Growing concerns about food safety and environmental protection have created a need for new and safe plant disease control strategies. The aim of this study was to find an alternative to synthetic fungicides currently used in the control of the devastating fungal pathogen Botrytis cinerea Pers., the causal agent of grey mould disease of strawberry (Fragariaananassa Duch). The antifungal activity of the essential oils of Origanumvulgare L., Monardadidyma L. and of a commercial formulation of thyme oil (Gloves Off®) was investigated against B. cinerea and compared with controls. Contact phase effects of different concentrations of the essential oils and commercial formulation were found to inhibit the growth of B. cinerea in a dose dependent manner. Complete growth inhibition of the pathogen was recorded at 200 µg/ml of ‘Gloves Off®’. The mycelial growth of the pathogen was significantly reduced at the highest concentration of the essential oils of O. vulgare and M. didyma tested, which was 51.2 µg/ml. Spore germination and germ tube elongation were also inhibited by the essential oils and Gloves Off®. Light microscopic observations revealed that the essential oils caused morphological degenerations, such as cytoplasmic coagulation, hyphal shrivelling and protoplast leakage of the fungal hyphae. The essential oils of O. vulgare L. and M. didyma L. are promising, antifungal agents against B. cinereasimilar to the commercial formulation ‘Gloves Off®’.

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A survey of southwestern Nigeria showed an outbreak of wilt disease caused by Ralstonia solanacearum in 80% of tomato (Lycopersicon lycopersicum) fields in the production area of Ogun State (7°15′N, 3°25′E) in June 1996. Subsequent surveys conducted in Edo (6°45′N, 5°30′E), Delta (5°15′N, 5°45′E), Lagos (6°30′N, 3°40′E), Oyo (8°40′N, 3°30′E), and Osun (7°50′N, 4°E) states between May and November 1998 identified 60 to 80% infected fields per state. Observations made at the experimental plots of the National Horticultural Research Institute (NIHORT) at Ibadan (7°23′N, 2°50′E) also showed similar infections. Affected plants exhibited initial wilting of terminal leaves followed (within 2 days) by sudden and permanent wilt. For further identification of the causal organism, 10 tomato plants showing wilt symptoms were collected from each of five fields in the vegetable blocks of the NIHORT at Ibadan and 20 farmers' fields in Ogun State. The 10 plants per field were thereafter bulked as one composite sample. Creamy bacterial sap from these samples was plated on tetrazolium chloride media, and plates were incubated at 30°C for 48 h (2). Colonies that were fluidal and white with pink centers were used for biovar determination. Basal media was prepared to include one of three disaccharides (cellobiose, lactose, or maltose) or three hexose alcohols (dulcitol, mannitol, or sorbitol). A loopful of bacterial cells of all 25 isolates was inoculated individually to each of the six media. Cultures were incubated at 30°C for 28 days and monitored daily for color changes. The pathogenicity of the 25 isolates was tested using 10 4-week-old seedlings each of eggplant cv. black beauty, tomato cv. Ibadan local, sweet pepper cv. California wonder, and potato cv. Kufri. Each inoculum was prepared by adjusting the concentration to 107 CFU/ml with a colorimeter at a wavelength of 600 nm (optical density of approximately 0.3). Plants were inoculated by pouring 10 ml of inoculum around the base of each plant. Ten uninoculated seedlings of each cultivar served as the control. Plants were assessed for wilt severity 30 days after inoculation. All isolates utilized the three disaccharides and three hexose alcohols, and according to Hayward's classification, all isolates were biovar 3 (1). Furthermore, the isolates caused rapid wilting of all four test plants. R. solanacearum was easily reisolated from the vascular bundles of the test plants. To our knowledge, this is the first report of this biovar of R. solanacearum affecting tomato crops in Nigeria. References: (1) A. C. Hayward. J. Appl. Bacteriol, 27:265, 1964 (2) A. Kelman. Phytopathology 44:693, 1954.

Tomato cultivation is severely affected by bacterial wilt disease caused by the soilborne pathogen Ralstonia solanacearum (previously known as Pseudomonas solanacearum Smith). Effects of rotation of tomato (Lycopersicon esculentum Mill.) with other crops on soil populations of R. solanacearum and on bacterial wilt disease incidence of tomato were evaluated in the field. Monocropped Cassava (Manihot esculenta Crantz), Mucuna puriens L., Crotalaria juncea L., and intercrops of Cassava/Crotalaria, Cassava/Mucuna, and a natural grass mix (control) were rotated with the tomato cvs. Mira, Ronita, Roma VFN, and Ibadan Local. Monocropped Mucuna significantly reduced soil population of R. solanacearum by the end of the rotation period, whereas the natural grass rotation had the highest population of the pathogen. Other crops with the exception of monocropped cassava also reduced the pathogen soil population. The incidence of wilt was delayed in cvs. Mira, Roma VFN, and Ronita compared to 'Ibadan Local', but all were 80% or more infected after 8 weeks.

Effect of mango mealybug and sooty mould attack on mango and the impact of the released Gyranusoidea tebygi Noyes on yield. Abstract-Introduction. The mango mealybug Rastrococcus invadens is a pest of horticultural crops, especially mango. Though this fact has been demonstrated and its parasitoid, Gyranusoidea tebygi, released for its control in many countries, quantitative information on the damage inflicted by the mealybug and post-release mango fruit production are still scanty. This study was therefore undertaken to investigate the damage caused by mango mealybug and its associated sooty mould on mango plants and to assess mango fruit production after the release of G. tebygi in 1989. Materials and methods. Laboratory experiments were set up to determine the effect of different populations of mango mealybug (0, 5, 10, 20, and 40 adults/cage) on the chemical constituents of mango leaves. The mould associated with the mango mealybug was identified and its effect on leaf temperature was studied. A mango orchard was studied for fruit production from the time of fruitlessness in 1990 to 1998 when fruit yield peaked. The resultant effect of the parasitism of mango mealybug by G. tebygi was monitored on the chemical composition of mango leaves during this period. Results. Protein, fat, carbohydrate, ash, crude fibre and moisture contents were depleted with increase in mealybug population. The isolated mould fungus Capnodium mangiferae was found to raise leaf temperature of infected mango seedlings. The population density of G. tebygi was found to be negatively but significantly correlated with mango mealybug population and positively correlated with mango fruit yield. Parasitism was highly correlated with mealybug population and yield, and was considered a major factor in the control of the pest and the subsequent increase in mango fruit yield. Rainfall did not have a significant impact on yield, mealybug population or sooty mould score. Discussion. The injury inflicted by R. invadens and its associated mould, and the enhancement of mango fruit production by the activities of G. tebygi on the mealybug were discussed. Nigeria / Mangifera indica / pest control / Rastrococcus invadens / Gyranusoidea tebygi / biological control organisms / yields Effet des attaques de la cochenille farineuse et de la fumagine sur manguiers et impact de la libération de Gyranusoidea tebygi Noyes sur leur rendement. Résumé-Introduction. Rastrococcus invadens, la cochenille farineuse du manguier, est un ravageur des productions horticoles, et du manguier en particulier. Bien que ce fait ait été démontré et que son parasitoïde, Gyranusoidea tebygi, ait été libéré dans de nombreux pays afin de contrôler le ravageur, des informations quantitatives sur les dommages qu'il inflige à la production en mangues sont encore minces. L'étude engagée a permis d'étudier les dommages provoqués sur manguiers par ce parasite et par la fumagine qui lui est associée et d'évaluer l'évolution des rendements après un lâcher de G. tebygi en 1989. Matériel et méth...