Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 12, 1999
Publication Date: N/A
Interpretive Summary: In order to combat fungal diseases of corn, it is important to understand how the fungi are moved about in the crop. One of these fungi, Fusarium verticillioides, causes a serious ear-rot disease in corn and also produces an important chemical mycotoxin called fumonisin. It is known that the fungus can be transmitted by sap beetles, but it was not known whether this transmission is incidental or is due to some close natural association between the fungus and the beetles. One indication of a close ecological tie would be if the fungus ordinarily produces chemicals that are attractive to the beetles. This research demonstrated clearly that the fungus does, in fact, produce such chemicals, and in amounts that would be attractive under natural conditions. The chemicals were identified, and it was demonstrated in laboratory wind-tunnel tests that fungal cultures and blends of synthetic chemicals prepared to simulate the cultures were comparably attractive to the beetles. This study adds to scientists' basic understanding of factors affecting disease propagation in the corn crop, and may be useful as new disease-managing strategies are developed.
Technical Abstract: It is known that sap beetles (Coleoptera: Nitidulidae) can vector the fungus, Fusarium verticillioides (= F. moniliforme), an important ear-rot fungus in corn that produces the mycotoxin, fumonisin. The volatiles produced by this fungus were studied to establish whether they could attract sap beetles. Such an association would suggest more than just an incidental role in transmission of the fungus by the beetles. F. verticillioides consistently produces a blend of five alcohols (ethanol, 1- propanol, 2-methyl-1-propanol, 3-methyl-1-butanol, and 2-methyl- 1-butanol), acetaldehyde, and ethyl acetate. Ethanol is the most abundant alcohol. The fungus also produces four phenolic compounds (the most abundant of which is ethylguaiacol), and a number of unidentified compounds in trace amounts. Solid-phase microextraction (SPME) was the key technique used in volatile analysis. The volatile profile changes over time: The alcohols, aldehyde, and ester always appeared first; and production of the phenolics lagged by several days. All volatile production eventually diminished. The volatiles were highly attractive to the sap beetle, Carpophilus humeralis (F.), in wind-tunnel bioassays. Attraction was correlated primarily to the presence of the alcohols, acetaldehyde, and ethyl acetate, rather than to the phenolics. Attractive cultures and synthetic mixtures prepared to simulate them, both qualitatively and quantitatively, compared favorably in wind-tunnel bioassays. The fungus produced the same volatiles under field conditions.