Progress 03/30/01 to 09/01/05
Outputs
4d Progress report. This project documents research conducted under a Trust Fund Cooperative Agreement with California Pistachio Commission. Additional details of this research can be found in the Parent CRIS report 5325-42000-031-00D, Biocontrol of Insects and Microorganisms Contributing to Mycotoxin Contamination. Aflatoxin contamination of food crops causes serious problems worldwide in agricultural commodities. When aflatoxin is found in the commodity, its market value is greatly reduced. Aflatoxin is a highly potent natural carcinogen that is a health hazard to both humans and mammals. The major aflatoxin-producing fungus, Aspergillus flavus has a broad ecological niche and reproduces copiously. These spores may infect early split nuts, nuts wounded by insects as well as nuts with cracks that occur during the growing season and are mechanically damaged during harvest. Nuts infected by A. flavus are the major sources of aflatoxin contamination in pistachios. There
is no conventional fungicide to control A. flavus. Aflatoxin continues to be a regulatory deterrent to pistachio industry. The grower and processor are looking for effective means to control Aspergillus infestations and subsequent contamination of edible nuts with aflatoxin. Pichia anomala WRL-076 is not known to produce any toxic compounds or causes disease in plants and animals and humans. Once field efficacy of the yeast has been demonstrated, growers will most likely use it because it can control A. flavus and possibly other fungal pathogens. Application of this biopesticide to pistachio will result in economic gain to the grower and industry. Field evaluation of the efficacy of the biocontrol agent, P. anomala strain WRL-076 was carried out. Pistachio nut-fruits on the tree were individually wounded with a dental needle and sprayed with aqueous suspension of yeasts at 3x107 cells/ml in July (experiment 1) and August(experiment 2) respectively. The wounded nut-fruits without
yeast- spray were used as controls. Wounded nut-fruit was hand picked from the tree and immediately placed to a special agar medium on 08/08/03 (Exp. 1) and 15/09/03 (Exp. 2). The nut-fruits were incubated at 280C for eight days. The viable fungal and yeast counts on individual nut were enumerated by determining the colony forming unit (CFU) of A. flavus spores and yeast. In order to see the variation among the nuts, every single nut collected was analysed for colonization of A. flavus and viable spores. In Exp. 1, colonization of nut fruits by A. flavus was 6. 8% for the control and 2.5% for wounded nut-fruits treated with yeast. In Exp. 2, the percent colonization of A. flavus on nut-fruits was 27.1% for the control and 5.1% for the yeast treated nut-fruits respectively. Higer colonization of A. flavus in Exp. 1 than in Exp. 2 indicted that the population of A. flavus in the orchard was higher in August than in July. In Exp. 1, the average spore production for the control and yeast
sprayed nuts was 1.4x107 and 3.1x103 respectively. Average spore production in A. flavus infected nuts was 5.6x106 and 1.3x106 respectively for the control and yeast sprayed nuts in Exp. 2 The experiments demonstrated that the yeast, P. anomala can modulate spore production of A. flavus in wounded the pistachio nut-fruits. A reduction of spore number was observed in the range of 77% and 99% for Exp. 1 and Exp. 2 respectively. The results clearly demonstrate that the production of A. flavus spores was drastically inhibited by spraying yeast onto wounded pistachio nuts. One can anticipate that field spraying of this effective yeast to pistachio trees will decrease the population of A. flavus in the orchards. The outcome will be a reduction of aflatoxin contamination in the edible nuts. Using pistachio as a model system, similar results can be predicted for almond.
Impacts
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Progress 10/01/03 to 09/30/04
Outputs
4. What were the most significant accomplishments this past year? This report serves to document research conducted under a a Trust Agreement with California Pistachio Commission. Additional details of this research can be found in the Parent project report 5325-42000-032- 00D Inhibition of Tree Nut Contamination by Aflatoxins and Related Mycotoxins Using Natural Products. Aflatoxin contamination of food crops causes serious problems worldwide in agricultural commodities. When aflatoxin is found in the commodity, its market value is greatly reduced. This causes a loss of millions of dollars per year to the producers. Aflatoxin is a highly potent natural carcinogen that is a health hazard to both humans and mammals. The major aflatoxin-producing fungus, Aspergillus flavus has a broad ecological niche and reproduce copiously. The spores of A. flavus can be airborne. These spores may infect early split nuts, nuts wounded by insects as well as nuts with cracks that
occur during the growing season and are mechanically damaged during harvest. Nuts infected by A. flavus are the major sources of aflatoxin contamination in pistachios. The spores of A. flavus in the air are the second most common etiologic agent of human aspergillosis after Aspergillus fumigatus. The use of chemical pesticides has caused the development of pest resistance and resurgence as well as environmental pollution and risks to human health. There is a growing interest in the food industry, including retail supermarkets, grower cooperatives and large food companies to consider biocontrol as a means to minimize risk. Field evaluation of the efficacy of the biocontrol agent, P. anomala strain WRL-076 was carried out. Twenty trees were randomly selected for field trial. Nut-fruits without yeast-spray were used as controls. Pistachio nut-fruits on the trees were sprayed with aqueous suspension of yeasts in mid-August. A second spray of yeasts was applied to the trees one week
later. Nut-fruits were collected for analysis 4 weeks after the second spray. Statistical analysis indicated the fungal counts on pistachio nut-fruits were significantly reduced on trees sprayed with the yeast P. anomala. The experiments demonstrated that the yeast, P. anomala can modulate spore production of fungi including A. flavus on the pistachio nut-fruits. Field spraying of these effective yeasts to pistachio trees may decrease the population of A. flavus in the orchards and thus lower the number of nuts infected by this fungus. The outcome may be a reduction of aflatoxin contamination in the edible nuts.
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