Evaluation of drench treatments with phosphonate derivatives against Pseudomonas syringae pv. syringae on pear under controlled environment conditions (original) (raw)
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Plant Pathology, 2018
Fosetyl-Al (the aluminium salt of ethyl-phosphite) is an acid product used to fight oomycete diseases sometimes used against bacterial diseases, but its antibacterial mode of action is largely unknown. Consequently, the direct effects of fosetyl-Al and neutralized fosetyl-Al on the colonization of leaf surfaces by Pseudomonas syringae were compared. Control of colonization was highest and almost complete in acidic conditions (99.7%), showing the importance of acidity for maximal antibacterial efficacy on plant surfaces. However, the high inhibition obtained with neutralized fosetyl-Al (88.9%) suggested another direct effect. Therefore, it was investigated in vitro whether ethyl-phosphite has antibacterial activity, possibly related to its phosphite content. Inhibition of P. syringae growth by ethyl-phosphite was observed and influenced by the carbon source and by phosphate. Growth inhibition reached 83.1% in unshaken conditions in a phosphatedepleted glucose medium. Phosphite drastically increased the effects and induced up to 99.7% growth inhibition. Mass spectrometric analysis indicated that P. syringae hydrolyzed ethyl-phosphite to phosphite using a cell-linked phosphatase activity. Specific phosphite toxicity was observed in phosphate-sufficient succinate media and phosphite-induced phosphorus starvation was observed in phosphate-depleted glucose media, indicating that ethyl-phosphite and phosphite have direct environmental impacts on bacteria. Phosphite toxicity for P. syringae probably occurred in the phyllosphere. The study indicates the potential and limitations of fosetyl-Al as a direct antibacterial product and helps in understanding the fosetyl-Al control of flower bud blast in pear. It raises the prospect of using phosphite in plant bacterial disease control.
European Journal of Plant Pathology, 2001
Blast of dormant flower buds (BDFB) of pear is a disease of economic importance in the major pear production areas of Europe. To obtain information concerning control measures and disease origin, chemical control trials were performed which included bactericides (kasugamycin and copper), phosphonates (fosetyl–Al and ethephon), and nutrient amendments (boron, calcium, and microelements). Although Cu levels in bactericidal treatments and microelements in nutrient amendments increased significantly in trees, there was no significant effect on disease control. However, incidence of disease was reduced significantly with phosphonate derivative compounds, and effects were observed only the year after the treatment was performed. Additional field trials were done to determine optimum dose and application timing, and a schedule consisting of three spray applications of fosetyl–Al (240 g a.i. hl-1) during May and June was the most effective treatment. This schedule was evaluated in 31 field trials performed in commercial orchard plots from 1989 through 1998. In the year after the treatment, average disease incidence decreased in 30 of 31 trials. The decrease of disease incidence was significant in 71% of the trials (average decrease of 46%). Neither the presence nor the population levels of P. syringae were consistently related to disease levels nor to the fosetyl–Al treatment effects on blast incidence of dormant flower buds.
Evaluation of plant defence activators for the potential control of Pseudomonas syringae pv. aesculi
Arboricultural Journal, 2014
Glasshouse trials were conducted using tobacco (Nicotiana benthamiana) to assess the efficacy of five plant defence activators (PDAs), namely harpin protein, potassium phosphite, salicylic acid analogue, silicon phosphite and a plant hormone -vitamin complex against the bacterial pathogen Pseudomonas syringae pv. aesculi (Pae), the causal agent of Pseudomonas bleeding canker of horse chestnut. PDAs were applied preventatively, i.e. before Pae inoculation of plants and therapeutically, i.e. after Pae inoculation of plants and as both as a foliar spray (FS) and root drench (RD). Irrespective of mode of application (i.e. FS, RD) or whether applied preventatively or therapeutically, PDAs containing salicylic acid analogues, plant hormone-vitamin complex and harpin protein possessed limited efficacy as Pae protectant and/or eradication compounds. Only application of potassium and silicon phosphite induced positive effects on plant vitality [increased leaf chlorophyll content, leaf chlorophyll fluorescence (F v /F m )], enhanced defensive enzyme activity (b-1,3-glucanase, peroxidase) and reduced Pae lesion size, the main proxy of Pae success or aggressiveness. Preventative rather than therapeutic phosphite application resulted in greater reductions in Pae severity. Little significance of mode of application was demonstrated, indicating that phosphites can be applied as either a FS or RD resulting in similar degrees of Pae control. Significant reductions in Pae severity recorded in this study give credence to the potential of phosphites as an alternative or complement conventional bactericides for Pae control.
Arboricultural Journal, 2015
Field trials were conducted using 4-year-old horse chestnut (Aesculus hippocastanum L.) to assess the efficacy of potassium and silicon phosphite as plant protection agents against the bacterial pathogen Pseudomonas syringae pv. aesculi (Pae) the causal agent of Pseudomonas bleeding canker of horse chestnut. Phosphites were applied preventatively, i.e. before Pae inoculation of trees, and curatively, i.e. after Pae inoculation of trees, and, as both a foliar spray (FS) and root drench (RD). Application of both phosphite forms induced positive effects on plant vitality (increased leaf chlorophyll content, leaf chlorophyll fluorescence (F v /F m )), enhanced defensive enzyme activity (b-1,3-glucanase, peroxidase) and reduced Pae lesion size, the main proxy of Pae success or aggressiveness. Preventative rather than curative phosphite application resulted in greater reductions in Pae severity. Little significance of mode of application (FS, RD) and phosphite anion (potassium, silicon) was demonstrated indicating both phosphites can be foliar applied or root drenched with similar degrees of resulting Pae control. Significant reductions in Pae severity recorded in this study gave credence to the potential of phosphites as an alternative or compliment to conventional bactericides for Pae control.
European Journal of Plant Pathology, 2014
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Australasian Plant Pathology, 2001
The ability of phosphite to control Phytophthora cinnamomi Rands in five Western Australian native plant species was examined. Foliar application of phosphite slowed, but did not completely inhibit, colonisation of stems by P. cinnamomi. For example, in Banksia hookeriana Meisn. inoculated 2 weeks after phosphite application, 5 g phosphite/L inhibited the growth rate of P. cinnamomi by 57% compared with the non-phosphite-treated plants. The longevity of phosphite efficacy varied with plant species. Foliar application of 5 and 10 g phosphite/L decreased the growth rate of P. cinnamomi in Dryandra sessilis (Knight) Domin. for at least 12 months after it was applied. Application rates of 5 and 10 g phosphite/L for Banksia grandis Willd. and 10 g/L for B. hookeriana were effective for at least 18 months after application. In Hibbertia commutata Steud. and Dampiera linearis R.Br., phosphite was effective for less than 6 and 12 months, respectively. In a second trial, plants were inoculated with P. cinnamomi at different time periods after phosphite was applied and time to death was recorded. There was a range of responses depending on the plant species and time of year they were inoculated. The initial levels of phosphite in roots and stems of B. grandis, B. hookeriana and D. sessilis and the rate of decrease of phosphite in these tissues differed between plant species. In general, concentrations of phosphite in stems were higher or equivalent to those in roots. This study indicates that the long-term efficacy of phosphite depends on both the plant species treated and the time of year the plants are infected with P. cinnamomi.
European Journal of Plant Pathology, 2003
The susceptibility of thirty-three pear cultivars and two pear rootstocks to four virulent strains of Pseudomonas syringae pv. syringae was evaluated by inoculating detached immature fruits and young leaves. The four strains were similarly virulent and did not show cultivar specificity although they were isolated from different pear cultivars and exhibited different biochemical profiles. The most frequently planted pear cultivars, Conference, Abate Fetel, General Leclerc, Williams, D. Comice, El Dorado, Alexandrine, B. Anjou, Passe Crassane and the rootstock OHxF 333 were susceptible to P. syringae pv. syringae. Maximal severity values were obtained on 'Preguystar' leaves (about 90%). The rootstock Winter Nelis was less susceptible. Results with immature fruit and detached leaf assays agreed with field observations on cultivar susceptibility to bacterial blast. However, the detached leaf test gave a more accurate prediction and has the advantages that symptoms develop quickly (48 h), and leaves are available for a longer period of time than fruits. This method is proposed as a rapid and reproducible screening system of cultivar susceptibility to bacterial blast of pear.
Sensitivity of Phacidiopycnis spp. Isolates from Pome Fruit to Six Pre- and Postharvest Fungicides
Plant Disease, 2018
Phacidiopycnis washingtonensis and P. pyri cause speck rot and Phacidiopycnis rot on apple and pear, respectively. Infection occurs in the orchard and remains latent, and symptoms appear after months of storage. Decay management relies on orchard sanitation and pre- and postharvest fungicides. In a 2017 survey, speck rot accounted for 6.4% of apple decay in central Washington, whereas Phacidiopycnis rot accounted for 3.9 and 6.7% of total pear decay in Washington and Oregon, respectively. Sensitivities of baseline populations of 110 P. washingtonensis and 76 P. pyri isolates collected between 2003 and 2005 to preharvest fungicides pyraclostrobin (PYRA) and boscalid (BOSC) and to postharvest fungicides thiabendazole (TBZ), fludioxonil (FDL), pyrimethanil (PYRI), and difenoconazole (DFC) were evaluated using a mycelial growth inhibition assay. Mean effective concentrations necessary to inhibit 50% growth (EC50) of P. washingtonensis were 0.1, 0.3, 0.8, 1.8, 2.1, and 4.8 µg/ml for FDL,...