Strawberry Mildew Research Articles

A Biostimulant Preparation of Brown Seaweed Ascophyllum nodosum Suppresses Powdery Mildew of Strawberry.

Strawberry, an important fruit crop, is susceptible to a large number of pathogens that reduce fruit quality and productivity. In this study, the effect of a biostimulant prepared from Ascophyllum nodosum extract (ANE) (0.1%, 0.2%, and 0.3%) was evaluated on powdery mildew progression under greenhouse and field conditions. In the greenhouse, application of 0.2% ANE showed maximum reduction in powdery mildew progression as compared to the control. Forty-eight hour post-inoculation, foliar spray of 0.2% ANE reduced spore germination by 75%. Strawberry leaves sprayed with ANE showed higher total phenolic and flavonoid content in response to powdery mildew infection. Furthermore, application of ANE elicited defense response in strawberry plants by induction of defense-related enzymes, such as phenylalanine ammonia lyase, polyphenol oxidase, and peroxidase activity. In field conditions, foliar spray of 0.2% ANE showed a reduction of 37.2% of natural incidence of powdery mildew infection as compared to the control. ANE sprayed plant also reduces the severity of powdery mildew infection under natural conditions. These results indicate that application of ANE induces the strawberry plant’s active defense against powdery mildew infection by induction of secondary metabolism and regulating the activities of defense-related enzymes.

High productivity of soilless strawberry cultivation under rain shelters

Abstract The effect of rain shelters on the performance of the day-neutral strawberry (Fragaria × ananassa) Monterey cultivar was studied in northern Quebec in trials extending over 2 years. The main objective of the study was to evaluate the benefits of growing strawberry crops under plastic rain shelters in terms of yield, fruit quality, disease incidence and economical returns for soilless strawberry production. Five treatments were carried out and these included four − under rain shelters cultivation (T1 to T4) and one under open-air conditions (the Control, C). Under rain shelters conditions, plants were grown in either peat (PE; T1 treatment) or peat-sawdust (PS25; T2 treatment) substrates. Early forcing of bare-root plants (T3) in combination with a rain shelter cover was also carried out in an attempt to generate consistent early yields by the end of July as such would allow producers to capture a niche market for strawberries in Quebec. Finally in T4, the PE substrate was laid onto a capillary mat to determine the potential of sub-surface water retention technology to minimize water use. In comparison to the Control treatment, protected cultivation led to a significantly lower incidence of strawberry mildew [Sphaerotheca macularis (Wall. ex Fries)] and consistently higher marketable yields which largely compensated for the initial costs associated with the rain shelters. When grown under greenhouse conditions, forced plants had a significant production peak earlier, coinciding with the period of high prices for fresh strawberries in 2013. However, the economical analysis revealed that this method was not always profitable. Balancing economical and environmental considerations, the conditions of the T4 treatment were found to be best for generating both consistent water savings and profits (CAD $ 724–1356 per 0.1 ha) compared to the Control. Taken together, our results highlight the potential for rain shelters for soilless strawberry production, and should be a more profitable and environmentally friendly cultivation method for strawberry producers.

Treatment Effect of High Concentration Carbon Dioxide on Powdery Mildew of Strawberry

Treatment Effect of High Concentration Carbon Dioxide on Powdery Mildew of Strawberry

Lagged Association Between Powdery Mildew Leaf Severity, Airborne Inoculum, Weather, and Crop Losses in Strawberry

Knowledge about epidemiology and the impact of disease on yield is fundamental for establishing effective management strategies. The purpose of this study was to investigate the relationship between foliar strawberry mildew severity, Podosphaera aphanis airborne inoculum concentration, weather, and subsequent crop losses for day-neutral strawberry. The experiment was conducted at three, five, and four sites in 2006, 2007, and 2008, respectively, for a total of 12 epidemics. At each site, data were collected on 25 plants at 2-day intervals from the end of May to early October for a total of 60 to 62 samplings annually. First, seasonal crop losses were statistically described; then, a lagged regression model was developed to describe crop losses from the parameters that were significantly associated with losses. There was a strong positive linear relationship between seasonal crop losses and the area under the leaf disease progress curve (R(2) = 0.90) and daily mean airborne conidia concentration (R(2) = 0.86), and a negative linear relationship between crop losses and time to 5% loss (R(2) = 0.76) and time to 5% leaf area diseased (R(2) = 0.61). Among the 53 monitoring- and weather-based variables analyzed, percent leaf area diseased, log10-transformed airborne inoculum concentration, and weather variables related to temperature were significantly associated with crop losses. However, polynomial distributed lag regression models built with weather variables were not accurate in predicting losses, with the exception of a model based on a combined temperature and humidity variable, which provided accurate prediction of the data used to construct the model but not of independent data. Overall, the model based on log10-transformed airborne inoculum concentration did not provide accurate crop loss predictions. The model built using percent leaf area diseased with a time lag of 8 days (n = 4) and a polynomial degree of 2 provided a good description of the crop-loss data used to construct the model (r = 0.99 and 0.90) and of independent data (r = 0.92). For the 12 epidemics studied, 5% crop loss was reached when an average of 17% leaf area diseased was observed since the beginning of symptom development. These results indicate that information on foliar powdery mildew must be considered when making strawberry powdery mildew management decisions.

Temperature Regulates the Initiation of Chasmothecia in Powdery Mildew of Strawberry

The formation of chasmothecia by the strawberry powdery mildew pathogen (Podosphaera aphanis) is widespread but often sporadic throughout the range of strawberry cultivation. In some production regions, notably in warmer climates, chasmothecia are reportedly rare. We confirmed that the pathogen is heterothallic, and that initiation of chasmothecia is not only dependent upon the presence of isolates of both mating types but also largely suppressed at temperatures >13°C. Compared with incubation at a constant temperature of 25°C, progressively more chasmothecia were initiated when temperatures were decreased to 13°C for progressively longer times. At lower temperatures, production of chasmothecia was associated with a decline in but not total cessation of conidial formation, and pairings of compatible isolates sporulated abundantly at 25°C. We developed mating-type markers specific to P. aphanis and used these to confirm the presence of both mating types in populations that had not yet initiated chasmothecia. The geographic discontinuity of chasmothecia production and the sporadic and seemingly unpredictable appearance of chasmothecia in P. aphanis are possibly due to the combined influence of heterothallism and suppression of chasmothecia formation by high temperatures.

Labor-saving Preservation of Powdery Mildew of Strawberry by Sterilized Seedling Culture

Various preservation methods at low temperature have been reported for several powdery mildew fungi, but the conidia of Podosphaera aphanis causing powdery mildew of strawberry could not be preserved either at low temperature or by freeze-drying and liquid-drying of conidial suspensions or diseased leaf discs. Here, we developed a new technique for a labor-saving preservation of the conidia of the fungus by using the aseptic seedling culture of strawberry. Conidia produced on the seedlings could be preserved at 5°C for six months. Using this method, we could obtain the stable stock cultures of 12 strains collected from various regions in Japan.

イチゴうどんこ病に対する Bacillus subtilis 芽胞水和剤ダクト内投入の防除効果

イチゴうどんこ病に対する Bacillus subtilis 芽胞水和剤ダクト内投入の防除効果

Effects of leaf surface and temperature on monocyclic processes in Podosphaera aphanis, causing powdery mildew of strawberry

Powdery mildew of strawberry, caused by Podosphaera aphanis, is an important constraint to production in tunnels and greenhouses. A better knowledge of the effect of environment on the disease is needed to design efficient management methods. In diseases such as strawberry powdery mildew, the very notion of lesion is difficult to grasp, and progress in disease management has been slow because observations pertaining to the monocyclic processes are difficult and time consuming. Experiments under controlled conditions were conducted to measure the effects of leaf surface (abaxial or adaxial) and air temperature on the different monocyclic processes of the disease. The fraction of germinated spores on the lower (abaxial) leaf surface (0.51–0.84) was 10%-20% larger than on the upper (adaxial) leaf surface. Infection efficiency was 10 times lower on the upper than on the lower leaf surface. Temperature strongly influenced all monocyclic processes considered: spore germination, infection efficiency, latent period, colony size, and colony sporulation. The optimum temperature was 22 °C, and no infection occurred at 32 °C. Implications of the results on disease management are discussed. Key words: monocyclic processes, Podosphaera aphanis, powdery mildew, strawberry, Sphaerotheca macularis f. sp. fragariae, temperature. L’oïdium du fraisier, causé par Podosphaera aphanis, est une importante contrainte pour la production de fraisiers en serre et sous tunnel. Une meilleure connaissance des effets de l’environnement sur cette maladie est nécessaire pour élaborer des méthodes de gestion efficaces. Comme c’est le cas pour de nombreuses maladies telles que l’oïdium du fraisier, où la notion même de lésion est difficile à appréhender, les progrès pour la gestion de cette maladie ont été lents car les observations liées aux processus monocycliques sont difficiles et laborieuses. Des expérimentations en conditions contrôlées ont été conduites pour mesurer les effets de la température de l’air et de la surface de feuille (abaxiale ou adaxiale) sur les différents processus monocycliques de cette maladie. Le taux de germination sur face inférieure (abaxiale) de feuilles (0.51–0.84) était 10 % à 20 % plus grand que sur la face supérieure (adaxiale). L’efficacité d’infection était 10 fois plus faible sur la face supérieure que sur la face inférieure de feuille. La température influençait fortement tous les processus monocycliques considérés : germination des spores, efficacité d’infection, période de latence, taille des colonies, sporulation. La température optimale était de 22 °C, et aucune infection ne s’est développée à 32 °C. Les implications de ces résultats pour la gestion de cette maladie sont discutées. Mots-clés : fraisier, oïdium, Podosphaera aphanis, Sphaerotheca macularis f. sp. fragariae, processus monocyclique, température.

UV-B RADIATION FOR CONTROL OF STRAWBERRY POWDERY MILDEW

Powdery mildew of strawberry (Fragaria × ananassa) caused by Sphaerotheca aphanis var. aphanis is one of the serious airborne diseases in Japan. We have used various methods in an attempt to control this disease. Among these methods, liquid potassium silicate was found to be a very useful liquid fertilizer for suppressing powdery mildew. However, various types of cultivating style are used in strawberry production, and it is difficult to apply the silicate using each cultivating type. Recently, we focused on the use of UV-B radiation as an alternative method of disease control. Many reports have described how UV-B induces plant resistance against many stresses. However, there are no examples of its practical application in horticulture. In the present study, radiation conditions were determined in order to prevent the disease in an experimental booth. The suppressive effect of UV-B radiation against powdery mildew was evaluated in a vinyl house from October to June using three susceptible cultivars: 'Akihime', 'Toyonoka', and 'Sachinoka'. All cultivars were protected from powdery mildew by UV-B radiation. For example, in 'Akihime' control plots, 41% of fruits were diseased, whereas in the UV-B plots, 0% of fruits were diseased. Similar results were obtained for the other cultivars. In a laboratory experiment, RT-PCR analysis revealed that UV-B radiation induced the expression of a disease-resistance gene (the gene encoding the PR-protein). These results indicate that UV-B prevents powdery mildew development by inducing disease resistance in the plants as one of its modes of action.

Hot Water Treatment for Control of Powdery Mildew of Strawberry

Hot Water Treatment for Control of Powdery Mildew of Strawberry

Spore dispersal and disease gradients in strawberry powdery mildew

Spore dispersal and disease gradients were measured in powdery mildew of strawberry (Fragaria x ananassa), caused by Podosphaera aphanis, under two production systems: a glasshouse and a plastic tunnel. All gradients could be well described by exponential and power law models, but the power law model provided a better description, particularly at large distances. Primary gradients were associated with spore dispersal occurring predominantly within 1.20 m. Slope estimates ranged between 0.025 and 0.075 cm−1 and between 0.8 and 1.7 for the exponential and power law models, respectively. Spore dispersal was considerably greater in the tunnel than in the glasshouse, where epidemics did not develop. Disease gradients in the tunnel became shallower as epidemics developed and were associated with decreasing slope estimates over time. The differences between tunnel and glasshouse were assumed to reflect differences in wind speed, which was about 10 times lower in the glasshouse than in the tunnel. Key words: disease gradient, Podosphaera aphanis, powdery mildew, spore dispersal gradient, strawberry, Sphaerotheca macularis f. sp. fragariae. Les gradients de dispersion de spores et de propagation de maladie ont été mesurés chez l’oïdium du fraisier (Fragaria × ananassa), causé par Podosphaera aphanis, dans deux systèmes de production : sous serre en verre et sous tunnel plastique. Tous les gradients ont pu être décrits de manière satisfaisante par les modèles exponentiels et puissance, mais le modèle puissance a permis une meilleure description des gradients notamment aux distances les plus grandes. Les gradients primaires étaient associés à une dispersion des spores effectuée principalement dans un rayon de 1,20 m. Les estimations de la pente du gradient variaient entre 0,025 et 0,075 cm−1 et entre 0,8 et 1,7, pour les modèles exponentiel et puissance, respectivement. La dispersion des spores était beaucoup plus importante en tunnel qu’en serre, où aucune épidémie ne s’est développée. Les gradients de propagation de maladie en tunnel devenaient plus plats, et étaient associés avec des paramètres de pente plus faibles, au fur et à mesure que les épidémies se développaient. Il est supposé que les différences entre tunnel et serre reflétaient les différences de vitesse de vent, celle-ci étant environ 10 fois plus faible en serre qu’en tunnel. Mots-clés : fraisier, gradient de dispersion de spores, gradient de propagation de maladie, oïdium, Podosphaera aphanis, Sphaerotheca macularis f. sp. fragariae.

Suppression of conidial germination and appressorial formation by silicate treatment in powdery mildew of strawberry

The mode of action of soluble silicon against strawberry powdery mildew (Sphaerotheca aphanis var. aphanis) was investigated in four experiments. First, silicon-treated leaves from plants grown with silicate (Si+) and control leaves were excised, inoculated with conidia, and subsequent germination and formation of appressoria in a petri dish was assessed after 24 h. The germination rate was 49.7% on Si+ leaves, and was 67.2% on control leaves (t-test, P < 0.01). Second, we soaked cellulose membranes in various solvents and then placed the membranes on 4% water agar, dusted the membranes with conidia, and examined after 12 h. No difference was apparent between any treatment and the control (distilled water). Third, strawberries growing hydroponically with additional silicon in the medium were inoculated with conidia, and leaves were observed with a scanning electron microscope 1–2 days after inoculation. Germ tubes and secondary hyphae were shorter and had fewer branches on Si+ leaves than on the control. Moreover, penetration appeared to be inhibited. Fourth, the cuticle was separated from leaves from plants grown as in the third experiment, placed on water agar, and dusted with conidia. Germination of conidia, observed with a light microscope, on Si+ leaves was suppressed markedly to 40%–60% of that of the control. These results suggested that soluble silicon induced physiological changes in the cuticle layer after absorption by the plant. In addition, soluble silicate reduced germination of conidia, formation of appressoria, and possibly the penetration of powdery mildew.

Suppressive effect of liquid potassium silicate on powdery mildew of strawberry in soil

A soil drench of soluble silicon (liquid potassium silicate) was tested for the control of powdery mildew of strawberry in soil for 2 years in a vinyl house under growers' conditions on two cultivars: very susceptible Toyonoka and slightly susceptible Sachinoka. Soluble silicon suppressed the disease more effectively as a preventive control than as a control to reduce initial incidence. The suppressive effect against this disease was more effective for Toyonoka than for Sachinoka. The control value of soluble potassium silicate was 85.6% for Toyonoka in the first year and 60.2% in the second year, while for Sachinoka it was 58% in the first year and 40.6% in the second year. Strawberry leaf hardness was measured for the control and silicate-treated leaves. Although silicate-treated leaves seemed to be harder than control leaves, leaf hardness did not vary significantly between controls and silicate-treated leaves in either of the 2 years, and the mode of preventive action of liquid potassium silicate remains unknown. A factor other than a physical action may be involved.

Effect of Climatic Factors on Powdery Mildew Caused by Sphaerotheca macularis f. sp. Fragariae on Strawberry

Powdery mildew of strawberry is caused by the obligate pathogenic fungus Sphaerotheca macularis f. sp. fragariae. The disease affects the leaves, flowers and fruit of this crop. This study examined the effects of different environmental factors on disease cycle components (germination, conidiation and survival) in strawberry to determine which conditions limit the progress of the disease. The optimal environmental conditions for conidial germination and conidial germ tube length ranged between 15 and 25 °C with relative humidity (RH) higher than 75%, but less than 98%. High light intensity reduced germination and hyphal growth. The viability of conidia on infected leaves was examined at temperatures ranging from 15 to 35 °C at 80–85% RH. Conidia survival declined over time, but a certain percentage of conidia remained active after 5 months incubation. The rate of conidial germination was significantly higher on young leaves than on older leaves. This observation was consistent across all four tested cultivars. Conidiation at 70–75% RH was similar to that at 80–85%, but greater than that at ≥95% RH. The shortest time from inoculation to appearance of the first disease symptoms was 4 days, at 20 and 30 °C with RH above 75%. In growth chambers, temperatures of 10 and 30 °C, RH above 95%, radiation of 7000 lux and the use of a more tolerant cultivar were all detrimental to disease development. In general, the environmental conditions required for germination and dispersal of powdery mildew are conducive to disease progress under strawberry production conditions in Israel. Furthermore, viability and survival of the pathogen during and between seasons appears to be dependent on asexual inoculum production.

Control Efficacy of Milk Concentration Against Powdery Mildew of Strawberry

The aim of this study was to determine the effect of milk as one of the environmental friendly materials that substitute chemical fungicides for control powdery mildew (Sphaerotheca aphanis) of strawberries <TEX>$(Fragaria{\times}ananassa\;Duch.)$</TEX>. 'Maehyang' and 'Akihime' varieties planted in greenhouses were evaluated for the control of powdery mildew. Applications of <TEX>$5\%,\;10\%\;and\;20\%$</TEX> milk had much better effects on controlling powdery mildew. In particular, <TEX>$10\%$</TEX> milk showed a higher efficacy than other concentrations applied onto straw­berry in greenhouse experiments. Foliar spray application of <TEX>$10\%$</TEX> milk was effective for powdery mildew, whereas drench application was not. Also, foliar spray of <TEX>$10\%$</TEX> milk was able to accelerate more firmness and calcium contents of strawberry fruits than the non-treated. The <TEX>$10\%$</TEX> milk applied with fertilizer salts <TEX>$(Ca(H_2PO_4)_2-H_2O\;and KH_2PO_4)$</TEX> showed there was a similar efficacy to <TEX>$10\%$</TEX> milk alone in greenhouse experiments. White crystals and cracks on strawberry fruits appeared by <TEX>$20\%$</TEX> milk. This result indicated that <TEX>$10\%$</TEX> milk was a useful substitute for fungicides to control powdery mildew of strawberry.

Suppressive effect of potassium silicate on powdery mildew of strawberry in hydroponics

From 1996 to 1997, potassium silicate (SiO2) was tested at 0, 25, 50, and 100 mg l−1 in hydroponics to control powdery mildew. Other elements were added in the usual amounts, and the strawberries were cultivated hydroponically in a greenhouse for 4 months (from October to January). The powdery mildew spread in the control plot, but little mildew developed in the plot with 25 mg l−1 silicate, and none in plots with more than 50 mg l−1 silicate. The suppressive effect lasted for about 4 months on fruits and even longer on leaves. On analysis of mineral content in the leaves, only the silicate content differed markedly between the control and treated plants. Nitrogen, phosphate, potassium, and calcium contents did not differ greatly. The maximum silicate content was about 24 times that of the control, and disease severity decreased significantly when the content was more than 1.5% in the leaves. The hardness of the strawberry leaves, measured by a creep meter, was increased by the silicate treatment.

Comparison of Epidemics of Botrytis Fruit Rot and Powdery Mildew of Strawberry in Large Plastic Tunnel and Field Production Systems.

Epidemics of Botrytis fruit rot (Botrytis cinerea) and powdery mildew (Sphaerotheca macularis f. sp. fragariae) in annual strawberry were compared in large plastic tunnel and field production systems during the 1998-99 and 1999-2000 seasons. Treatments were factorial combinations of two main plots (field and tunnel) and four subplots, including combinations of two cultivars (Camarosa and Sweet Charlie) and two captan schedules arranged in a split-plot design with three replications. The mean incidence of Botrytis fruit rot was 88 to 94% lower in tunnels than in the field. The incidence of Botrytis fruit rot for the untreated control in tunnels was less than 2%, which was 89% lower than that of the 7-day captan schedule in the field. This indicates that Botrytis fruit rot can be controlled effectively without fungicides in a tunnel cultural system. Powdery mildew was severe on susceptible cultivar Camarosa in tunnels. Early season yields of cultivar Sweet Charlie were significantly higher in tunnels than in the field. Shorter periods of leaf wetness and higher temperatures in tunnels may have contributed to a lower incidence of Botrytis fruit rot and a higher incidence of powdery mildew on fruit in tunnels compared with open field plots.

Regarding how cold storage of plant methods influence on occurrence and growth of strawberry mildew

Regarding how cold storage of plant methods influence on occurrence and growth of strawberry mildew

The effects of glass cloche and coloured polyethylene tunnels on microclimate, growth, yield and disease severity of strawberry plants

SUMMARYMarked differences in the microclimate and the performance of strawberry plants were observed under glass cloches and clear polyethylene tunnels as compared with coloured polyethylene tunnels. Under glass and clear film the average air and soil temperatures were higher and fluctuated more, and the vapour pressure deficit was greater during the day, than under coloured film. The plants under glass and clear film made more vigorous early growth and cropped earlier than those under the other tunnels, but the heaviest yields were picked from plants under red and pink covers. Flowering and fruiting were delayed under green and blue covers by at least one month, and yields were comparatively small owing to poor pollination and fruit set.Both strawberry mildew (Sphaerotheca macularis (Wallr. ex Fr.) Lind.) and Botrytis fruit rot were more severe on plants under the coloured films than under glass or clear film.

Sphaerotheca macularis . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Sphaerotheca macularis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Humulus lupulus and many other plants, e.g. Fragaria vesca , especially in the Rosaceae (Junell, 1967; Blumer, 1967; Dennis, 1960). The fungus usually occurs in the conidial state on leaves and stems, sometimes also on sepals and fruits. DISEASE: Hop and strawberry mildew. Mostly infecting nursery plants. GEOGRAPHICAL DISTRIBUTION: World wide on Fragaria spp. and Humulus spp. TRANSMISSION: New infection in spring (usually May) comes from dormant mycelium in the leaves (41: 161; 45: 1443).