LOMAS DE ZAMORA, ARGENTINA
Inst. Fitotécnico Sta. Catalina and Centro de Inv. Genéticas

Pathogenic behaviour of spontaneus populations of U. maydis (DC) Corda on maize commercial hybrids
--Sandoval, MC

Field studies to determine the pathogenic behaviour of spontaneous populations of Ustilago maydis (Um) from several regions of Argentina were carried out. These populations were artificially inoculated on maize commercial hybrids (Hirschhorn, E. Las Ustilaginales de la Flora Argentina. CIC. 530 p., 1986). The statistical analysis through Anova-1 and Tukey test showed the existence of significant differences for pathogenicity among the Um populations tested.

The response obtained with the maize hybrids inoculated let us group the 5 Um populations into 2 population groups (Table 1). The first group only includes the Um population named Necochea, in which greater degree of disease resulted in less vigorous and smaller maize plants (level 2 of the scale of pathogenicity). The second group, including the Um populations Pergamino, Paraná, Balcarce and Sta. Catalina, produced fewer symptoms on the maize hybrids inoculated (levels 0 and 1 of the same scale).

The Um populations artificially inoculated showed a loss of pathogenicity compared to the spontaneous populations of the fungi. This phenomenon is surely due to the presence of mutations determining pathogenicity in the inoculated populations.

 Table 1. Results of inoculation of commercial hybrids of corn with 5 U. maydis populations.
 
Treatment Means1 Homogeneous Groups2
1. Necochea 15.00  a
2. Pergamino 4.286 ..b
3. Sta. Catalina 2.143 ..b
4. Balcarce 1.286 ..b
5. Paraná 0.000 ..b
1Affected plants
2Significant at P <0.05 (Tukey test) 


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