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.

Disease incidence and disease severity of avocado fruit rot were assessed on cv. Hass and cv. Fuerte during 2019 and 2020 growing seasons. The highest percentages of disease incidence and disease severity were recorded in cv. fuerte in the market at El-Qanater El-Khayria, Qaliobia Governorate. On the other hand, the lowest percentages of disease incidence and disease severity were recorded in cv. Hass in the field at El-Rahawy, Giza Governorate during the two growing seasons. Four different fungi, i.e., Colletotrichum gloeosporioides, Lasiodiplodia theobromae, Fusarium moniliforme and Penicillium expansum were isolated from the naturally infected avocado fruits in the surveyed regions. Pathogenicity tests showed that the maximum percentage of disease severity on cv. Hass and cv. Fuerte resulted from infection by L. theobromae, followed by C. gloeosporioides, while the lowest percentage of disease severity was incited by P. expansum. The efficacy of alternative products namely essential oils of Lemongrass (Cymbopogon citratus L.), Rosemary (Rosmarinus officinalis L.) and Thyme (Thymus vulgaris L.) and Serenade ASO (Bacillus subtilis QST713) was evaluated in in vitro and in vivo as well as under field conditions for controlling fruit rot of avocado comparing with Imazalil, Copper oxide and Copper oxide nanoparticles. Complete inhibition of colony growth and protection from fruit rot was recorded with essential oils and Copper oxide at concentration of 3 ml or g/L of each. Meanwhile, the same effect was recorded at concentration of 1 ml/ L in case of Imazalil, Copper oxide nanoparticles and Serenade ASO. However, under field conditions, Copper oxide nanoparticles and Imazalil gave the highest efficacy for controlling avocado fruit rot disease, followed by Serenade ASO, Copper oxide and Thyme, while the lowest efficacy was recorded when trees sprayed with Lemongrass and Rosemary, respectively. The results indicated that avocado fruit rot disease could be controlled using suitable concentration of the tested treatments.

During propagation of avocado by grafting in 2019 and 2020, the maximum % grafting failure (GF) of avocado seedlings was recorded on cv. Hass and cv. Fuerte, followed by cv. Benkerton and cv. Reed. While cv. Etinger was the less susceptible one. Lasiodiplodia theobromae was the most frequently isolated from graft failure seedlings in all avocado cultivars, followed by Fusarium moniliforme. While Alternaria alternata recorded the lowest frequency. The highest percentage of grafting failure and death of scions was obtained by the fungus L. theobromae, followed by F. moniliforme and the lowest percentage of grafting failure was observed for A. alternata in all avocado cultivars. The efficacy of biological and chemical control was tested in vitro and in vivo as well as under nursery conditions for controlling GF on avocado seedlings. Amistar Top and Bellis gave the highest reduction in colony growth of the three pathogens, followed by Kocide (2000) and Star copper. While Serenade ASO and Bio Zeid were the lowest ones. Dipping scions in each of the tested suspensions before dipping in spore suspension of each fungus suppressed the spores of the pathogen during grafting and increased the percentage of success of grafted seedlings in the two tested cultivars Hass and Fuerte compared with the control. In this respect, Amistar Top and Bellis were the most effective treatments for controlling the pathogens in the two tested cultivars, followed by Kocide (2000) and Star copper. The lowest efficacy was recorded when scions were dipped on Serenade ASO and Bio Zeid. Also, dipping scions in the suspension of each tested commercial product during grafting increased the percentage of grafting success for all tested cultivars compared with the control. Considering the means of efficacy of the tested treatments on the tested cultivars in the two seasons, Amistar Top, Bellis and Kocide (2000) were the most effective which recorded (91.00 and 94.00%), (85.00 and 87.00%) and (84.00 and 87.00%), respectively (%) success of avocado grafted seedlings on all cultivars in the two years, followed by Serenade ASO (83.00% and 87.00%). While the least (%) success of avocado grafted seedlings on all cultivars in the two seasons was observed on Star copper and Bio Zeid (81.00 and 86.00%) and (81.00 and 84.00%), respectively. Also, the highest effect of all treatments was on cv. Etinger, cv. Reed and cv. Benkerton, while the lowest effect was on cv. Fuerte and cv. Hass in the two seasons. The highest values of production of peroxidase and polyphenoloxidase activities in the two tested avocado cultivars Hass and Fuerte were observed after dipping the scions in Amistar Top and Bellis, followed by Kocide (2000) and Serenade ASO. While the lowest values of peroxidase and polyphenoloxidase activities were recorded after dipping the scions in Star copper and Bio Zeid.