الفهرس 
GENERALINTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Late-blight of potato and tomato is a serious and widespread disease caused by Phytophthora infestans. There is evidence that the disease spread throughout the world from Mexico 150 years ago Recently migration of the A2 mating type and new A 1 mating types from Mexico has initiated sexually reproducing populations which may be more difficult to control. Because molecular markers are available and the sexual cycle can be manipulated in vitro, attempts can be made to isolate and sequence avirulence genes which determine pathogenicity on potato genotypes carrying known single genes for resistance. A virulence genes thus need to be identified in suitable parents by their pattern of inheritance in progeny of matings in which avirulence/vh-ulence is segregating. The thesis records results of experiments aimed at producing segregating progenies and identifying genes controlling pathogenicity
1- Ninety-three isolates were isolated from blighted tubers from many countries, obtained from shops in Bangor, Gwynedd, U.K. and potato and tomato foliage and fruits from different locations in U.K. during the period 1992-1993.
2- All isolates were tested for mating type. This isolation revealed that isolates of the A 1 mating type were widely distributed throughout the growing areas of potato and constituted 92.47% of the total isolates collected; 6.45% of isolates were A2
3- The A2 mating type were present in Egypt in 1993.
4- The A2 mating type was identified in imported potato tubers from Portugal This is the first record of A2 mating type in Portugal.