Meloidogyne incognita Survival in Soil Infested with Paecilomyces lilacinus and Verticillium chlamydosporium

Meloidogyne incognita-infected tomato seedlings were transplanted into sterilized soil or unsterilized soil collected from 20 California tomato fields to measure suppression caused by Paecilomyces lilacinus, Verticillium chlamydosporium, and other naturally occurring antagonists. Unsterilized soils Q, A, and H contained 35, 39, and 55% fewer M. incognita second-stage juveniles (J2) than did sterilized soil 1 month after infected tomato seedlings were transplanted to these soils and placed in a greenhouse. Three months after infected seedlings were transplanted to unsterilized or sterilized soil, unsterilized soils K, L, and Q had 97, 62, and 86% fewer J2 than the corresponding sterilized soils. Unsterilized soils of M. incognita-infected seedlings that were maintained 1 month in a greenhouse followed by 1 or 2 months of post-harvest incubation contained J2 numbers equal to, or greater than, numbers in the corresponding sterilized soil. The most suppressive of the unsterilized soils, K and Q, were not infested with V. chlamydosporium. Paecilomyces lilacinus and V. chlamydosporium increased in colony forming units in unsterilized soil of all bioassays, but they were not associated with lower numbers of J2.     

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.     

Association of Verticillium chlamydosporium and Paecilomyces lilacinus with Root-knot Nematode Infested Soil

Population densities of Meloidogyne incognita and the nematophagous fungi, Paecilomyces lilacinus and Verticillium chlamydosporium, were determined in 20 northern California tomato fields over two growing seasons. Paecilomyces lilacinus was isolated from three fields, V. chlamydosporium was isolated from one field, and both fungi were isolated from 12 fields. Verticillium chlamydosporium numbers were positively correlated with numbers of M. incognita and P. lilacinus. Paecilomyces lilacinus numbers were positively correlated with V. chlamydosporium numbers, but they did not correlate with M. incognita numbers. The correlation coefficients were low (R < 0.5) but significant (P < 0.05). All P. lilacinus and V. chlamydosporium field isolates parasitized M. incognita eggs in vitro. In a greenhouse study, numbers of V. chlamydosporium and P. lilacinus increased more in soils with M. incognita-infected tomato plants than in soil with uninfected tomato plants. After 10 weeks, the Pf/ Pi of second-stage juveniles in soils infested with P. lilacinus, V. chlamydosporium, and M. incognita was 47.1 to 295.6. The results suggest V. chlamydosporium and P. lilacinus are not effectively suppressing populations of M. incognita in California tomato fields.     

Hirsutella rhossiliensisand Verticillium chlamydosporium as Biocontrol Agents of the Root-knot Nematode Meloidogyne hapla on Lettuce

Hirsutella rhossiliensis and Verticillium chlamydosporium infected second-stage juveniles (J2) and eggs of Meloidogyne hapla, respectively, in petri dishes and in organic soil in pots planted to lettuce in the greenhouse. In vitro, H. rhossiliensis produced 78 to 124 spores/infected J2 of M. hapla. The number of J2 in roots of lettuce seedlings decreased exponentially with increasing numbers of vegetative colonies of H. rhossiliensis in the soil. At an infestation of 8 M. hapla eggs/cm³ soil, 1.9 colonies of H. rhossiliensis/cm³ soil were needed for a 50% decrease in J2 penetration of lettuce roots. Egg-mass colonization with V. chlamydosporium varied from 16% to 43% when soil was infested with 8 M. hapla eggs and treated with 5,000 or 10,000 chlamydospores of V. chlamydosporium/cm³ soil. This treatment resulted in fewer J2 entering roots of bioassay lettuce seedlings planted in the infested soils after harvesting the first lettuce plants 7 weeks after infestation with M. hapla. Hirsutella rhossiliensis (0 to 4.3 colonies/cm3 soil), V. chlamydosporium (500 to 10,000 chlamydospores/cm3 soil), or their combination, added to organic soils with 8 M. hapla eggs/cm³ soil, generally did not affect lettuce weight, root galling, or egg production of M. hapla. However, when lettuce was replanted in a mix of infested and uninfested soil (1:3 and 1:7, v:v), egg production was lower in soils with V. chlamydosporium than in soils without the fungus. Both fungi have potential to reduce the M. hapla population, but at densities below 8 eggs/cm³ soil.     

Greenhouse and field evaluations of potassium phosphonate: the control of Phytophthora foot rot of black pepper in Vietnam

Phytophthora foot rot of black pepper caused by Phytophthora capsici is a major disease of black pepper throughout production areas in Vietnam. The disease causes collar, foot and tap root rots and eventual death of the infected vine. Potassium phosphonate was evaluated for the control of this disease in greenhouse and field trials. In greenhouse trials three-month-old vines treated with phosphonate by soil drenching (10–20 g a.i./l) and then inoculated with P. capsici mycelium (2% v/v soil) had significantly less foot rot compared to vines grown in non-treated soil. In field trials mature vines were treated with phosphonate at 50–100 g a.i/pole soil drenching or 10 g a.i./l by root infusion. After 10 days root, stem and leaf specimens were removed for bioassay by inoculation with 5 ml of P. capsici zoospores suspension (10⁶–10⁸ spores/ml). Soil drenching with phosphonate inhibited the colonisation of pathogen on excised leaf, stem and root tissues, significantly more than phosphonate root infusion. Our study provides further evidence supporting the efficacy of potassium phosphonate in the management of black pepper foot rot caused by P. capsici. The excised leaf and stem bioassay used in this study is a rapid and useful technique for testing the efficacy of systemic fungicides in controlling this disease.     

Influence of Fusarium solani on citrus root rot caused by Phytophthora parasitica and Phytophthora citrophthora

Interactions between Fusarium solani and Phytophthora parasitica or F. solani and P. citrophthora influenced the development of root rot of citrus but depended on the temporal order of inoculation with F. solani or the two Phytophthora spp. Inoculation of citrus with either Fusarium solani and Phytophthora parasitica or Phytophthora citrophthora increased root rot compared to inoculation with P. parasitica or P. citrophthora alone when plants were inoculated with Phytophthora by dipping their roots in zoospore suspensions and subsequently transplanted into soil infested with F. solani. However, root rot was not increased by simultaneous co-inoculation of P. parasitica and F. solani or when plants were inoculated with F. solani first. Root rot was not increased when heat-stressed or non-stressed plants were inoculated with P. parasitica 30 days after transplanting into soil infested with F. solani. In most but not all experiments, F. solani alone reduced growth of tops or roots a small but significant amount.Co-inoculation of citrus by root-dipping into zoospore suspensions of P. parasitica and transplanting into soil infested with F. solani reduced feeder root length by 62% and root weight by 61% but did not significantly reduce the percentage of living roots when compared to inoculation with P. parasitica alone. When citrus roots were immersed in zoospore suspensions of P. citrophthora and transplanted into soil infested with F. solani, feeder root length was reduced by 68%, but feeder root weight and the percentage of living roots were not significantly reduced when compared to plants inoculated with P. citrophthora alone.Propagule densities of both P. parasitica and P. citrophthora in the rhizosphere of plants inoculated by root-immersion and then transplanting into soil infested with F. solani were not significantly different than propagule densities from plants transplanted into non-infested soil. Propagule densities of P. parasitica were suppressed an average of 41% when citrus was inoculated with P. parasitica 30 days after transplanting into soil infested with F. solani and by 41% when citrus was co-inoculated by transplanting into soil infested with both F. solani and P. parasitica.     

A novel Arabidopsis–oomycete pathosystem: differential interactions with Phytophthora capsici reveal a role for camalexin,indole glucosinolates and salicylic acid in defence

Phytophthora capsici causes devastating diseases on a broad range of plant species. To better understand the interaction with its host plants, knowledge obtained from a model pathosystem can be instrumental. Here, we describe the interaction between P. capsici and Arabidopsis and the exploitation of this novel pathosystem to assign metabolic pathways involved in defence against P. capsici. Inoculation assays on Arabidopsis accessions with different P. capsici isolates revealed interaction specificity among accession‐isolate combinations. In a compatible interaction, appressorium‐mediated penetration was followed by the formation of invasive hyphae, haustoria and sporangia in leaves and roots. In contrast, in an incompatible interaction, P. capsici infection elicited callose deposition, accumulation of active oxygen species and cell death, resulting in early pathogen encasement in leaves. Moreover, Arabidopsis mutants with defects in salicylic acid signalling, camalexin or indole glucosinolates biosynthesis pathways displayed severely compromised resistance to P. capsici. It is anticipated that this model pathosystem will facilitate the genetic dissection of complex traits responsible for resistance against P. capsici.     

An investigation of biological attributes that may contribute to the importance of Phytophthora capsici as a vegetable pathogen in Florida

During the 1999–2000 and 2000–2001 seasons, 19 commercial squash fields in the vicinity of Homestead, Florida (USA) were examined for diseases caused by Phytophthora capsici. In each of the six fields in which two or more isolates of P. capsici were recovered, both the Al and A2 mating types were present, and both mating types were recovered from the same plant five times. Insensitivity to mefenoxam was common among isolates, with EC50s ranging from 5 μg mefenoxam ml^?1 to more than 60 μg ml^?1. Of 15 weed species that were examined as possible alternative hosts of the pathogen, only common purslane, Portulaca oleracea, was infected by P. capsici. Few or no oospores of the pathogen formed in a glasshouse (c. 28°C) when artificially inoculated pepper plants were covered with plastic bags or kept under continuous mist. In studies in the laboratory (c. 22°C) with detached pepper leaves, no oospores were formed on wire screens over water reservoirs. Consistent production of oospores occurred only when leaves were in constant contact with water. Maximum production occurred at 18°C, and production also occurred at 14°C, 20°C, 24°C and 26°C, but not at 6°C, 12°C, 30°C and 32°C.     

Survival and recovery of Phytophthora capsici and oomycetes in tailwater and soil from vegetable fields in Florida

A current trend in Florida agriculture to conserve water is to irrigate with surface runoff water (tailwater) recovered in retention ponds and canals. Water filtration and lemon leaf baiting recovered Phytophthora capsici and other plant pathogenic Oomycetes in runoff water from ponds and canals. A total of 196 isolates of Phytophthora spp. and 471 isolates of Pythium spp. were recovered. Phytophthora spp. included P. capsici, P. cinnamomi, P. lateralis, P. nicotianae, P. citricola, P. cryptogea and P. erythroseptica. Species of Pythium were P. aphanidermatum, P. catenulatum, P. helicoides, P. irregulare, P. myriotylum, and Pythium‘group F’. Isolates of P. aphanidermatum, P. irregulare, P. myriotylum, and Pythium‘group F’ were pathogenic on pepper and tomato. Recovery of P. capsici propagules was related to soil moisture‐holding capacity and time interval but not temperature. Recovery of P. capsici propagules at 100% soil moisture‐holding capacity and 30° C was 57 days. In tailwater, recovery of propagules of P. capsici was 63 days at 24°C to 25°C. The potential exists to reintroduce and disseminate species of Phytophthora and Pythium when using tailwater for irrigation or other practices.     

Use of Oospore Formulations of Pythium oligandrum for Biological Control of Pythium Damping-off in Cress

Oospore preparations of Pythium oligandrum produced by liquid and solid-substrate fermentations were evaluated for biocontrol activity against Pythium damping-off in cress in artificially infested sand and naturally infested soil. Oospore biomass preparations from liquid fermentation of six isolates of P. oligandrum were equally effective in reducing damping-off in sand when tested as seed-coatings, whereas this type of preparation of a single isolate formulated as a kaolin dust, on Perlite and as alginate pellets incorporated into sand gave little or no control. None of the formulations containing oospores produced by solid-substrate fermentation incorporated into sand had any effect. In soil, a formulation containing oospores produced in a barley-Perlite solid-substrate fermentation and all oospore-biomass formulations which were prepared increased seedling survival, but none of these were as effective as a propamocarb HCl drench.     

Diverse mechanisms adopted by fluorescent <Emphasis Type="Italic">Pseudomonas</Emphasis> PGC2 during the inhibition of <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> and <Emphasis Type="Italic">Phytophthora capsici</Emphasis>

Rhizoctonia solani and Phytophthora capsici are two of the most destructive phytopathogens occurring worldwide and are only partly being managed by traditional control strategies. Fluorescent Pseudomonas isolates PGC1 and PGC2 were checked for the antifungal potential against R. solani and P. capsici. Both the isolates were screened for the ability to produce a range of antifungal compounds. The results of this study indicated the role of chitinase and β-1,3-glucanase in the inhibition of R. solani, however, antifungal metabolites of a non-enzymatic nature were responsible for inhibition of P. capsici. The study confirmed that multiple and diverse mechanisms are adopted by the same antagonist to suppress different phytopathogens, as evidenced in case of R. solani and P. capsici.     

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.     

Effect of Bacterial Antagonist on Phytopthora cactorum and Apple Crown Rot

Bacterial antagonist B8 produced an inhibition zone with each of four Phytophthora cactorum isolates on corn meal agar (CMA) plates. Infections with three P. cactorum isolates were significantly reduced when the soil was simultaneously inoculated with B8. Growth of P. cactorum was completely inhibited on CMA amended with 40–100 per cent 10 fold concentrated B8 extract. Percent oospore germination of P. cactorum was significantly reduced when B8 was present in suspension for 9, 12 and 15 days from inoculation. Survival of oospores was significantly reduced at 60 and 90 mm depths in soil. Bacterial antagonist B8 significantly reduced the population of viable P. cactorum oospores in the top 30 mm of soil where oospores generally survive.     

New Insights in the Life Cycle and Epidemics of Phytophthora porri on Leek

White tip, caused by Phytophthora porri, is a devastating disease in the autumn and winter production of leek (Allium porrum) in Europe. This study investigated the disease cycle of P. porri in laboratory and field conditions. Oospores readily germinated in the presence of non‐sterile soil extract at any temperature between 4 and 22°C, with the formation of sporangia which released zoospores. The zoospores survived at least 7 weeks in water at a temperature range of 0 till 24°C. Microscopic examinations revealed that zoospores encysted and germinated on the leek leaf surface and hyphae entered the leaf directly through stomata or by penetrating via appressoria. Oospores were formed in the leaves within 6 days, while sporangia were not produced. By monitoring disease progress in fields with a different cropping history of leek, it could be deduced that P. porri survives in soil for up to 4 years. Disease progress during three consecutive years was correlated with average daily rainfall in the infection period. Disease incidence on leek was reduced when rain splash was excluded by growing the plants in an open hoop greenhouse. Based on these findings, we propose a disease cycle for P. porri in which oospores germinate in puddles, and zoospores reach the leaves by rain splash and survive in water in the leaf axils, from where they infect the plant by direct penetration or via stomata. When conditions become unfavourable, oospores are produced in the leaves which again reach the soil when leaves decay. Secondary spread of the disease by sporangia does not seem to be important.     

Antagonistic Activity of Neocosmospora vasinfecta var. africana (von Arx) Cannon & Hawksworth against Soil-borne Fungi

An isolate of Neocosmospora vasinfecta var. africana (F-2) was assayed for its antagonistic activity against 15 soil-borne fungi; 14 of them were important plant pathogens. The fungus exhibited a strong antibiotic effect against most of the fungi under test. While Pythium debaryanum, Macrophomina phaseolina, Phytophthora capsici, Sclerotinia sclerotiorum, Cochliobolus sativus and Alternaria alternata showed a very high degree of sensitivity as evidenced by the respectivezones of inhibition caused by the antagonist, Phoma betae, Rhizoctonia solani and Verticillium dahliae proved to be the most resistant. A mutual antibiosis existed between N. vasinfecta var. africana and five of the test fungi. The culture filtrate of the antagonist, diluted ten times with PDA, suppressed the mycelial growth of P. debaryanum and P. capsici completely. Whereas in this test R. solani proved to be the least sensitive, the remaining test fungi showed some differences in their susceptibility, but in any case their growth was inhibited significantly as compared to the controls.     

Effect of oligochitosan-coated silver nanoparticles (OCAgNPs) on the growth and reproduction of three species Phytophthora in vitro

Phytophthora diseases cause billions of dollars annually in damage to crops. Nanotechnology provides various metallic nanoparticles exhibiting a strong activity against microbial pathogens. Silver nanoparticles-based products are outstanding samples, which has been produced in large scale and performed well with a high activity against several fungal pathogens. Our previous study indicated oligochitosan-coated silver nanoparticles (OCAgNPs) which were prepared from 3,4 dihydroxyphenyl acetic acid – conjugated oligochitosan and silver nitrate salt performed an enhancement in antibacterial ability at a very low concentration. Objective of this study was to determine the effect of the OCAgNPs on growth and reproduction of Phytophthora capsici, P. nicotianae and P. colocasiae in vitro. The study shown that strong inhibition of mycelial growth, sporangium production, zoospore release and zoospore germination of P. capsici, P. nicotianae and P. colocasiae occurred when exposed to at 9 ppm of OCAgNP. The results demonstrated a great potential of OCAgNPs for controlling growth of Phytophthora.     

Genome sequencing and mapping reveal loss of heterozygosity as a mechanism for rapid adaptation in the vegetable pathogen Phytophthora capsici

The oomycete vegetable pathogen Phytophthora capsici has shown remarkable adaptation to fungicides and new hosts. Like other members of this destructive genus, P. capsici has an explosive epidemiology, rapidly producing massive numbers of asexual spores on infected hosts. In addition, P. capsici can remain dormant for years as sexually recombined oospores, making it difficult to produce crops at infested sites, and allowing outcrossing populations to maintain significant genetic variation. Genome sequencing, development of a high-density genetic map, and integrative genomic or genetic characterization of P. capsici field isolates and intercross progeny revealed significant mitotic loss of heterozygosity (LOH) in diverse isolates. LOH was detected in clonally propagated field isolates and sexual progeny, cumulatively affecting >30% of the genome. LOH altered genotypes for more than 11,000 single-nucleotide variant sites and showed a strong association with changes in mating type and pathogenicity. Overall, it appears that LOH may provide a rapid mechanism for fixing alleles and may be an important component of adaptability for P. capsici.     

Isolation and Identification of Bacillus amyloliquefaciens IBFCBF‐1 with Potential for Biological Control of Phytophthora Blight and Growth Promotion of Pepper

In this study, 76 bacterial strains were isolated from the rhizosphere soil of pepper. Of these, 23 bacterial isolates capable of inhibiting Phytophthora capsici growth were selected. Among the antagonistic bacteria, one strain, IBFCBF‐1 showed the strongest antagonistic activity, and was identified as Bacillus amyloliquefaciens based on the results of 16S rRNA gene sequence analysis, physiological and biochemical testing, and morphological characteristics. When tested with a dual‐culture method and with laboratory greenhouse studies, the strain IBFCBF‐1 was found to be a potential biocontrol agent for controlling the plant pathogen, P. capsici. Moreover, it showed high efficiency and broad‐spectrum antifungal properties in vitro. Under greenhouse conditions, IBFCBF‐1 could significantly promote the growth of pepper seedlings, and was able to solubilize phosphate, and produce indole acetic acid (IAA) and ammonia. This study clearly demonstrated that IBFCBF‐1 is a potential candidate exhibiting phytophthora blight‐suppressive and plant growth‐promoting effects on pepper.     

Inoculation of Paenibacillus illinoisensis alleviates root mortality, activates of lignification-related enzymes, and induction of the isozymes in pepper plants infected by Phytophthora capsici

To investigate the variations of the enzymes responsible for lignification, after inoculation with Phytophthora capsici and/or Paenibacillus illinoisensis KJA-424, in relation to biocontrol of Phytophthora blight in pepper, roots of two-month-old plants were inoculated with P. capsici inoculation (P), and co-inoculation of P. capsici and P. illinoisensis cell cultures (P + A). Root mortality of pepper plants induced by inoculation of P. capsici was completely recovered by co-inoculation with antagonistic KJA-424. At day 7, peroxidase (POD) activity increased by 36.7% in P-treated roots but by 7.1% only in P + A-treated, compared with control. Polyphenol oxidase (PPO) activity increased for 3 days and then drastically decreased in P-treated roots but maintained a constant level in control and P + A-treated. At day 7, PPO activity in P-treated leaves decreased but recovered to the level of control in the P + A-treated. Three major POD isozymes (45, 53, and 114 kDa) were shown in P-treated roots, while two major (53 and 114 kDa) in control and P + A-treated, suggesting that the 45 kDa of POD was actively induced in P-treated roots but not induced in P + A-treated roots. A PPO isozyme of 80 kDa was induced in P-treated roots but not induced by co-treated with KJA-424. In leaves, the POD isozyme of 45 kDa appears to be systemically induced in P-treated only. The PPO isozyme of 80 kDa in leaves was not induced by pathogen challenge but recovered by co-inoculated with P. illinoisensis. All these results suggest that the inoculation of an antagonist, P. illinoisensis alleviates root mortality, activates of lignification-related enzymes and induction of the isozymes in pepper plants infected by P. capsici.