Phytophthora fragariae var. fragariae
English names: Red core, Red stele
Nordic names: Jordbærrødmarv(DK), Mansikan punamätä (FI), Rød marg (NO), Rödrota (SE)
Major host plants
The principal host is cultivated strawberries (Fragaria x ananassa). Only one other host, loganberries (Rubus hybrid), has been found naturally infected, but a number of genera within the tribe Potentilleae in the Rosaceae family have been infected artificially.
Above-ground symptoms are most noticeable in low, poorly drained areas of the field. Infected plants lack vigor and are stunted. They may die just before fruiting or produce a few small fruits.
Root symptoms are characterized by red discoloration in the stele. The normally cream-colored stele of the root turns a wine-red to brick-red. Infected plants have very few new roots compared to the bushy roots of a healthy plant. Roots die from the tip upwards. Lateral roots are usually badly rotted and are commonly lost by the time plants are dug, giving main roots a "rat tail" appearance.
The origin of P. fragariae var. fragariae is unknown. The fungus is now present on several continents and also in the EPPO region.
A map can be downloaded from EPPO's website. See instructions here.
The fungus overwinters in infected roots. In spring, when soils are cool and have abundant free water, the fungus produces motile zoospores. These zoospores swim and are chemically attracted to the tips of strawberry roots. They penetrate the tips of young feeder roots and the fungus grows up the stele. During summer, when soil becomes warm and dry, the fungus forms dormant oospores in the soil or dead root residues. When the soil becomes cool and moist again in fall, oospores germinate and zoospores are released into the soil. Zoospores may swim to the soil surface where they can be carried long distances in surface run-off. Zoospores are most active in soil between 7-15°C. The fungus can survive for many years as resistant oospores in soil.
The main form of spread is in infected planting material. However, the fungus can spread in surface or drainage water, and this can be important for local spread.
Detection and inspection
To confirm the presence of the fungus, carefully inspect the stele by slicing the main roots longitudinally. The stele of an infected plant appears brick-red or brownish-red, whereas the stele of the healthy plant is yellowish-white.
Red stele is most visible in spring between bloom and fruit ripening, and therefore difficult to detect in plants from cold storage.
Pest status and importance
P. fragariae var. fragariae is generally most severe in cool, wet regions where the same strawberry plants are grown and harvested for several years.
Source of information
See further information here:
Author: Christiane Scheel
Editor: Elise T. Yamamoto Buch