CURRENT STATUS OF THE DOWNY MILDEWS OF MAIZE IN THE AMERICAS

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Only three species of maize downy mildew (DM) pathogens are know in the Americas. These are Sclerospora graminicola (Sacc.) Schrote, S. sorghi Weston and Uppal and Scleropthora macrospore (Sacc.) Thirm. Et al. Melhus et al. reported two natural occurrences of S. graminicola; one in 1925 on dent maize (Zea mays :.) seedings and the second in 1927 on sweet maize (23). Apparently, the pathogen never became an important factor because there have been essentially no reports of the disease in maize since then. S. macrospore, causing crazy top of maize, was reviewed by Ullstrup in 1940 (34). To my knowledge little has been done to initiate further studies on control of crazy top in maize since then. The sporatic nature and broad host range of the disease will require adaptation of efficient techniques before a host resistance program can be initiated. Sources of genctically controlled resistance have not been described, although differences among commercial hybrids have been noted (34).