This study focuses on the evaluation of some chemical food preservatives to control gray mold disease in strawberry fruits. Six compounds, i.e. acetic acid, sodium benzoate, benzoic acid, sodium citrate, citric acid and potassium citrate were tested at concentrations 10, 20, 40 and 80 mM for inhibiting mycelial growth of the pathogen. In vitro studies, data obtained showed that all treatments significantly (P ≤ 0.05) inhibited the mycelial growth of the pathogen. Sodium benzoate especially at concentration of 80 mM caused complete mycelial growth inhibition of the pathogen. Under laboratory conditions, dipping the strawberry fruits in solutions of these compounds were effective in reducing the disease severity. Also, applications of these compounds as fruits spraying gave a significant reduction of the disease. Sodium benzoate had a better effect on the disease in vitro and in vivo. Laboratory estimates showed that treated fruits with the tested compounds contained a high percentage of total soluble solids (TSS) compared to untreated fruits and healthy control. Also, titratable acidity (TA) increased in treated fruits compared to the healthy fruits; as a result, TSS/TA ratio was increased. Furthermore, treated fruits contained a high level of total phenol contents (TPC) compared to untreated fruits. All studied treatments improved the quality attributes of strawberry fruits, i.e. T.S.S, TA%, TSS/TA ratio and TPC. It is concluded that these compounds were effective on the disease, so they can be used as safe alternatives to fungicides in treating fruits to protect them from the fungal decay during storing or marketing.
The impact of six local isolates of Penicillium frequentans recovered from healthy sugar beet (Beta vulgaris L.) leaves was evaluated against Cercospora beticola, the causal pathogen of Cercospora sugar beet leaf spot under laboratory and field conditions. In in vitro studies, all the six isolates were able to inhibit the mycelial growth of C. beticola with variation in their antagonistic capability. P. frequentans isolates produce pectinase and cellulase at different degrees. There was a correlation between enzyme activity and the antagonistic ability for each isolate. The high antagonistic ability isolates had the most enzyme activity. In field studies, some adhesives such as agar, starch flour, white glue, gum, and commercial adhesive (Triton Mok) were added to conidia spore suspensions of P. frequentans at 1% to improve conidial adhesion to sugar beet plant surface. Data also showed that all adhesives increased (P = 0.05) the efficiency of the spore suspension of P. frequentans to control the disease. The starch flour at 1% gave a significant reduction in disease severity from 43.23 to 10.42% pre-infection and from 43.23 to 10.52% post-infection. The application of P. frequentans led to improved root yield and the sugar percent of sugar beet crop in two tested seasons.
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