In vitro and in vivo effects of some chemical fungicides against Pythium ultimum and Phytophthora citrophthora associated with peach seedlings decline

Peach decline, responsible for seedlings root and collar rot in nurseries, is an important disease that causes reduction in plant production. Several oomycetes species were associated with this disease. The aim of this study was to control this serious peach decline disease using several assays such as; in vitro poisoned food technique and in vivo greenhouse assay. About six chemical fungicides were evaluated for their in vitro and in vivo inhibitory potentials against Pythium ultimum and Phytophthora citrophthora associated with this disease, respectively. The in vitro poisoned food technique demonstrated highly significant difference in the efficacy of the fungicides used at the five tested doses (10, 25, 50, 100 μg\ l and application rate). Carbendazim inhibited Pythium ultimum and P. citrophthora by 75.30 % and 100 % at 250 μg\ l. For Mancozeb, the inhibition % achieved by the registered dose was 100 % for Pythium ultimum and 50 % for P. citrophthora at 2000 μg\l. The registered dose (2000 μg\ l) of Fosetyl-Al inhibited Pythium ultimum and P. citrophthora by 51 % and 100 %, respectively. The highest rates of inhibition induced by Hymexazol were recorded at 60 μg\ l (90.55 % for Pythium ultimum and 94.49 % for P. citrophthora). In case of Chinosol, inhibition percentages of 90.30 % and 90.96 % for P. citrophthora and Pythium ultimum; respectively, were achieved at the tested concentration of 50 μg\ l, and the same inhibition values were also recorded for both tested concentrations of 100 and 2000 μg\ l. The highest inhibition rates for Metalaxyl-M against Pythium ultimum were observed at the dose of 100 μg\ l (79.70 %), whereas the used dose of 120 μg\ l recorded 86.59 %. The in vivo greenhouse assays demonstrated the efficacy of the Fosetyl-Al and Metalaxyl-M in reducing the peach seedling root browning induced by Pythium ultimum by 62.55 %. However, all the tested chemicals neither improved the growth and health status of the peach seedlings, nor reduced root browning of the seedlings inoculated with P. citrophthora.