In the summer of 1981, field experiments were carried out to determine the levels of resistance in corn to the corn leaf aphid. Thirteen widely used corn inbreds were planted in two locations in Southern New Hampshire. Sufficient natural infestations of the corn leaf aphid occurred in both locations, and a visual rating scale and index system used by Long et al. (Crop Science 17:55, 1977) was used to measure the levels of resistance.
A modified version of the procedure developed by Argandona et al. (Phytochem. 19:1665, 1980) was used to determine the hydroxamic acid content in the corn tassels. A significant correlation (r = .63) was found between hydroxamic acid concentration and resistance to the corn leaf aphid in the thirteen corn inbreds.
Evaluations of several lab procedures which quantify hydroxamic acid content including the rapid procedure are also being performed. Recent results suggest the presence of interfering compounds in corn stem extracts obtained using the rapid procedure. Also, certain environmental conditions (i.e., soil medium, light intensity) under which the corn is grown have been found to affect the results obtained using the rapid procedure.
G. M. Dunn and David Beck
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