The purpose of the current work is to determine the degree of resistance of wild and cultivated species of the genus Zea to Ustilago maydis D.C. Corda (U.m.) which will subsequently be used in crosses to obtain new forage plants. The host materials used were the population c.v. Colorado Klein, the inbred lines SC66, B73 and E642A88 of Zea mays ssp. mays as well as clones of Zea diploperennis and Zea perennis. All the materials were inoculated with different of strains of U.m. isolated at Santa Catalina, Necochea, Balcarce, Paran·, 25 de Mayo, RÌo Cuarto. Strains were cultivated in a liquid medium of 2% C.P.G., under shaking for 8 days running at 25 C. The pathogen was inoculated using a hypodermic syringe. The trial involved three replications and a tester (non-inoculated plants). The plants were evaluated using a reaction scale (Table 1) to determine the mean percent infection of the U.m. fungus.

Table 1. Reaction scale in hosts.
 

Behaviour	Host Reaction
Inmune (o)	No reaction
Resistant (1)	Partial Chlorosis
Medium resistant (2)	Accent chlorosis and/or presence of stripe or anthocyanin stain.
Medium susceptible (3)	Necrosis and diminution of growth in plants
Susceptibles (4)	Formation of tumors (galls)

Wild and cultivated species of the genus Zea showed different reaction grades from resistant to susceptible (graphic 1-6), depending both on the Zea genotype or the geographic origin of U.m. strain inoculated.

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