Resistance to Phytophthora cactorum in diploid Fragaria species

Abstract

Sixty accessions/genotypes (entries) of diploid Fragaria sp. were tested for susceptibility to Phytophthora cactorum in greenhouse tests. Four experiments, each with four to 35 entries, were conducted, and each entry was represented by 36 to 45 plants per experiment. The plants were graded according to the number of weeks of survival during the first 4 weeks and for plants surviving more than the first 4 weeks, scoring was based on amount of necrosis in the crown. Statistical analysis showed no significant difference among the four experiments. A majority of the accessions (48) were categorized as being resistant or moderately resistant to Phytophthora cactorum. The disease score for this group varied from 1.06 to 3.09. Five accessions with disease scores ranging from 6.25 to 7.43 were considered highly susceptible. Within F. vesca, a highly significant proportion of the total variation in disease scores (57.6%) was attributable to the differences between accessions and, hence, of genetic nature. There was no indication of any Fragaria species being more resistant or susceptible than others and no systematic differences resulting from geographic origin.