Potential use of Zataria multiflora essential oil to control postharvest Aspergillus flavus fruit rot of strawberry

Postharvest fruit rot is a major problem in strawberry production chain worldwide. Aspergillus sp. is one of the major fungi associated with fruit rot of strawberry. In this study, an Aspergillus flavus was isolated from a rotten strawberry fruit. Based on the nucleotide sequence analysis of the internal transcribed spacer regions of rDNA, the fungus was confirmed as A. flavus. Pathogenicity of the isolated fungus was confirmed by artificially inoculating strawberry fruits under laboratory conditions. This strain was capable of producing aflatoxin B1 in vitro as determined by liquid chromatography-mass spectrometry analysis. Postharvest dip treatment of mature strawberry fruits with Zataria multiflora essential oil (ZEO) (0.1%) completely suppressed A. flavus infection and prevented rotting of fruits. The results of this study suggest that ZEO can be used as a sustainable and safe alternative to chemical fungicides for the control of Aspergillus fruit rot of strawberry

Antagonistic bacterial strains isolated from cabbage rhizosphere release antimicrobial volatile organic compounds against Pythium aphanidermatum

In a previous study, we isolated four antagonistic bacterial strains viz., Pseudomonas aeruginosa B1-SQU, Pseudomonas indica B2-SQU, Serratia marcescens B3-SQU and Pseudomonas brenneri B4-SQU from the rhizosphere of cabbage which suppressed damping-off in cabbage caused by Pythium aphanidermatum. In this study, potential of these bacterial isolates to produce antimicrobial volatile organic compounds (VOCs) against P. aphanidermatum was tested. The results of the two-sealed-base-plates assay revealed that all four bacterial strains produced VOCs against P. aphanidermatum with the maximum inhibition with P. brenneri B4-SQU followed by S. marcescens B3-SQU, P. aeruginosa B1-SQU and P. indica B2-SQU. Solid-phase microextraction coupled with gas chromatography-mass spectrometry was used to profile the VOCs of bacteria. A total of 20 VOCs were detected in P. aeruginosa B1-SQU and the major compounds identified were Carbon dioxide, 1-Butanol, 3-methyl- and Disulfide, dimethyl. The main volatile compounds detected in P. indica B2-SQU were 1-Butanol, 3-methyl-, Disulfide, dimethyl and 1,2-Propanediamine. Disulfide, dimethyl and 1,2-Propanediamine were the predominant compounds identified in S. marcescens B3-SQU among others. The major compounds detected in P. brenneri B4-SQU were 1-Butanol, 3-methyl-, 1,2-Propanediamine and Disulfide, dimethyl. Dimethyl disulfide, a well-known antimicrobial compound, was detected in the volatile profiles of all four antagonistic bacterial isolates. These results suggest that VOCs of antagonistic bacteria may be involved in the suppression of P. aphanidermatum and these antagonistic bacterial strains may be used as biofumigants for controlling damping-off of cucumber

Occurrence of aflatoxin contamination in maize kernels and molecular characterization of the producing organism, Aspergillus

Aflatoxins are toxic metabolites produced mainly by Aspergillus flavus and Aspergillus parasiticus. Aflatoxin B1 (AFB1) is a potent carcinogen, teratogen and mutagen. 660 pre- and post- harvest maize samples were collected from major maize growing areas in Tamil Nadu, India. Aflatoxin contamination was observed in 40.22% of the samples tested of which, 22.97% of pre-harvest and 53.93% post-harvest maize samples were found to be infected with AFB1 and 12.05% of the total samples exceeded WHO permissible limit of 20 μg/kg. AFB1 contamination ranged from 0 to 149.32 μg/kg. 28 A. flavus isolates were isolated and grouped into three sets based on aflatoxin producing potential viz., highly aflatoxin producing isolates, medium producing isolates and no aflatoxin producer or traces of aflatoxin producing isolates. The genetic coefficient matrix analysis using random amplified polymorphic DNA (RAPD) with ten random primers revealed minimum and maximum percent similarities among the tested A. flavus strains ranging from 35 to 89%. Cluster analysis separated the three sets of isolates into two groups (groups I and II) with each two subgroup confirming the genetic diversity among the A. flavus isolates from maize.Keywords: Maize, survey, Aspergillus flavus, aflatoxin, random amplified polymorphic DNA (RAPD).African Journal of Biotechnology Vol. 12(40), pp. 5839-584

Antifungal Activity of Shirazi Thyme (Zataria multiflora Boiss.) Essential Oil against Hypomyces perniciosus, a causal agent of wet bubble disease of Agaricus bisporus

Wet bubble disease (WBD) caused by Hypomyces perniciosus is a major constraint of button mushroom (Agaricus bisporus) cultivated worldwide. A few synthetic chemical fungicides are used to control WBD. In our study, the potential of essential oil (EO) from Zataria multiflora in inhibition of H. perniciosus was evaluated as an alternative to chemical fungicides. An isolate of H. perniciosus was isolated from wet bubble diseased A. bisporus and pathogenicity of the mycoparasite was determined under artificially inoculated conditions. The mycoparasitic fungus was identified using sequences of the internal transcribed spacer (ITS) region of ribosomal DNA. The EO was extracted from the aerial parts of Z. multiflora by microwave extraction method and evaluated in vitro for its antifungal activity against H. perniciosus. The EO of Z. multiflora (ZEO) at the tested concentrations (50% and 100%) inhibited the growth of H. perniciosus in the agar diffusion test. The minimum inhibitory concentration (MIC) of ZEO was 0.04% as assessed by the poisoned food technique. The chemical composition of ZEO was determined by gas chromatography-mass spectrometry analysis. A total of 23 compounds were identified. Among them, the most abundant compounds were Linalool (20.3%) and Bornyl acetate (15.5%). Linalool at the tested concentrations of 0.25% and 0.125% completely inhibited the mycelial growth of H. perniciosus in an in vitro assay. These results suggest that ZEO can be exploited for control of WBD

Assessment of aflatoxin B1 content and aflatoxigenic molds in imported food commodities in Muscat, Oman

Aflatoxins, mainly produced by Aspergillus flavus and A. parasiticus are considered as serious food safety and human health issues due to their hepatotoxic effects. In the present study, the occurrence of aflatoxin B1 (AFB1), the most potent human liver carcinogen, and prevalence of toxigenic isolates of Aspergillus spp. were assessed in 140 food commodities in Muscat markets, Oman, and the 95 quarantined imported food commodities. These samples consisted of rice, corn, peanut, red chilli powder, soybean, dried dates and tree nuts. AFB1 was analyzed using competitive ELISA/LC-MS and the aflatoxigenic fungi were detected using plating technique followed by molecular identification. No AFB1 was detected in 89 (63.6%) samples collected from local markets, while 44 (31.4%) samples contained 1-5 ppb and the remaining 7 (5%) samples (red chili powder) contained 6-10 ppb. None of the samples exceeded the maximum permissible limit of 10 ppb set for foods by Oman legislation. Of the 95 quarantined samples, only 17 (17.9%) samples were positive and contained AFB1 at concentrations ranging from 1-3.4 ppb. Four isolates of Aspergillus pp. were isolated from the collected samples and were identified as Aspergillus flavus (A14, A16 and A23) and A. chevalieri (A46) on the basis of internal transcribed spacer (ITS) sequences of ribosomal DNA. Among them, A. flavus strain A14 alone produced AFB1 (7.6 ppb), while A16, A23, and A46 were non-toxigenic. This is the first detailed report on the occurrence of AFB1 in food commodities imported into Oman

The effect of salt-tolerant antagonistic bacteria from tomato rhizosphere on plant growth promotion and damping-off disease suppression under salt-stress conditions

A total of 24 morphologically distinct salt-tolerant bacteria were isolated from the tomato rhizosphere soil and tested in vitro against Pythium aphanidermatum, causing damping-off disease in tomato. Among them, five bacterial isolates viz., BTR1.0, BTR1.1, BTR4.4, BTR7.0 and BTR8.6 were found to inhibit the mycelial growth of P. aphanidermatum. The maximum antagonistic effect was shown by BTR1.0 followed by BTR7.0 and BTR1.1. Based on the MALDI Biotyper analysis, these bacterial isolates were identified as Serratia marcescens (BTR1.0 and BTR1.1), Pseudomonas aeruginosa (BTR7.0 and BTR8.6) and Alcaligenes faecalis (BTR4.4). Analysis of plant growth stimulating activity of bacterial strains revealed that A. faecalis BTR4.4 recorded the highest vigour index followed by S. marcescens BTR1.0. The biocontrol activity of bacterial antagonists against tomato damping-off was tested under salt-water irrigation. Among the bacterial strains tested, S. marcescens BTR1.1 was found to be highly effective under non-saline water irrigation, which suppressed the disease by 68% compared to infected control. However, at 50 mM NaCl concentration, S. marcescens strain BTR1.0, P. aeruginosa strain BTR7.0 and A. faecalis BTR4.4 provided a significant level of control of the disease. At 100 mM NaCl concentration, no significant effect of the bacterial strains on the disease incidence was observed

Aspergillus terreus obtained from mangrove exhibits antagonistic activities against Pythium aphanidermatum-induced damping-off of cucumber

A study was conducted to investigate the potential of Aspergillus terreus obtained from Avicennia marina mangrove roots in inhibiting Pythium aphanidermatum and damping-off disease of cucumber. Aspergillus terreus exhibited in vitro inhibition of Pythium aphanidermatum growth. Electron microscope examination revealed that the antagonistic fungal isolate resulted in shrinking and groves in Pythium hypha. When Aspergillus terreus culture filtrate was added to Pythium aphanidermatum, it resulted in a significant increase (by 73%) in electrolyte leakage from Pythium hypha compared to the control, as well as significant reduction (by 71%) in oospore production. The Aspergillus terreus culture was also found to produce a cellulase enzyme, which is suggested to be involved in the antagonism against Pythium aphanidermatum. Adding Aspergillus terreus to soil infested with Pythium aphanidermatum significantly reduced percent mortality in cucumber seedlings by 70%. Aspergillus terreus, when applied alone on cucumber seedlings, did not show any suppressive effects on cucumber growth (length and fresh and dry weight). This appears to be the first report of isolation from mangrove of Aspergillus terreus with antagonistic activity against Pythium aphanidermatum-induced damping-off of cucumber. The study indicates that fungal isolates obtained from marine environments may serve as potential biocontrol agents against some plant pathogens

Fungal Diversity in Tomato Rhizosphere Soil under Conventional and Desert Farming Systems

This study examined fungal diversity and composition in conventional (CM) and desert farming (DE) systems in Oman. Fungal diversity in the rhizosphere of tomato was assessed using 454-pyrosequencing and culture-based techniques. Both techniques produced variable results in terms of fungal diversity, with 25% of the fungal classes shared between the two techniques. In addition, pyrosequencing recovered more taxa compared to direct plating. These findings could be attributed to the ability of pyrosequencing to recover taxa that cannot grow or are slow growing on culture media. Both techniques showed that fungal diversity in the conventional farm was comparable to that in the desert farm. However, the composition of fungal classes and taxa in the two farming systems were different. Pyrosequencing revealed that Microsporidetes and Dothideomycetes are the two most common fungal classes in CM and DE, respectively. However, the culture-based technique revealed that Eurotiomycetes was the most abundant class in both farming systems and some classes, such as Microsporidetes, were not detected by the culture-based technique. Although some plant pathogens (e.g., Pythium or Fusarium) were detected in the rhizosphere of tomato, the majority of fungal species in the rhizosphere of tomato were saprophytes. Our study shows that the cultivation system may have an impact on fungal diversity. The factors which affected fungal diversity in both farms are discussed

Potential of indigenous antagonistic rhizobacteria in the biological control of Monosporascus root rot and vine decline disease of muskmelon

Monosporascus root rot and vine decline (MRVD) of muskmelon, caused by Monosporascus cannonballus, is an economically important disease worldwide. The objectives of this study were to isolate native rhizobacterial strains and to evaluate their ability to promote plant growth and to provide protection against M. cannonballus. Thirty eight native bacterial isolates from the rhizosphere soil of muskmelon and cucumber were screened for their antagonism against M. cannonballus in a dual culture assay. Among them, five isolates viz., Bacillus amyloliquefaciens (B4), Pseudomonas mendocina (B7), Bacillus endophyticus (B10), Pseudomonas resinovorans B11 and P. aeruginosa AT3, identified based on the 16S rRNA gene sequence analysis, showed a significant level of antagonism and the inhibition zone ranged from 5.6 mm to 25.9 mm. Scanning electron microscopic observation of the hyphae of M. cannonballus at the inhibition zone revealed morphological abnormalities including shrinkage, loss of turgidity, pit formation and deformation. These bacterial isolates showed compatibility with one another and with Trichoderma viride. Greenhouse experiments revealed that P. resinovorans B11 was the most effective among the bacterial antagonists in controlling MRVD in melon. When applied as seed treatment and soil application, P. resinovorans B11 reduced the incidence of MRVD by 93.1%, relative to the infected control