Studies on the resistance to late blight in potatoes. II. Field infection of interspecific hybrid potatoes with newly appeared Strain of Phytophthora iufestales.

Abstract

Field infection of 15 demissulee-hydrids and progeny of 48005-3 x Voran has heen observed In parallel with artificial inoculation test with common strain of Phytophthora ilefestans in 1954. Among 15 deinissum-hybrids, four seedling varieties, viz. 529-1, 48005-46, 48005-59 and 48005-83 were found to have lower resistance to P. infesta, es through the artificial inoculation on leaves with common strain H₁ These seedling varieties with the exception of 529-1 gave varying degrees of field infection and it has been observed that the infection was due to the appearance of new pathogenic strain H₂. As to the seedlings of 48005-3XVoran the same result was obtained ; those resistant to strain Hi became spontaneously iufected by late August, showing. quite various degrees of infection. The variation in the degree of field infection may be partly due to the so called partial resistance and since little is known on the nature of partial resistance further study will be required in order to clarify the problem of endless host-parasite competition.