No abstract

The influence of the two substrates tested on 18 isolates of Fusarium oxysporum f. sp. albedinis (Foa) was studied in order to compare the fungus behaviour on Casein and Glucose. It has shown that there is a mycelia growth of 63.63 % using casein, compared to 36.36 % using the Glucose. It has also been observed that the isolate "Foa Mtl 8" has shown a superior growth compared with the other isolates on liquid and solid casein medium, with a weight of 3 g, and it has completely covered the Petri dishes in first (in 6 days). On the same isolate, the detection of proteolytic activity by measuring the clarification diameters was most significant (4.2 cm diameter). On these criteria we had been based in order to select the isolate "Foa Mtl 8" for the determination of proteolytic activity. The colorimetric protein assay was performed by the method of Folin and Ciocalteu at different initial pH (4, 6 and 8). It had also shown that the isolate "Foa Mtl 8" produce a protease in pH range of 7.1 to 7.8.

Fusarium oxysporum forma specialis albedinis is the causal agent of Phoenix dactylifera vascular fusariosis. It hydrolyzes the pectocellulosic wall of Phoenix dactylifera vascular tissue. Pectinases hydrolyze cell wall pectin, but they are not active in all strains, so it is not clear whether such hydrolysis is a mechanism of pathogenesis. This research tries to answer this question by testing the significance of pectin methylesterase and endo-polygalacturonase activity in hydrolyzing P. dactylifera cell wall pectin and suggests their mechanism of pathogenesis. Six F. oxysporum strains isolated from P. dactylifera of Beni Abbes and Ghardaia provinces were grown in glucose and in pectin, and the enzyme activity was measured with titrimetric methods. The activity in all strains was quantified and then compared with growth carbohydrates and provinces with statistical tests. We found that pectin methylesterase from both growth conditions hydrolyzed pectin, but endo-polygalacturonase was not active in glucose. Surprisingly, statistical tests showed that this inhibition was not caused by carbon catabolite repression. Pectin methylesterase was more active than endo-polygalacturonase in pectin and in strains isolated from P. dactylifera of Beni Abbes. We suggest that F. oxysporum inhibits endo-polygalacturonase, using an unknown mechanism. We conclude that the product of hydrolysis gradually blocks sap circulation and causes maceration of the rachis. We revealed that F. oxysporumhas a significant pectin methylesterase and endo-polygalacturonase activity, which can hydrolyze the cell wall pectin of P. dactylifera. Themaceration of date palms may be caused by these enzymes, and endo-polygalacturonase inhibition is not directly caused by glucose.

In this study, four lactic acid bacteria (Lactococcus lactis subsp. lactis, Lactococcus lactis subsp. lactis biovar. diacetylactis, Leuconostoc mesenteroides subsp. mesenteroides and Leuconostoc mesenteroides subsp. mesenteroides biovar. dextranicum) were screened in vitro for antifungal activity against twelve strains of Fusarium oxysporum f. sp. albedinis (Foa), causal agent of the "Bayoud", the most destructive disease of date palm (Phoenix dactylifera L.) in Algeria. The results of the direct confrontation of LAB against (Foa) on MRS agar and PDA medium showed that there is a better inhibition by the LAB on MRS agar. Lactococcus lactis subsp. lactis biovar. diacetylactis gave the most effective rate inhibition, between 13.51 and 40.29 % on PDA medium and 41.17 and 100% on MRS Agar medium, followed by the other strains with inhibition reached 35.82 % on PDA medium and between 19.29 and 100 % on MRS agar medium. When we used cell-free supernatant, there was appearance of inhibition zones after 24 h incubation, with a percentage of inhibition reached 49.41 %.The microscopic observations in the areas of confrontation of the fungus with the LAB have shown that there is an inhibition of the conidia germination.