Abstract: Fungal endophytes (Geniculosporium sp.) isolated from cacao leaves were screened for biological control of Phytophthora megakarya the cacao black pod disease pathogen, using Cacao Pod Husk Pieces(CPHP). CPHP were pre-treated with spore suspensions of Geniculosporium sp.[BC13(GJS 01-
196), BC108 (GJS 01-192), BC118 (GJS 01-197), BC177 (GJS 01-198)], and were infected with P. megakarya zoospore suspensions (105 zoospores/ml). Effects on P. megakarya were noticed at pod infection, mycelia growth inside infected tissues, and fungal sporulation, that are major stages of the black pod disease cycle on cacao pods. CPHP pre-treated with BC108 expressed the lowest early Infection Index (EII), but could not control disease progress into infected cacao pod husk tissues. On CPHP pre-treated with BC13, average growth rate of the necrosis was significantly reduced, but no control on P. megakarya sporulation was observed, while CPHP pre-treated with BC177 significantly reduced P. megakarya sporulation.
Abstract:Phytophthora parasitica causes serious widespread, and difficult–to–control root rots in warmer regions. This oomycete is one of the most important pathogen of citrus. This paper reports the biological control of
the pathogen by a strain of Serratia marcescens R-35, isolated from citrus rhizosphere. In greenhouse trials, the bacterium suppressed more than 50% of the disease and promoted the plant growth.
Abstract:Penicillium striatisporum Pst10 was isolated from the rhizosphere of chilli peppers. In dual culture agar plate assays, this isolate showed very high antagonistic effects on mycelium growth of Phytophthora spp., Cladosporium cucumerium, and Sclerotinia sclerotiorum. In in vitro assays, the toxicity of sterilized liquid culture filtrates (SLCF) of Pst10 grown in potato-dextrose broth (PDB) was tested against Phytophthora capsici mycelium growth and sporangia/spore formation or germination. The SLCF completely inhibited mycelium growth and even at a 100-fold dilution led to abnormal mycelium. A 20-fold dilution of SLCF inhibited formation and germination of sporangia and spores. Three antifungal substances were separated by thin-layer chromatography (TLC) from organic solvent extracts of liquid culture filtrate of Pst10. Composted pig manure slightly increased the colonization of the chilli rhizosphere by Pst10. In pot tests, the incidence of Phytophthora root rot of chilli was significantly reduced when artificially infested soil was treated with conidia and SLCF of Pst10.
Abstract: Factors influencing vegetative growth and spore germination of strain F603 of Epicoccom sp., an antagonistic fungus for Phytophthora infestans (Mont) de Bary, were studied. Among the different growth media tested, Rye agar
was the best medium for its vegetative growth. The range of temperature and pH value for mycelial growth was 5–35°C and 2–12, respectively, with the optimum 25°C and 6–9, respectively. The fungus grew better in Czapek medium with maltose and dextrose as carbon sources and peptone, KNO3, and NaNO3 as nitrogen sources. The range of temperature for spore germination of strain F603 was 5–35°C, the optimum was 20°C. The range of temperature for sporulation was 10–30°C, and the optimum was 15–18°C.
Abstract: Foliar infection during five days period of incubation at 18°C and humidity above 90% revealed no appearance of Phytophthora infestans lesions till 96 h of incubation where five leaflets in each set were abaxially sprayed with 106 cfu/ml suspension of biocontrol agent Bacillus subtilis B5 and 0.2% concentration of a mancozeb + metalaxyl formulation. The leaflets in control set exhibited average infection severity index of 1.8 and 3.8 after 72 and 96 h of incubation, respectively. After 120 h of incubation, the average infection severity index of 0.6 and 0.2 was recorded in bca B5 and fungicide formulation sprayed leaves compared to control where infection severity index of 4.0 to 5.0 was recorded in foliar tissues of all the five leaflets of a set resulting in an average infection severity index of 4.8.
Abstract: Among the antagonists, Trichoderma isolates were most effective in inhibiting the growth of P. capsici. Least inhibition was noticed with Pseudomonas isolate followed by Bacillus sp. Among the ten plant extracts tested, garlic cloves extract was highly inhibitory to P. capsici and was followed by leaf extracts of duranta, eupatorium, neem and lantana. The least effective was tikki weed followed by adusoge. Out of ten fungicides tested in vitro Akomin, Melody duo, Ridomil and Secure at all three concentrations (0.1%, 0.2 % and 0.3 %), Aliette and Bordeaux mixture 0.3 per cent concentration were also highly inhibitory to the pathogen P. capsici. The least effective was Verita followed by Copper oxychloride.
Abstract: Witches’ broom and pod rot are the two most devastating diseases of cocoa in South America and Africa, respectively. Their control by means of phytosanitation and chemical fungicides is labor-intensive, costly and, in many cases, environmentally undesirable. Therefore efforts are made in order to identify alternative, environmentally safe and cost-efficient methods for the control of these pathogens. Promising candidates are components of the neem tree (Azadirachta indica), that have been used for centuries in Asia as insecticides, fungicides, anticonceptionals in popular medicine. Here we report about tests on the effect of various concentrations of extracts from neem leaves on growth of mycelia of Crinipellis and Phytophthora
and on germination of spores of Crinipellis. We show a 35% growth reduction of mycelia of Phytophthora on neem leaf extract media, whereas growth of mycelia of Crinipellis was not affected, even at the highest concentration of neem leaf extracts used (35%). However, the most dramatic effect of neem leaf extracts is observed on Crinipellis spore germination, here the extracts (20–35%) reduced germination almost completely. Based on these results, we believe that the neem tree might be a source for the production, on small and medium scale, of an effective and cheap formulation for the control of Crinipellis and Phytophthora.
Abstract:Stenotrophomonas maltophilia was isolated from the rhizosphere of eggplant in the Nile Delta of Egypt, and its antagonistic potential against Ralstonia solanacearum race 3 biovar 2, the causal agent of potato brown rot, was in vitro evaluated on KB agar medium and in vivo on potato plants. In vitro, four isolates of S. maltophilia (PD3531, PD3532, PD3533, and PD3534) appeared antagonistic. The isolate (PD3533) was screened as the most promising antagonist for the in vivo tests. In the greenhouse, the antagonist was applied directly to soil or by bacterization of potato eyepieces. Stenotrophomonas maltophilia significantly suppressed potato brown rot in Egyptian clay soil but not in Dutch clay soil. Survival of a rifampicin and chloramphenicol-resistant S. maltophilia strain PD4560 was investigated in two pairs of clay soils, conventionally and organically managed, from Egypt and the Netherlands. The survival of S. maltophilia was significantly less in Dutch than in Egyptian soils, while the converse occurred for R. solanacearum. These results are in agreement with those obtained in the in vivo biocontrol tests. In conclusion, S. maltophilia may be useful for control of brown rot in the area where it was originally isolated, the Nile Delta in Egypt.
Abstract: Fifteen native Western Australian legumes were assessed for their potential to biologically control Phytophthora cinnamomi. Biological control was assessed in a controlled situation, conducive to P. cinnamomi, and was based on susceptibility to the pathogen, ability to reduce soil inoculum, amount of asymptomatic root infection and ability for P. cinnamomi to effectively sporulate from asymptomatically infected roots. Acacia extensa, Acacia stenoptera and Acacia alata along with Acacia pulchella, were identified as species with the highest potential for biological control of P. cinnamomi. Acacia urophylla and Viminaria juncea exhibited the least potential for biological control; these are more likely to harbour the pathogen and provide a source of inoculum when conditions become conducive for P. cinnamomi growth and development. These findings have important implications for managing the rehabilitation of bauxite-mined P. cinnamomi-infested areas and severely disease-affected forest. By manipulating rehabilitation seed mix ratios, the density of legume species that suppress P. cinnamomi inoculum in the soil can be increased and the density of those that harbour the pathogen can be reduced. This could potentially contain the activity of P. cinnamomi soil inoculum in infested areas to protect susceptible species and enhance species diversity. Further research is required to ascertain the action of suppression before implementing control measures.
Abstract: A collection of 53 antibiotic-producing Streptomyces isolated from soils from Minnesota, Nebraska, and Washington were evaluated for their ability to inhibit plant pathogenic Phytophthora medicaginis and Phytophthora sojae in vitro. Eight isolates having the greatest pathogen-inhibitory capabilities were subsequently tested for their ability to control Phytophthora root rots on alfalfa and soybean in sterilized vermiculite and naturally infested field soil. The Streptomyces isolates tested significantly reduced root rot severity in alfalfa and soybean caused by P. medicaginis and P. sojae, respectively (P < 0.05). On alfalfa, isolates varied in their effect on plant disease severity, percentage dead plants, and plant biomass in the presence of the pathogen. The same eight isolates of Streptomyces were also tested for inhibitory activities against each other and against three strains of Bradyrhizobium japonicum and two strains of Sinorhizobium meliloti isolated from soybean and alfalfa, respectively. Streptomyces isolates clustered into two major compatibility groups: isolates within the same group were noninhibitory toward one another in vitro. The compatibility groups corresponded with groupings obtained based upon inhibition of B. japonicum and S. meliloti strains.
Abstract