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Our investigation aimed to evaluate the efficacy of applying Boric, Ascorbic and Oxalic acids as foliar treatments on two strawberry cultivars, i.e., Fortuna and Sensation, during field growth, on controlling gray mold in post-harvest stage. In vitro experiment revealed that all the tested acids were found to have direct fungicidal effect on B. cinerea growth. Oxalic acid was the most effective causing total inhibition to the fungal growth. The disease severity on strawberry fruits stored at 0±1°C for 21 days was significantly reduced in all treatments of acids on both tested cultivars. However, Boric acid (40 mM) was, in general, the most effective treatment in reducing disease severity followed by Ascorbic acid (40 mM), especially for artificially inoculated strawberry fruits, while Oxalic acid and Ascorbic acid were the least efficient in reducing disease severity at the lower concentration. The effect of different acid treatments on the activity of oxidative enzymes revealed a correlation between the reduction in disease severity and increase in enzymes activity of polyphenoloxidase (PPO) and peroxidase (POX). However, there was no consistency in the activity of catalase (CAT) in correlation with disease severity. The total phenols concentrations in fruits were significantly increased with all treatments. The free radical scavenging activity analysis in fruits showed a high correlation between the total phenols concentrations and antioxidants scavenging activities in both tested cultivars. The overall conclusion is that the acids under investigation induced a resistance against B. cinerea in fruits during storage and significantly suppressed gray mold severity.

Pepper fruits are subjected to various postharvest diseases such as black mold caused by Alternaria alternata. The efficacy of exogenous applications of salicylic acid (SA) in bulk and nanoscale forms to control the black mold was studied. In vitro studies revealed that both SA bulk materials and SA nanoparticles (SANPs) at 1.4 mM significantly suppressed the growth of A. alternata, yet SANPs showed a higher suppressive effect compared to SA bulk equivalent. Examinations using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed hyphal and conidial deformations in addition to changes in cellular structure of A. alternata when treated with both forms of SA at 1.4 mM concentration. The preharvest spraying of SANPs at 1.4 mM displayed the highest significant suppression of disease severity under artificial inoculation and natural infection of pepper fruits. The efficiency of SA bulk materials and SANPs as elicitors to stimulate the innate immune responses in pepper plants were also investigated. The basic PR-1 gene (CaBPR1), beta-1, 3-glucanase (CaBGLU) and peroxidase (CaPO1) defense-related genes showed upregulation expression in leaves of pepper plants treated by both forms of SA. The expression of the three studied genes was affected by SA concentrations. Levels of expression of PR-1, β-1, 3-glucanase and peroxidase genes were the highest (8.8, 8.1 and 7.2 fold change, respectively) in pepper tissues treated with SANPs at 1.4 mM. This study contributes to our understanding of the potential use of SA nanoparticles as a safe strategy to inhibit the fungal infection.

The authors tested the efficacy of two salt nanoparticles (NPs), namely, copper dioxide (CuO) and tri‐calcium phosphate [Ca(3) (PO(4))(2)] to induce resistance in green bean pods against grey mould and white rot diseases caused by Botrytis cinerea and Sclerotinia sclerotiorum, respectively. High amounts of phytoalexins, kievitone, coumestrol, phaseollidin, 6‐ά‐hydroxyphaseollin, and phaseollin, were detected in naturally infected and artificially inoculated green bean pods in response to the tested NPs. Green bean plants treated in the field with CuO and Ca(3) (PO(4))(2) NPs had the highest mRNA quantity of all the studied defence genes, receptor‐like kinase (PvRK20), pathogenesis‐related protein (PR1), 1,3‐β‐D‐glucanase (pvgluc), polygalacturonase inhibitor protein (PvGIP), and alpha‐dioxygenase (a‐DOX) than that of the control group. CuO NPs followed by Ca(3) (PO(4))(2) NPs at 0.15 mg ml(−1) were the most potent in increasing the transcriptomic levels of pk20, DOX, PR1, PvGIP, and pvgluc. Field applications of both chemical elicitor NPs exhibited a non‐genotoxic effect on the Paulista green bean DNA using eight ISSR primers. The field application of the studied NPs could effectively extend the shelf life of green bean pods by up to 21 days at 7 ± 1°C during marketing and export due to its potent effect against grey mould and white rot diseases.

Pepper is planting widely in plastic houses and the fields; Botrytis cinerea infection starts in the field, but is strongly appear during storage. Results revealed that spraying pepper plants under plastic houses condition with salicylic, citric acids and clove or olive oils at different concentration (Salicylic acid at 8 mM and citric acid at 30 Mm, meanwhile clove and olive oils at rate 5 m/l) reduced development of grey mold on fruits during cold storage. The mycelial growth of B. cinerea was the most sensitive to salicylic acid, where it completely inhibited the growth of tested fungus at concentrations 4 and 8 Mm. Clove and olive oils at their tested concentrations (2.5 and 5 m/l) reduced the growth of Botrytis cinerea to 100%. All tested plant oils and citric acid increased the epidermis and cuticle thickness and decreasing simultaneously the disease infection incited by Botrytis cinerea on pepper fruits. Spraying pepper plants with all tested treatments increased peroxidase and polyphenoloxidase activities at 2 and 5 days from storage in naturally infected pepper fruits and at 5 days from storage in infected fruits with B. cinerea. The total phenolic compounds (TPC) and antioxidant activity (2,2-Diphenyl-1-picrylhydrazyl DPPH) were determined. Natural infection treated by clove 2.5 m/l had the highest content of TPC. The high antioxidant activities of clove treated pepper fruits were attributed to its high contents of total phenolic compounds.