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The potential of Burkholderia sp. strain TNAU-1 for the management of mung bean (Vigna radiata L.) root rot caused by Macrophomina phaseolina was evaluated under greenhouse conditions. Burkholderia sp. strain TNAU-1 inhibited the mycelial growth of M. phaseolina in vitro and produced an inhibition zone of 18.8 mm. Mung bean seeds when treated with the bacterial suspension, showed significant increase in root length, shoot length and seedling vigour. A talc-based powder formulation of Burkholderia sp. strain TNAU-1 was developed and evaluated for its efficacy in the management of mung bean root rot under greenhouse conditions. Seed treatment or soil application of the powder formulation of Burkholderia sp. strain TNAU-1 significantly reduced the incidence of root rot and increased the germination percentage and plant height. Seed treatment with the powder formulation of Burkholderia sp. strain TNAU-1 alone was effective in controlling root rot disease; but the combined seed treatment and soil application of Burkholderia sp. strain TNAU-1, increased the efficacy. Seed treatment and soil application with Burkholderia sp. reduced the root rot incidence from 52.6 per cent (with non-bacterized seeds) to 16.7 per cent. Control of root rot with the application of Burkholderia sp. by seed treatment and soil application was not statistically different from that obtained with seed treatment with carbendazim. The endophytic movement of Burkholderia sp. in the stem, roots and leaves of mung bean was confirmed through PCR using Burkholderia sp. specific primers which resulted in the amplification of a 417 bp product.
Rhizobacteria isolated from cotton roots exhibiting antagonism towards seedling blight and leaf blight of cotton were tested for their efficiency against the insect pest American bollworm (Helicoverpa armigera). The bioformulation developed using Bacillus subtilis (isolate DGL9) + chitin was found to be detrimental to the developmental stages of H. armigera (larva, pupa and adult) by causing larval mortality, pupal and adult malformation with reduced adult emergence. Generally, the larvae exhibited antifeeding behaviour when fed on bolls collected from rhizobacterial treatments. Hence, the developmental stages were altered leading to early pupation. Further, the efficacy of the isolate DGL9 was confirmed by culturing the bacteria in a suitable medium and incorporating the cell suspension and supernatant obtained form the broth culture in larval diet. The larvae fed to the diet exhibited defective developmental stages which was more significant in case of diet incorporated with supernatant. The percentage of pupal malformation, adult emergence and adult malformation was high at 96 h of incubation with the supernatant.
Aflatoxins, a group of mycotoxins mainly produced by Aspergillus flavus and A. parasiticus, have adverse health effects on humans and livestock that ingest aflatoxin- contaminated food products and feeds. To secure the safety of food and feed, regular monitoring of aflatoxin levels is necessary. In order to understand the magnitude of aflatoxin contamination, a survey was conducted in different agro-ecological zones of Tamil Nadu, India and 242 samples consisting of pre- and post-harvest maize kernels, food products, poultry and livestock feeds were collected from farmers' fields, poultry farms, retail shops and supermarkets and analyzed for aflatoxin B1 (AFB1) contamination by enzyme- linked immunosorbent assay (ELISA) using antiserum raised against aflatoxin B1-Bovine serum albumin (AFB1-BSA). The results indicated that 61.3% of the maize kernel samples were contaminated with AFB1 and the levels of AFB1 in 26% of the pre- and post-harvest maize kernels exceeded 20 μg/kg. The highest level of AFB1 (245 μg/kg) was recorded in post-harvest maize kernel samples. In food products AFB1 was detected only in two samples out of 30 samples tested. Furthermore, the levels ranged from 0.6 to 3.7 μg/kg. In poultry feeds, AFB1 was detected in 30 out of 53 samples and the levels ranged from 0.7 to 31.6 μg/kg. Among the 40 livestock feed samples evaluated 29 samples were contaminated with AFB1 at level ranging from 1.8 to 244.9 μg/kg.
A total of seventeen isolates of Aspergillus flavus from maize were collected from different agro-ecological zones of Tamil Nadu, India. The isolates were tested for their ability to produce aflatoxin B1 (AFB1) in vitro by indirect competitive enzyme-linked immunosorbent assay (ELISA). The amount of AFB1 produced by the isolates of A. flavus ranged from 1.9 to 206.6 ng/ml. Among the various isolates of A. flavus, the isolate AFM46 produced the highest amount of AFB1. DNA was extracted from A. flavus isolates and their molecular variability was investigated by using restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified internal transcribed spacer (ITS) regions of ribosomal DNA. PCR amplification with ITS1 and ITS4 primers resulted in the amplification of a product of approximately 600 bp. Digestion of the PCR products with the restriction enzymes EcoRI, HaeIII and TaqI produced fragments of different sizes. Analysis of the genetic coefficient matrix derived from the scores of RFLP profiles showed that minimum and maximum per cent similarities among the tested A. flavus strains ranged from 0 to 88%. Cluster analysis using the unweighted pair-group method with arithmetic average (UPGMA) clearly separated the isolates into five groups (group I–V) confirming the genetic diversity among the A. flavus isolates from maize.
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