title: Generation of the volatile spiroketals conophthorin and chalcogran by fungal spores on polyunsaturated fatty acids common to almonds and pistachios.
abstract: The spiroketal (E)-conophthorin has recently been reported as a semiochemical of the navel orangeworm moth, a major insect pest of California pistachios and almonds. Conophthorin and the isomeric spiroketal chalcogran are most commonly known as semiochemicals of several scolytid beetles. Conophthorin is both an insect- and plant-produced semiochemical widely recognized as a nonhost plant volatile from the bark of several angiosperm species. Chalcogran is the principal aggregation pheromone component of the six-spined spruce bark beetle. Recent research has shown conophthorin is produced by almonds undergoing hull-split, and both spiroketals are produced by mechanically damaged almonds. To better understand the origin of these spiroketals, the volatile emissions of orchard fungal spores on fatty acids common to both pistachios and almonds were evaluated. The volatile emission for the first 13 days of spores placed on a fatty acid was monitored. The spores investigated were Aspergillus flavus (atoxigenic), A. flavus (toxigenic), Aspergillus niger, Aspergillus parasiticus, Penicillium glabrum, and Rhizopus stolonifer. The fatty acids used as growth media were palmitic, oleic, linoleic, and linolenic. Spores on linoleic acid produced both spiroketals, those on linolenic acid produced only chalcogran, and those on palmitic and oleic acid did not produce either spiroketal. This is the first report of the spiroketals conophthorin and chalcogran from a fungal source.
authors.affiliation: Plant Mycotoxin Research, Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, California 94710, United States. john.beck@ars.usda.gov
authors.forename: John J
authors.initials: JJ
authors.lastname: Beck
authors.forename: Noreen E
authors.initials: NE
authors.lastname: Mahoney
authors.forename: Daniel
authors.initials: D
authors.lastname: Cook
authors.forename: Wai S
authors.initials: WS
authors.lastname: Gee
mesh_terms: D001230:Aspergillus / Q000502:physiology; D001231:Aspergillus flavus / Q000502:physiology; D005231:Fatty Acids, Unsaturated / Q000737:chemistry / Q000378:metabolism*; D005663:Furans / Q000378:metabolism; D019787:Linoleic Acid / Q000737:chemistry / Q000378:metabolism; D010407:Penicillium / Q000502:physiology; D027927:Pistacia / Q000737:chemistry* / Q000382:microbiology; D027861:Prunus / Q000737:chemistry* / Q000382:microbiology; D012233:Rhizopus / Q000502:physiology; D013141:Spiro Compounds / Q000737:chemistry / Q000378:metabolism*; D013172:Spores, Fungal / Q000378:metabolism* / Q000502:physiology; D055549:Volatile Organic Compounds / Q000378:metabolism; D017962:alpha-Linolenic Acid / Q000737:chemistry / Q000378:metabolism
chemical_list: C481308:Conophthorin; D005231:Fatty Acids, Unsaturated; D005663:Furans; D013141:Spiro Compounds; D055549:Volatile Organic Compounds; C585844:chalcogran; C520774:spiroketal; D017962:alpha-Linolenic Acid; D019787:Linoleic Acid