In parts of central Mexico, galls of common smut, caused by Ustilago maydis (Syn = Ustilago zeae Ung.), on ears of corn (Zea mays L.) are an edible delicacy known as cuitlacoche. Preliminary studies were done to identify methods to increase formation of ear galls on sweet corn. Of 370 sweet corn hybrids evaluated in disease nurseries, 38 hybrids were identified for which incidence of ear galls exceeded 40% in 1987 or 1988 or exceeded 12% in 1990. Inoculation techniques for inducing ear galls were: 1) spraying sporidial suspensions between leaf sheaths and stalks at the sixth to eighth nodes; 2) injecting sporidial suspensions into the sixth to eighth internodes; 3) wounding leaf sheaths at the sixth to eighth nodes with sand, followed by spraying a sporidial suspension into wounds; and 4) wounding leaf sheaths at the sixth to eighth nodes with sand in which teliospores were mixed. Only the sporidial injection technique substantially increased the incidence of smut, but it increased the incidence of stalk, tassel, and leaf galls more than ear galls. Thus, additional research is needed to determine when and how to inoculate with U. maydis to induce the formation of ear galls necessary to commercially produce cuitlacoche and to screen for disease resistance.
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