S. K. Hemida

MICROBIAL POPULATIONS AND ENZYME ACTIVITY IN SOIL TREATED WITH HEAVY METALS

Effects of two concentrations (200 and 2000μg g−1 soil) of two heavy metals (copper and zinc as sulphates) applied to clay or sandy soil for 12 weeks on the total counts of fungi, bateria and actinomycetes were studied. Activities of three soil enzymes (urease, nitrate reductase and amidase) were also investigated. Application of heavy metals to the clay soil reduced the microbial populations. However, although neither heavy metal showed any significant increasing effect on microorganisms populations in clay soil samples, some stimulatory effects were noted in sandy soil. Activities of urease and nitrate reductase were inhibited by heavy metal application in both soils. Amidase activity was inhibited only with the higher application rate after some experimental periods.

Studies on fungi associated with tomato fruits and effectiveness of some commercial fungicides against three pathogens

Among 39 fungal species and one variety belonging to 16 genera isolated from 116 healthy tomato fruits collected from markets in Assiut, Egypt, during 1994,Aspergillus niger was found to be the most prevalent, being isolated from 84.6% of the samples. Of 11 species recovered from 156 diseased tomatoes,Alternaria alternata, Rhizopus stolonifer andA. niger were the most common and isolated from 52.7%, 35.9% and 25.0% of the samples, respectively. Experiments for comparison of the effects of medium containing tomato juice with synthetic medium on the mycelial growth of nine fungal species indicated that, the tomato juice medium was more suitable for growth of all fungal species. The effect of five commercial fungicides and sodium hypochlorite when applied as post-harvest dips after inoculation was studied in laboratory againstA. alternata, A. niger andR. stolonifer. At 10 and 100 µg ml−1, neither of the fungicide caused a noticeable inhibition ofAlternaria rot. At 1000 µg ml−1 benlate, rovral and sumisclex completely preventedAlternaria andAspergillus rot, whereas cuprosan and ridomil were ineffective against rotting caused byA. niger. Rhizopus rot development was inhibited by over 50% with one treatment only (rovral at 1000 µg ml−1). Sodium hypochlorite has good curative properties against fruit rots especially those caused byA. alternata andA. niger.

Fungal succession and decay of herbicide-treated wheat straw

The effects of alachlor and haloxyfop on wheat straw decay and fungal succession were studied in laboratory trials. Wheat straw segments were immersed in (100 and 1 000 mg/L) herbicides, buried in soil and incubated at 28±1°C for 8 weeks. Both herbicides significantly stimulated the mass loss and N-mineralization of wheat straw. CO2 evolution was not significantly affected while C-mineralization was inhibited. The pattern of succession of fungi was slightly affected in herbicidetreated wheat straw. However, the frequency of occurrence ofRhizopus stolonifer was lowered throughout all experimental periods. In a pure culture experiment, both alachlor and haloxyfop at 100, 500 and 1 000 mg/L reduced the radial growth ofAlternaria alternata, Aspergillus niger, A. flavus, Penicillium funiculosum, R. stolonifer andTrichoderma harzianum.

Terrestrial fungi inhabiting certain species of nile fishes in Egypt

Twenty specimens of six species of Nile fishes were examined for the presence of fungi. Of which 2 were from Alestes nurse; 3 from Bagrus docmac; 4 from Barbus bynni; 6 from Chrysichthys auratus; 4 from Lates niloticus and 1 from Malapterurus electricus. Forty-three fungal species in addition to 1 variety appertaining to fifteen genera were recovered from skin (15 genera and 34 species + 1 variety); gills, kidney (12 genera and 30 species + 1 variety, each); liver (11 genera and 30 species + 1 variety) and intestine (13 genera and 30 species + 1 variety) of all specimens, using glucose Czapek-Dox medium at 28 degrees C. The most common genera were Aspergillus, Penicillium and Trichoderma.

Influence of a pyrethroid insecticide on soil fungi

The selective effect of the pyrethroid insecticide (Polytrin) on soil fungi was studied at three doses when incorporated in soil or in agar or liquid medium.Polytrin induced an inhibitory effect on soil fungi after 2, 5 and 40 days when applied at certain levels and a stimulatory effect after 20 days of treatment with the high dose. When incorporated in the agar medium, Polytrin decreased the total counts of fungi, particularly, Aspergillus and Penicillium at the high dose (10.0 ppm). In liquid medium, it showed no significant effect except in case of A. terreus which was significantly enhanced by the three doses.

Response of soil fungi to the herbicide Primextra

Summary Primextra 500 FW (acetanilide and triazine combination) was significantly toxic to the total counts of soil fungi after 2, 5 and 60 days of application with the three doses (0.94, 1.88 and 4.70 mg a.i/kg). In the agar medium, it was significantly inhibited the total counts of the fungi, Aspergillus and A. niger; and promoted the counts of A. Candidus and A. carneus. The mycelial growth of A. niger, A. terreus, A. fumigatus and Trichoderma harzianum was significantly raised by the high dose (390 p.p.m.).

Fungal flora of cement polluted soils in Egypt

Summary Mycoflora of 40 soil samples collected from cultivated and desert soils, exposed to cement dust were studied. Ten species belonging to 7 genera of zoosporic fungi, in addition to Dactylella rhompospora (aquatic hyphomycetes) were recovered from cultivated and desert soils, using baiting technique. Pythium debaryanum and Dictyuchus sterilis were the commonest species. Seventy-one species in addition to two varieties, which belong to 34 genera were collected from 20 samples of each of cultivated (20 genera and 45 species + 1 var.) and desert (31 genera and 61 species + 2 var.) soils, on glucose-agar medium. On cellulose-agar medium, fifty-six species and 2 varieties representing 26 genera were collected from 20 samples of each of cultivated (24 genera and 40 species + 2 var.) and desert (20 genera and 40 species + 2 var.) soils. Aspergillus, Penicillium and Emericella were the most frequent genera in the studied soils on both media.

Thermophilic and thermotolerant fungi isolated from cultivated and desert soils, exposed continuously to cement dust particles in Egypt

Summary Thermophilic and thermotolerant fungi of forty soil samples collected from cultivated and desert soils, exposed continuously to cement dust particles were studied. Ten genera and 16 species in addition to two varieties of Aspergillus flavus and Malbranchia pulchella were recovered from all soil samples, on three types of media at 45 °C. From cultivated soils, 11 species and 2 varieties representing 7 genera were collected on yeast starch agar; on glucose- (3 genera and 3 species) and on cellulose-Czapeks agar (2 genera and 2 species). From desert soils, 12 species and 1 variety which belong to 8 genera were isolated on yeast starch agar and on both glucose- and cellulose Czapeks agar (1 genus and 1 species). In this investigation, the most dominant species was A. fumigatus . Truly thermophilic fungi were encountered and these were: Chaetomium thermophile, Malbranchea pulchella var. sulfurea, Rhizomucor pusillus, Myriococcum albomyces, Talaromyces thermophilus and Torula thermophila . Yeast starch agar was the best medium for isolation of thermophilic and thermotolerant fungi in the present study.