Leveillula Taurica Research Articles

Bicarbonate solutions control powdery mildew (Leveillula taurica) on sweet red pepper and reduce the development of postharvest fruit rotting

Disease severity of powdery mildew (causal agentLeveillula taurica (Lev.) Arn.) on pepper (Capsicum annuum), defoliation and fruit sunscald rating were significantly reduced (P=0.05) by foliar applications of sodium or potassium bicarbonate solutions, compared with water or penconazole (Ophir). Preharvest application of bicarbonate solutions significantly reduced (P=0.05) postharvest decay development on sweet red pepper fruits.

First Report of Powdery Mildew in Greenhouse-Grown Tomatoes in New Jersey.

Powdery mildew of tomatoes caused by an Erysiphe sp. has been reported to occur in greenhouses in New York (2). In March and April of 1996, outbreaks of this disease were found in greenhouse-grown tomato plants of cv. PSR55809 at the Cook College campus in New Brunswick, NJ, and in cv. Match in commercial greenhouses in Burlington County, NJ. Identification of an Erysiphe sp. was made by comparative morphology of the conidial state since the perfect stage was not observed. Symptoms included development of patches of white mycelium predominantly on upper surfaces of older leaves followed by chlorosis of tissues colonized by the fungus. Microscopic examination of mycelium revealed the presence of typical Oidium conidiogenous cells and conidia. Conidiogenous cells were short and cylindrical and produce conidia in chains apically. Conidia were hyaline, cylindrical to ellipsoidal, and measured 36 + 4.9 × 16.7 + 2.2 μm (n = 20). Both conidia and symptoms of this powdery mildew are comparable to those previously given for the Erysiphe sp. described in New York (2). Another powdery mildew of tomato, caused by Oidiopsis sicula Scalia, occurs in the western U.S., Mediterranean Basin, Africa, and Asia. However, the conidia of O. sicula are of two types, pyriform and cylindrical, and they are larger than those of an Erysiphe sp. (1). To verify pathogenicity of this Erysiphe sp. to tomatoes, conidia washed from leaves were misted onto uninfected leaves of young tomato plants. After 1 week in a growth chamber (25°C; 80% relative humidity; 12 h of light), typical powdery mildew symptoms were evident on inoculated plants, while unmisted plants remained free of symptoms. Microscopic examination of the fungus on surfaces of leaves confirmed it to be an Erysiphe sp.

Resistance to Leveillula taurica in pepper (Capsicum annuum) is oligogenically controlled and stable in Mediterranean regions

AbstractThe resistance to Leveillula taurica from an african pepper line H3 Capsicum annuum) was evaluated and analysed, using the androgenetic haplodiploid progeny from an F1 hybrid between H3 and a susceptible line. Tests were performed in natural infection conditions in two locations (France and Sicily). Stable behaviour of the parental and haplodiploid lines was observed in both locations, confirming the high level and stability of this resistance source in Mediterranean countries. Heritability of resistance was high and genetic analysis suggested that it is under oligogenic control. However, the number of genetic factors involved in resistance depended on infection conditions: two or three genetic factors with additive and partial dominance effects appear sufficient to confer resistance at the beginning of the epidemic or in weak infection conditions. However, additional genes are necessary to slow down further disease progress and secondary infections and at least five genetic factors are necessary to confer resistance in severe infection. In this case, both additive and epistatic effects are significant. The transfer of this resistance into cultivars will require the use of artificial inoculation procedures to control the severity of the test.

First Report of Powdery Mildew on Kenaf Caused byLeveillula tauricain the Lower Rio Grande Valley of Texas

First Report of Powdery Mildew on Kenaf Caused by<i>Leveillula taurica</i>in the Lower Rio Grande Valley of Texas

Causal Agents of Powdery Mildew of Cucurbits in Sudan

In a survey of cucurbit crops in Sudan, 234 samples of melon, cucumber, and squash showing symptoms of powdery mildew were infected with Sphaerotheca fuliginea, while Erysiphe cichoracearum was only observed on two samples of watermelon showing mild symptoms. Leveillula taurica was not observed on any sample. Field trials with differential lines of melon revealed the presence of race 1 of S. fuliginea in Gezira (Central Sudan) in the summer of 1993, and race 2 in the following winter. Virulence tests in controlled conditions on a limited number of isolates suggest that a shift in prevalence of those races may have occurred on that site over time. The geographic scale of this shift was probably limited as race 0 was observed in late autumn in northeast Sudan in the Gash Delta

Powdery Mildew of Eustoma Caused by Leveillula taurica in California

Powdery Mildew of Eustoma Caused by Leveillula taurica in California

Species spectrum, host range and distribution of powdery mildews on Cucurbitaceae in Crete

Examination of mycelial and conidial features of 436 samples of cucurbit powdery mildews in Crete during 1991‐92 revealed the presence of three species: Erysiphe sp., Sphaerotheca fusca and Leveillula taurica. S. fusca predominated both in the field and in the greenhouse. Characteristics of the three pathogens are compared.

Chromosomal localization and molecular-marker tagging of the powdery mildew resistance gene (Lv) in tomato

We report the tagging of a powdery mildew [Leveillula taurica (Lév.) Arnaud.] resistance gene (Lv) in tomato using RAPD and RFLP markers. DNA from a resistant (cv Laurica) and a susceptible cultivar were screened with 300 random primers that were used to amplify DNA of resistant and susceptible plants. Four primers yielded fragments that were unique to the resistant line and linked to the resistance gene in an F2 population. One of these amplified fragments, OP248, with a molecular weight of 0.7 kb, was subsequently mapped to chromosome 12, 1 cM away from CT134. Using RFLP markers located on chromosome 12, it was shown that approximately one half of chromosome 12 (about 42 cM), in the resistant variety is comprised of foreign DNA, presumably introgressed with the resistance gene from the wild species L. chilense. Further analysis of a backcross population revealed that the Lv gene lies in the 5.5-cM interval between RFLP markers, CT211 and CT219. As a prelude to map-based cloning of the Lv gene, we are currently enriching the density of markers in this region by a combination of RAPD primers and other techniques.

Effect of compost water extracts on grey mould ( Botrytis cinerea)

Water extracts of fermented mature composts prepared from animal sources (cattle manure and chicken-cattle manure) and a plant source (grape mare) were tested in growth chamber experiments for their ability to control leaf grey mould on tomato and pepper plants and grey mould on grape berries. Disease was reduced by 56–100% by extracts after a fermentation that lasted more than 10 days. In some cases, even a shorter fermentation time was sufficient. Addition of nutrients to the fermenting mass did not generally improve disease control. Pasteurization of the extracts nullified their efficacy in part and only in some cases. Two bacterial strains isolated from the extracts controlled grey mould effectively. Dilution of the extracts (25-fold) resulted in retention of their efficacy only when they were prepared from grape mare compost. In an experiment conducted under commercial greenhouse conditions, extract of cattle manure compost reduced tomato leaf grey mould significantly ( p < 0.05) compared with the water control, but superior disease suppression was achieved with the fungicide vinclozolin. In another experiment, involving a heavy natural powdery mildew ( Leveillula taurica) infestation on tomato leaves, partial control of the disease was obtained by all extracts tested.

Fungicidas evaluados para combatir el añublo polvoriento en pimiento

Se evaluó bajo condiciones de campo la eficacia de los fungicidas benomyl, hidróxido de cobre, dinocap, azufre y triadimefon para combatir el añublo polvoriento del pimiento (Leveillula taurica). Los resultados obtenidos demuestran que las aplicaciones semanales de los fungicidas benomyl y triadimefon reprimieron el patógeno, aminoraron la severidad de infección y aumentaron significativamente el rendimiento. En la primera prueba se obtuvieron rendimientos de 20.2 y 17.2 kg./parcela con aplicaciones de triadimefon (0.35 L./ha.) y benomyl (0.55 kg./ha.), respectivamente, mientras que en las parcelas sin tratar el rendimiento obtenido fue de 13.9 kg. En la segunda prueba, aun cuando los resultados fueron similares a los anteriores, se obtuvieron mejores rendimientos. Se obtuvieron rendimientos de 41.0 y 41.3 kg. en parcelas tratadas con triadimefon (0.70 L./ha.) y benomyl (0.55 kg./ha.); en las parcelas sin tratar se obtuvo un rendimiento de 29.0 kg./ha.

Developpement de Leveillula taurica en Fonction des Facteurs Climatiques et Sensibilité de Capsicum annuumà Differents Stades Végétatifs

AbstractInfluence of environmental factors on the development of L. taurica on pepper genotypes To our knowledge, the effects of certain environmental factors, as well as those of host genotype on the development of Leveillula taurica on pepper have not been extensively investigated. To study effects of the above factors on the development of this parasite, two Capsicum genotypes (‘Yolo Wonder' and ‘line 815’) have been tested and compared under different light and relative humidity conditions. In vitro, optimal light intensity for spore germination was situated between 20 and 80 μE/m2/s, and for the growth of germ tubes it was 20 μE/m2/s. In vivo, under continous darkness during 20 days, the different organs of the hosts were only slightly affected. Under light conditions, during 20 days after inoculation, the highest infection level on leaves was observed at 20 μE/m2/s, (60 % of leaves) while with the cotyledons it was observed between 20–80 μE/m2/s.Effects of relative humidity on the development of this parasite were also studied on ‘Yolo Wonder’ and ‘line 815′. With relative humidity below 50 %, 60 % of ‘Yolo Wonder’ plants and 33 % of ‘line 815’ were infected. Under conditions of saturated relative humidity, the level of infection was the inverse, i. e. 13 and 55 %, respectively.Moreover, ‘Yolo Wonder’ plants were found more or less susceptible to infection with L. taurica during their different development stages. At the cotyledon stage all plants were infected. After this stage, up to flowering, susceptibility depended on the physiological age of the leaves. First leaves (older leaves) were not infected, while young ones near the apex became progressively susceptible.

Powdery Mildew of Greenhouse Cucumbers and Tomatoes Caused by Leveillula taurica in Idaho

Powdery Mildew of Greenhouse Cucumbers and Tomatoes Caused by Leveillula taurica in Idaho

First Report of Powdery Mildew (Oidiopsis taurica) of Gazania

First Report of Powdery Mildew (Oidiopsis taurica) of Gazania

Additional first records of perfect stages of some powdery mildew fungi in South Africa, including a new species

Teleomorphs of Erysiphe aquilegiae. Leveillula taurica and Phyllactinia guttata are recorded and described from South Africa for the first time. Descriptions of the anamorphs of the first two fungi have been added. Phyllactinia cassiae is a new species collected and described from the Transvaal.

Source of Inoculum, Yield, and Quality of Tomato as Affected by Leveillula taurica

Source of Inoculum, Yield, and Quality of Tomato as Affected by Leveillula taurica

Host Range, Specificity, and Biometrical Measurements of Leveillula taurica in California

Host Range, Specificity, and Biometrical Measurements of Leveillula taurica in California

Germinability of Leveillula taurica (powdery mildew) conidia obtained from water-stressed pepper plants

Both host plant water stress during sporulation and low relative humidity during germination caused decreased germination and germ tube elongation of Leveillula taurica (Lev.) Am. conidia on glass. This may explain the low incidence of powdery mildew disease of pepper plants (Capsicum annuum L.) caused by L. taurica during the harmattan (dry) season in Ghana.

Manifestation et Mode de Conservation de Leveillula taurica, Agent de l'Oïdium de la Tomate au Maroc

Abstract Manifestation and conservation of Leveillula taurica on tomatoes in Morocco Powdery mildew of tomato, caused by Leveillula taurica, was considered a minor disease until 1978 when serious outbreaks occurred. These outbreaks coincided with periods of a draught and the introduction of new hybrids from Europe.The pathogen infects a variety of plants, including eleven cultivated and five wild species. Infections of tomato plants were obtained by isolates collected from cultivated plants (Cynara cardunculus, Cicerarietinum, Medicago sativa, Capsicum annuum, Tropaeolum majus) and wild species (Chenopodium ambrosioides, Sonchus asper, Oxalis cemua, Urtica urens).

Water Stress‐Induced Changes in the Morphology of the Powdery Mildew, Leveillula taurica (Lèv.) Arn.

AbstractWater stress in Capsiucm annuum L., induced by means of polyethylene glycol influenced the length and branching frequency of conidiophores and conidial dimensions of the powdery mildew, Leveillula taurica (Lèv.) Arn. Conidiophore branching frequency and length as well as conidial length and width decreased with decreasing relative water content. The availability of water to host plants seems to have a direct effect on the growth vigour and development of the powdery mildew possibly is suggested that water stress may be imposed on host plants by the dry harmattan season resulting in reduced growth vigour of the powdery mildew. Morphology of powdery mildew developing under low water potential may be altered.

Powdery Mildew (Leveillula taurica) on Native and Cultivated Plants in Arizona

Powdery Mildew (<i>Leveillula taurica</i>) on Native and Cultivated Plants in Arizona