A field survey was conducted to investigate the importance of saline soil factors on the occurrence of arbuscular mycorrhizal (AM) fungi in three localities (Baltim, New Damietta and Gamasa). Out of the 45 species of native and cultivated plants collected from three sites, 36 species including all agronomic were infected with arbuscular mycorrhizal fungi. However, few plant species belonging to the families Chenopodiaceae, Cruciferae and Cyperaceae were found to be non-mycorrhizal. In general, soil pH and CaCO3 content have no direct effect on the number of mycorrhizal spores in the rhizosphere of all plants tested. A positive correlation between densities of Glomales and the organic matter in the rhizosphere of cultivated salt tolerant plants were observed. Generally, spore densities and subsequent level of mycorrhizal infection were negatively correlated with the degree of salinity in the soil. However, number of mycorrhizal spores in the rhizosphere of wild halophytes were not significantly correlated to infectivity. Arbuscular mycorrhizal spores isolated from the collected soils were identified as two genera, Glomus and Acaulospora. Spores belonging to the genus Glomus were abundant in this survey, many of these were identified as Glomus mosseae and Glomus etunicatum. G. mosseae was the most frequent species reported in the salt rhizosphere. Thus, the results suggest that soil salinity and organic matter might play an important role in regulating the distribution of AM fungal communities in the saline soil.
The effect of benomyl as a fungicide on growth rate and ultrastructure of two isolates (P623 and P1319) of Phytophthora infestants is compared. Using different concentrations (50, 100, 200 and 500 ppm) of benomyl caused an inhibition of the mycelial growth of both isolates depending on the degree of concentration. The isolate P1319 was found to be more sensitive to benomyl than the isolate P623. Ultrastructural studies confirmedthese observations. The hyphae of isolate P1319 subjected to 100 and 500 ppm benomyl showed severe changes in the cítoplasm more than isolate P623. The increase of lipid bodies and vacuoles in hyphal cytoplasm of both isolates was the characteristic phenomenon after treatment of benomylparticulary at the concentration of 500 ppm.