Blue rot disease caused by Penicillium expansum is one of the most widespread fungal diseases that affects apples worldwide. This work was to verify the effect of chitosan (2 and 4 g/L) and its nano-form (0.2 and 0.4 g/L) against blue rot disease on apples and their effect on the expression of six defense-related genes as well as fruit quality parameters. Regarding disease incidence, in most cases, chitosan NPs performed better as compared to their raw materials for both artificial and natural infections. The highest efficacy was obtained for chitosan NPs at 0.4 g/L for artificial and natural infection in both 2019 and 2020 seasons. All treatments kept fruit quality parameters regarding firmness, total soluble solids, and titratable acidity for artificial and natural infection in both seasons. As expected, the exogenous application of chitosan NPs and bulk form triggered an increase in the expression levels of six defense-related genes including chitinase, peroxidase, β-1,3-glucanase, Xyloglucan endotransglycosylase (XET), pathogenesis-related protein (PR8), and phenylalanine ammonia lyase-1 (PAL1). Moreover, the highest mRNA quantity of all the studied genes was detected in leaves treated with chitosan NPs at both concentrations compared to other treatments. Chitosan NPs can be considered an eco-friendly and effective approach against blue mold of apples and can be integrated into management programs to maintain postharvest quality and extend the shelf life of fruits.

The field application of safe chemical inducers plays a vital role in the stimulation of systematic acquired resistance (SAR) of plants. In this study, the efficacy use of three and six field applications with chitosan, lithovit, and K-thiosulfate at 4 g L⁻¹ and salicylic acid at 1.5 g L⁻¹ in improving tomato productivity, quality, and modifying the defense signaling pathways to the Alternaria alternata infection was investigated. Salicylic acid was the most effective in vitro where it completely inhibited the growth of Alternaria alternata. The highest yield quantity was recorded with six applications with Chitosan followed by Salicylic acid; also, they were the most effective treatments in controlling the Alternaria alternata infection in tomato fruits. The maximum increase in chitinase and catalase activity of tomato fruits was observed at five days after inoculation, following treatment with six sprays of salicylic acid followed by chitosan. The transcript levels of seven defense-related genes: ethylene-responsive transcription factor 3 (RAP), xyloglucan endotransglucosylase 2 (XET-2), catalytic hydrolase -2 (ACS-2), proteinase inhibitor II (PINII), phenylalanine ammonia-lyase 5 (PAL5), lipoxygenase D (LOXD), and pathogenesis-related protein 1 (PR1) were upregulated in response to all treatments. The highest expression levels of the seven studied genes were recorded in response to six foliar applications with chitosan. Chitosan followed by salicylic acid was the most effective among the tested elicitors in controlling the black mold rot in tomato fruits. In conclusion, pre-harvest chitosan and salicylic acid in vivo application with six sprays could be recommended as effective safe alternatives to fungicides against black mold disease in tomato fruits.

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.