Abstract: Sensitivity to the new carboxylic acid amide (CAA) fungicide mandipropamid (MPD) in Phytophthora infestans was measured for isolates collected between 1989 and 2002 in Israel prior to the commercial use of MPD (baseline sensitivity, 44 isolates), and from MPD-treated (25 isolates) and untreated fields (215 isolates) in nine European countries and Israel between 2001 and 2005. All isolates were sensitive to MPD, with EC50 values ranging between 0·02 and 2·98 µg mL-1. Plastic-tunnel (UK), shade-house (Israel) and field experiments (Israel) conducted during 2001–05 showed that enforced selection pressure, applied preventively or curatively, imposed by repeated sublethal (5 µg mL-1) or excessive (500–1000 µg mL-1) doses of MPD on mixed isolates of P. infestans produced no isolates resistant to the compound. The results of this study indicate that the probability of a buildup of resistant sub-populations of P. infestans to mandipropamid in the field is low.
Abstract: Greenhouse and field experiments evaluated the effect of sewage sludge incorporation to the soil against Phytophthora nicotianae in cravo lemon plants. Six sludge doses, ranging from 0 to 30% (v/v), were tested per assay on plants at different developmental stages and with different pathogen inoculum levels. The increase in sewage sludge dose resulted in pH reduction, electric conductivity and soil microbial activity increases (evaluated by FDA hydrolysis and microbial respiration), and reduction in P. nicotianae recovery, both from the soil and from the plant roots. The pathogen recovery was significant and negatively correlated with soil microbial activity and electric conductivity. Better plant development was observed with sludge incorporation up to 20%. These results indicate that the incorporation of sewage sludge can suppress P. nicotianae, by nonchemical management of the pathogen and is a potential means of disposal of this residue.
Abstract: Oaks and tanoaks in California and Oregon coastal forests are being ravaged by sudden oak death. The exotic causal agent, Phytophthora ramorum, is an oomycete in the Straminipile group, a relative of diatoms and algae. P. ramorum also infects many popular horticultural plants (i.e. camellia and rhododendron), causing ramorum blight, with symptoms expressed as leaf spots, twig blight and shoot dieback. P. ramorum has raised important biosecurity issues, which continue to reverberate through the agriculture, forestry and horticulture industries as well as associated government management, regulatory and scientific agencies. The continued spread of this and other new Phytophthora spp. presents significant impetus for adjustments in the management and regulation of forest pathogens and nursery stock.
Abstract: Enzymatic degradation of chitosan polymer with Pectinex Ultra SPL was used to obtain derivatives with biological potential as protective agents against Phytophthora parasitica nicotianae (Ppn) in tobacco plants. The 24 h hydrolysate showed the highest Ppn antipathogenic activity and the chitosan native polymer the lowest. The in vitro growth inhibition of several Phytophthora parasitica strains by two chitosans of different DA was compared. While less acetylated chitosan (DA 1%) fully inhibited three P. parasitica strains at the doses 500 and 1000 mg/l the second polymer (DA 36.5%) never completely inhibited such strains. When comparing two polymers of similar molecular weight and different DA, again the highest antipathogenic activity was for the less acetylated polymer. However, degraded chitosan always showed the highest pathogen growth inhibition. Additionally, a bioassay in tobacco seedlings to test plant protection against Ppn by foliar application demonstrated that partially acetylated chitosan and its hydrolysate induced systemic resistance and higher levels of glucanase activity than less acetylated chitosan. Similarly, when treatments were applied as seeds coating before planting, about 46% of plant protection was obtained using chitosan hydrolysate. It was concluded that, while less acetylated and degraded chitosan are better for direct inhibition of pathogen growth, partially acetylated and degraded chitosan are suitable to protect tobacco against P. parasitica by systemic induction of plant resistance.
Abstract: The leaves of pepper (Capsicum anuum L.) were inoculated with Phytophthora capsici Leonian 3 d after treatment with acibenzolar-S-methylbenzo [1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester (ASM) and resistance to Phytophthora blight disease was investigated. Results showed that P. capsici was significantly inhibited by ASM treatment by up to 45 % in planta. The pepper plants responded to ASM treatments by rapid and transient induction of L-phenylalanine ammonia-lyase (PAL), increase in total phenol content and activities of chitinase and b-1,3-glucanase. No significant increases in enzyme activities were observed in water-treated control plants compared with the ASM-treated plants. Therefore it may be suggested that ASM induces defense-related enzymes, PAL activity, PR proteins and phenol accumulation in ASM-treated plants and contribute to enhance resistance against P. capsici.
Abstract: Eleven isolates of Trichoderma harzianum were screened for their potential to induce systemic resistance against Phytophthora capsici in red pepper plants. The effect of talc formulations of these eleven isolates on induction of glucanase activity and phenol content was studied. There was
a signiicant increase in glucanase activity in plants treated with Th8 and Th1 (94 and 90 µg glucose released min-1 g-1) compared to control (77 µg). Similarly phenol content also increased in plants treated with Th4, Th7 and Th10 (48-59 µg g-1) compared to control (34 µg g-1). Cell wall glucan elicitors were extracted from T. harzianum isolate Th10 that had been reported earlier as an eficient
biocontrol agent. Treatment with elicitor preparations also induced high glucanase activity (40 µg glucose released min-1 g-1)and increased phenol content (42 µg g-1) compared to control where the
glucanase activity was 33 µg glucose released min-1 g-1 while phenol content was 27 µg g-1. Similarly the elicitor treatment as seedling dip reduced P. capsici infection to 23% compared to control (93%). The potential use of ISR eliciting isolates in the biocontrol of P. capsici in red pepper is discussed.
Abstract: An innovative field observation by a farmer indicated that common salt (sodium chloride) is effective in controlling Phytophthora foot rot of black pepper (Piper nigrum L.) caused by Phytophthora capsici. This is validated through a series of in vitro and in vivo experiments. Initially mycelial growth, sporangial formation and zoospore germination of P. capsici were studied on a range of concentrations from 0.01 M to 3.0 M of NaC1. It was found that mycelial growth is inhibited by 1 M, Sporangial production by 0.75 M and zoospore germination by 0.5 M sodium chloride respectively. But, in vivo studies by challenge inoculation with P. capsici showed that the maximum inhibitory concentration under in vitro (1 M) is insufficient to inhibit P. capsici in the soil. Hence, higher concentrations, viz 2 M to 8 M were tested in soil. The results showed that 3 to 4 M concentrations of sodium chloride are the maximum required to destroy the soil inoculum but was found phytotoxic. Modification of the treatment by washing-off the soil amended with salt resulted in nullifying the phytotoxic effect without affecting the total microbial biomass, nutrient status, pH or electrical conductivity of the soil. This method can be used as a pre- planting practice while rejuvenating a diseased garden or while gap-filling or while raising nursery plants in potting mixture.
Abstract: Benthiavalicarb-isopropyl, a novel member of the amino acid amide carbamate group of fungicides, is effective against all Oomycete fungal plant pathogens except Pythium spp. Our results demonstrate that this fungicide effectively controls potato and tomato late blight caused by metalaxyl-sensitive and -resistant strains of Phytophthora infestans. Experiments in vitro demonstrated that benthiavalicarb-isopropyl was ineffective in stopping the discharge of zoospores from zoosporangia and suppressing their motility; but strongly inhibited mycelial growth, sporulation, and the germination of sporangia and cystospores. Experiments in a greenhouse showed that benthiavalicarb-isopropyl has not only a strong preventive, but also a curative effect; its translaminar properties are effective along with its rainfastness and residual activity. In field trials, it was effective in controlling tomato and potato late blight at 25–75 g a.i./ha.
Abstract: From 1991 to 1997, field observations on trials involving the use of metalaxyl and copper-based fungicides were made on farmers farms in four Phytophthora megakarya affected cocoa growing regions of Ghana to control Phytophthora pod rot disease. Data on farm management practices, cocoa and shade tree types and densities, plot sizes, yield, land tenure and labour arrangements for farm operations, disease incidence and profitability of disease control were collected. Lower disease incidence and higher yields were recorded on fungicide-treated plots than on the untreated plots. The profitability of fungicide application depended on the level of farm management, nature of land tenure and labour arrangements for farm operations. The challenges involved in conducting trials with active participation by farmers are discussed. The involvement of farmers in the development of disease control programmes is crucial for subsequent adoption of the technology.
Abstract: Epidemiological studies were conducted in five cocoa growing districts in the Eastern Region of Ghana solely infected by Phytophthora palmivora and five districts in the Ashanti and Brong Ahafo Regions prevalently infected by Phytophthora megakarya to determine the natural incidence, the vertical distribution on trees and the probable sources of stem canker infections, and to isolate and identify the causal pathogens. The incidence of canker in the solely P. palmivora infected area was higher (between 0% and 16.0%) than in the area mainly infected with P. megakarya (0.5–8.0%). Differences were found in the natural height distribution of cankers in the two areas, whilst the areas solely infected with P. palmivora showed a near normal curve, those prevalently infected with P. megakarya were positively skewed. Most of the cankers caused by P. megakarya were found at the base or near the base of the tree trunks (1–40thinspcm above ground level), while those of P. palmivora were concentrated between 41 and 100thinspcm from the ground level. The majority (71.8%) of cankers in the solely P. palmivora infected area were cushion-borne, followed by 24.3% from unknown sources and only 3.9% from the soil. In contrast, a significantly large proportion (32.6%) of the cankers in the prevalently P. megakarya infected area were soil-borne, although cushion-borne cankers formed the majority (48.4%) due to the presence of P. palmivora infection whilst those of unknown sources constituted 19.0%. Phytophthora megakarya was frequently isolated from all the three sources of canker infections, indicating P. megakarya readily causes stem canker on cocoa. These results emphasise the importance of different reservoirs as sources of primary inoculum for diseases caused by the two Phytophthora species particularly pod rot infection on cocoa.
Abstract