The goal of this investigation was to evaluate the in vitro and in vivo efficiency of Raphanus raphanistrum extracts against Fusarium and Pythiaceae species associated with apple and peach seedling decline in Tunisian nurseries. A chemical composition of organic extracts was accomplished using liquid chromatography, thin layer chromatography, and gas chromatography analysis. The in vitro test of three aqueous extract doses of R. raphanistrum against some apple and peach decline agents showed its efficacy in reducing mycelia growth. The in vivo assay of fine powder of this plant on peach seedlings revealed that treatment 8-weeks before the inoculation and planting was more efficient than the treatment before one week. This experiment revealed that the root weight of peach seedlings inoculated by F. oxysporum was improved to 207.29%. For apple seedlings, the treatment 8 weeks before the inoculation and plantation was more efficient than the treatment one week before; it reduced the root browning index. The study of R. raphanistrum chemical composition and its efficiency showed that the glucosinolates products: nitrile (4-Hydroxy-3-(4-methylphenylthio) butane nitrile, benzene acetonitrile, 4-fluoro,butane nitrile, 4-hydroxy-3-[(4-methylphenyl) thio] nitrile), and thiocyanate molecules (thiocyanic acid, ethyle) are responsible for the anti-fungal activities.

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 µgl. 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.

Apple decline, which is responsible for seedlings root and collar rot in the nurseries, is a serious disease that causes reduction in apple plant production. The aim of this study was to evaluate the regional and seasonal distribution of the fungi and Oomycetes, which were associated with the apple decline disease in the Tunisian nurseries. In this study, surveys were conducted from autumn, 2015 to summer, 2016. Apple plants were sampled to detect and quantify the inoculum density of these pathogens. Based on the morphological characteristics; two Fusarium and two Pythiaceae spp. were obtained. The most dominant species were F. oxysporum (33.9 %); Pythium ultimum (33.05 %), F. solani (16.95 %), and Phytopythium mercuriale (16.1 %). Results of the seasonal variation showed that Fusarium spp. and Pythiaceae populations had peaked in June. The populations of F. oxysporum and F. solani were significantly and positively correlated to temperature. In relation to the soil physicochemical characteristics; the Pearson correlation showed that the population of P. ultimum was positively related to the nitrogen (N) content (r = 0.59); sand (r= 0.82), organic matter (r = 0.85), and organic carbon (r = 0.84). However, this species was negatively correlated with the silt content (r = -0.79); clay (r = -0.84), and electrical conductivity (r = -0.74). The Phytopythium mercuriale population was positively correlated with nitrogen content (r = 0.64), and negatively correlated with soil pH (r = -0.62); clay content (r = -0.47), and silt (r = -0.54).