Article

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

Plant Biology Research Institute, Department of Biological Sciences, Montreal University, 4101 Sherbrooke Est, Montréal, Que., H1X 2B2 Canada
Biological Control (Impact Factor: 1.64). 12/2009; 51(3):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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    • "Lahlali et al. (2008) established a model for the survival of Pichia anomala (strain K) and C. oleophila (strain O), exposing populations on treated apples to different temperatures (5, 15 and 25 °C) and RH (75% and 98%). Furthermore, the efficacy and survival of C. oleophila (strain O) was also tested in extreme conditions of water activity and RH (Lahlali and Jijakli, 2009). However, there are no similar studies on grapes, and none has evaluated the in vivo survival of a BCA under selected T and RH regimes in controlled conditions. "
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    ABSTRACT: Candida sake CPA-1 is an antagonistic yeast that has previously been shown to effectively control Botrytis bunch rot in grapes. The efficacy of biological control agents is dependent on their survival, which may also depend on climatic conditions. However, few studies have evaluated the effect of abiotic factors affecting the survival of biological control agents, such as temperature (T) or relative humidity (RH). In this study, efficacy of C. sake (5 x 10(7) CFU mL(-1)), which was applied with the additive Fungicover (FC; 50 g L-1), was tested against BBR in the laboratory and in field trials under the Atlantic climate conditions of the Bordeaux region (France). The study also evaluated the survival of C sake under T and RH regimes simulated in climatic chambers. Two or five applications of C sake plus FC during the growing season significantly reduced BBR severity at harvest by 48% and 82%, respectively, when compared to the control. Similar reductions were achieved after inoculation with selected virulent Botrytis cinerea strains (75% compared to control) in laboratory experiments. C. sake populations showed minimal decreases between field applications and were favored by simulated Atlantic climate conditions. The survival pattern of C. sake exposed to 40 and 45 degrees C combined with 30% and 100% of RH was described, demonstrating a sharp decrease during the first 24 h. Allowing 48 h for C sake to incubate and become established on fruits prior to the exposure to 40 degrees C and 30% RH increased survival (P < 0.05). These results confirm the efficacy of treatment with C. sake plus FC under favorable climatic conditions for BBR development, while survival studies may help to improve the survival and efficacy of yeast BCAs, such as C sake CPA-1.
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    • "Thiabendazole (TBZ) and imazalil are the most commonly used chemicals for preventing and controlling postharvest infections caused by Penicillium spp. on apples and citrus fruits (Jijakli et al., 1993). Unlike preharvest treatments, these products are applied after harvesting by dipping or drenching (Lahlali et al., 2009). However, this practice attracts criticism because of the possibility of fungicide resistance development and other environmental effects. "
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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.
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