First Confirmation of Sphaerotheca macularis on Strawberry Plants in Southwestern Spain

Rapid immunochemical methods for the analysis of proquinazid in strawberry QuEChERS extracts

Proquinazid is a new-generation fungicide authorized in the EU for combating powdery mildew infections in high-value crops. Due to the perishable nature of fruits, alternative analytical methods are necessary to protect consumer's health from pesticide residues. Currently, immunoassays are a well-established approach for rapidly monitoring chemical contaminants. However, the production of high-quality immunoreagents, such as antibodies and bioconjugates, is essential. This study presents a newly designed hapten that maintains the characteristic moieties of proquinazid unmodified. The linear aliphatic substituents of this molecule were used to introduce the spacer arm. A three-step synthesis strategy was optimized to prepare a hapten that displays the entire 6-iodoquinazolin-4(3H)-one moiety with excellent yields. The N-hydroxysuccimidyl ester of the hapten was activated and purified to prepare a protein conjugate with high hapten density, which was used as an immunogen. Antibodies were raised and competitive enzyme-linked immunosorbent assays were developed. To enhance the assay's sensitivity, two additional heterologous haptens were prepared by modifying the halogenated substituent at C-6. The optimized assays demonstrated low limits of detection in buffer, approximately 0.05 μg/L. When applied to the analysis of proquinazid in QuEChERS extracts of strawberry samples, the immunoassays produced precise and accurate results, particularly in the 10-1000 μg/kg range.

Real-Time Collection of Conidia Released from Living Single Colonies of Podosphaera aphanis on Strawberry Leaves under Natural Conditions with Electrostatic Techniques

Powdery mildew fungi produce progeny conidia on conidiophores, and promote the spread of powdery mildew diseases by dispersal of the conidia from conidiophores in the natural environment. To gain insights and devise strategies for preventing the spread of powdery mildew infection, it is important to clarify the ecological mechanism of conidial dispersal from conidiophores. In this study, all of the progeny conidia released from single colonies of strawberry powdery mildew fungus (Podosphaera aphanis (Wallroth) U. Braun and S. Takamatsu var. aphanis KSP-7N) on true leaves of living strawberry plants (Fragaria × ananassa Duchesne ex Rozier cv. Sagahonoka) were consecutively collected over the lifetime of the colony with an electrostatic rotational spore collector (insulator drum) under greenhouse conditions, and counted under a high-fidelity digital microscope. The insulator drum consisted of a round plastic container, copper film, thin and transparent collector film, electrostatic voltage generator, and timer mechanism. When negative charge was supplied from the voltage generator to the copper film, the collector film created an attractive force to trap conidia. The electrostatically activated collector film successfully attracted progeny conidia released from the colony. Experiment was carried out at just one colony on one leaf for each month (in February, May, July, October, November, and December in 2021), respectively. Each collector film was exchanged for a new collector film at 24 h intervals until KSP-7N ceased to release progeny conidia from single colonies. Collection experiments were carried out to estimate the total number of conidia released from a single KSP-7N colony over a 35-45-day period after inoculation. During the fungal lifetime, KSP-7N released an average of 6.7 × 10⁴ conidia from each of the single colonies at approximately 816 h. In addition, conidial release from KSP-7N colonies was largely affected by the light intensity and day length throughout a year; the number of conidia released from single KSP-7N colonies in night-time was clearly smaller than that in daytime, and the time of conidial release from single KSP-7N colonies was shorter by approximately 2 to 4 h in autumn and winter than in spring and summer. The ecological characteristics related to conidial releases from KSP-7N colonies will be helpful information for us to successfully suppress the spread of strawberry powdery mildews onto host plants under greenhouse conditions.

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.