Potatoes in Mexico

The highlands of Central Mexico are the centre of origin of the potato blight fungus, Phytophthora infestans, which occurs on wild tuber-bearing species of Solanum. The Toluca Valley, in particular, has high altitude cool summers, with a tendency for morning fog to sit over the potato crops until about midday. In Ireland, this would be called "real blight weather". Functional oospores are common, and the blight epidemics are particularly severe. The popular Dutch cultivar Alpha, for example, must be sprayed up to twenty five times with protective fungicides. Without spraying, the loss of crop is total.

Apparently, the Spanish took potatoes from South America to Mexico at an early date, but soon discovered that it was impossible to cultivate them. The reason for this failure remained a mystery but, with hindsight, it was clearly due to blight. The Spanish discovered that potatoes could be grown in Mexico, but only under irrigation, during the dry season, and at low altitude. This agro-ecosystem provided the necessary warmth and moisture under blight-free conditions.

Working in Mexico for the Rockefeller Foundation, John S. Niederhauser tested vertically resistant potato cultivars and discovered that their resistance 'broke down' with extreme rapidity. He also noticed that the levels of susceptibility varied among cultivars whose vertical resistance had failed. These differences in susceptibility were due to differences in the level of horizontal resistance. Although this alternative form of resistance had been known for some time, Niederhauser was the first scientist who attempted to utilise it in preference to vertical resistance. This made him the modern pioneer of horizontal resistance breeding. Niederhauser's cultivars need be sprayed only once or twice in Mexico, where Mexican breeders have continued his breeding. In 1991, Niederhauser was awarded the World Food Prize for this work.

Sad to relate, however, the number of scientists who have followed Niederhauser's lead in potato breeding is small. And few have followed it in other crops.

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