Reduction of Phytophthora cactorum in Strawberry Fields by Trichoderma spp. and Soil Solarization.

Field experiments were conducted in southwest Spain for three consecutive years from 2000 to 2003 to evaluate the effectiveness of solarization and Trichoderma spp., alone and combined, in reducing Phytophthora cactorum soil populations and consequently leather rot on fruit of strawberry plants. Plots (12.5 by 3.3 m), never treated with methyl bromide, were naturally infested by P. cactorum. Solarization was conducted during the summer, using clear 50-µm low-density polyethylene mulch. Trichoderma spp. were applied via drip and dip, adding to the soil 7 days before planting (108 conidia/m2), and strawberry roots were dipped in a suspension of Trichoderma spp. (106 conidia/ml) prior to planting. Solarization reduced the soil P. cactorum population 100% in year 1, 47% in year 2, and 55% in year 3 relative to the untreated control. Trichoderma spp. applications reduced soil populations of P. cactorum and reduced leather rot incidence 76.6% in year 1 and 33.8% in year 2 compared with the untreated control. The combination of solarization and Trichoderma spp. reduced P. cactorum soil population the most each year, 88.9% in January 2001, 97.6% in 2002, and 99.0% in 2003. The very promising effect of Trichoderma spp. and solarization against P. cactorum indicates that there may be future alternatives to traditional chemicals for disease control.

Osmotically induced membrane tension facilitates the triggering of living cell electropermeabilization.

Very little is known about the molecular mechanisms supporting living cell membrane electropermeabilization. This concept is based on the local membrane permeability induced by cell exposure to brief and intense external electric field pulses. During the electric field application, an electro-induced membrane electric potential difference is created that is locally associated with the dielectric properties of the plasma membrane. When the new membrane electric potential difference locally reaches a critical value, a local alteration of the membrane structure is induced and leads to reversible permeabilization. In our study, we attempted to determine whether mechanical tension could modulate the triggering of membrane electropermeabilization. Change in lateral tension of Chinese Hamster Ovary cell membrane has been osmotically induced. Cell electropermeabilization was performed in the minute time range after the osmotic stress, i.e., before the regulatory volume decrease being activated by the cell. Living cell electropermeabilization was analyzed on cell population using flow cytometry. We observed that electropermeabilization triggering was significantly facilitated when the lateral membrane tension was increased. The main conclusion is that the critical value of transmembrane potential needed to trigger membrane electropermeabilization, is smaller when the membrane is under lateral mechanical constraint. This supports the hypothesis that both mechanical and electrical constraints play a key role in transient membrane destabilization.

Relationship Among Concentrations of Sphaerotheca macularis Conidia in the Air, Environmental Conditions, and the Incidence of Powdery Mildew in Strawberry.

Atmospheric concentrations of Sphaerotheca macularis conidia were monitored for 2 years on a strawberry crop in Huelva (southwestern Spain). The presence of airborne conidia was determined to assess the role of weather conditions on conidial release. The relationship between airborne conidia and incidence of powdery mildew on fruit was also studied. Concentrations of conidia were estimated with a Burkard volumetric spore sampler. The presence of conidia was related to temperature, relative humidity, and rainfall, with a positive correlation for the first factor and a negative correlation with the other two. The presence of conidia in the air was positively correlated with disease incidence. A diurnal pattern of conidia release was observed.

Total dose incurred by patients and staff from BMD measurement using a new 2D digital bone densitometer.

Dual energy X-ray absorptiometry (DXA) is a widely used and precise technique for non-invasive assessment of bone mineral density. The DXA systems have evolved from pencil X-ray beam (single detector) to fan beam (linear array detector) and recently cone beam densitometers (bi-dimensional detector), allowing for an examination to occur without any scanning and with a short acquisition time. The purpose of this study was to evaluate patient and staff dose from a new cone beam densitometer, the DMS Lexxos. Measurements were performed on a DMS Lexxos bone densitometer prototype. An anthropomorphic phantom and thermoluminescent dosimeters were used to evaluate the effective dose. Ionization chambers and electronic personal dosimeters were used to evaluate the staff dose. The effective dose is 8.4 micro Sv for an anteroposterior spine examination and 4.8 micro Sv for a femoral neck in standard mode. The averaged scattered dose rate (ambient dose equivalent) at 1 m from the beam is evaluated at 226 micro Sv/h. Assuming six patients per hour with two views per patient, the time averaged dose rate is evaluated at 2.9 micro Sv/h. By the personal dosimeter, the staff dose (Hp 10) at 1 m from the beam is evaluated at 0.23 micro Sv per examination. For one examination, patient and staff dose from this new technology remains low: in the same range as the fan-beam densitometer.

First Report of Leaf Rust of Southern High-Bush Blueberry Caused by Pucciniastrum vaccinii in Southwestern Spain.

Leaf rust was first observed in 1997 on southern high-bush blueberry (Vaccinium corymbosum L.) cvs. Sharpblue, Gulfcoast, and Misty, in two production fields in Huelva Province of Andalucía, in southwestern Spain. Depending on environmental conditions, these cultivars may remain evergreen in this region. In early spring, when the temperature reaches 20°C, typical yellowish-orange pustules first appear on the abaxial side of older leaves and later on new leaves. Leaf lesions began as chlorotic dots and developed into necrotic spots. As much as 85% of the fruits on symptomatic bushes showed pustules on the scar area. Multiple infection cycles were possible during the growing season as urediniospores reinfect leaves at the end of summer. Disease was considered of minor importance, but defoliation occurred when spotting was severe. Urediniospores were yellowish-orange, abovoid to elliptical (15 to 26 × 10 to 20 µm), with a thick, slightly roughened wall and a central pore. Telia formed in the lower epidermis and were smooth and brown. Teliospores (7 to 10 × 12 to 15 µm) were sessile, oblong to columnar, with two or more cross walls. Urediniospore and teliospore dimensions and morphology agree with the description of P. vaccinii, (G. Wint.) (1). A pathogenicity test was carried out with 2-year-old 'Sharpblue' and 'Star' plants. Expanded leaves were sprayed with freshly collected urediniospores suspended in a 0.05% solution of Tween 20 in water; plants were covered with plastic bags for 48 h and held in a chamber at 20 to 25°C in the shade. After 10 days, yellowish-orange pustules, similar to the original symptoms, developed on 80% of inoculated leaves of 'Sharpblue', while 'Star' plants remained symptomless. Leaf rust has not been reported on Ericaceae in Spain. The evergreen state of some southern high-bush cultivars in this area could allow the pathogen to overwinter as urediniospores. To our knowledge, this is the first report of P. vaccinii on blueberry plants in Spain. Reference: (1) P. R. Bristow and A. W. Stretch. Pages 20-22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN, 1995.

First Confirmation of Sphaerotheca macularis on Strawberry Plants in Southwestern Spain.

In February 2001, in seven small tunnel production fields in southwestern Spain, symptoms and signs of powdery mildew were detected on strawberry (Fragaria × ananassa) cvs. Camarosa, Andana, and Carisma. On 'Camarosa' plants, white patches of mycelium developed on the lower leaf surface. Later, the leaf edges rolled upward, and reddish or necrotic irregular spots appeared on the lower leaf surface. Some immature fruits were abnormally hard and covered with a dense white mycelium. Symptoms were much less severe on 'Andana' and 'Carisma'. Microscopic observations revealed conidia in chains, ellipsoidal to barrel-shaped, with fibrosin granules. Mean dimensions of conidia (N= 70) were 31.2 µm ± 2.8 × 20.39 µm ± 4.1. Cleistothecia were not detected. Based on these characteristics, the causal agent was identified as Sphaerotheca macularis (Wallr.:Fr.) Lind. (1). Pathogenicity was confirmed by inoculating leaves of 2-month-old potted 'Camarosa' plants. S. macularis obtained from field-grown plants was maintained on 'Camarosa' strawberry leaves in a growth chamber (20°C and 100% relative humidity). Inoculum was obtained from freshly sporulating infected leaves 11 days after inoculation. Conidia of S. macularis were gently brushed into 100-ml distilled water containing two drops of Tween 20. Ten strawberry 'Camarosa' plants were inoculated by misting with a conidial suspension (104 conidia per ml) (2). The plants were incubated at 100% relative humidity for 48 h in the greenhouse (15 to 25°C). Colonies of powdery mildew were observed on leaves after 18 days. To our knowledge, this is the first confirmation of S. macularis on strawberry in Spain. References: (1) K. G. Mukerji. No. 188 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, UK, 1968. (2) R. Reuveni et al. Crop Prot. 19:335, 2000.

First Report of Phytophthora cactorum on Strawberry Plants in Spain.

Crown rot of strawberry (Fragaria × ananassa Duch. cv. Camarosa) was observed in three and two production fields in 2000 and 2001, respectively, in Huelva, southwestern Andalucia, Spain. Affected plants did not exhibit typical symptoms of red stele. Instead, there was an internal red-brown discoloration of the upper crown, a bluish discoloration of leaves, and the plants were wilted. Eventually, plants collapsed and died. Fungi were isolated from surface-disinfested necrotic crown tissue on P5ARPH medium (1). Plates were placed at 21°C for 5 to 10 days. One species was isolated consistently from symptomatic tissue. Microscopic observations revealed spherical oogonia with thin walls. Antheridia were paragynous and were attached to the oogonium near the oogonial stalk. Single oospores were spherical and had double-layered, yellow-brown walls (20 to 25 µm in diameter). Sporangia were usually borne terminally and were colorless and papillate (22 to 30 µm in diameter). Based on these characteristics, the causal agent was identified as Phytophthora cactorum (Lebert & Cohn) J. Schröt. (2). The fungus was transferred to V8 juice agar and maintained at 21°C in the dark. Disks (9-mm diameter) were removed from 7-day-old cultures of P. cactoru and used to inoculate five 2-month-old 'Camarosa' strawberry plants grown in sterilized peat in the greenhouse. Three disks were placed in the crown of each plant at soil level. Five noninoculated plants were similarly treated with sterile V8 juice agar disks only. After 2 weeks, the pathogen was reisolated from red-brown lesions visible on crowns of all inoculated plants. Noninoculated plants did not show any symptoms. To our knowledge, this is the first report of P. cactorum attacking strawberry plants in Spain. References: (1) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986. (2) G. M. Waterhouse and J. M. Waterston. No. 111 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, UK, 1996.

First Report of Colletotrichum acutatum in Blueberry Plants in Spain.

An anthracnose disease was observed affecting leaves of high-bush blueberry plants (Vaccinium corymbosum L. 'Sharpblue') in small areas within two production fields in Huelva Province of Andalucía, in southwestern Spain. The first symptoms observed in late spring were circular, necrotic lesions, red to salmon in color, and ranging from 3 to 20 mm in diameter. Later, lesions became salmon colored in the center with a brilliant red halo. Fungal isolations were made from the lesions. Infected tissues were surface-disinfected in 1% sodium hypochlorite for 1 min, blotted dry on sterile filter paper, and plated on 2% water agar. The plates were incubated at 25°C for 5 to 10 days. Fungal colonies isolated from the tissues were transferred to potato dextrose yeast agar (PDYA). Only one fungal species was consistently isolated from affected leaf tissues and was identified as Colletotrichum acutatum J.H. Simmonds based on morphological characteristics (2) and enzyme-linked immunosorbent assay (1). Colonies of the fungus on PDYA showed a white-to-gray dense mycelium covered with salmon-colored spore masses. The reverse of the plates was a pink-salmon color. Colony diameter on PDYA averaged 50 mm after 7 days at 25°C. Conidia were hyaline, aseptate, fusiform to cylindrical, and 12.5 × 3.2 µm. Inoculation of leaves and fruits of blueberry cv. Misty with a conidial suspension (106 conidia per ml) of C. acutatum produced lesions on the leaves and fruits similar to those observed on diseased plants in the field. The pathogen was isolated from lesions on inoculated plants. To our knowledge, this is the first report of C. acutatum in high-bush blueberry plants in Spain. References: (1) T. A. Cooke et al. EPPO Bull. 25:57, 1995. (2) B. C. Sutton. The Coelomycetes. CMI, Kew, England, 1980.