Maize in tropical Africa

The behaviour of maize in tropical Africa, following the introduction of the re-encounter disease Puccinia polysora, is now the classic example of horizontal resistance (Vanderplank, 1968; Robinson, 1976, 1987). On the appearance of the disease, in the 1940s and 1950s, the horizontal resistance of local landraces was minimal and, in areas of maximal epidemiological competence, the crop loss was total. Some ten to fifteen maize generations later, the horizontal resistance was maximal, and the crop loss was negligible. This natural accumulation of horizontal resistance occurred without any 'good source' of resistance, and without any assistance from plant pathologists or plant breeders. It has also provided us with guidelines for the breeding of all other crops for horizontal resistance (see 7.2).

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