Were you to take a map of the countries where the A2 is present and overlay it with a map of countries that purchase seed potatoes from Europe, you would find you have an almost perfect match. The problem comes to a head when A1 and A2 are present in the same environment and recombine sexually. The result is an explosion of genetic variation of the fungus and the enhanced probability that even more virulent forms of the disease will be produced. The new forms of the disease could be resistant to some of the most powerful fungicides and to existing sources of genetic resistance within the crop. Moreover, due to the formation of oospores, which are the product of sexual reproduction between the A1 and A2 types, late blight could become an earlier blight and begin infecting the plant immediately after it emerges.
Oospores can survive between cropping seasons and become active soon after planting.
With just the A1 present, infestation usually takes place quite late in the season when the disease is easier to manage. Earlier infection means that farmers are battling the problem soon after emergence. The general implications of this development are likely to result in dramatic increases in the use of fungicide sprays and the development of even more powerful chemicals, both of which carry important consequences for the environment and health. In addition, farmers face substantial annual increases in the costs of production. By the year 2000 developing countries will be producing more than a third of the world's potato crop.