucumber lines were tested for genetic homozygosity and performed pairwise comparison to identify a pair with the highest DNA polymorphic level. Cucumber accessions CSL0067 and CSL0139 were selected to generate 315 F2 populations. The genetic linkage map based on 66 polymorphic SSR markers was constructed. It composed of eight linkage groups (LGs) spanning 474.4 cM. Downy mildew disease reaction was evaluated in cotyledons, first and second true leaf on 7, 10, and 14 day after inoculation. The results showed that downy mildew resistance was controlled by multiple recessive genes. The susceptible to resistant ratio of F2 progenies fit 9:7 susceptible/resistant segregation types corresponding to duplicate recessive epistasis. Fourteen QTLs were detected. The phenotypic variance ranged from 5.0 to 12.5%, while LOD values ranged from 3.538 to 9.165. Two major QTLs and two QTL hotspots were identified. Moreover, the additive effects data explained that these QTL reduced downy mildew susceptibility

The Effectiveness of Trichoderma spp. against Downy Mildew Disease of Corn

Introduction: One of environmentally friendly method for controlling plant diseases is the use of Trichoderma spp. as a natural controlling agent. Objectives: The objective of this research was to find out the effectiveness of Trichoderma spp. against downy mildew disease. Methodology: This research was conducted in the Plant Pest and Disease Laboratory in the Plant Protection Department of Faculty of Agriculture in Lampung University. This research used completely randomized design consisting without treatment (0), Trichoderma spp. Gading Rejo Region (GDR) isolate (1) Trichoderma spp. Nusantara Tropical Farm (NTF) isolate (2), and Trichoderma spp. Trimurjo (TRJ) isolate (3) treatments which were applied to the plant growing points as fungicide (B) and as inducer of plant resistance to be applied in the plant roots (P). Results: The research results showed that the Trichoderma spp. treatments could reduce the disease occurrence at 4 and 5 days after inoculation, but they could not reduce the disease severity and improve stover dry weight of corn plant. Conclusion: The Trichoderma spp. Treatment as biofungicide and plant resistance inducer are effective against the incubation period and suppress the disease occurrence of downy mildew disease significantly at the early course of the disease.

Bremia itoana (Oomycota, Peronosporales), a Specialized Downy Mildew Pathogen on an East Asian Plant, Crepidiastrum sonchifolium (Asteraceae)

Crepidiastrum sonchifolium, a flowering plant in the daisy family (Asteraceae), is native to East Asia. In Korea, this plant is a locally cultivated vegetable, and its market size is gradually growing. Since the plants with downy mildew infection were initially found at a private farm of Chuncheon city, the occurrences have continued in commercial farms of other regions, highlighting that this disease is spreading throughout Korea. The pathogen was attributed to a member of the genus Bremia that contains many specialized species, each of which displays a narrow host spectrum on Asteraceae. Based on morphological and molecular phylogenetic analyses, along with the high host specificity recently proven for Bremia species, the identity of the causal agent was confirmed as a so far undescribed species of Bremia. Here, we introduce Bremia itoana sp. nov., specific to C. sonchifolium.

Diversity, Phylogeny, and Host-Specialization of Hyaloperonospora Species in Korea

The genus Hyaloperonospora (Peronosporaceae; Oomycota) is an obligate biotrophic group that causes downy mildew disease on the Brassicaceae and allied families of Brassicales, including many economically relevant crops, such as broccoli, cabbage, radish, rape, and wasabi. To investigate the diversity of Hyaloperonospora species in northeast Asia, we performed a morphological analysis for the dried herbarium specimens collected in Korea, along with molecular phylogenetic inferences based on internal transcribed spacer rDNA and cox2 mtDNA sequences. It was confirmed that 14 species of Hyaloperonospora exist in Korea. Of these, three species, previously classified under the genus Peronospora, were combined to Hyaloperonospora: H. arabidis-glabrae comb. nov. (ex Arabis glabra), H. nasturtii-montani comb. nov. (ex Rorippa indica), and H. nasturtii-palustris comb. nov. (ex Rorippa palustris). In addition, finding two potentially new species specific to northeast Asian plants is noteworthy in support of the view that the species abundance of Hyaloperonospora has been underestimated hitherto.

rDNA-ITS and 28 S rDNA D1/D2 sequence analysis of downy mildew pathogen from Aconitum carmichaeli / 中草药

Objective: To define sequences about rDNA-ITS and 28 S rDNA D1/D2 of Peronospora aconiti separated from cultivated Aconitum carmichaeli in Jiangyou area of Sichuan province and provide a theoretical basis for the diagnosis and prevention of downy mildew disease. Methods: Spores and hyphae of P. aconiti from diseased plants were collected and total genomic DNA of pathogen were extracted and then rDNA-ITS and 28 S rDNA D1/D2 fragment were amplified and sequenced. According to the above results, the abutment (Neighbor-joining, NJ) phylogenetic tree of pathogen was constructed and analyzed. Results: The rDNA-ITS and 28 S rDNA D1/D2 sequences of P. aconiti were sequenced and compared according to the database from NCBI. Compared that with P. pulveracea and P. aparines, the similarity of rDNA-ITS sequences of P. aconiti was 94%. The similarity of 28 S rDNA D1/D2 sequences of P. aconiti was 97% compared that with P. pulveracea, P. ficariae and P. bulbocapni. Conclusion: The results of morphological identification of downy mildew pathogen separated from A. carmichaeli are consistent with those from molecular identification (rDNA-ITS and 28 S rDNA D1/D2 sequences) and the pathogen of Aconitum downy mildew should be P. aconiti. Therefore, rDNA-ITS and 28 S rDNA D1/D2 sequences constructed in this paper can be used to identify downy mildew pathogen from Aconitum carmichaeli Debx.

Biochemical Constituents in Malformed Tissues of Pearl Millet Cultivars Caused by Aggressive Pathotype of Sclerospora graminicola Causing Downy Mildew Disease.

Downy mildew (DM) of pearl millet [Pennisetum glaucum (L.) R. Br.] caused by Sclerospora graminicola is the most widespread and destructive disease. In DM affected plants disease symptoms appear suddenly with the emergence of green ear, which exhibits all possible degrees of proliferations and malformation of the panicle. The pathogen population at Jodhpur, India is more virulent among other prevalent pathotypes as highly resistant pearl millet lines turned susceptible at this location. Virulence of pathotype rapidly changes host physiology producing varied symptoms in leaves and ear heads. Biochemical components including carbohydrates, phenols, free proline, photosynthetic pigments and enzymes like polyphenol oxidase (PPO), peroxidase (POX), IAA oxidase (IAAO) and catalase were found considerably deranged in malformed tissues. Results indicated that in two highly susceptible cultivars (Nokha local and Eknath) high soluble sugars were recorded in DM necrotic/chlorotic leaves and malformed ear heads, whereas starch contents were reduced in infected ear heads. Total and O-dihydroxy phenols were higher in DM infected leaves as well as in the malformed ear heads. Free proline contents were increased manifold in DM infected leaves and in proliferated panicles. Total chlorophyll contents reduced drastically in DM infected leaves. In ear heads showing tufting and complete malformation, total chlorophyll and carotenoids were low when compared to healthy and diseased leaves. Activities of PPO, POX, IAAO and catalase were higher in DM affected leaves and suppressed and completely malformed ear heads in comparison to their healthy counterparts. The study suggests that accumulation of total phenols caused the hyperphenolicity in infected host tissues despite increased activities of POX, PPO, catalase and IAA oxidase.

Effect of Raw Cow Milk and Gliocladium virens in Pearl Millet against Downy Mildew Disease Caused by Sclerospora graminicola.

Pearl millet [Pennisetum glaucum (L.) R. Br.] downy mildew (DM) is caused by the fungus Sclerospora graminicola (SACC.) SCHRŐT. is the most widespread and destructive disease of pearl millet affecting yield and quality in all the millet cultivating tracts of India. Since pearl millet is a crop of low economic value grown by resource-poor farmers, conventional technological interventions are not cost feasible. Integration of indigenous knowledge with biocontrol agents appeared as a logical strategy in the present case. Studies were, therefore, undertaken to manage DM in rainfed crop of pearl millet using raw cow milk together with Gliocladium virens. Seed and soil treatments resulted in the lowest disease incidence. Biochemical constituents (metabolites and oxidative enzymes) were analysed to determine possible mode of action of Raw Cow Milk (RCM) and Gliocladium virens. A considerable increase in sugars, phenols and ortho-dihydroxy phenols (OD) in healthy and DM infected leaves of treated pearl millet plants was recorded when compared to untreated controls. A marked increase in all the photosynthetic pigments in both healthy and diseased treated plants was observed. The induction of resistance was accompanied by increased activities of defense related enzymes. It is assumed that the combination of RCM and G. virens is capable of stimulating different systemic responses in host plant.

Mutations in retrotransposon AtCOPIA4 compromises resistance to Hyaloperonospora parasitica in Arabidopsis thaliana

Retrotransposons (RTEs) are a principal component of most eukaryotic genomes, representing 50 percent-80 percent of some grass genomes. RTE sequences have been shown to be preferentially present in disease resistance gene clusters in plants. Arabidopsis thaliana has over 1,600 annotated RTE sequences and 56 of these appear to be expressed because of the exact expressed sequence tag (EST) matches and the presence of intact open reading frames. Of the 22 represented in the Affymetrix ATH1 array, AtCOPIA4 was found to be expressed at a higher level than all other RTEs across different developmental stages. Since AtCOPIA4 is located in the RPP5 gene cluster and is adjacent to RPP4 which confers resistance to the downy mildew oomycete Hyaloperonospora parasitica isolate EMWA1, we evaluated AtCOPIA4 mutants for resistance to this pathogen. T-DNA insertional and antisense knockout of AtCOPIA4 was found to reduce the resistance of wild type plants by 2-4 folds. Our results suggest that retrotransposon can be exapted to participate in plant defense response.

DIVERSIDAD GENÉTICA DE Peronospora sparsa (PERONOSPORACEAE) EN CULTIVOS DE ROSA DE COLOMBIA / Genetic Diversity of Peronospora sparsa (Peronosporaceae) on Rose Crops From Colombia

El mildeo velloso de la rosa es la enfermedad más limitante de este cultivo en Colombia . Aunque algunos trabajos de investigación se han adelantado recientemente sobre la epidemiología de esta enfermedad, uno de los campos menos estudiados es el nivel de variabilidad de su agente causal. El conocimiento de este aspecto es fundamental para definir las estrategias de manejo, especialmente aquellas relacionadas con la resistencia genética y el control químico. Los objetivos de esta investigación fueron confirmar la identidad taxonómica del agente causal del mildeo velloso de la rosa y profundizar en el conocimiento de su estructura poblacional en Colombia . Para esto se colectaron 34 aislamientos del pseudohongo en cultivos de rosas ubicados en Antioquia y la sabana de Bogotá y se extrajo su ADN, para proceder a la amplificación mediante PCR de la región ITS del ADNr utilizando los primers especieespecíficos PS3 y PS1. Dichos productos se emplearon tanto para su secuenciación directa como para la evaluación de variabilidad genética mediante la técnica PCRRFLP, resultados que se complementaron con la utilización de los marcadores RAPD y RAMS. La presencia de un amplicón de aproximadamente 700 pb que compartió un porcentaje de identidad del 100% con secuencias depositadas en el GenBank, permitió confirmar a los aislamientos como pertenecientes a Peronospora sparsa, mientras que el análisis de RFLP, RAPD y RAMS indicó un muy bajo nivel de variabilidad entre todos los aislamientos, concluyéndose que la población de P. sparsa en Colombia es predominantemente clonal.

Downy mildew of roses is the most restrictive disease of this crop in Colombia . Although some studies have been carried out on the epidemiology of this disease, one of the fields less studied is the level of variability of its causal agent. The knowledge of this aspect is fundamental to define management strategies, especially those related with the genetic resistance and the chemical control. The objectives of this research were to confirm the taxonomic identity of the causal agent of downy mildew of rose and to deepen in the knowledge of their population structure in Colombia. Thirtyfour isolates of the pseudofungi were collected in rose crops located in Antioquia and the Savanna of Bogota and their DNA was extracted to amplify by PCR the ITS region of the DNAr using the species-specific primers PS3 and PS1. The products were used for their direct sequencing and to evaluate genetic variability by PCR-RFLP. Additionally the study was complemented throught RAPD and RAMS markers. Presence of a band of approximately 700 pb that shared a percentage of identity of 100% with sequences deposited in the GenBank, allowed to confirm the identity of the isolates as belonging to Peronospora sparsa, while the analysis of RFLP, RAPD and RAMS indicated a very low level of variability among all the isolates, concluding that the population of P. sparsa in Colombia is predominantly clonal.

Application of autoregressive integrated moving average model in establishing disease index time series model of cucumber downy mildew disease / 第二军医大学学报

Objective:To explore the forecasting method of disease index time series of cucumber downy mildew disease.Methods: Using the time series of cucumber downy mildew disease,we established an autoregressive integrated moving average model,ARIMA(2,2,0) based on model identification,comparison of residual variance,estimation and verification of parameter,observation of the correlation of the estimates matrix,autocorrelation check of the residuals,analysis of the fitting of model and so on.Results: An ARIMA model(2,2,0) was established:(1+0.487 1B+0.554 7B~2)(1-B)~2y_t=a_t,with the Sum of Squared Error(SSE) being 0.001 822 and the Root of Mean Squared Error(RMSE) being 0.008 537.The predicted values of validating date fitted well with the primary values.The established model showed satisfactory forecasting ability and was suitable for forecasting the middle stage and late stage cucumber downy mildew disease.Conclusion: Limiting the alternatives of model by residual variance, together with parameters estimation,the correlation of the estimates matrix,the autocorrelation check of the residuals and the fitting test,can help to search for suitable model quickly and accurately.