A novel technique for greenhouse evaluation of plant extracts for management of downy mildew of sorghum

Antipathogenic potential of 16 plants was evaluated in the form of aqueous extracts against Peronosclerospora sorghi, causing downy mildew of sorghum. A novel method was developed in which conidial suspension and plant extracts were mixed individually and allowed to stand for 5?min and then used to inoculate the host by sprout-dip method. The sprouts thus inoculated were grown in pots, and disease incidence was observed. Three extracts (Parthenium hysterophorus, Duranta repens and Oxalis latifolia) suppressed the disease at par with chemical fungicide (Mancozeb 75%). In form of spray, D. repens extract with tween-20 adjuvant (1.9% disease) performed closest behind mancozeb (0% disease), while negative control showed 21% disease incidence. Organic management of airborne inoculum of downy mildew of sorghum is feasible and preferable as compared to the use of chemical fungicides, considering human and environmental health concerns. Use of water extract keeps the technology simple so that it can be directly prepared and used by farmers. Short listing of three most effective water extracts would help in self-reliance of farmers, reducing their dependence on commercial products.     

Comparative evaluation of composts and dried powdered biomass of botanicals for organic management of downy mildew of sorghum

The biomass of 10 selected botanicals was evaluated as soil amendments, in the form of composts and dry powder biomass, to compare their potential to suppress downy mildew disease caused by oosporic inoculum of Perenosclerospora sorghi. Eight botanicals (Allium cepa, Lantana camara, Polyalthia longifolia, Hyptis suaveolens, Azadirachta indica, Nerium oleander Eucalyptus globulus and Tamarindus indica) proved effectively in the form of dry biomass powder at 4% (w/w) rate to control infection by oospores, while two (Croton sparsiflorus and Tagetes erecta) promoted it. In the form of composts (2% rate), the efficacy of botanicals was generally found reduced with the appearance of more disease than negative control in case of all botanicals except one (A. cepa). At the 4% compost rate, only four botanicals namely, A. cepa, P. longifolia, H. suaveolens and L. camara were found to suppress the disease. At higher amendment rates of 6, 8 and 10%, six botanicals suppressed the disease. Dry powders are not only superior in disease suppression but confer additional benefits like reduced bulk, increased shelf life, consistent composition and results.     

Evaluation of uncomposted botanical-based soil amendments for organic management of downy mildew of Sorghum

Uncomposted dried, powdered biomass of 38 selected botanicals was evaluated as soil amendments in a pot experiment for their potential to suppress downy mildew of sorghum caused by soil-borne oosporic inoculum of Perenosclerospora sorghi. A negative control showed 11.1% disease incidence. Six botanicals proved effective in form of dry biomass powder at 0.5% (w/w) amendment rate to control infection by oospores (Allium cepa 0%, Lantana camara 1.6%, Polyalthia longofolia 0%, Hyptis suaveolens 1.5%, Eucalyptus globulus 0% and Nerium oleander 1.6% of disease incidence). Dry powders are not only effective in disease suppression but confer additional benefits over composts like reduced bulk, increased shelf-life, consistent composition and results.     

Enhancement of downy mildew of sorghum by some organic soil amendments: a caution to organic farmers

Matured botanical compost of Croton sparsiflorus and Azadirachta indica were evaluated for promotion of sorghum downy mildew at the rate of 0.5% (w/w). Exceptionally high promotional rates of 26.9% (C. sparsiflorus) and 30.1% (A. indica) were observed as compared to negative control (8.8%). The enhancement of disease was higher than that obtained by the supply of recommended dose of urea (13.3%). As the pathogen (Peronosclerospora sorghi) is a biotroph and cannot multiply by using organics as nutrient source in the absence of a host, the mechanism of disease enhancement is inferred to be through stimulation of oospore germination by organic compounds.     

Exploiting medicinal plants and phylloplane microflora for the management of grapevine downy mildew

Abstract

Grapevine downy mildew is the most devastating disease throughout the world causing huge monetary losses. Twenty medicinal plant extracts and six phylloplane microfloras were evaluated for their efficacy against sporangial germination of grapevine downy mildew pathogen Plasmopara viticola in vitro. The results revealed that the Neem Seed Kernel Extract (NSKE) at 5% significantly inhibited the sporangial germination (75.36%) of P. viticola. Among the phylloplane microflora Pseudomonas fluorescens was highly effective in reducing the sporangial germination (64.26%). Post inoculation spraying of NSKE (5%) and P. fluorescens (0.2%) effectively inhibited the disease development in the greenhouse. Three sprays with NSKE (5%) and phylloplane P. fluorescens (0.2%): first spray after initial appearance of disease and the second and third at 10 day intervals were found to be promising in reducing disease incidence in the field.     

An efficient technique to obtain conidial inoculum of Peronosclerospora sorghi causing downy mildew of sorghum

An effective and simple technique to obtain conidial inoculum of Peronosclerospora sorghi has been devised, which confers many advantages over the conventional method. Systemically infected sorghum leaves were packed into folds of paper-towel. The end of folded paper-towel containing cut-ends of leaves was dipped in 3?cm deep water in a container. The container was exposed to moist field conditions at night and sporulated leaves were harvested with chilled distilled water in the morning to obtain the inoculum. Advantages of the technique include lower cost and effort, rapid harvesting and daily production of inoculum for up to seven consecutive days from same leaves. Though conventional method of plating leaf pieces in Petri plates proves superior in terms of the amount of sporulation, paper-towel method has the edge under working conditions.     

Seed treatment with aqueous extract of Viscum album induces resistance to pearl millet downy mildew pathogen

Abstract

Downy mildew (Sclerospora graminicola [Sacc.] Schroet.) is a serious agricultural problem for pearl millet (Pennisetum glaucum [L.] R. Br.) grain production under field conditions. Six medicinally important plant species Azadirachta indica, Argemone mexicana, Commiphora caudata, Mentha piperita, Emblica officinalis and Viscum album were evaluated for their efficacy against pearl millet downy mildew. Seeds of pearl millet were treated with different concentrations of aqueous extract of the plants to examine their efficacy in controlling downy mildew. Among the plant extracts tested, V. album treatment was found to be more effective in enhancing seed quality parameters and also in inducing resistance against downy mildew disease. Germination and seedling vigor was improved in seeds treated with V. album extracts over control. Seeds treated with 10% concentration of V. album showed maximum protection against downy mildew disease under greenhouse and field conditions. The downy mildew disease protection varied from 44–70% with different concentrations. Leaf extract of V. album did not inhibit sporulation and zoospore release from sporangia of Sclerospora graminicola, indicating that the disease-controlling effect was attributed to induced resistance. Seed treatment with V. album extract increased pearl millet grain yield considerably. In V. album, treated pearl millet seedlings increased activities of peroxidase, and phenylalanine ammonia-lyase enzyme was detected. FTIR analysis of V. album extracts showed the presence of amides and other aromatic compounds which are antimicrobial compounds involved in plant defense.     

Inheritance pattern of downy mildew resistance in advanced generations of sorghum*

In a project aimed to incorporate downy mildew resistance into sorghum hybrid seed parents, we screened F₄ and F₅ families for resistance to the ICRISAT Centre isolate of the pathogen using a greenhouse seedling screening technique. The families originated from a cross of 296B (susceptible) and IS 18757 [(QL-3) resistant]. The F₄s were obtained from agronomic selection in F₂s and F₃s, and the F₅ families from advancing plants identified as resistant in segregating F₄ families. The resistant plants were more than double the number of susceptible plants in the F₄ and almost so in the F₅ suggesting that resistance to downy mildew was dominant. Of the four genetic models examined (a single-locus model and three two-locus models with complementary, inhibitory, and a combination of complementary and inhibitory interactions), the two-locus model with independent segregation and a combination of complementary and inhibitory inter-allelic interaction appeared to be most appropriate in explaining the segregation patterns within and among F₄ and F₅ families. Accordingly, for resistance to P. sorghi, the suggested genotypes for IS 18757 is Pl_aPl_aPl_bPl_b and for 296B is Pl_aPl_aPl_bPl_b.     

虎尾兰水提取物对黄瓜霜霉病的防治研究

明确虎尾兰水提取物对黄瓜霜霉病菌无性阶段的抑制作用及对黄瓜霜霉病的防治效果。采用凹玻片法和离体叶五点接种法分别测定该提取物对游动孢子的释放和游动、休止孢的萌发和芽管伸长以及菌丝生长和孢子囊产生的抑制作用,采用离体叶五点接种法测定该提取物的保护作用、治疗作用和持效期,并采用盆栽试验测定该提取物的保护作用和治疗作用。一系列试验结果显示,虎尾兰水提取物对黄瓜霜霉病菌游动孢子的释放和游动,休止孢的萌发和芽管伸长以及菌丝生长和孢子囊产生的EC₅₀值分别为1.19、0.77、0.70、2.13、9.09和13.15 mg/mL。在离体叶片条件下,虎尾兰水提取物对黄瓜霜霉病的保护和治疗作用的EC₅₀值分别为3.69 和14.57 mg/mL,持效期达14 d以上。盆栽条件下,该提取物对黄瓜霜霉病保护作用和治疗作用的防效分别为68.38%和21.33%。虎尾兰水提取物对黄瓜霜霉病具有很好的保护作用和较长的持效期。     

Effect of certain plant extracts and fungicides against powdery mildew disease of Grapevines in Upper Egypt

The efficiency of azadirachtin, jojoba oil, Reynoutria sachalinensis, azoxystrobin + difenoconazole, kresoxim methyl, propiconazole and sulphur in controlling powdery mildew disease of Grapevines caused by Uncinula necator (Schlecht.) was evaluated during 2015 and 2016 seasons. Laboratory study showed that all the tested plant extracts and fungicides significantly (p < 0.05) reduced germination of conidia of the causal pathogen. Spraying of the extracts on vine trees significantly (p < 0.05) decreased the disease severity (D.S. %) compared with infected control. The tested plant extracts as well as fungicide have high effect in disease reduction; no significant differences (p < 0.05) in the disease reduction were found in the effect of the extracts between tested compounds in both seasons. Moreover, treatment of trees with Reynoutria extract exhibited the highest increment in peroxidase activity (PO), polyphenol-oxidase (PPO) activity and phenol content compared to other treatments after 9 days from spraying.     

黄瓜霜霉病及寄主抗性机制研究进展

在黄瓜生产中,由古巴假霜霉菌(Pseudoperonospora cubensis)引起的霜霉病危害严重,影响叶、茎和花序生长发育,导致黄瓜产量及品质降低。通过对黄瓜霜霉病的病原菌检测和防御途径、影响及调控因素、抗病原菌候选基因发掘、蛋白质组和基因组分析、黄瓜霜霉病QTL连锁标记开发及其抗病育种等多方面的最新进展进行综述,以期为今后进一步揭示黄瓜乃至农作物对霜霉病的抗性机制研究提供借鉴和参考。     

Microsatellite DNA markers for Plasmopara viticola,the causal agent of downy mildew of grapes

Microsatellite loci were isolated from Plasmopara viticola (Oomycetes), the causal agent of downy mildew of grape, one of the most damaging fungal diseases of grapevine worldwide. Seven polymorphic loci were obtained from an enriched partial genomic library. A low genetic diversity was observed at all loci, with a mean observed allele number of 3.75 and an observed heterozygosity ranging from 0.074 to 0.547. Cross‐amplification tests on three closely related taxa indicated that two loci could be used in other Oomycetes species. These microsatellite loci were proved to be useful for population genetic analysis.     

Effect of combination between inducer resistance chemicals and systemic fungicides on management of sweet melon downy mildew

The efficiency of some inducer resistance chemicals (IRCs) like bion, chitosan, humic acid and salicylic acid as well as the fungicides like Folu-Gold, Galben Copper, Previcure-N and Redomil Gold Mancozeb on management of sweet melon downy mildew, caused by Pseudoperonospora cubensis was evaluated in vitro and in vivo. Also, the efficiency of the alternation between the sprayed two fungicides and IRCs on management of the disease and the produced fruit yield and its total soluble solids (TSS) under field conditions were assessed. The inhibitory effect of the IRCs and the tested fungicides on sporangial germination of P. cubensis resulted in a significant reduction in the germinated sporangia. In addition, IRCs were less effective than the fungicides. Disease management revealed the same trend of the in vitro experiment when they sprayed fungicides on sweet melon plants artificially inoculated with the sporangia of the causal fungus under greenhouse conditions. Furthermore, under field conditions, spraying sweet melon plants with the two tested fungicides was the most efficient in decreasing the disease and increasing fruit yield and its TSS, to somewhat, followed by the alternation between them and the tested IRCs. In addition, IRCs treatments showed the lowest efficiency in this regard.     

Characterisation of pathogenic and molecular diversity in Sclerospora graminicola,the causal agent of pearl millet downy mildew

Genotypic diversity among 46 isolates of Sclerospora graminicola collected from seven states in India during 1992–2005 was determined through pathotyping and AFLP analysis. A high level of variation was observed among the isolates for downy mildew incidence, latent period and virulence index. Based on the reaction on a set of nine pearl millet lines, 46 isolates were classified in 21 pathotypes. Quantitative differences in virulence levels of the test isolates were assessed by calculating the virulence index (disease incidence × latent period ^? 1). A dendrogram generated by the average linkage cluster analysis of virulence index clustered the 46 isolates into eight groups. Region-specific grouping of five isolates from Gujarat and six from Rajasthan was observed within two distinct groups. Temporal variation was also observed among the isolates collected from the same location and same host over the years. A total of 297 bands were scored following selective amplification with three primer combinations E-TT/M-CAG, E-AT/M-CAG and E-TG/M-CAT and all of them were polymorphic. Cluster analysis of AFLP data clustered the test isolates into seven groups. Analysis of molecular variance indicated that variation in the S. graminicola populations was largely due to differences among the isolates within the states.     

Cerebroside as an elicitor for induced resistance against the downy mildew pathogen in pearl millet

Innate defence mechanisms in plants can be triggered and enhanced by certain agents, which are referred to as inducers. Inducing resistance against a broad spectrum of pathogens in otherwise susceptible plants is seen as a potentially safer alternative to other methods of chemical control of plant diseases. Cerebrosides, which are glycosphingolipids extracted from various plant pathogens, have been reported as resistance elicitors in the rice‐pathogen system. In the present study, cerebroside elicited resistance against downy mildew disease (caused by Sclerospora graminicola) of pearl millet (Pennisetum glaucum) that was highly significant. The resistance was of systemic nature and the time required for the resistance to build up was from 2 days onwards. There was a significant yield enhancement due to disease suppression by cerebroside treatment. Promising results were obtained in a preliminary field trial.     

ACC deaminase‐containing plant growth‐promoting rhizobacteria protect Papaver somniferum from downy mildew

Aims

Analysis of the stability and safety of Sulfolobus monocaudavirus 1 (SMV1) during passage through the mammalian GI tract.

Methods and Results

A major challenge of using nano‐vectors to target gut microbiome is their survival during passage through the extremely acidic and proteolytic environment of the mammalian GI tract. Here, we investigated the thermo‐acidophilic archaeal virus SMV1 as a candidate therapeutic nano‐vector for the distal mammalian GI tract microbiome. We investigated the anatomical distribution, vector stability and immunogenicity of this virus following oral ingestion in mice and compared these traits to the more classically used Inovirus vector M13KE. We found that SMV1 particles were highly stable under both simulated GI tract conditions (in vitro) and in mice (in vivo). Moreover, SMV1 could not be detected in tissues outside the GI tract and it elicited a nearly undetectable inflammatory response. Finally, we used human intestinal organoids (HIOs) to show that labelled SMV1 did not invade or otherwise perturb the human GI tract epithelium.

Conclusion

Sulfolobus monocaudavirus 1 appeared stable and safe during passage though the mammalian GI tract.

Significance and Impact of the Study

This is the first study evaluating an archaeal virus as a potential therapeutic nanoparticle delivery system and it opens new possibilities for future development of novel nanoplatforms.     

Phenol metabolism in downy mildew resistant and susceptible genotypes of pearl millet

Biochemical characterisation of pearl millet genotypes was carried at pre- (45 DAS) and post-infection (57 DAS i.e. 7 days after infection) stages. Total phenol content at pre-infection stage did not show inherent resistance or susceptibility. While the total phenol content was found to be higher in susceptible genotypes at post-infection stage, qualitative analysis of phenol through high-performance thin layer chromatography showed absence of ferulic acid in resistant genotypes at pre-infection stage. Peroxidase (POX) activity was higher in susceptible genotypes at both the stages of analysis. Constitutive activity of phenylalanine ammonia lyase was higher in resistant genotype whereas induced activity was recorded higher in susceptible genotypes. Native poly-acrylamide gel electrophoresis isozyme banding pattern of POX showed some inducible band(s) due to disease infection in resistant and susceptible genotypes.     

Screening of antifungal activity of various plant leaves extracts from Indian plants

The present study was designated to evaluate the antifungal activity and to root out the antifungal plant leaf extracts from this Indian folk-flore. The in vitro antifungal assay was performed by agar diffusion test and minimum inhibitory concentration (MIC) for hexane, ethyl acetate, methanol and distilled water plant leaf extracts. Extraction of 17 different plant leaves was carried out in different solvents such as hexane, ethyl acetate, methanol and distilled water. Among them extractive yield of methanol was maximum than the rest of the three solvents. These extracts were screened for their antifungal activity against nine different fungi. Among these ethyl acetate extracts of Adhatoda vasica, Ocimum sanctum and Holoptelea integrifolia exhibited maximum antifungal activity against Alternaria sp., Aspergillus parasi, Aspergillus nidulans, Trichoderma harzianum and Aspergillus flavus with MIC of 80, 40 and 20 ppm against Aspergillus nidulans and Alternaria sp. Ethyl acetate extracts showed promising antifungal activity against Adhatoda vasica, Ocimum sanctum and Holoptelea integrifolia against Aspergillus nidulans, and Alternaria sp. might be applicable as fungicide against fungal plants disease.     

The effect of fungicides, irrigation and plant density on the development of Peronospora sparsa, the cause of downy mildew in rose and blackberry

Downy mildew of rose (Rosa spp.) and blackberry (Rubus fructicosus), caused by Peronospora sparsa, can cause significant losses in production. In a series of experiments, fungicides with different modes of action to the commonly used phenylamide‐based products were examined for efficacy on both crops. Cymoxanil + mancozeb + oxadixyl and fluazinam gave good downy mildew control on both rose and blackberry. On outdoor, container‐grown rose, high volume sprays of fosetyl‐aluminium were also effective, but on young micropropagated blackberry plants, application as a drench treatment was better than as a spray. Good control was also achieved on blackberry with chlorothalonil and with metalaxyl in formulation with either thiram or mancozeb. There was no evidence of loss of control with phenylamide fungicides due to resistance. Irrigation regimes were also examined on blackberry and sub‐irrigation of plants in propagation on a sand bed led to significantly lower disease levels than those found where plants had been irrigated by overhead sprinklers. Reducing the density of container‐grown rose plants had a measurable effect on the progress of downy mildew, though this was small and temporary when compared with the effect of fungicide treatment. Fungicide programmes which gave season‐long control of rose downy mildew resulted in significantly improved extension growth.     

Sclerospora graminicola- and arachidonic acid-induced autofluorescence in downy mildew resistant and susceptible genotypes of pearl millet

Autofluorescence of downy mildew resistant and susceptible cells of pearl millet seedlings undergoing hypersensitive reaction (HR) upon Sclerospora graminicola-inoculation and arachidonic acid (AA)-treatment was studied. Two-day-old seedlings of a highly resistant (IP 18296) and a highly susceptible (23D₂B) genotype of pearl millet were either inoculated with zoospore suspension of S. graminicola or treated with AA for 24 h. The coleoptiles with hypersensitive necrotic spots were processed by the standard procedure, and the tissues were subjected to fluorescence microscopy. A differential accumulation of autofluor-escent compounds in resistant and susceptible pearl millet genotypes was observed with most accumulation occurring in resistant cells treated with AA. The variation in the degree of fluorescence and the spatial accumulation of autofluorescent compounds among the two inoculated/treated genotypes is discussed.