Browsing by Author "Gadoum, Horiya"
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- Effects of Cryphonectria parasitica infection by CHV1 hypovirus in the pathogenesis‐related OAH activityPublication . Gadoum, Horiya; Gouveia, Maria Eugénia; Jorge, Lurdes; Noui, AbdallahCryphonectria parasitica, the causal agent of chestnut blight, causes necrotic lesions (cankers) on the bark of stems and branches of susceptible host trees leading to wilting of the plant part distal to the infection. Cryphonectria hypovirus 1 (CHV1) infects C. parasitica and reduces the fungus virulence (hypovirulence). The interaction between C. parasitica and CHV1 has been studied intensively at the molecular level. In addition to the reduced virulence the CHV1 infected strains also display other phenotypic symptoms, including reduced pigmentation and sporulation. It has been shown that CHV1 generates these phenotypic changes by interfering with parasitic sign transduction pathways. After infection and mycelium spread, wound periderm formation is continuously inhibited in susceptible chestnut species because the advancing mycelial fans stop the host cells by means of toxins and cell wall‐degrading enzymes. The oxalic acid is one of the metabolites which is associated in this process. It has a toxic effect on host cells and is creted by C. parasitica at the advancing edge of the infection. The objectives of this work were to evaluate the oxalic acid production, in microbiological culture medium of wild type virulent C. parasitica and in hypovirulent isogenic strains. The evaluation of the virulence of C. parasitica, virulent and hypovirulent isolates was performed by inoculation in young branches of C. sativa. This method allows us to characterize the degree of virulence of six virulent isolates; Cast13, VBC02, Cast26, Cast13, Cast17, Cast 07, VDP 11 and hypovirulent converted by RBB 111. Determination of oxalic acid by spectrophotometry allows us to evaluate production of oxalic acid in each virulent isolate and their converted ones.
- Evaluation of virulence and the oxalic acid production on Cryphonectria parasitica virulent and converted strains by CHV1 hypovirusPublication . Gadoum, Horiya; Coelho, Valentim; Noui, Abdallah; Jorge, Lurdes; Gouveia, Maria EugéniaChestnut Blight, caused by Cryphonectria parasitica (Murrill) Bar, is a major disease in Castanea sativa Mill. on the European continent. Biological control by hypovirulence is a sustainable and efficient method to control the disease. The presence of Cryphonectria hypovirus 1 (CHV1) in C. parasitica reduces the fungus virulence that promote canker healing and tree recovery. Hypovirus infection results in phenotypic and metabolic changes, including the reduction of ligninolytic enzymes activity, and decreased oxalic acid production. The aim of this work was to evaluate the oxalic acid production in both virulent and converted strains on PDB (Potato Dextrose Broth, 24g/L) and to access the virulence of these strains on chestnut stems. Six isolates were converted with two characterized hypovirulent C. parasitica isolates (RBB111, SR44.2) and the presence of CHV1 was detected by molecular methods. Oxalic acid production was evaluated by spectrophotometry after the growth of the strains on 100 ml of PDB supplemented with 2mM MnSO4 in an orbital incubator during five days. To evaluate the virulence of the isolates, chestnut stems were inoculated with the virulent isolates, their converted ones and the hypovirulent isolates. The characterized hypovirulent isolates used in this work has complete ability to convert virulent isolates with effective hypovirus transmission and PCR detection of CHV1 was obtained in all C. parasitica converted strains. The obtained results by spectrophotometric analysis have revealed that virulent strains always produced more oxalic acid than converted strains. The infection area on chestnut stems caused by virulent strains was significantly higher (P<0.05) than the infection area caused by converted strains. The converted strains Cast26/RBB111 and Cast26/SR44.2 showed 50% and 88.6% reduction in the content of oxalic acid present in supernatant, respectively. This suggests that the reduction in enzymatic activities caused by hypovirulent strains is variable with the hypovirulent donor used in conversion.