Protecting Avocado Seedlings from Grafting Failure During Propagation in Nursery Using Biological and Chemical Control

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 forA. 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.