Sabrine Mannai

Seedlings root and collar rot is an important disease that causes a reduction in plant production. The goal of this investigation was to evaluate the in vitro and in vivo efficiency of powdered preparation of dried Asphodelus microcephalus of fruits (PPDF), leaves (PPDL), and roots (PPDR) against species of Fusarium and Pythiaceaes associated with this disease in Tunisian nurseries. The in vitro tests of methanolic and aqueous extracts of different Asphodelus organs showed their efficacy in reducing the pathogen mycelium growth. The in vivo assay of powdered preparation of this dried plant revealed that its effect depends on the pathogens, Asphodelus organs, and the period duration between the treatment and inoculation of seedlings. This study showed that this plant has some positive effects, such as disease severity reduction and plant growth stimulation. In fact, for Fusarium solani, the powder of different organs of Asphodelus was used one week before the plantation, and inoculation significantly improved the peach plant’s height. The treatments eight weeks before the inoculation enhanced the root weight of the plants. Meanwhile, the PPDL and PPDR were used eight weeks before the plantation, and inoculation induced the plant disease index. However, the A. microcephalus treatments also have some toxic effects on peach and apple seedlings, such as the improvement of root browning induced by some pathogens.

Background: Citrus black spot (CBS), even recently reported in Tunisia, could be responsible for considerable losses in lemon growing areas. The present study evaluated different Trichoderma species against Phyllosticta citricarpa causative agent of CBS using two assays. Results: The obtained in vitro results exhibited the efficacy of these antagonists to reduce P. citricarpa mycelial growth and the inhibition rate values varied. Trichoderma species showed the highest mycelial growth inhibition with 54.33%, noted for P. citricarpa isolate CBS1 treated with Trichoderma atroviride (A3), and 51.76 and 53.51% for P. citricarpa isolate CBS4 confronted with T. atroviride and Trichoderma asperellum, respectively. The in vivo assay on Citrus lemon fruits confirmed the decrease of the lesions development caused by four P. citricarpa isolates. In fact, the decrease varied from 28.28 to 72.83% for the P. citricarpa CBS3 isolate treated with Trichoderma kunmingense and Trichoderma atroviride, respectively. Conclusions: Based on the current results, the used Trichoderma species reduced P. citricarpa mycelial growth in vitro and the lesions appearance due to P. citricarpa on Citrus limon variety Eureka. The efficacy varied upon on the antagonist species and pathogen isolates. Thus, they showed a promising potential to be used to control CBS.

Citrus black spot, caused by Phyllosticta citricarpa, has been reported in Tunisia since 2020 and has negatively impacted yield and marketability. The environmental conditions required for the growth of P. citricarpa remain poorly understood, limiting further biological and epidemiological studies. In the present study, the effects of different pH levels, culture media, temperatures, and citrus juices on the development of P. citricarpa were evaluated both in vitro and in vivo. The results showed significant differences in mycelial growth based on pH values, culture media, and their interaction. Mycelial growth ranged from 0 cm on OA medium at pH 5 to 7.26 cm on the same medium at pH 9, one month after incubation. Furthermore, P. citricarpa was able to grow within a temperature range of 15°C to 35°C, with optimal colony growth observed at 25°C. Among the citrus juices tested, juice from mature fruits of Citrus aurantium exhibited the strongest inhibitory effect on the mycelial growth of P. citricarpa in vitro and reduced symptom development in vivo assay. These findings enhance our understanding of the optimal conditions for P. citricarpa growth and highlight the potential of C. aurantium juice as a natural inhibitor for managing citrus black spot.

Citrus black spot (CBS), caused by Phyllosticta citricarpa, is an important disease of citrus, an economically important fruit crop worldwide and particularly in Tunisia. CBS was recently detected in Tunisia and this study revealed that it is widespread in the governorates of Nabeul and Sousse. The highest incidence of CBS was found in the Bouargoub region (73.7%), while the lowest was observed in Soliman (25.0%) in the Nabeul governorate. The surveys revealed that CBS affected mainly lemon (Citrus limon). The symptoms of CBS observed were hard spots on fruits, twigs, and leaves, as well as false melanose on fruits. Symptoms were observed in both mature and immature citrus fruits, but disease incidence was higher in mature (97.0%) than that in immature fruits (2.95%). In this study, morphological and molecular identifications confirmed the presence of P. citricarpa. This is the first time that the extent of CBS has been documented in a Mediterranean citrus area.

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).

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.

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.