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 antifungal activity of citric acid and its salt (sodium citrate) as chemical food preservatives was evaluated against Cercospora beticola in vitro and in vivo. The inhibitory effect of both compounds was studied against mycelial growth of the pathogen in vitro at concentrations, i.e. 0, 10, 20, 30, 40 and 50 mM. Both of citric acid and sodium citrate were able to inhibit the mycelial growth of the pathogen when they were added to the medium at the tested concentrations. Citric acid at 50 mM had the highest effect on the inhibition growth of the pathogen being 83.70% and also had antifungal activity. The percentage of inhibition growth increased as the tested compounds concentration increased. Data also indicate that microscopic examination of treated plates with citrate shows that this treatment reduced the numbers of C. beticola spores on the medium at all tested concentrations and reached its maximum reducing at concentration 50 mM of citric acid compared to untreated plates. The results revealed that spraying of diseased plants with citric acid and sodium citrate either alone or in combination at concentration 50 mM was effective in decreasing disease severity of Cercospora leaf spot compared to untreated plants. The highest reduction in disease severity was observed in case of citric acid treatment. The results revealed that foliar application of these compounds enhanced significantly root yield and sugar percentage as compared to the control.
Nineteen isolates of Helminthosporium sesami were obtained from infected sesame plants with Helminthosporium leaf spot taken from different locations in Nubaria region, El-Behera Governorate, Egypt. All the obtained isolates of the pathogen were able to infect Del Al-Jamal sesame variety plants causing Helminthosporium leaf spot disease symptoms with different degrees. The objectives of this study were to evaluate the efficiency of some zinc and phosphorus sources against the pathogen and their effect on some agronomic characters of sesame. In vitro studies, the effects of zinc oxide (ZnO), zinc sulfate (ZnSO 4 ) as sources of zinc and dipotassium phosphate (K 2 HPO 4 ) and disodium phosphate (Na 2 HPO 4 ) as sources of phosphorus on the pathogen have been studied by using different concentrations on potato dextrose agar medium (PDA). These results suggest that these compounds reduced the mycelial growth of the pathogen. The highest reduction of mycelial growth was obtained when ZnSO 4 at concentration 100 mM (78.57%), followed by ZnO. Under field experiments, foliar spraying of sesame plants with ZnO, ZnSO 4 , K 2 HPO 4 and Na 2 HPO 4 at the rate of 100 mM reduced disease severity compared to the control treatment. ZnO gave the highest reduction in disease severity followed by ZnSO 4 . These compounds improved agronomic characters of sesame, i.e. plant height, number of branches and capsules/plant, weight of 1000 seeds (g), seed yield/feddan and percentage of oil seeds. K 2 HPO 4 treatment was the most effective on all studied agronomic characters than other compounds.
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