The antagonism activity of bacteria isolated from potato cultivated soil.

Soil-borne fungal and bacterial root pathogens can cause serious losses to agricultural crops. Resistant plant varieties are not available for several soil-borne pathogens and chemical control is often insufficiently effective in soil. The enhancement of disease suppressive properties of soils will limit disease development, thus, being of great importance for sustainable agriculture as well as organic farming systems. The aim of this research is to find and identify suppressive soils in the Sétif's areas (potato field located in different regions of Sétif); this allows the selection of the indigenous soil bacteria that are able to develop several mechanisms of action related to biocontrol of phytopathogenic fungi affecting potato crops. Among 50 bacterial strains only 14 showed a wide range of antifungal action against the tested phytopathogenic fungi. With a range of inhibition percent from 0 to 92.30% especially Fusarium oxysporum f. sp. albedinis with 92% inhibition.

Production of Ascochyta rabiei lacking solanapyrone A toxin production.

Ascochyta rabiei, agent of Ascochyta blight of chickpea produces three toxins, Solanapyrones A, B and C of which solanapyrone A is the most toxic. All isolates of the fungus so far examined produce at least one of the Solanapyrone toxins, usually Solanapyrone A. The universality of solanapyrone production argues strongly for the importance of the toxins in virulence or pathogenicity. However, further evidence for this awaits the development of mutants lacking toxin production. Generation and isolation of fungal mutants defective in pathogenicity has been very useful for understanding the genetic and enzymatic processes responsible for infectivity in a number of pathosystems. Numerous tools have been used to transform plants and micro-organisms but the most widely micro-organism employed is Agrobacterium tumefaciens. In the present experiments, two strains of A. tumefaciens, AGL1 and LBA1126, harbouring two different plasmids, both encoding a gene for hygromycin resistance in the T-DNA region were used to transform isolate Tk21 of A. rabiei. The transformation of Ascochyta rabiei, gave rise to 498 colonies which grew on media supplemented with the selective agent; hygromycin B. The 30 sporulated transformants produced solanapyrone A on the specific medium at different rates. Solanapyrone A production, as demonstrated by the absorption of light at 327 nm, varied from 2.11 microg/ml to 4.32 microg/ml, representing a reduction of 74.11% to 46.99% in comparison with the wild type (8.15 microg/ml).

The effect of essential oil of Ammoides pusilla (brot.) breistr on the growth and the production of solanapyrone a by Ascochyta rabiei.

Biological control such as the use of plant extracts has emerged as promising option to the phenomena of fungi resistance to chemical. Several constituent of essential oil have been studied for their biological activity including antibacterial and antifungal activity. In this study the effect of Ammoides pusilla essential oil with different concentrations was test against the growth of Ascochyta rabiei and the production of solanapyrone A by the fungus. After 14 days the mycelium was collected and the dry weight measured. A. rabiei did not grow at a final concentration of 6 and 3 mg/ml, at 1.5 mg/ml and 0.625ml there was little growth of the fungus with a dry weight of 55 mg and 99 mg respectively compared to the control with 519 mg dry weight, but there was no solanapyrone A produced. However a new compound appeared at the HPLC at 10 min. 30 sec. compared with the solanapyrone A which elutes at nearly 14 minutes.

Antifungal activity of rhizospheric bacteria.

Fluorescent Pseudomonad spp. were isolated from the rhizosphere of potato plants (Algeria) by serial dilutions of rhizosphere soils on Kings B medium and were tested for their antifungal activity. The antifungal activity of the Pseudomonas isolated from Potatoes rhizosphere was tested against Pythium ultimum, Rhizoctonia solani and Fusarium oxysporum in dual culture with bacteria on PDA. The Petri dish was divided into tow, on one the bacteria was spread and on the opposite side fungal plugs were inoculated and incubated for one week. Fourteen bacteria were isolated; only one isolate inhibited the growth of Pythium ultimum, Rhizoctonia solani, Fusarium solani; Fusarium oxysporum f.sp. albedinis and Fusarium oxysporum f. sp. Lycopersici with inhibition zones of 39.9, 33.7, 30.8, 19.9 and 22.5 mm respectively.

Vitamin D3 a new drug against Candida albicans.

OBJECTIVE: In this study, we demonstrate that vitamin D3 had fungicidal activity against Candida albicans. MATERIAL AND METHODS: The susceptibility of the yeast strain to the vitamin D3 was investigated by the antimicrobial screening using modified agar diffusion method, minimum fungistatic concentrations (MFCs) and minimum fungicide concentrations (MFCC) of the vitamin D3 were determined by the broth dilution method. RESULTS: The antifungal activity indicted that 100µg/ml of vitamin D3 had a power inhibition in the growth of C. albicans with zone of inhibition 12.5mm and CMFC and CMFs were 1.58±0.0764µg/ml. CONCLUSION: These values indicate that vitamin D3 can be considered to have fungicide activity. This antifungal effect may be due to the large lipsolubility of vitamin D3 changing the integrity of the cell membrane.

Study of the effect of Ammoides pusilla (Brot.) Breist, essential oil against Pseudomonas sp.

The economic losses caused by plant pathogens, the development of genetic resistance to applied pesticides by major pathogenic bacteria and public concerns about the use of synthetic chemicals on food and environment, increased interest in the search of alternative safe methods to control diseases spreading. Biological control with plant extracts has emerged as a promising option. The present study was carried out to determine the effect of Ammoides pusilla essential oil on the growth of two pathogenic bacteria, Pseudomonas syringae pv. syringae and Pseudomonas syringae pv. mosprunorum Three essential oil treatments, 1/2 v/v, 1/5 v/v and 1/10 v/v concentrations, were tested onto these bacteria, using the agar diffusion test. The results showed that 1/2 v/v concentration treatment completely inhibited Pseudomonas syringae pv. mosprunorum growth and produced a 35 mm diameter inhibition zone for Pseudomonas syringae pu. syringae. 1/5 v/v essential oil concentration produced inhibition zones of 19 and 17 mm diameter for Pseudomonas syringae pv. syringae and Pseudormonas syringae pv. mosprunorum respetively, while 1/10 v/v essential oil concentration gave inhibition plates of 11 and 12 mm diameter for both stains in the order cited. In in vitro culture essential oil gave promising results suggesting that future studies should be carried out and focus on determining appropriate formulation of this bio-molecule to be use as a bio-control agent.

The effect of solanapyrone a produced by Ascochyta rabiei on seed germination and the elongation of radicles and hypocotyls of chickpea (Cicer areitinum L.).

Three Algerian isolates of A. rabiei (72, Mat 1.2 and 9216) were grown on Czapek Dox medium supplemented with cations and incubated for 14 days. After incubation, the mycelium of the fungus was removed by filtration through four layers of muslin cloth and spores were removed from the filtrate by centrifugation at 10,000 g for 20 min. Solanapyrone A was partially purified by liquid phase extraction into ethyl acetate and, after removal of the ethyl acetate, the toxin samples were dissolved in methanol and quantified by analytical High Performance Liquid Chromatography (HPLC). Solanapyrone A was identified by superimposition of its UV spectrum, obtained from the diode array detector of the HPLC, on the spectrum of an authentic sample. The action of solanapyrone A solution on seed germination and elongation of radicles and hypocotyls was tested using a concentration of 18.2 microg/ml and a two-fold dilution series of this solution in distilled water. The three Isolates, 72, Mat1.2 and 9216 produced solanapyrone A at concentrations of 37.2, 14.2 and 11.09 microg/ml, respectively. When probit % inhibition of seed germination was plotted against log2 of solanapyrone A concentration, there was a linear relationship and the EC50 concentration was determined as 7.2 microg/ml. Similarly, when radicle and hypocotyl elongation was plotted against log2 of solanapyrone A concentration, both gave linear relationships and the EC50 concentrations were determined as 5.37 and 6.02 microg/ml, respectively. It was concluded that solanapyrone A has a considerable inhibition of chickpea. However radicles and hypocotyls were susceptible than seed germination.