Abstract: The effects of several inorganic elements contained in B5 medium on Phytophthora stem rot disease reduction of Glycine max (L.) Merr. cv. Chusei-Hikarikuro, fungal growth of Phytophthora sojae isolate and zoospore release were investigated. Application of B5 solution and macro inorganic nutrients in the B5 medium prior to inoculation significantly inhibited infection, compared with controls. Various concentrations of KNO3, (NH4)2SO4, MgSO4, CaCl2 and NaH2PO4 in the presence of macro inorganic nutrients were investigated in an effort to determine the elements most effective in suppressing the incidence of disease. A concentration of 2.47–24.7 mm KNO3 and 0.1–10.2 mm CaCl2 greatly inhibited infection. Although mycelium growth of the isolate was affected by the potassium and calcium concentration, no significant relationship was observed between inhibition of the growth rate and disease reduction at 2.47 mm KNO3 and 0.1–5.1 mm CaCl2 application. Disease suppression recorded in laboratory experiments using pathogen mycelium was due to the response of plant tissues rather than a direct inhibition of pathogen fungal growth by the application of potassium or calcium. The extent of disease reduction was related to an increased potassium and calcium uptake by plants, suggesting that the effective elements in reducing Phytophthora stem rot were potassium and calcium. The presence of 2.47–247 mm KNO3 and 5.1–10.2 mm CaCl2 decreased the release of zoospores, although 0.1–2.5 mm CaCl2 significantly induced zoospore release. These results suggest that applying a solution containing more than 2.47 mm of potassium and 5.1 mm of calcium can decrease the incidence of disease in agricultural fields by the inhibition of zoospore release.
Abstract: Effects of dried garlic, peppermint, cabbage, lentil, alfalfa, onion, radish, and garden cress plant materials on Phytophthora blight (Phytophthora capsici Leon.) of pepper were determined, in both in vitro and in vivo conditions. Extracts of the plant materials were used in vitro. The plant materials were extracted in ethanol and were added to corn meal agar (CMA) at 5 and 10 µg ml-1. The extracts of alfalfa, garlic, cabbage, and peppermint reduced colony diameter of P. capsici on corn meal agar between 3.46% and 13.73%, whereas mycelial growth of P. capsici was increased by onion, radish, garden cress, and lentil extracts. The plant materials inhibitory to mycelial growth of P. capsici were incorporated into soil inoculated with P. capsici, in pots and also in the field, in order to determine their effects on Phytophthora blight severity. The severity of Phytophthora blight of pepper was markedly reduced by cabbage, garlic, and alfalfa materials by 15.3%, 39.8% and 46.9%, respectively, in pot trials. No significant effect of peppermint on disease severity was found. In the field infested with P. capsici, disease severity decreased with cabbage, garlic, and alfalfa by 89.5%, 40%, and 10.7%, respectively. Peppermint slightly increased the disease severity (3.4%). In this study, dry cabbage, garlic, and alfalfa materials were effective in reducing the severity of disease caused by P. capsici, in both in vitro and in vivo conditions.
Abstract:Phytophthora cryptogea was isolated from field plantings of the red raspberry cultivars Glen Clova, Canby and Willamette which showed wilting, dieback, stem lesions and root rotting. Pathogenicity of P.cryptogea to raspberry was demonstrated in glasshouse experiments. Twelve cultivars of raspberry were screened for resistance to the disease by growing them in artificially infested soil. Glen Clova and Canby were highly susceptible whilst Chilcotin, Nootka, Haida and Puyallup were resistant. Soil treatments
with either metalaxyl, phosphorous acid or fosetyl aluminium controlled the disease. This is the first record of a phytophthora root rot of raspberry in Australia, and the first demonstrating the pathogenicity of P. cryptogea to raspberry.
Abstract: Isolates of the oomycete Phytophthora infestans exhibit a wide range of intrinsic sensitivities to fungicides, which potentially influences the application rates of chemicals needed to control potato late blight. To help understand what determines such levels of sensitivity, a genetic approach was employed which followed the segregation of sensitivities to structurally diverse fungicides such as metalaxyl and trifloxystrobin. Progeny exhibited broad
distributions of sensitivity phenotypes, consistent with the behaviour of a quantitative trait. Measurements of the inhibition of strains by seven fungicides revealed that basal sensitivities to metalaxyl and trifloxystrobin, and to cymoxanil and dimethomorph, correlated at the 95% confidence level. These compounds have distinct modes of action, suggesting the involvement of a
multifungicide efflux phenomenon mediated by ABC transporters. To determine whether such proteins contribute to variation in sensitivity, 41 full transporters and 13 half transporters were identified from P. infestans and their mRNA levels compared in strains exhibiting higher or lower sensitivities to fungicides. No correlation was observed between the expression of any ABC transporter and fungicide sensitivity. Other genes, or variation in
the activities of the transporters, may therefore explain the differences between strains. Five ABC transporters were induced by several fungicides in strains with both higher and lower sensitivities to fungicides, which probably reflects the existence of a network for protecting against natural and artificial toxins.
Abstract:Phytophthora spp. is one of the phytopathogenic Oomycete responsible for many important crop losses. Relevant species are P. infestans (causing potato late blight) and P. capsici (causing blight in pepper). In recent years, the use of conventional fungicides has favoured the appearance of different resistant strains. This study analyses the effect of various compounds on these two Phytophthora species. Those compounds were designed on the basis of known structures of natural compounds to obtain a rational control of these fungal-like species. All the analysed products showed a fungistatic activity against both strains, one of them reduced mycelial growth by over 46% at 100 p.p.m.
Abstract: Foot rot of black pepper caused by Phytophthora capsici causes heavy crop losses. Ecofriendly biological control was given high priority in the Integrated Disease Management programs (IDM). Strains of P. fluorescens which were antagonistic to P. capsici, the foot rot pathogen in black pepper produced inhibitory metabolites. Up to 72% inhibition of mycelial growth of P. capsici was observed in dual culture experiments. The metabolites of P. fluorescens strain, IISR-6 completely inhibited the sporangial production the most explosive phase in P. capsici. The indirect germination of sporangia (release of zoospores)also was inhibited considerably. The percent inhibition varied from 89 - 98%. The germination of zoospores of P. capsici was negatively influenced by the metabolites of P. fluorescens. Up to 90% inhibition of germination was noticed. Partial characterization of the metabolites let to the detection of two antibiotics - Pyoluteorin and pyrrolnitrin. The volatile metabolites of P. fluorescens also inhibited the different phases in life cycle of P. capsici, particularly mycelial growth and production of sporangia. HCN was detected in the volatile metabolites of the bacterial strains in varying quantities. The results are discussed in relation to the mechanism of disease suppression.
Abstract: Late blight of potato is caused by Phytopthora infestans (Mont.) de Bary is responsible for considerable economic losses. The disease appears regularly in epiphytotic proportion in the hilly regions of the country and cause considerable reduction in yield and quality. Most of the recommended fungicides often fail to provide adequate control if not applied at appropriate time. Moreover, there is high risk of development of fungal races resistant to systemic fungicides. Josepovits and Dobrevalszky (1985) reported that the use of mixture of fungicides with different mode of action as the best strategy to delay the buildup of resistance. Application of alternate sprays of systemic fungicides has also been reported to restrict the development of resistant strains of pathogen (Skylakakis, 1981). In the present communication, potential to control late blight have been studied with a view to develop an effective and safe spray schedule for management of this disease.
Abstract: Control of late blight by alternative products is important for reduction of fungicide inputs and potato production costs. The efficacy of essential oils and biopesticides for inhibition of growth of Phytophthora infestans on media and suppression of late blight on potato plants in growth chambers was examined. Growth of pathogen isolates of diverse genotypes was evaluated on Rye B media amended with essential oils (lavender, thyme, thyme borneal, and oregano) and the biopesticide Serenade (Bacillus subtilis strain QST 713). Over 90% inhibition of pathogen growth was achieved with oregano and Serenade amendments. The protective foliar application of Serenade, an aerated compost tea (ACT), Effective Microorganism mix (EM), and oregano, resulted in disease suppression of 5-40% relative to the untreated control. ACT had no significant suppressive effects (0-15% reduction), EM resulted in mild suppression (15-30% reduction), and oregano and Serenade consistently resulted in moderate disease reduction (20-40%). No oil or biological treatment produced disease control comparable to the chemical control chlorothalonil, which resulted in disease reductions of 80-98%. Both oregano and Serenade resulted in some phytotoxicity at high doses. These results suggest that the natural products and biological amendments tested are not sufficient for effective late blight control by themselves; however, when used in combination with other established disease control practices, these approaches may contribute to improved, integrated, and more sustainable management options for late blight.
Abstract: The influence of four commercial biological products on incidence of the phytopathogenic root fungi Phytophthora capsici, Rhizoctonia solani, and Fusarium oxysporum was evaluated, as well as their influence on growth
of tomato plants cv. Rio Grande. P. capsici (5 x 104 zoospores
mL-1), R. solani (2% infected grain, v:v; grain:soil), F.
oxysporum (5 x 10-1 conidia mL-1), and a mixture ofthe three fungi at the same concentration were used as inocula. Disease incidence was evaluated 50 days after inoculation, and seedling height and total dry biomass were quantified when they were 35 days old in the gennination trays. A completely randomized design with three replications per treatment was used. The experimental unit consisted of five seedling per replication. The products evaluated did not protect tomato seedlings from infection by P. capsici, F. oxysporum, and tlie mixture ofthe three phytopathogens. However, infection by R. solani was reduced efficiently with these products: T22 (Trichoderma harzianum) which gave a 100% protection, while Bio, End, and 343 gave 73.3%. Plant height increased 162.7, 149.4, and 47% with Bio, Bio + End, and End + 343, respectively, while total dry biomass increased 320.7,314.6, and 57.3%, respectively, in relation to the control.
Abstract:Phytophthora ramorum, causal agent of sudden oak death, is an emerging plant pathogen first observed in North America associated with mortality of tanoak (Lithocarpus densiflorus) and coast live oak (Quercus agrifolia) in coastal forests of California during the mid-1990s. The pathogen is now known to occur in North America and Europe and have a host range of over 40 plant genera. Sudden oak death has become an example of unintended linkages between the horticultural industry and potential impacts on forest ecosystems. This paper examines the biology and ecology of P. ramorum in California and Oregon forests as well discussing research on the pathogen in a broader management context.
Abstract