Abdulaziz A. Al-Askar

Antimicrobial activity of some plant extracts against bacterial strains causing food poisoning diseases

Prevention of food spoilage and food poisoning pathogens is usually achieved by use of chemical preservatives which have negative impacts including: human health hazards of the chemical applications, chemical residues in food & feed chains and acquisition of microbial resistance to the used chemicals. Because of such concerns, the necessity to find a potentially effective, healthy safer and natural alternative preservatives is increased. Within these texts, Plant extracts have been used to control food poisoning diseases and preserve foodstuff. Antimicrobial activity of five plant extracts were investigated against Bacillus cereus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhi using agar disc diffusion technique. Ethanolic extracts of Punica granatum, Syzygium aromaticum, Zingiber officinales and Thymus vulgaris were potentially effective with variable efficiency against the tested bacterial strains at concentration of 10 mg/ml while extract of Cuminum cyminum was only effective against S. aureus respectively. P. granatum and S. aromaticum ethanolic extracts were the most effective plant extracts and showed bacteriostatic and bactericidal activities against the highly susceptible strains of food borne pathogenic bacteria (S. aureus and P. aeruginosa) with MICs ranged from 2.5 to 5.0 mg/ml and MBC of 5.0 and 10 mg/ml except P. aeruginosa which was less sensitive and its MBC reached to 12.5 mg/ml of S. aromaticum respectively. These plant extracts which proved to be potentially effective can be used as natural alternative preventives to control food poisoning diseases and preserve food stuff avoiding healthy hazards of chemically antimicrobial agent applications.

Characterization of alkaline protease produced by Streptomyces griseorubens E44G and its possibility for controlling Rhizoctonia root rot disease of corn

The antifungal activity of Streptomyces griseorubens E44G against Rhizoctonia solani, the causal agent of root rot disease of corn, was investigated. The mycelial growth of R. solani was inhibited by S. griseorubens E44G, indicating that it has an antifungal potential. The antagonist, S. griseorubens E44G, was detected to have proteolytic activity, using the method of casein hydrolysis. Moreover, the protease production was optimized under submerged conditions. The purification and precipitation of protease were achieved by ammonium sulphate and Sephadex G-100 gel filtration chromatography. Protease activity was detected spectrophotometrically based on the production of tyrosine. The molecular weight of the enzyme (35 kDa) was determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis . The optimum activity of the enzyme was detected at pH 8.5 and 60 °C. The results indicated that the enzyme was thermostable and retained full activity even after 1 hour of incubation at 60 °C. The purified enzyme substantially inhibited the growth of R. solani, indicating that this enzyme may be actually involved in the antagonistic process.

Occurrence and distribution of tomato seed-borne mycoflora in Saudi Arabia and its correlation with the climatic variables

One hundred samples of tomato seeds were collected in 2011 and 2012 from tomato‐cultivated fields in Saudi Arabia and screened for their seed‐borne mycoflora. A total of 30 genera and 57 species of fungi were recovered from the collected seed samples using agar plate and deep‐freezing blotter methods. The two methods differed as regards the frequency of recovered seed‐borne fungi. Seven fungi among those recovered from tomato seeds, which are known as plant pathogens, were tested for their pathogenicity and transmission on tomato seedlings. The recovery rate of these pathogens gradually decreased from root up to the upper stem, and did not reach to the stem apex. The distribution of tomato seed‐borne fungi was also investigated throughout Saudi Arabia. In this concern, Al‐Madena governorate recorded the highest incidence of fungal flora associated with tomato seeds. The impact of meteorological variables on the distribution of tomato seed‐borne mycoflora was explored using the ordination technique (canonical correspondence analysis). Among all climatic factors, relative humidity was the most influential variable in this regard. Our findings may provide a valuable contribution to our understanding of future global disease change and may be used also to predict disease occurrence and fungal transfer to new uninfected areas.

Seed-borne mycoflora of alfalfa (Medicago sativa L.) in the Riyadh Region of Saudi Arabia

Fifteen seed samples of local alfalfa (Medicago sativa L.) cultivar (Hegazy) collected from fields at different governorates of the Riyadh region in Saudi Arabia were screened for their seed-borne mycoflora. Standard moist blotter and deep-freezing blotter methods recommended by the International Seed Testing Association, in addition to an innovative alkaline seed-bed method were applied. A total of 24 genera and 35 species of fungi were isolated using the above-mentioned techniques. Alternaria alternata, Cladosporium sp., Aspergillus sp., Stemphylium sp. and Penicillium sp. were the genera most commonly isolated. Among the various techniques adopted for detection, the alkaline NaOH method was found to be effective and yielded the maximum number of pathogenic fungi. Syndromes of seed discoloration were also investigated. The alkaline seed-bed method using NaOH was used to detect saprophytic and pathogenic seed-borne fungi associated with discolored seeds. A total of 15 genera and 26 species of fungi were isolated. Cladosporium sp., Alternaria alternata and Aspergillus species were the saprophytic species detected most, while Stemphylium botryosum and Fusarium incarnatum were common pathogenic fungi found on discolored seeds. The average of incidence and occurrence percentages of most detected fungi were higher in discolored seeds than in normal seeds. Seed germination was also affected significantly by discoloration. The data also indicate that seed discoloration decreases seed germination significantly (by 26.3–60%).

Trichoderma Harzianum WKY1: an indole acetic acid producer for growth improvement and anthracnose disease control in sorghum

ABSTRACT The efficiency of two isolates of Trichoderma harzianum (WKY1 and WKY5) as bio-control agents against anthracnose disease in sorghum was investigated. In vitro, T. harzianum WKY1 isolate showed superiority in terms of inhibition of both mycelial growth and spore germination of Colletotrichum sublineolum, the causative agent of sorghum anthracnose, as well as induction of the sorghum seed germination over T. harzianum WKY5 isolate. The culture filtrate of the selected isolate (T. harzianum WKY1) was analysed using GC-MS system to determine their chemical constituents. Twenty-nine components with varied existence percentages were identified. Although T. harzianum WKY1 produced the phytohormone indole-3-acetic acid (IAA) on tryptophan free medium, a marked dependency on tryptophan for the production of IAA was noticed. Nutritional components were optimized for maximizing IAA production using the central composite design. The optimum levels were 1.06, 29.86 and 2.93 g L−1 from tryptophan, sucrose and NaNO3, respectively, with a maximum IAA biosynthesis (138.9 µg mL−1) after five days of incubation. Production of IAA in the culture filtrate of T. harzianum WKY1 was qualitatively and quantitatively analysed by LC-MS system using a reference standard of IAA. Under greenhouse conditions, application of T. harzianum WKY1 and/or its filtrate reduced greatly the disease severity as well as improved the plant growth of sorghum. From the present data, we can recommend the application of T. harzianum WKY1 as a dual purpose bio-agent for biological control of anthracnose disease and plant growth promotion.

Chitinase production by Bacillus subtilis ATCC 11774 and its effect on biocontrol of Rhizoctonia diseases of potato

Stem canker and black scurf of potato, caused by Rhizoctonia solani, can be serious diseases causing an economically significant damage. Biocontrol activity of Bacillus subtilis ATCC 11774 against the Rhizoctonia diseases of potato was investigated in this study. Chitinase enzyme was optimally produced by B. subtilis under batch fermentation conditions similar to those of the potato-growing soil. The maximum chitinase was obtained at initial pH 8 and 30 °C. In vitro, the lytic action of the B. subtilis chitinase was detected releasing 355 μg GlcNAc ml⁻¹ from the cell wall extract of R. solani and suggesting the presence of various chitinase enzymes in the bacterial filtrate. In dual culture test, the antagonistic behavior of B. subtilis resulted in the inhibition of the radial growth of R. solani by 48.1% after 4 days. Moreover, the extracted B. subtilis chitinase reduced the growth of R. solani by 42.3% when incorporated with the PDA plates. Under greenhouse conditions, application of a bacterial suspension of B. subtilis at 109 cell mL⁻¹ significantly reduced the disease incidence of stem canker and black scurf to 22.3 and 30%, respectively. In addition, it significantly improved some biochemical parameters, growth and tubers yield. Our findings indicate two points; firstly, B. subtilis possesses a good biocontrol activity against Rhizoctonia diseases of potato, secondly, the harmonization and suitability of the soil conditions to the growth and activity of B. subtilis guaranteed a high controlling capacity against the target pathogen.