Abstract: The aim of this study was to find an alternative to synthetic fungicides currently used in the control of devastating oomycete pathogen Phytophthora infestans, causal agent of late blight disease of tomato. Antifungal activities of essential oils obtained from aerial parts of aromatic plants such as oregano (Origanum syriacum var. bevanii), thyme (Thymbra spicata subsp. spicata), lavender (Lavandula stoechas subsp. stoechas), rosemary (Rosmarinus officinalis), fennel (Foeniculum vulgare), and laurel (Laurus nobilis), were investigated against P. infestans. Both contact and volatile phase effects of different concentrations of the essential oils used were determined by using two in vitro methods. Chemical compositions of the essential oils were also determined by GC-MS analysis. Major compounds found in essential oils of thyme, oregano, rosemary, lavender, fennel and laurel were carvacrol (37.9%), carvacrol (79.8), borneol (20.4%), camphor (20.2%), anethole (82.8%) and 1,8-cineole (35.5%), respectively. All essential oils were found to inhibit the growth of P. infestans in a dose-dependent manner. Volatile phase effect of oregano and thyme oils at 0.3 μg/ml air was found to completely inhibit the growth of P. infestans. Complete growth inhibition of pathogen by essential oil of fennel, rosemary, lavender and laurel was, however, observed at 0.4–2.0 μg/ml air concentrations. For the determination of the contact phase effects of the tested essential oils, oregano, thyme and fennel oils at 6.4 μg/ml were found to inhibit the growth of P. infestans completely. Essential oils of rosemary, lavender and laurel were inhibitory at relatively higher concentrations (12.8, 25.6, 51.2 μg/ml respectively). Volatile phase effects of essential oils were consistently found to be more effective on fungal growth than contact phase effect. Sporangial production was also inhibited by the essential oil tested. Light and scanning electron microscopic (SEM) observation on pathogen hyphae, exposed to both volatile and contact phase of oil, revealed considerable morphological alterations in hyphae such as cytoplasmic coagulation, vacuolations, hyphal shrivelling and protoplast leakage.
Abstract: Azoxystrobin at 0.25 g/m2 applied by spraying roots achieved very good control of Phytophthora cryptogea an important pathogen of witloof chicory. Its efficacy was better than propamocarb-HCl at 7.22 g/m2, with a reduction of 50–90% in the root infection rate at the end of the forcing period. In one trial, the efficacy of azoxystrobin was better than that obtained with fosetyl-Al at 12 g/m2.
Abstract: The protective effect of β-aminobutyric acid (BABA) on two potato cultivars (Bintje and Pampeana) with different levels of horizontal resistance against Phytophthora infestans was investigated during the crop cycle. Plants were treated with BABA 16, 23, 30, 38, 44, 51, 61 or 75 days after emergence. After each application, the percentage of protection and the content of glucanases, chitinases and phenolic compounds were determined in detached leaves. The foliar pretreatment with BABA up to 30 days after emergence showed a 60% protection percentage against P. infestans in cv. Pampeana, while cv. Bintje almost reached 20%. The results indicated that the time of application of BABA and the susceptibility of the cultivars affect both the protection against late blight and the expression of defence molecules like glucanases, chitinases and phenolic compounds.
Abstract: Four fungicides were evaluated for their effectiveness against Phytophthora cactorum affecting apple trees and their ability to be absorbed and translocated by roots of apple tree. Ridomil gold MZ68 (metalaxyl+mancozeb) and curvax M (cymoxanil+mancozeb) suppressed the in vitro development of this fungus at high doses (100 and 1000 ug m-1). Mikal flash (fosetyl-Al+folpet) and melody duo (iprovalicarb+propineb) reduced mycelium growth of P. cactorum when used at all tested doses. In vivo, melody duo was the less effective. The in vivo treatment of plant was more significant when the plant is not severely infested.
Abstract:Phytophthora nicotianae is a common and destructive pathogen of numerous ornamental, agronomic and horticultural crops such as tomato, tobacco and citrus. Three monobranched C13 alcohol alkoxylate non-ionic surfactants were evaluated for in vitro inhibitory activity against the different asexual structures of P. nicotianae. The same surfactants, labelled MBA1301, MBA1303 and MBA1306, were tested for their in vivo control capacity against P. nicotianae root rot of tomato (Lycopersicon esculentum) under glasshouse conditions. MBA1301, MBA1303 and MBA1306 differ in the molecular structure of the hydrophilic portion. The molecular weight of MBA1301 is comparable to that of MBA1303 and is eight times lower than that of MBA1306. The main in vitro activity for MBA1301 and MBA1303 was a direct lytic effect on the zoospores. Zoospore lysis was already observed in the presence of 1 ug ml-1 of these two surfactants and almost no zoospores survived an addition of 5 ug ml-1 surfactant. In addition, MBA1301 and MBA1303 reduced sporangia formation at a concentration of 5 ug ml-1. Both surfactants only affect mycelium growth at concentrations as high as 100 ug ml-1. MBA1306 did not show any effect on sporangia formation, zoospore release and mycelium growth of P. nicotianae at a concentration 10 times that of the other two surfactants. A good in vivo control of P. nicotianae on tomato in substrate culture was obtained for MBA1301 and MBA1303 whereas the control capacity of MBA1306 was significantly lower. The results of this research indicate that non-ionic alcohol alkoxylate surfactants can be used to control tomato root rot caused by P. nicotianae in substrate culture. In addition, the size rather than the arrangement of the polymers in the hydrophilic portion of the surfactant molecule determines the efficacy to control tomato root rot caused by P. nicotianae in substrate culture.
Abstract: Three experiments aiming to explore the efficacy of fungicides to protect newly developing potato leaves were carried out between 2000 and 2002. Contact, translaminar and systemic fungicides were applied in field trials at Lelystad in the centre of the Netherlands. Efficacy of the fungicides was established using a bioassay in which detached new grown leaflets (cv Bintje) were inoculated with Phytophthora infestans. The interval between the last fungicide application and picking the leaves to be used in the bioassay varied between 4 and 11 d. Disease incidence was assessed after incubation for approximately a week.
Protection of the newly developed leaves depended on the intrinsic property of the fungicides, time since the last fungicide application and growth rate of potato leaves in the field since the last fungicide application. Shorter time intervals between spraying and inoculation resulted in better (re)distribution of (contact) fungicides on newly developed leaves resulting in better protection. Also, there was less dilution of the fungicide due to less leaf expansion during a 4 d compared with 7 d spray interval. A similar effect occurs when crop growth rate decreases.
Ridomil Gold MZ, with the systemic active ingredient metalaxyl and Ranman (cyazofamid) resulted in the best protection of newly developed leaves at the beginning of the growing season when crop growth rate was high. Contact fungicides containing cyazofamid or to a lesser extent, mancozeb can protect newly developing leaves, due to good redistribution of the compounds.
Abstract: Black pod rot, caused by Phytophthora megakarya, is the main cause of cocoa harvest losses in Cameroon. Field experiments were carried out over two successive years in two smallholders plots of cocoa trees, in order to assess the impact of diseased pod removal (phytosanitary pod removal) on disease progress, total production and final harvest. The generalized linear mixed model proved to be the most appropriate for comparing the two treatments (without and with pod removal) set up in a randomized complete block design. Removing diseased pods helped to reduce the black pod rate by 22% and 31% in the two sites in the first year, and by 9% and 11% in the second year, compared to a plot in which no preventive control measures were taken. The rate of cherelle (very young pod) appearance was also higher when pod removal was carried out. Total production was higher in the plots with pod removal, but the difference between the two treatments was not significant. This study allowed an evaluation of the respective roles of primary and secondary inoculum in the spread of the disease. The cultural practice of phytosanitary pod removal was found to be a potentially efficient control method. However, it would need to be associated with other control methods to establish an integrated management system for cocoa farmers.
Abstract: Black pod disease caused by Phytophthora megakarya is the most important fungal disease on cocoa in Ghana. The current recommended control method of combining sanitation practices with 6 - 8 fungicide applications in a year is considered unfriendly to the environment, too expensive and time consuming. Consequently, fungicide adoption rate by farmers is extremely low. Studies were therefore conducted to determine the effectiveness of combining 1 - 3 fungicide application in June and/or September/October with crop sanitation for the control of cocoa black pod disease caused by P. megakarya. Sanitation practices were common to all the treatments and the fungicide application(s) superimposed. A semi-systemic fungicide, Ridomil 72 plus (12% metalaxyl + 60% copper-1-oxide), was used as the test fungicide. Fungicide application combined with crop sanitation practices were effective in the management of the severe form of black pod disease caused by P. megakarya, resulting in 25% to 48% disease reduction and 10.9% to 51.8% yield increase. Combining the sanitation practices with three fungicide applications gave significantly better results, in terms of disease control and yields than either sanitation practices alone or combining them with one or two fungicide applications. However, the combination of sanitation practices and three fungicide applications was significantly less effective than the standard fungicide application of six times a year. All the fungicide applications and/or crop sanitation practices were profitable with a Benefit Cost Ratio (BCR) ranging from 1.8 - 2.1.
Abstract: Phosphite has been recommended to enhance plant resistance against Phytophthora. This work evaluated the response of hot and sweet pepper (Capsicum annuum L.) to Phytophthora capsici from juvenile up to the adult stage following treatment with phosphite. Sweet pepper hybrids considered to be resistant to P. capsici, like Reinger, Nathalie and Athenas, were evaluated. The susceptible checks were hybrid Magali R and cvs. Myr 10 and Ikeda. Hot pepper Criollo de Morelos 328, CM 334, BGH 3756, BGH 5122, CNPH 294 and Locorte were used as referential resistant lines. Phosphite did not have an effect on the hot pepper resistant lines because of their genetic homozygozity, while no protection was observed for the Athenas hybrid claimed to be resistant. Heterozygous hybrids recognized as resistant, like Reinger and Nathalie, showed higher survival following phosphite treatment, and their reaction was equivalent to the resistant cvs. CM 328 and CM 334, except for the fruiting stage. Depending of the hybrid heterozygous genotype, phosphite possibly acts through indirect phytoalexin induction through the inhibited pathogen.
Abstract: Mefenoxam applied on chicory roots at 4.8 g active ingredient 100l-1 achieved a very effective control of Phytophthora cryptogea, one of the main pathogens of witloof chicory. In seven trials, less than 10% of the roots treated with mefenoxam showed necrosis. The mefenoxam efficacy was better than that of propamocarb-HCl at 180 g 100l-1 (89–100% of infected roots) or mancozeb at 300 g 100l-1 (97–100% of infected roots). The efficacy of fosetyl-Al appeared to be irregular (2–98% of infected roots). Sensitivity to mefenoxam and azoxystrobin of some P.cryptogea strains was studied on amended media. Among the six strains tested, one was resistant to mefenoxam and two were moderately sensitive to azoxystrobin. The risk of occurrence of resistant strains in practice has to be considered; management of resistance to the two fungicides by application scheduling is proposed.
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