The role of rhizospheric Aspergillus flavus in standing maize crop contamination in different ecological zones of Khyber Pakhtunkhwa, Pakistan

Soil and un-husked maize samples were collected from 29 different locations belonging to three distinct ecological zones (Swat, Hazara and Peshawar) of Khyber Pakhtunkhwa, Pakistan. The samples were evaluated for the incidence of aflatoxigenic strains of Aspergillus flavus. The soil samples collected from Peshawar (100%) and Hazara (66%), and grain samples collected from Swat (64%) and Peshawar (55%) were severely infected with aflatoxigenic strains of A. flavus. The strains isolated from maize kernels of Manyar, Jalala (Swat zone), Palosi and Takkar (Peshawar zone) produced the highest amount of aflatoxin B1 (324 to 514 μg g-1) and B2 (23 to 486 μg g-1). Similarly, the strains isolated from soils of Bannu (Peshawar) and Huripur (Hazara) were prominent in B1 (662 to 1323 μg g-1) and B2 (145 to 826 μg g-1). Microbial analysis of the surface sterilized grains showed that the strains isolated from Jalala (Swat) and Palosi (Peshawar) samples were high in B1 (62 to 79 μg g-1) and B2 (21 to 36 μg g-1). It was concluded, therefore, that A. flavus from soil might contaminate maize crop, but not directly from the same field. The most probable contamination occurred through air borne spores. It is thus recommended that protection from air borne spore should be devised.Keywords: Aspergillus flavus, aflatoxin, ecology, maize crop, field, soil toxicolog

Withering timings affect the total free amino acids and mineral contents of tea leaves during black tea manufacturing

AbstractThe aim of the present study was to investigate the effect of withering timings (i.e. 0, 21, 22, 23 and 24h) on the moisture, total free amino acids, ash, essential and toxic mineral element contents of tea (Camellia sinensis L.) leaves during black tea manufacturing. Moisture, ash, Na, P, Mg, Cu, Zn, Mn, Al, Ni and Pb contents were significantly (P<0.05) affected by withering, whereas non-significant (P>0.05) results were noted for total free amino acids, K, Fe and Cd contents. The highest moisture content (76.4%) was examined in fresh leaves that progressively decreased to 63.8% in 24h withering. Total free amino acid contents gradually increased up to 23h and then decreased. Ash, P, Cu, Zn and Mn contents showed an increasing trend with withering time. Conversely, significantly lowered amounts of Na (162.5mg/kg) and Mg (803mg/kg) were recorded in tea leaves after 24h withering. Among the toxic elements, Al, Ni and Pb contents were progressively increased over withering time. It was concluded that tea is a potential source of essential chemical constituents and during processing proper care should be taken to produce high quality black tea

Water availability affects extracellular hydrolytic enzyme production by Aspergillus flavus and Aspergillus parasiticus

The objectives of this study were to examine the effect of different water activities (a(w); 0.99, 0.96 and 0.94) and time (up to 120 h) on quantitative and specific enzyme production during germination and initial growth of Aspergillus flavus and A. parasiticus strains at 25 degrees C. This is an important early indicator of potential for aflatoxin production under conducive conditions. Qualitative API ZYM generic enzyme strips were used to identify key hydrolytic enzymes produced. Subsequently, the temporal effects of a(w) on the total/specific activity of the key 4-5 hydrolytic enzymes were determined using 4-nitrophenyl substrates in a 96-well microtitre plate assay. The main enzymes produced by germinating conidia of A. flavus were esterase, lipase, acid phosphatase, beta-glucosidase and N-acetyl-beta-D-glucosaminidase, while for A. parasiticus these were alkaline phosphatase, lipase, acid phosphatase and beta- fucosidase for both total (mu mol 4-nitrophenol/min/g) and specific activity (nmol beta-nitrophenol/min/mu g protein). There were significant increases in the specific activity of all these enzymes of germinating spores of A. flavus (0-120 h) except for beta-glucosidase which was maximum at 72 h. The total/ specific activities of the enzymes produced by A. flavus were maximum at 0.99 a (w) with the exception of acid phosphatase and N-acetyl-beta-D-glucosaminidase at 0.94 a(w) For A. parasiticus, maximum total activity occurred at 0.99 aw for fucosidase activity, while specific activity was found to be higher at lower a (w) levels. These enzymes are important in early colonisation of food matrices by these species and single factors (a(w) time) and two-way interactions were all statistically significant for the enzymes assayed for both species. These enzymes could be used as an early and rapid indicator of the activity of Aspergillus section flavi species and suggests that rapid infection may occur over a wide range of a(w) conditions

Synergistic Effects of Acacia Prunings-Derived Biochar and Nitrogen Application on the Mineral Profile of Maize (<i>Zea mays</i> L.) Grains

Despite the proven impact of biochar (BC) on crop yield, little is known about its effect on cereal grain quality. We explored the effect of acacia pruning-derived biochar and nitrogen (N) applications on the mineral profile of maize grains in a field study. Biochar was applied at the rates of 5, 10, 15, and 20 t ha−1 and N at 100, 150, and 200 kg ha−1 along with the control (BC or N not applied) in a split-plot arrangement using a randomized complete block design. At crop maturity, the grains were analyzed for K, P, Ca, Mg, Zn, Fe, and Cu content. The results showed that BC application at the rate of 10 t ha−1 along with N at 200 kg ha−1 resulted in the highest concentrations of K, P, Ca, and Mg in grains. The Fe content was the maximum at the N application rate of 200 kg ha−1 while Zn and Cu had the highest concentration at 150 kg N ha−1 with no BC. It was concluded that the integrated use of BC and N could be a valuable strategy to improve the nutritional quality of maize grains. The enrichment of BC with micronutrients is recommended to achieve the desired concentration of micronutrients in maize grains to help cure malnutrition. However, further investigation is warranted to validate the impact of BC made of different feedstocks on soils of contrasting mineralogy as organo-mineral interactions might mask the true potential of BC

Pigment Produced by Glycine-Stimulated <i>Macrophomina Phaseolina</i> Is a (−)-Botryodiplodin Reaction Product and the Basis for an In-Culture Assay for (−)-Botryodiplodin Production

An isolate of Macrophomina phaseolina from muskmelons (Cucumis melo) was reported by Dunlap and Bruton to produce red pigment(s) in melons and in culture in the presence of added glycine, alanine, leucine, or asparagine in the medium, but not with some other amino acids and nitrogen-containing compounds. We explored the generality and mechanism of this pigment production response using pathogenic M. phaseolina isolates from soybean plants expressing symptoms of charcoal rot disease. A survey of 42 M. phaseolina isolates growing on Czapek-Dox agar medium supplemented with glycine confirmed pigment production by 71% of isolates at the optimal glycine concentration (10 g/L). Studies in this laboratory have demonstrated that some pathogenic isolates of M. phaseolina produce the mycotoxin (−)-botryodiplodin, which has been reported to react with amino acids, proteins, and other amines to produce red pigments. Time course studies showed a significant positive correlation between pigment and (−)-botryodiplodin production by selected M. phaseolina isolates with maximum production at seven to eight days. Pigments produced in agar culture medium supplemented with glycine, beta-alanine, or other amines exhibited similar UV-vis adsorption spectra as did pigments produced by (±)-botryodiplodin reacting in the same agar medium. In a separate study of 39 M. phaseolina isolates, red pigment production (OD520) on 10 g/L glycine-supplemented Czapek-Dox agar medium correlated significantly with (−)-botryodiplodin production (LC/MS analysis of culture filtrates) in parallel cultures on un-supplemented medium. These results support pigment production on glycine-supplemented agar medium as a simple and inexpensive in-culture method for detecting (−)-botryodiplodin production by M. phaseolina isolates