Remission of Symptoms on Maize Plants Infected with Downy Mildew in Northern Nigeria. O. M. Olanya, Maize Research Program, International Institute of Tropical Agriculture, PMB 5320, Oyo Road, Ibadan, Nigeria, and IITA/SAFGRAD, 01 B.P. 1495, Ouagadougou, Burkina Faso. J. M. Fajemisin, Maize Research Program, International Institute of Tropical Agriculture, PMB 5320, Oyo Road, Ibadan, Nigeria, and IITA/SAFGRAD, 01 B.P. 1495, Ouagadougou, Burkina Faso. Plant Dis. 76:753. Accepted for publication 10 July 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0753E.
Symptom remission was observed on maize (Zea mays L.) plants after infection by Peronosclerospora sorghi (Weston & Uppal) C. G. Shaw in Zaria, northern Nigeria. In 1989, 3-wk-old maize plants from five genotypes that were naturally infected with P. sorghi were tagged. In 1990, 684 maize plants from 20 genotypes were first inoculated by spraying conidial suspensions into leaf whorls, then tagged. Tagged plants were observed for disease incidence, type of infection, symptom remission, and effect of downy mildew on cob formation. Incidence of downy mildew ranged from 3 to 37%, and all infected plants showed systemic, half-leaf symptoms with mild chlorosis on leaves. At 8 wk after inoculation (growth stage 8), the mild chlorosis was not readily observed on susceptible maize genotypes TZESR-W, TZESR-Y, Pool 16-SR, 9490, and 9450. Mean percentage of infected plants with symptom remission ranged from 70 to 100%. Cobs formed normally on plants with symptom remission but weighed significantly less than those on uninfected plants. Plants without symptom remission had total yield loss. When seed produced on maize plants with symptom remission were planted, seedlings did not develop downy mildew symptoms. The symptom remission phenomenon possibly is a resistance mechanism.