Biochemical Basis of Resistance in Corn to the Corn Leaf Aphid1

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Abstract
Field experiments were conducted to determine the relationship between hydroxamic acid, total phenol, and orthodihydroxyphenol concentrations in corn (Zea mays L.) tassels and resistance to the corn leaf aphid [Rhopalosiphum maidis (Fitch)]. Eleven corn inbreds were evaluated for aphid resistance soon after tassel emergence using a visual rating scale and index system. The corn tassels were harvested and analyzed for hydroxamic acid, total phenol, and orthodihydroxyphenol content. A highly significant negative correlation (r = −0.63) was obtained between aphid infestation and hydroxamic acid concentration. Poor correlations were found between aphid infestation and both the total phenol and orthodihydroxyphenol concentrations. Seven corn inbred lines were further evaluated for corn leaf aphid resistance by artificial infestation in the greenhouse. A highly significant correlation (r = 0.90) was found between the greenhouse and field results.