Abstract: The efficacy of the essential oil and various organic extracts from flowers of Cestrum nocturnum L. was evaluated for controlling the growth of some important phytopathogenic fungi. The oil (1000 ppm) and the organic extracts (1500 ug/disc) revealed antifungal effects against Botrytis cinerea, Colletotrichum capsici, Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Rhizoctonia solani and Sclerotinia sclerotiorum in the growth inhibition range of 59.2–80.6% and 46.6–78.9%, respectively, and their MIC values were ranged from 62.5 to 500 and 125 to 1000 ug/mL. The essential oil had a remarkable effect on spore germination of all the plant pathogens with concentration and time-dependent kinetic inhibition of P. capsici. Further, the oil displayed remarkable in vivo antifungal effect up to 82.4–100% disease suppression efficacy on greenhouse-grown pepper plants. The results obtained from this study may contribute to the development of new antifungal agents to protect the crops from fungal diseases.
Abstract: Compost teas are fermented watery extracts of composted materials that are used for their ability to decrease plant disease. Non-aerated compost teas (NCT) prepared from five types of compost were tested for their ability to inhibit the growth of Alternaria solani, Botrytis cinerea, and Phytophthora infestans in vitro. Weekly applications of NCT were also used in greenhouse trials to assess their suppressive effect on powdery mildew (Oidium neolycopersici) and gray mold (B. cinerea) on tomato plants. All NCT significantly inhibited the mycelial growth of A. solani (37–66%), B. cinerea (57–75%), and P. infestans (100%), whereas sterilized teas did not inhibit growth of the tested pathogens. Although NCT failed to efficiently control powdery mildew, they were able to control tomato gray mold for up to 9 weeks in greenhouse experiments. Among the tested compost teas, NCT prepared from sheep manure compost consistently provided the highest inhibition of mycelial growth and the highest disease suppression, in particular of gray mold (>95% disease reduction). The overall relative efficacy of the various NCT did not correlate well with microbial communities or physico-chemical composition of the prepared NCT. Results also suggest that the presence of the microorganisms in the NCT is a prerequisite for inhibition.
Abstract: The effect of phenol concentration on growth and biodegradative capacity of Ralstonia eutropha regarding phenol was examined. Kinetic analysis indicated that phenol had a strong inhibitory effect on phenol metabolism and growth rate, although biomass yields remained constant, indicating that this phenomena was not caused by increased maintenance requirements. Measurements of specific enzyme activities involved specifically in the catabolic pathway of meta fission of phenol indicated that gene expression cannot explain the diminished metabolic rates at inhibitory phenol concentrations. This phenomenon is due to in vivo inhibition of enzyme activities and notably to phenol hydroxylase activity. Furthermore, other nonmetabolizable organic alcohols provoked a similar effect on both specific growth rate and phenol hydroxylase activity, indicating that inhibition was probably associated with modified membrane fluidity, partially offset by a change in the fatty acid composition of cellular lipids.
Abstract: The influence of site on effectiveness of low-volume spray of phosphite for the control of Phytophthora cinnamomi was compared between sites differing in soil nutrient status. The sites ranged from infertile deep grey sands to a red loamin the Esperance Plains bioregion, and infertile gravelly sand of the Havel site-vegetation type P to a red loam of Havel site-vegetation type Q in the northern Jarrah Forest bioregion. Following low-volume spray of 0, 24 or
48 kg phosphite/ha, phosphite effectiveness was determined from assessment of rate of colonisation and inhibition of stem colonisation by P. cinnamomi, and stem phosphite concentration in challenge inoculation stems of Lambertia inermis var. inermis in Esperance Plains bioregion sites and Banksia grandis in Jarrah Forest bioregion sites. Phosphite effectiveness was mainly influenced by plant species rather than site. Phosphite spray significantly controlled P. cinnamomi colonisation in B. grandis, but not in L. inermis var. inermis. Site had no consistent influence on the effect of phosphite on P. cinnamomi despite large differences in soil nutrient status between sites. Differences between sites and site ranking changed with inoculation time and rate of phosphite spray, and duplicate sites differed significantly fromeach other. Site, rate of phosphite spray, time after spray and plant species significantly affected stem phosphite concentrations. In both Esperance Plains bioregion and Jarrah Forest bioregion sites, stem phosphite concentrations were greatest in fertile loam sites and least in infertile sand or gravelly sand sites. Stem phosphite concentrations increasedwith rate of phosphite spray with concentrations in stems receiving 48 kg phosphite/ha being 1.2 to 3-times-greater than that in stem sprayed with 24 kg phosphite/ha. Six months after low-volume spray, phosphite concentrations in L. inermis var. inermis stems had declined for all sites and spray rates to only 4–17% of original concentrations. Decline of phosphite concentrations in B. grandis stems was slower than that for L. inermis var. inermis stems. The results indicate that effectiveness of phosphite against P. cinnamomi infection in different communities will depend more on plant species composition than soil nutrient status. Differences in phosphite effectiveness between plant species may be related to differences in phosphite concentration thresholds yet to be quantified, above which tissue concentrations must be achieved before inhibition of P. cinnamomi colonisation occurs. In rapid colonisation/phosphite low-responsive species such as L. inermis var. inermis, the threshold may be greater than that required for a response in a rapid colonisation/phosphite high-response species such as B. grandis. These results demonstrate the need to determine thresholds for individual plant species and in different environments.
Abstract: The Iberian forests are suffering severe disease and mortality as a result of decline, with Quercus ilex the major species at risk. Trunk injections with potassium phosphonate, which have been used successfully to control Phytophthora cinnamomi, were tested against decline. In an area in which P. cinnamomi was isolated, Q. ilex trees showing different degrees of decline were trunkinjected. Soil properties, and measurements of soil
water content (θ) and depth to soil water table were assessed at three sites with markedly different decline incidences. Over the 5 years following the initiation of the experiment, mean symptoms among spring-treated trees and autumn-treated trees, or among trees injected twice a year (spring and autumn), once a year, and non-injected, were not significantly different. No effects of the treatments on shoot growth and acorn production were observed. However, θ values under trees which recovered from decline were higher than θ values under trees which did not recover from decline. At the site with the highest incidence of decline and tree mortality, P. cinnamomi was rarely isolated, and the presence of gravel, soil infiltration capacities and water table depth values were significantly higher than at the other sites, water stress being more likely to contribute to decline than P. cinnamomi. In areas in which θ is low, the distribution of phosphonate on the tree would be limited. Since the thresholds for phytotoxicity of potassium phosphonate in Q. ilex trees at the site studied would be higher than the amounts used, rates of the chemical slightly less than those that cause phytotoxicity
should be tested.
Abstract: Pink rot caused by the pathogen Phytophthora erythroseptica Pethyb. causes severe pre- and post-harvest losses in potato. Severe losses of potato from pink rot infection suggest the need for better information on cultural factors associated with disease development. Soil pH has been regarded as a strong influence on disease development as observed by previous studies and by commercial potato growers. A hydroponic growth system was established to study the effects of pH on P. erythroseptica infection and colonization in Russet Norkotah potato roots. Russet Norkotah plantlets were grown in hydroponic nutrient solutions buffered at pH 5, 6, 7, and 8 and evaluated for infection by means of quantitative Real Time PCR. Acidic pH solutions produced a higher proportion of pathogen to host DNA in root tissue, indicating increased infection and colonization at low pH. Thus, pH has a unique and significant influence on the levels of infection from P. erythroseptica and that commercially grown potatoes would likely develop reduced tuber rot if grown in soils with pH at or above 7.
Abstract:Phytophthora erythroseptica Pethyb. causes a disease known as pink rot in potatoes, which is responsible for substantial pre and post harvest tuber loss. Disease outbreaks are associated with excessive soil moisture, moderate temperature, late season development, and a lack of potato cultivar resistance. Because disease resistance is becoming less effective, understanding other potential solutions is critical. Mineral nutrition of plants is known to be associated with disease development and severity of many diseases, but is not generally considered in relation to outbreaks of pink rot. Calcium (Ca) is essential and considered one of the most important nutrients associated with plant defense, but it has not been studied or consequently linked to the severity of pink rot in potato. A hydroponic growth system was established to study the effects of calcium on P. erythroseptica infection and colonization in Russet Norkotah potato roots. Russet Norkotah potatoes were grown with 3, 86, 172, and 343 mg L-1 Ca in association with the pathogen. The degree of disease severity was assessed by means of quantitative real time polymerase chain reaction (RT PCR). The suppression of infection and disease severity by increased available Ca was statistically significant, decreasing with each increment of Ca between 3 and 343 mg L-1. These data provide strong evidence that Ca nutrition is important in disease suppression and that the amount of available soil Ca can affect plant health and the ability of P. erythroseptica to infect the host.
Abstract: A potato (Solanum tuberosum Gp Tuberosum) breeding programme is described and analysed in which resistances to late blight [Phytophthora infestans (Mont.) de Bary] and the white potato cyst nematode (Globodera pallida) have been combined with a modest increase in yield and acceptable fry colour for processing. It began in 1991 and has involved cycles of crossing, selection between from 120 to 145 progenies (full-sib families), and clonal selection within the selected progenies. We have shown that the breeding scheme can operate on a 3-year cycle with limited within progeny selection, and on a 5- or 6-year cycle with more extensive within progeny selection. Six years are required when resistance to late blight is assessed in the tubers as well as the foliage. The more extensive within progeny selection is recommended once genes have been combined from sufficient parents to achieve one’s objectives. The yield increase after three cycles of indirect selection through breeders’ visual preference was only modest because it was operating against a decrease which would occur in the absence of selection. A practical improvement in the scheme would be to increase the number of progenies assessed to over 200, given the moderate to high heritabilities of the progeny and clonal tests. But this would require a considerable effort because the success rate achieved with the potato pollinations was typical at just over 30%. In the fourth cycle we showed how new breeding objectives and germplasm could be accommodated whilst continuing to maintain progress, something that is important in any long term breeding strategy.
Abstract: Culture filtrates of five strains of Clitocybe nuda displayed various degrees of antimicrobial activity against plant pathogenic fungi and/or bacteria tested. The culture filtrate of C. nuda strain LA82was very
effective in reducing the incidence of Phytophthora blight of pepper caused by Phytophthora capsici and the incidence of leaf spot on pepper caused by Xanthomonas axonopodis pv. vesicatoria. The inhibitory
substance in the C. nuda strain LA82 culture filtrate was stable at low and high pH. It was also stable at high temperature. The inhibitory substance was dialyzable in the membrane tubing with molecular weight cut-off of 1000 but not 500 or 100. It was also exchangeable by anion but not cation exchange
resins, indicating that the inhibitor has a molecular weight between 1000 and 500, and negative charge on its molecule. The inhibitor is a hydrophilic compound, but not a protein.
Abstract: This research was aimed on evaluating the effect of organic fertilizers on
susceptibility of durian seedlings to Phytophthora palmivora. The green compost, chicken manure and rice husk, alone or in a mixture, significantly increased seedling survival. Therefore, such growing media composition should be taken into account as one of the elements of integrated Phytophthora control in durian. On the other hand, goat manure has a ruinous effect on the growth and survival of durian seedlings and shall be avoided in durian orchards.
Abstract