Enhancement of the biocontrol agent Candida oleophila (strain O) survival and control efficiency under extreme conditions of water activity and relative humidity

Plant Pathology Unit, Gembloux Agricultural University, Passage des Déportés 2, 5030 Gembloux, Belgium; Plant Biology Research Institute, Department of Biological Sciences, Montreal University, 4101 Sherbrooke Est, Montréal, Que., H1X 2B2 Canada; Received 20 May 2008. Accepted 23 July 2009. Available online 29 July 2009.
Biological Control (Impact Factor: 1.92). 01/2009; 51:403-408. DOI: 10.1016/j.biocontrol.2009.07.014

ABSTRACT The objective of this work is to evaluate the ability of some additive substances in protecting the biocontrol agent Candida oleophila (strain O) against the adverse effects of environmental factors, such as water activity (aw, 0.93 and 0.98) and relative humidity (75% and 98%). The protection obtained with various protectant substances, skimmed milk (SM), peptone, maltose, sucrose, sorbitol, lactose and polyethylene glycol was assayed under in vitro and in vivo conditions. The yeast cells with the highest level of protecting agents (1%) had higher viability than those with low protectant levels (0.1% and 0.5%). SM, sucrose and sorbitol improved significantly the C. oleophila survival on apple fruit surface by 80.8%, 42.26% and 37.27% and gave a significant protection (from 96% to 100%) against Penicillium expansum under dried conditions. The highest strain O density and efficacy was obtained with SM. Under experimental conditions reflecting practical conditions, SM applied in combination with the strain O resulted in improved biocontrol efficacy by 74.65%. Therefore, SM could be used as material substrate with the best sugar protectants during the formulation process of this antagonistic yeast for eventual pre-harvest application.

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    ABSTRACT: This study investigated the influence of UV-B radiation (280–320 nm) on survival of Candida oleophila strain O, an antagonist yeast that prevents postharvest diseases caused by Botrytis cinerea and Penicillium expansum on apple and pear fruits. Lethal doses (LD50 and LD90) were, respectively, 0·89 and 1·45 Kj m−2 for in vitro exposure and 3·06 and 5·5 Kj m−2 for in vivo exposure. A screening test of UV-B protectants for strain O was also evaluated under in vitro and in vivo conditions. The in vitro results showed that sodium ascorbate (0·1% and 0·01%), riboflavin (0·1%) and uric acid (0·1% and 0·01%) were the most effective and most suitable protectants. However, only riboflavin (0·1%) and uric acid (0·1%) were effective under in vivo conditions. The efficacy obtained with strain O against P. expansum, when subjected to UV-B radiation, was 75·0% and 49·2% for pathogen concentrations of 105 and 106 spores mL−1, respectively. Adding riboflavin to strain O gave a similar efficacy (64·2%). Applying strain O together with uric acid (0·1%) was less active (47·7%). Nonetheless, its efficacy when applied with the antioxidants sodium ascorbate (71·1%) or ascorbic acid (82·5%) was the greatest. Riboflavin and uric acid were the most cost-effective protectants, and could be included in the final formulation of strain O when applied preharvest.
    Plant Pathology 01/2011; 60:288-295. · 2.73 Impact Factor
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    ABSTRACT: When applied preharvest, antagonistic yeasts that act as biocontrol agents of postharvest fruit diseases must survive the environmental conditions in the field. In particular, UV-B radiation (280 to 320 nm) can greatly reduce their survival and effectiveness. The influence of artificial UV-B radiation on Pichia anomala strain K, an antagonistic yeast with potential for control of postharvest fruit diseases, was evaluated in vitro and in vivo. The in vitro 50 and 90% lethal dose values were 0.89 and 1.6 Kj/m2, respectively, whereas lethal values in vivo were 3.2 and 5.76 Kj/m2, respectively. UV protectants tested in combination with strain K included congo red, tryptophan, riboflavin, lignin, casein, gelatine, folic acid, tyrosine, and four mixtures. Riboflavin, folic acid, and the mixtures 1% folic acid + 0.5% tyrosine + 0.5% riboflavin (formula 2), 0.5% folic acid + 1% tyrosine + 0.5% riboflavin (formula 3), and 0.5% folic acid + 0.5% tyrosine + 1% riboflavin (formula 4) reduced yeast mortality caused by UV-B radiation in petri dish assays. Riboflavin, folic acid, gelatine, lignin, and tyrosine reduced yeast mortality caused by UV-B radiation on apple fruit surfaces. With the exception of lignin and folic acid, none of the compounds or mixtures increased significantly the ability of strain K to control the postharvest pathogen Penicillium expansum on wounded apple fruit. In contrast, casein, gelatine, tyrosine, congo red, riboflavin, and formulas 1 to 4 significantly reduced the effectiveness of strain K. Further investigations are justified to verify a potential benefit of lignin and folic acid for UV protection of strain K in preharvest applications.
    Plant Disease 01/2011; 95:311-316. · 2.74 Impact Factor
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    ABSTRACT: Lahlali, R., Brostaux, Y., and Jijakli, M. H. 2011. Control of apple blue mold by the antagonistic yeast Pichia anomala strain K: Screening of UV protectants for preharvest application. Plant Dis. 95:311-316.

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