Diversity and activity of biosurfactant-producing Pseudomonas in the rhizosphere of black pepper in Vietnam

Aims: Phytophthora capsici is a major pathogen of black pepper and zoospores play an important role in the infection process. Fluorescent pseudomonads that produce biosurfactants with zoosporicidal activities were isolated from the black pepper rhizosphere in Vietnam, and their genotypic diversity and potential to control Phy. capsici root rot was determined. Methods: Biosurfactant‐producing pseudomonads were genotypically and biochemically characterized by BOX‐polymerase chain reaction (PCR), 16S‐rDNA sequencing, reverse‐phase‐high‐performance liquid chromatography and liquid chromatography‐masss spectrometry analyses. Results: Biosurfactant‐producing fluorescent pseudomonads make up c. 1.3% of the culturable Pseudomonas population in the rhizosphere of black pepper. Although BOX‐PCR revealed substantial genotypic diversity, the isolates were shown to produce the same biosurfactants and were all identified as Pseudomonas putida. When applied to black pepper stem cuttings, several of the biosurfactant‐producing strains provided significant disease control. In absence of the disease, several of the bacterial strains promoted shoot and root growth of black pepper stem cuttings. Conclusions: Biosurfactant‐producing pseudomonads indigenous to the rhizosphere of black pepper plants are genotypically diverse and provide a novel resource for the control of Phy. capsici root rot and growth promotion of black pepper stem cuttings. Significance and Impact of the Study: The results of this study provide a strong basis for further development of supplementary strategies with antagonistic bacteria to control foot and root rot of black pepper and to promote plant growth.     

Pre-plant bacterisation: a strategy for delivery of beneficial endophytic bacteria and production of disease-free plantlets of black pepper (Pipernigrum L.)

Naturally occurring endophytic bacteria from black pepper vines were found to exhibit strong antagonistic activities against Phytophthora capsici and Radopholus similis. In order to deliver these bacterial strains, as well as to produce disease-free plantlets of black pepper, a pre-plant stem and root bacterisation was standardised. Stem bacterisation with endophytic Pseudomonas spp. was found to suppress P. capsici infection (over 90% reduction in lesion length) on cut shoots. Pre-plant root bacterisation with Pseudomonas aeruginosa, Pseudomonas putida and Bacillus megaterium yielded over 60% of plantlets free from P. capsici infection on roots. Curtobacterium luteum and B. megaterium recorded over 70% reduction of nematode population in soil with concomitant production of over 65% of nematode-free plantlets. Besides protecting the plants from the pathogens, the bacteria were also found to enhance the growth of rooted cuttings. The biocontrol potential of the above endophytic bacteria and their exploitation for disease management in the black pepper nursery are discussed.     

Susceptibility assessment of bell pepper genotypes to crown and root rot disease

Bell Pepper (Capsicum annuum) is one of the important vegetable crops with valuable food sources, which is used almost around the world. Crown and root rot disease caused by Phytophthora capsici is one of the most important diseases of bell pepper in Iran. The present study was conducted to evaluate the susceptibility of different varieties of bell pepper to crown and root rot disease under glasshouse condition. Fourteen commonly planted genotypes of bell pepper in Iran were evaluated for their susceptibility to infection with the pathogen. For this purpose, disease severity of the chosen genotypes in different growth stages was evaluated. The results indicated that the bell pepper genotypes respond differently to pathogenicity tests. Based on cluster analyses confirmed by the results of SAS analyses, bell pepper cultivars were categorised in five distinct groups.     

Endophytic bacterial flora in root and stem tissues of black pepper (Piper nigrum L.) genotype: isolation, identification and evaluation against Phytophthora capsici

Aim:  To isolate and identify black pepper ( Piper nigrum L) associated endophytic bacteria antagonistic to Phytophthora capsici causing foot rot disease.
Methods and Results:  Endophytic bacteria (74) were isolated, characterized and evaluated against P. capsici . Six genera belong to Pseudomonas spp (20 strains), Serratia (1 strain), Bacillus spp. (22 strains), Arthrobacter spp. (15 strains), Micrococcus spp. (7 strains), Curtobacterium sp. (1 strain) and eight unidentified strains were isolated from internal tissues of root and stem. Three isolates, IISRBP 35, IISRBP 25 and IISRBP 17 were found effective for Phytophthora suppression in multilevel screening assays which recorded over 70% disease suppression in green house trials. A species closest match (99% similarity) of IISRBP 35 was established as Pseudomonas aeruginosa ( Pseudomonas EF568931), IISRBP 25 as P. putida ( Pseudomonas EF568932), and IISRBP 17 as Bacillus megaterium ( B. megaterium EU071712) based on 16S rDNA sequencing.
Conclusion:  Black pepper associated P. aeruginosa , P. putida and B. megaterium were identified as effective antagonistic endophytes for biological control of Phytophthora foot rot in black pepper.
Significance and Impact of the Study:  This work provides the first evidence for endophytic bacterial diversity in black pepper stem and roots, with biocontrol potential against P. capsici infection.     

Evaluation of Oospore Hyperparasites for the Control of Phytophthora Crown Rot of Pepper

Nine isolates of known oospore mycoparasites comprised of six actinomycetes (Actinoplanes missouriensis, A. philippinensis, A. utahensis, Amorphosporangium auranticolor, Ampullariella regularis, Spirillospora albida) and three fungi (Acremonium sp., Humicola fuscoatra, Verticillium chlamydosporium) were tested in the greenhouse for their ability to suppress or delay the onset of crown rot of pepper caused by Phytophthora capsici. Verticillium chlamydosporium applied as a root dip increased the number of healthy plants by more than 100% when peppers were transplanted into soil artificially infested with oospores of Phytophthora capsici, but not when peppers were transplanted into soil naturally infested with P. capsici. The other mycoparasites were ineffective in the greenhouse. All the mycoparasites tested parasitized oospores of P. capsici in vitro.     

Control of Late Blight (Phytophthora capsici ) in Pepper Plant with a Compost Containing Multitude of Chitinase-producing Bacteria

Compost sustaining a multitude of chitinase-producing bacteria was evaluated in a greenhouse study as a soil amendment for the control of late blight (Phytophthora capsici L.) in pepper (Capsicum annuum L.). Microbial population and exogenous enzyme activity were measured in the rhizosphere and correlated to the growth and health of pepper plant. Rice straw was composted with and without a chitin source, after having been inoculated with an aliquot of coastal area soil containing a known titer of chitinase-producing bacteria. P. capsici inoculated plants cultivated in chitin compost-amended soil exhibited significantly higher root and shoot weights and lower root mortality than plants grown in pathogen-inoculated control compost. Chitinase and β-1,3-glucanase activities in rhizosphere of plants grown in chitin compost-amended soil were twice that seen in soil amended with control compost. Colony forming units of chitinase-producing bacteria isolated from rhizosphere of plants grown in chitin compost-amended soil were 10³ times as prevalent as bacteria in control compost. These results indicate that increasing the population of chitinase-producing bacteria and soil enzyme activities in rhizosphere by compost amendment could alleviate pathogenic effects of P. capsici.     

Selection of antagonistic soil microbes against a few fungal pathogens of piper betle L

Summary Against the fungal pathogens,Phytophthora parasitica, Sclerotium rolfsii, Colletotrichum capsici andGlomerella cingulata responsible for leaf and foot rot of betel vines, 3 fungus, 9 actinomycetes and 4 bacterial antagonists were screened out from 61 fungus, 28 actinomycetes and 4 bacterial organisms isolated from 3 sources of soils. One each from the 3 groups of antagonists when further tested, was found quite effective against the pathogens towards neutral side of H-ion concentration. The antagonists (P. citrinum, Streptomyces sp. and bacterial organism B-7) were also found effective against 18 among 32 isolated fungus organisms from potted soil (collected from betel vine soil) and except one which happened to beP. citrinum, the rest had no adverse effect upon their growth.This work is a part of a scheme supported by Food and Agriculture Council of Pakistan and conducted in Jute Research Institute.     

Effect of oxathiapiprolin on asexual life stages of Phytophthora capsici and disease development on vegetables

Phytophthora blight caused by Phytophthora capsici is a serious disease in the production of peppers and other vegetables worldwide. Application of fungicides is an important component in developing effective disease management programmes. However, resistance in P. capsici populations to some commonly used fungicides has been documented. Identification of effective new fungicides with different mode of actions is highly desirable. This study was conducted to determine baseline sensitivity of P. capsici isolates to oxathiapiprolin, the first member of a new class of isoxazoline fungicides, and efficacy of this compound for reduction of Phytophthora blight on bell pepper. A collection of 126 P. capsici isolates were evaluated and all the isolates were sensitive to oxathiapiprolin. EC₅₀ values of oxathiapiprolin in inhibiting mycelial growth, sporangium formation and zoospore germination of 25 selected isolates averaged 0.001, 0.0003 and 0.54 µg mL^?1, respectively. It appeared that asexual life stages of P. capsici were more sensitive to oxathiapiprolin than other compounds used for control of oomycete pathogens. In field studies, oxathiapiprolin applied at different rates through drip irrigation tubes, or by soil drench plus foliar sprays, reduced Phytophthora blight and increased pepper yield significantly. This is the first report of the efficacy of oxathiapiprolin in suppression of P. capsici, which indicates that oxathiapiprolin is effective in inhibiting the pathogen and has the promise to be a viable option for managing Phytophthora blight in bell pepper production.     

The volatile-producing Flavobacterium johnsoniae strain GSE09 shows biocontrol activity against Phytophthora capsici in pepper

Aims: Previously, we selected a bacterial strain (GSE09) antagonistic to Phytophthora capsici on pepper, which produced a volatile compound (2,4‐di‐tert‐butylphenol), inhibiting the pathogen. In this study, we identified strain GSE09 and characterized some of the biological traits of this strain in relation to its antagonistic properties against P. capsici. In addition, we examined bacterial colonization on the root surface or in rhizosphere soil and the effect of various concentrations of the volatile compound and strain GSE09 on pathogen development and radicle infection as well as radicle growth. Methods and Results: Strain GSE09 was identified as Flavobacterium johnsoniae, which forms biofilms and produces indolic compounds and biosurfactant but not hydrogen cyanide (HCN) with little or low levels of antifungal activity and swimming and swarming activities. Fl. johnsoniae GSE09 effectively colonized on pepper root, rhizosphere, and bulk (pot) soil, which reduced the pathogen colonization in the roots and disease severity in the plants. Various concentrations of 2,4‐di‐tert‐butylphenol or strain GSE09 inhibited pathogen development (mycelial growth, sporulation, and zoospore germination) in I‐plate (a plastic plate containing a center partition). In addition, germinated seeds treated with the compound (1–100 μg ml^?1) or the strain (10²–10¹⁰ cells ml^?1) significantly reduced radicle infection by P. capsici without radicle growth inhibition. Conclusions: These results indicate that colonization of pepper root and rhizosphere by the Fl. johnsoniae strain GSE09, which can form biofilms and produce indolic compounds, biosurfactant, and 2,4‐di‐tert‐butylphenol, might provide effective biocontrol activity against P. capsici. Significance and Impact of the Study: To our knowledge, this is the first study demonstrating that the Fl. johnsoniae strain GSE09, as a potential biocontrol agent, can effectively protect pepper plants against P. capsici infection by colonizing the roots.     

Biological Control of Phytophthora Root Rot of Pepper Using Trichoderma harzianum and Streptomyces rochei in Combination

A combination of two compatible micro‐organisms, Trichoderma harzianum and Streptomyces rochei, both antagonistic to the pathogen Phytophthora capsici, was used to control root rot in pepper. The population of the pathogen in soil was reduced by 75% as a result. Vegetative growth of the mycelium of P. capsici was inhibited in vitro on the second day after P. capsici and T. harzianum were placed on the opposite sides of the same Petri plate. Trichoderma harzianum was capable of not only arresting the spread of the pathogen from a distance, but also after invading the whole surface of the pathogen colony, sporulating over it. Scanning electron microscopy showed the hyphae of P. capsici surrounded by those of T. harzianum, their subsequent disintegration, and the eventual suppression of the pathogen's growth. Streptomyces rochei produced a zone of inhibition, from which was obtained a compound with antioomycete property secreted by the bacteria. When purified by high‐pressure liquid chromatography, this compound was identified as 1‐propanone, 1‐(4‐chlorophenyl), which seems to be one of the principal compounds involved in the antagonism. A formulation was prepared that maintained the compound's capacity to inhibit growth of the pathogen for up to 2 years when stored at room temperature in the laboratory on a mixture of plantation soil and vermiculite. The two antagonists, added as a compound formulation, were effective at pH from 3.5 to 5.6 at 23–30°C. The optimal dose of the antagonists in the compound formulation was 3.5 × 10⁸ spores/ml of T. harzianum and 1.0 × 10⁹ FCU/ml of S. rochei. This is the first report of a compound biocontrol formulation of these two antagonists with a potential to control root rot caused by P. capsici.     

Outbreak of basal stem rot and wilt disease of pepper in Katsina,Nigeria

Abstract

A survey was conducted in February 2004 on the outbreak of stem rot and wilt disease of pepper at the Kitabawa/Danzakara and Ajiwa irrigation sites in Katsina State, Nigeria. Laboratory investigations revealed that it was elicited by Phytophthora capsici (Leon). The disease caused severe loss in yield and $1,700.00 to $3,200.00 loss in revenue/ha. The pathogen was probably further aggravated by the presence of Fusarium sp. as well as ecto- and endo-parasitic nematodes. Reasons for the outbreak were elucidated and solutions proffered.     

In vitro and in vivo antimicrobial activity of Xenorhabdus bovienii YL002 against Phytophthora capsici and Botrytis cinerea

Aims: Developing new bio‐agents to control plant disease is desirable. Entomopathogenic bacteria Xenorhabdus spp. have potential antimicrobial activity in agriculture. This work was conducted to evaluate the antimicrobial activity of Xenorhabdus bovienii YL002 on plant pathogenic fungi and oomycete in vitro and the efficiency of this strain to reduce the in vivo incidence of grey mould rot on tomato plants caused by Botrytis cinerea and leaf scorch on pepper plants caused by Phytophthora capsici. Methods and Results: The antimicrobial activity of X. bovienii YL002 was firstly determined on in vitro plant pathogenic fungi and oomycete and then on tomato fruits and plants infected with B. cinerea and pepper plants infected with P. capsici. The cell‐free filtrate of X. bovienii YL002 exhibited highest inhibition effects (>98%) on mycelia growth of P. capsici and B. cinerea. The 50% inhibition concentration (EC₅₀) of the methanol‐extracted bioactive compounds (methanol extract) of the cell‐free filtrate against P. capsici and B. cinerea were 164·83 and 42·16 μg ml^?1. The methanol extract also had a strong effect on the spore germination of P. capsici and B. cinerea, with a EC₅₀ of 70·38 and 69·33 μg ml^?1, respectively. At 1000 μg ml^?1, the methanol extract showed a therapeutic effect of 70·82% and a protective effect of 77·4% against B. cinerea on tomato plants compared with the control. The methanol extract also showed potent effect against P. capsici, with a therapeutic effect of 68·14% and a protective effect of 65·46% on pepper plants compared with the control. Conclusions: Xenorhabdus bovienii YL002 produces antimicrobial compounds with strong activity on plant pathogenic fungi and oomycete and has the potential for controlling grey mould rot of tomato plants and leaf scorch of pepper and could be useful in integrated control against diverse plant pathogenic fungi and oomycete. Significance and Impact of the Study: This study showed the potential that X. bovienii YL002 can be used to control the grey mould rot caused by B. cinerea on tomato plants and leaf scorch caused by P. capsici on pepper plants with the objective to reduce treatments with chemical fungicides.     

Selecting Bacterial Strains for Use in the Biocontrol of Diseases Caused by <Emphasis Type="Italic">Phytophthora capsici</Emphasis> and <Emphasis Type="Italic">Alternaria alternata</Emphasis> in Sweet Pepper Plants

More than 500 isolates of bacteria were obtained from the aerial part and rhizosphere of sweet pepper (Capsicum annuum L.) plants harvested from different places in the Region of Murcia (Spain). The isolates were purified and assayed in vitro against Phytophthora capsici and Alternaria alternata. Sixty isolates (12 %) produced an inhibition zone against at least one of the pathogens, while ten had a strongly inhibitory effect on both pathogens assayed. Microscopic observation of interactions zone showed cell vacuolisation, hyphae lysis and spilling of cytoplasm content of the pathogens in the culture media. These ten isolates were then chosen for biocontrol of Phytophthora root rot and Alternaria leaf spots of pepper plants in vivo. Four of them denominated HS93, LS234, LS523 and LS674 reduced P. capsici root rot by 80, 51, 49 and 54 %, respectively, and A. alternata leaf spots by 54, 74, 62 and 53 %. HS93 belongs to the genus Bacillus and probably the species subtilis, while LS234, LS523 and LS674 belong to the genus Bacillus and probably the species licheniformis. Dry mass of plants treated with these bacteria was significantly higher than that of non-treated and inoculated plants.     

Zinc influences nodulation,disease severity,leaf drop and herbage yield of alfalfa cultivars

Zinc deficiency is an important limiting factor in sustainable crop production and is a factor often overlooked in determining the benefits and overall success of alfalfa pastures in rotations. A field experiment was conducted to investigate the effects of zinc and alfalfa cultivars on nodulation, herbage yield, leaf drop and disease severity (Phytophthora root rot disease and common leaf spot disease) in alfalfa (Medicago sativa L.). Ten cultivars of alfalfa (Hunter River, Hunterfield, Sceptre Aurora, Genesis, Aquarius, Venus (Y8622), PL69, P5929 and PL34HQ) were tested at two levels of zinc (+Zn: 4 kg ha^–1, -Zn: no zinc added) on a Zn-deficient soil (DTPA zinc of top 0–15 cm soil was 0.4 mg kg^–1 soil, while 15–30 cm subsoil Zn was 0.1 mg kg^–1 soil) under field conditions. Zinc application significantly increased number and dry weight of nodules, herbage yield and leaf to stem ratio of alfalfa plants. There was a significant reduction in leaf drop, and occurrence of Phytophthora root rot (caused by fungus Phytophthora megasperma f. sp. medicaginis) and common leaf spot (caused by fungus Pseudopeziza medicaginis) diseases with Zn application. Alfalfa cultivars had a differential response to low Zn. Hunter River and Hunterfield were the most affected by omitting zinc application, while Sceptre, PL34HQ and Aquarius were comparatively less affected. The present study suggest that Zn nutrition effects nodulation, leaf drop, disease occurrence and production potential of alfalfa. The alfalfa cultivars have differential ability to low Zn supply. Growing of Zn-efficient cultivars and adequate Zn nutrition may also improve the N₂-fixation by alfalfa on low-Zn soils.     

Some effects of differently-acting nematicides on the cereal cyst-nematode (Heterodera avenae) and on the appearance of ''scorch'' in spring wheat on light loamy sand

In fungitoxicity tests against Phytophthora cinnamomi on Chamaecyparis lawsoniana cv. Ellwoodii, a drench of furalaxyl (1000 mg a.i./l) applied to the compost in which 1-yr-old plants were growing, 1 wk before they were inoculated with 650 000 zoospores, controlled disease for at least 12 months. With an inoculum dose of 650 zoospores/plant, furalaxyl at 500 mg a.i./l controlled disease even when inoculation was 12 wk after fungicide treatment. Aluminium tris (ethyl phosphonate) (2000 mg a.i./l) applied as a drench 1 wk before inoculation with 650 000 zoospores/plant did not prevent root infection but delayed foliar symptoms for 9 months: the same treatment, using etridiazole (500 mg a.i./l) only slightly reduced disease incidence. When applied as a single drench 2 days before inoculation, prothiocarb (2000 mg a.i./l) and cuprammonium compounds (200 mg a.i./l) were much less effective than furalaxyl (1200 mg a.i./l), sodium ethyl phosphonate (1500 mg a.i./l), aluminium tris (ethyl phosphonate) (1500 mg a.i./l) or etridiazole (500 mg a.i./l). However, a drench of furalaxyl at 1000 mg a.i./l, aluminium tris (ethyl phosphonate) at 2000 mg a.i./l or etridiazole at 500 mg'a.i./l did not eradicate P. cinnamomi from compost containing infected root debris. Pre-planting drenching of the compost was ineffective. All fungicide treatments were non-phototoxic to 1-yr-old C. lawsoniana cv. Ellwoodii. These results are of special relevance to the control of P. cinnamomi on container-grown woody ornamentals.     

Chemical Control of Basal Stem Rot Disease of Tomato (Lycopersicon esculentum Mill.) in Northern Nigeria

Six fungicides (Aatopam-N, Aldrex T, Calixin M, PCNB, captan and captafol) were evaluated at 200 mg a.i.l^?1 for their effectiveness in reducing basal stem rot disease incited by Sclerotium rolfsii on tomato in pre- and post-inoculation soil drenches in the glasshouse. The results showed that only PCNB effectively reduced disease severity when applied to soil 10 days before inoculation. Of the two application methods only pre-inoculation soil drenching with the fungicides was efficacious in reducing disease severity. In field trials conducted in Samaru with Aldrex T, captan and PCNB, only PCNB was effective in combating the severity of the disease. It reduced the disease by about 88% in one trial.     

Plant growth promoting rhizhobacteria (PGPR)-mediated root proliferation in black pepper (Piper nigrum L.) as evidenced through GS Root software

Abstract

Pseudomonas fluorescens strains which are proven biocontrol agents in black pepper against foot rot (caused by Phytophthora capsici ) were also found to enhance root proliferation and fibre root production. Experiments conducted in the greenhouse with five efficient strains of P. fluorescens (IISR-6, IISR-8, IISR-11, IISR-13 and IISR-51) showed that the bacterial strains could significantly increase the root biomass of the plants (30 – 135%). Parameters for total root length, root area and root tips were estimated by scanning the entire root system and analysis through GS Root® software (PP systems, Winterstreet, USA). All the strains increased the root length in the treated plants (12 – 127%), the highest being with IISR-6, which was on a par with IISR-11 and IISR-51. A similar trend was observed with the total root area after bacterization (43 – 200%). The P. fluorescens treated plants had a higher number of feeder roots as evidenced by the increased number of root tips (82 – 137%). The enhanced growth parameters upon root bacterization could be corroborated with the production of the plant growth hormones IAA & GA by the bacterial strains and their P-solubilization potential.     

Plant-Plant-Microbe Mechanisms Involved in Soil-Borne Disease Suppression on a Maize and Pepper Intercropping System

Background

Intercropping systems could increase crop diversity and avoid vulnerability to biotic stresses. Most studies have shown that intercropping can provide relief to crops against wind-dispersed pathogens. However, there was limited data on how the practice of intercropping help crops against soil-borne Phytophthora disease.

Principal Findings

Compared to pepper monoculture, a large scale intercropping study of maize grown between pepper rows reduced disease levels of the soil-borne pepper Phytophthora blight. These reduced disease levels of Phytophthora in the intercropping system were correlated with the ability of maize plants to form a “root wall” that restricted the movement of Phytophthora capsici across rows. Experimentally, it was found that maize roots attracted the zoospores of P. capsici and then inhibited their growth. When maize plants were grown in close proximity to each other, the roots produced and secreted larger quantities of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) and 6-methoxy-2-benzoxazolinone (MBOA). Furthermore, MBOA, benzothiazole (BZO), and 2-(methylthio)-benzothiazole (MBZO) were identified in root exudates of maize and showed antimicrobial activity against P. capsici.

Conclusions

Maize could form a “root wall” to restrict the spread of P. capsici across rows in maize and pepper intercropping systems. Antimicrobe compounds secreted by maize root were one of the factors that resulted in the inhibition of P. capsici. These results provide new insights into plant-plant-microbe mechanisms involved in intercropping systems.     

Effect of tissue wounding and time of soil inoculation on pepper root rot development

Five-week-old pepper plants with wounds created on stems and roots were transplanted to soils having inoculum of Phytophthora capsici incorporated for different lengths of time. Disease severity (39.99%) on root trimmed seedlings was not significantly different (P ≤ 0.05) from the severity (36.24%) obtained on stem lacerated seedlings. The wound treatments did not result in significantly different rates of lesion extension per day; stem lacerated seedling had the fastest, 1.99 mm/day lesion extension rate, followed by 1.90 and 1.89 mm/day extension rates obtained on root trimmed and unwounded treatments, respectively. However, time of soil inoculation had significant effect on severity; root trimmed and stem lacerated treatments had 46.3% and 39.8% severities, respectively. Tissue wounding × time of soil inoculation interaction did not have significant effect on disease severity; stem lacerated seedlings transplanted to 1-day and 3-day inoculated soils gave highest severity (49.9%), followed by seedlings inoculated at the time of transplantation. Root trimmed seedlings inoculated at the time of transplantation had highest severity (61.1%), while the lowest severity was obtained on seedlings transplanted to 5-day inoculated soil.     

Optimization of Culturing Conditions of a Strain of Phytophthora capsici Pathogenic to Habanero Pepper (Capsicum chinense)

Phytophthora capsici is an oomycete known as the causal agent of wilting disease in Capsicum spp., which causes rotting of roots, crowns, stems, leaves and fruits. To date, little is known about the production of phytotoxic metabolites by P. capsici or their role in the infection process. As part of a project directed towards the isolation and identification of phytotoxins produced by a strain of P. capsici pathogenic to habanero pepper (Capsicum chinense), we have evaluated the effect of factors such as aeration, light and culture medium on the production of mycelium and phytotoxic metabolites by P. capsici. The results showed that culturing P. capsici in potato dextrose broth (PDB) containing habanero pepper leaf infusion, in the dark and under still conditions, results in a high production of mycelium and a high phytotoxicity of the culture filtrate, in the shortest period of time.