'Mechanism' of Phytophthora-Resistance of Potatoes

USING as a basis the American 'native forms' of the tuber-bearing species of Solanacesæ ; German breeders during the last two decades have developed potato varieties with both leaves and tubers resistant to most of the origin races of Phytophthora infestans. It is true that the origin and initial constitution of the material which was used for the breeding of these varieties is only imperfectly known ; but we know that its Detractory behaviour towards the Phytophthora funguses associated with a gene R which is not found in any European variety of the old-fashioned type. Furthermore, according to K. O. Müller, this resistance gene has several associated alleles and is inherited independently of other economically important characters, such as yield capacity, time of maturity, and the like.. Therefore it did not take very long to combine the Phytophthora resistance of these 'W varieties' with the high yielding-capacity and other inherent qualities of the European cultivated potato. The first German commercial varieties resistant to P. infestans which appeared on the market were Erika (1941), Robusta (1941), Frueh-nudel (1941), and Aquila (1942). There are at present in Germany ten new registered potato varieties, all of which possess this resistance gene.