Preliminary studies to determine the degree of resistance to Ustilago maydis D.C. Corda in wild and cultivated species of the genus Zea
--Astiz Gassó, MM; Molina, MC

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 (Um), which will subsequently be used in crosses to obtain new forage plants (Molina M.C. and Rosales ;T.P., Rev. Facultad Agr. 54:579-586, 1984). The host materials used were the population cv. Colorado Klein and the inbreds SC66, B73 and E642A88 of Zea mays ssp. mays as well as clones of Z. diploperennis and Z. perennis. All the materials were inoculated with a strain of Um belonging to the collection of the Phytopathology Lab. of the Instituto Fitotécnico de Sta. Catalina. The strain was 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, in which 60-30 seedlings were inoculated (Hirschhorn, E., Las Ustilaginales de la Flora Argentina CIC 530 p., 1986). The plants were evaluated using a reaction scale (Table 1) to determine the mean percent infection of the Um fungus. pBR> The results obtained point out that the population cv. Colorado Klein and the inbred SC66 (Z. mays ssp. mays), as well as the clones of Z. perennis and Z. diploperennis, are the most tolerant and show a good response to Um. Some plants of the inbreds B73 and E642A88 were lightly susceptible or susceptible (Table 2).

Table 1. Reaction scale in hosts.

BehaviourHost reaction
Immune (0)No reaction
Resistant(1) Chlorosis partial
Medium resistant (2) chlorosis accent and /or presence stripe or anthocyanin stain
Medium susceptible (3)Necrosis and diminution growth in plants
Susceptibles (4)Formation of tumors (galls)

Table 2. Result of the reaction in species of Gro. Zea with isolates of U. maydis. (Sta. Catalina) in Argentina.

HostsNo. PlantsTotal plants InfectedMeans of the reaction in plants (%)
0 1 2 3 40 1 2 3 4
Colorado Klein 605 25 26 4 01.66 8.33 8.66 1.33 0.00
SC66 605 25 25 4 01.66 8.33 8.33 1.33 0.00
B73 604 19 20 10 71.33 6.33 6.66 3.33 2.33
E642A88 601 17 22 16 40.33 5.66 7.33 5.33 1.33
Zea perennis 3015 4 8 2 15.00 1.33 2.66 0.66 0.33
Zea diploperennis 3011 7 10 1 13.66 2.33 3.33 0.33 0.33
Testigo 30 0 0 0 0 00.00 0.00 0.00 0.00 0.00


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