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George H. Clough, Sarah Blatchford and Philip B. Hamm

) with yields averaging 23.5 t·ha −1 . The area under production of processing sweet corn increased from ≈24,600 ha in 1987 to 56,000 ha in 2002. Common smut, caused by the fungus Ustilago maydis , occurs worldwide and can cause yield losses in dent corn

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Jerald K. Pataky and Paul M. Richter

Common smut, incited by Ustilago maydis (DS) Corda (syn. = Ustilago zeae Ung.), reduces the number of marketable ears and adds to the cost of harvesting and processing sweet corn. All meristematic tissues are susceptible to U. maydis , but

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Sarah Blatchford, George H. Clough* and Philip B. Hamm

Impact of natural infection of common corn smut (Ustilago maydis) on processing characteristics of three F1 hybrid sweet corn (Zea mays L.) cultivars was evaluated in a two-year study with early and late spring-planting dates. At harvest maturity, size and location of galls were recorded and quality characteristics measured. Galls on the lower stalk, upper stalk and tassel reduced fresh weight and diameter of husked ears while galls on the base of the plant reduced fresh weight only. Ear length was reduced by galls on the upper stalk. As gall size increased from 0 to >10.2 cm. diameter, ear fresh weight and diameter decreased. The presence of galls >10.2 cm diameter reduced ear length. Kernel depth was not affected by size or location of gall. Additional ears of the same three cultivars were sampled from commercial fields planted in mid-season near Walla Walla and Patterson, Wash. Galls located on the upper and lower stalk reduced fresh weight, length, diameter and kernel depth, while galls on the tassel or base had reduced or no effect on these parameters. As gall size increased, fresh weight, length, diameter, and kernel depth decreased.

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J.K. Pataky

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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M.E. Valverde, P. Fallah Moghaddam, M.S. Zavala-Gallardo, J.K. Pataky, O. Paredes-Lopez and W.L. Pedersen

Ear gall development was evaluated after inoculating sweet corn (Zea mays L.) hybrids with Ustilago maydis (DC) Corda by injecting sporidial suspensions into silk channels when silks had emerged ≈3 to 6 cm from ear shoots. Gall incidence was ≈35% in two inoculation trials. About 0.5% of the noninoculated control plants was infected. Gall weight increased ≈250% to 500% between 14 and 21 days after inoculation, reaching a maximum of ≈280 to 600 g. Gall tissue was nearly 100% black and had lost its spongy integrity 19 to 21 days after inoculation, when mycelial cells formed powdery teliospores. A 1- or 2-day harvest window during which huitlacoche yield and quality were optimized corresponded to the time at which 60% to 80% of the gall tissue was black. The optimal huitlacoche harvest time varied among hybrids from 17 to 19 days after inoculation, but we suspect that optimal harvest time varies from ≈15 to 24 days after inoculation, depending on the growth stage at which the host is inoculated and the environmental conditions following inoculation. Differences among sweet corn hybrids in gall incidence, gall size, and coverage of mature galls by husk leaves were observed and could be used to select sweet corn hybrids that are well suited for producing huitlacoche.

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James L. Brewbaker

common in breeding nurseries were rotting Erwinia caratovora f. sp. zeae , aflatoxin-inducing Aspergillus spp., common smut [ Ustilago maydis (DC) Cda.], and maydis blight [ Bipolaris maydis (Nisik.) Shoem.]. These were diseases to which the