SPORANGIAL PRODUCTION (SECONDARY INOCULUM): A COMPONENT OF PARTIAL RESISTANCE IN STRAWBERRY TO PHYTOPHTHORA FRAGARIAE VAR. FRAGARIAE

Seven strawberry cultivars with different levels of susceptibility to Phytophthora fragariae var. fragariae were inoculated with encysted zoospores of isolates NC-1, A-4, A-8, and A-10. Root pieces (40 mm long) were excised after 48-hr-incubation in the dark at 15°C and placed in nonsterile soil leachate to induce sporangia.
The total number of sporangia per root was recorded after 6, 8, and 10 days.
High numbers of sporangia (30–50) were produced on root pieces of the highly susceptible cultivars Tennessee Beauty, Titan, and Marlate by all isolates tested.
Although ‘Sunrise’ is highly susceptible to infection by isolate NC-1, the number of sporangia produced was extremely low (mean of 1.4 sporangia per root). Very few to no sporangia were produced on ‘Surecrop’ roots.
The lack of sporangial formation and production of secondary inoculum (zoospores) in the cultivars Sunrise and Surecrop appears to be a component of partial resistance in strawberry that allows these cultivars to grow and produce a good crop despite being susceptible to infection by Phytophthora fragariae var. fragariae.

III International Strawberry Symposium

R.D. Milholland, M.E. Daykin

Fragaria x ananassa, disease resistance, red stele, root rot

https://doi.org/10.17660/ActaHortic.1997.439.25