Abstract: The Black-Pod Rot of cacao (Theobroma cacao) caused by Phytophthora species is one of the most important diseases affecting this crop worldwide, with average annual losses above 30%. The aim of this work was to assess the potential for the endophytic Trichoderma martiale strain ALF 247 to control Phytophthora palmivora. When ALF 247 was applied at concentrations ranging from 1*104 to 5*107 conidia per milliliter, the disease severity decreased proportionally. Addition of vegetable oil and/or sucrose in the formulations did not affect the biocontrol results. Fungicides such as copper hydroxide and fosetyl-Al had no effect on conidial germination of this T. martiale strain, with the germination percentage maintained above 90%. Once sprayed, the population of T. martiale tended to decrease progressively on the surface of cacao pods (30–40 days post-application), with a concomitant increase in the severity of pod disease.Production of 1.02*108 conidia g-1 was obtained after culturing ALF 247 on solid substrate (rice grains)supplemented with calcium carbonate. The results indicate a clear-cut potential of the T. martiale ALF 247 to be used for control of Black-Pod Rot of cacao, although further studies are required to render this isolate technically and economically efficient as a biocontrol agent on agronomic scale.
Abstract:Phytophthora root rot, crown rot, leaf and stem blight, and fruit rot of cucumber can cause serious losses, and are difficult to control. Although composts can be used successfully for control of Phytophthora root rots, little is known about their effects on Phytophthora diseases of above-
ground plant parts. This research shows that the severity of Phytophthora root and crown rot of cucumber caused by Phytophthora capsici was suppressed significantly in cucumber transplants produced in a composted cow manure–amended mix compared with those in a dark sphagnum peat mix. In split root bioassays, Trichoderma hamatum382 (T382) inoculated into the compostamended potting mix significantly reduced the severity of Phytophthora root and crown rot on paired roots in the peat mix. This effect did not differ significantly from that provided by a drench with benzothiadiazole (BTH) or mefenoxam (Subdue MAXX). Based on area under disease progress curves, T382 also significantly reduced the severity of Phytophthora leaf blight in transplants produced in the compost mix compared with controls not inoculated with T382. Efficacy of T382 did not differ significantly from that provided by a drench with BTH. T382 remained spatially separated from the pathogen in plants in both the split root and leaf blight bioassays, suggesting that these effects were systemic in nature.
Abstract: Myxobacteria are soil dwelling gram-negative gliding bacteria that form fruiting bodies containing myxospores. Although myxobacteria produce a wide range of antibiotics and lytic enzymes that assist in their ability to prey on other microorganisms, their role in agriculture has received little attention. Myxococcus spp. were isolated from soils in organic and conventionally managed strawberry production and transplant fields in the absence of soil fumigation. Fumigation with methyl bromide and chloropicrin virtually eliminated these organisms from soil. However, soil fumigation had no effect on the frequency of isolation of Myxococcus spp. from strawberry roots. Six Myxococcus spp. were tested in vitro against eight soilborne plant
pathogenic fungi (Cylindrocarpon spp., Fusarium oxysporum f. sp. apii, Phytophthora capsici, Pythium ultimum, Rhizoctonia spp., Sclerotinia minor, Verticillium albo-atrum, and V. dahliae) and against two fungal biological control agents (Gliocladium virens and Trichoderma viride).
Phytophthora capsici, Pythium ultimum, Rhizoctonia spp., S. minor, and T. viride were completely inhibited by all of the Myxococcus spp. tested. F. oxysporum f. sp. apii was the least sensitive to the myxobacteria, and no inhibition occurred with some Myxococcus spp. Inhibition of the other fungi tested was variable. Myxococcus coralloides inhibited nearly all the fungi tested. The ability of bacterial biological control agents to produce antibiotics and other secondary metabolites determined whether or not they were lysed by myxobacteria. Secondary metabolite production regulated by gacS protected Pseudomonas fluorescens strain CHA0 from lysis by myxobacteria. More specifically, phenazine antibiotics produced by Pseudomonas aureofaciens strain 30-84 protected it from lysis.
Abstract: Two bacterial isolates and one strain of Trichoderma harzianum were tested alone and in combination with chitin for efficacy in control of root rot disease caused by Phytophthora capsici and Rhizoctonia solani in pepper plants under greenhouse conditions. These bacteria (Bacillus subtilisHS93 and B. licheniformisLS674) were isolated from repeatedly washed roots of pepper plants. In in vitro assays, HS93, LS674 and T. harzianum were antagonistic against P. capsici and R. solani and produced high levels of chitinase. Seed treatment and root drenching with bacterial suspensions of HS93 with 0.5% chitin was more effective against Phytophthora and Rhizoctonia root rot than addition of the organisms without chitin. LS674 and T. harzianum reduced Rhizoctonia but not Phytophthora root rot. In two greenhouse tests, seed treatment and root drenching with HS93 amended with chitin enhanced its biocontrol activity against P. capsici but not on R. solani. The effects of LS674 and T. harzianum against R. solani were significantly enhanced when they were used as suspensions with 0.5% chitin for root drenching, but this had no effect on P. capsici. In both greenhouse experiments, the use of 0.5% chitin alone for root drenching reduced Rhizoctonia root rot. Reduction of root rot disease was accompanied by increased yield. These results show that the antagonistic activity of HS93, LS674 and T. harzianum may be stimulated by chitin resulting in significant improvements in their effectiveness against pathogens.
Abstract: Biocontrol efficiency of various Bacillus preparations (BB11 and FH17 strains, and a mixture of both strains (BF) at a 1:1 ratio by
concentration) and diVerent application methods against Phytophthora blight of bell pepper were studied. The application methods included (A) mixing (mixing BF with rapeseed residue and then immediately applying in the Weld), (B) composting (mixing BF with rapeseed residue and made compost before application), (C) spraying (spraying diluted BF into Weld or rhizosphere of plants), and (D) watering (watering diluted BF into Weld or rhizosphere of plants). In greenhouse experiments, the addition of BF increased biocontrol eYciency (60.3%), and yield increase (200%) was better than with BB11 (55.8 and 80.6%, respectively) or FH17 (37.1 and 50.0%, respectively). In Weld trials at Huai’an in 2001, the best dosages of BF mixture (1010 cfu/ml) with the four above-mentioned application methods were 15, 7.5, 15, and 22.5L/ha, respectively. When preparations were applied at the best dosage in the same Weld, the BF mixture provided superior biocontrol eYciency and greater yield increase with treatment B than those with treatment A or C. Combining the Weld trial results from 2002 to 2003 at Huai’an and Wu’han, the total average control eYciencies and yield increases for treatments A, B, and C reached 81.0,88.0, and 79.1% and 33.1, 44.3, and 29.1%, respectively, with their best dosages. However, method B, composting, provided better disease control and greater yield increases than all other methods, and did so at a lower application rate.
Abstract: The effects of selected arbuscular mycorrhizal (AM) fungi, Glomus mosseae, Glomus etunicatum, Glomus fasciculatum and Gigaspora margarita, on growth of pepper seedlings and Phytophthora blight caused by Phytophthora capsici and the role of the phytoalexin, capsidiol were investigated. Root colonization by AM fungi reached between 61.3% and 68.1% in roots of pepper 4 weeks after transplanting. All tested AM fungi increased the shoot height between 23.4% and 31.7% and fresh and dry weights of shoots and roots of plants were enhanced by G. etunicatum, G. fasciculatum and Gigaspora margarita compared to uninoculated plants in pot experiments. G. fasciculatum increased yield significantly by 22%under greenhouse conditions. G. mosseae reduced the disease severity of P. capsici by 91.7%, 43.0% and 57.2% under pot, greenhouse and field conditions, respectively. Compared to the control, the capsidiol level was
increased by preinoculation with G. mosseae and in the necrotic stems of P. capsici-inoculated pepper plants. In conclusion, AM fungi,
especially G. mosseae enhanced the development of plants and reduced Phytophthora blight of pepper.
Abstract: Antifungal activity of oligochitosan against nine phytopathogens was investigated in vitro. Oligochitosan was more eVective than chitosan in inhibiting mycelial growth of Phytophthora capsici and its inhibition on diVerent stages in life cycle of P. capsici was observed. Rupture of released zoospores induced by oligochitosan was reduced by addition of 100mM glucose. The eVects of oligochitosan on mycelial growth and zoospore release, but not zoospore rupture, were reduced largely when pH value was above 7. The ultrastructural study showed that oligochitosan caused distortion and disruption of most vacuoles, thickening of plasmalemma, and appearance of unique tubular materials. Plasmalemmasomes in hyphal tip cells were not found in the presence of oligochitosan. These results suggest polycationic nature of oligochitosan contributes only partly to its antifungal activity and multiple modes of action of oligochitosan exist including the disruption of endomembrane system.
Abstract: Phytophthora blight induced by Phytophthora capsici is a major constraint in vegetable production worldwide. Limited information is available regarding potential systemic acquired resistance (SAR)inducers that may provide protection of squash (Cucurbita pepo) plants against the disease and the direct effect of the products on the pathogen. In this study, the effect of DL-3-aminobutyric acid (BABA), 2,6- dichloroisonicotinic acid (INA), Saver (a.i. salicylic acid), Syrup (nutrient supplement), and acibenzolar-S-methyl (ASM) on mycelial growth, zoospore germination and sporangium production of P. capsici was evaluated. The products were tested in in vitro studies at concentrations ranging from 25 to 2000 mgml1. Mycelial growth and zoospore germination were generally not significantly affected by BABA and ASM and sporangium production was not significantly affected by BABA. INA and Saver reduced mycelial growth and sporangium production significantly at 100 mgml1 or higher concentrations and zoospore germination at 500 and 1000 mgml1. In greenhouse studies, all the products applied as a soil drench or foliar spray at 25 or 50 mgml 1 significantly reduced disease severity on squash, compared with the pathogen-only control, and zoospores at a concentration of 103 spores ml1 were used to inoculate the leaves. INA, BABA, and ASM also reduced disease significantly when zoospores at 103 spores ml1 were used to inoculate the root. The results indicated that most of the SAR inducers did not inhibit the growth of the pathogen at concentrations generally recommended for use but had the potential to suppress the disease on squash significantly.
Abstract: This study was conducted to select antagonistic rhizobacteria against Phytophthora capsici using a sequential screening procedure and to evaluate control efficacy of drench or root-dip treatments with the selected strains against Phytophthora blight of pepper in the field. Out of 439 bacterial strains, 16 potentially antagonistic strains were screened through radicle and seedling assays and in planta trials, and five candidate strains, CCR04, CCR80, GSE09, ISE13, and ISE14, were selected for field tests. In 2005 and 2006 tests, the control efficacy of the five strains was examined against Phytophthora blight of pepper plants drenched with the bacterial suspension in artificial pathogen inoculation. Three strains, CCR04, CCR80, and ISE14, consistently reduced the disease in both tests. As another form of appli-
cation, the control efficacy of root-dip treatment was examined on pepper plants just prior to transplanting in the field with natural inoculation in 2006 and 2007. In these tests, four strains, CCR04, CCR80, GSE09, and ISE14, showed consistently good control efficacy against P. capsici, and strains CCR80 and ISE14 increased pepper fruit yield. The strain-treated roots had less infection rates by P. capsici compared with control roots regardless of drench or root-dip treatments. In addition, the strains did not affect the populations of bacteria and fungi in the rhizosphere soil. Therefore, the antagonistic strains selected from the screening procedure provided significant
protection against P. capsici through pepper root colonization. These strains could be applied by either drench or root-dip treatment as alternatives to agricultural chemicals to control Phytophthora blight of pepper.
Abstract: Three fungi, isolated from soil from which Phytophthora was not obtained, were evaluated for antagonism of Phytophlhora spp, shown to cause root rot of chestnut in South Australia, Trichoderma iiatnatum and T. pseudokoningii appeared to inhibit P. cinnamomi by mycoparasitism. with evidence of parallel growth and coiling, and both Trichoderma spp, and Gliocladium lirciis grew over P cinnamomi in vitro, preventing further growth of this pathogen. Antibiotics produced by young T. hamatum cultures and G. lirens in culture filtrate experiments inhibited growth of P. cinnamomi and P. citricola. with filtrate from 4-day-old cultures of G. rirens showing the greatest potential for biocontrol, Al! three antagonists prevented F. cinnamomi and P. citricola from causing infection symptoms on micropropagated shoots of chestnut cvs Goldsworthy and Buffalo Queen in an in vitro excised shoot bioassay for biocontrol,
Abstract