In case of plants, inbreeding depression can be measured through comparison of the fitness of selfed individuals with outcrossed individuals. In this paper the effect of repeated inbreeding on fruit yield and yield component of strawberries (Fragaria × ananassa Duch.) was examined. Five strawberry cultivars (from 10 initial ones) including ‘Kent’, ‘Teresa’, ‘Senga Sengana’, ‘Chandler’ and the breeding clone 1387 were examined and self-pollinated in order to obtain first (S₁), second (S₂) and third (S₃) inbreeding generations. 5 cultivars differing in pedigree which were assumed to have the inbreeding coefficient of zero (F = 0) were compared with self-pollinated populations with expected inbreeding coefficients F = 0.5 (S₁), F = 0.75 (S₂) and F = 0.87 (S₃). The effects of different inbreeding levels were estimated for the following traits: number of inflorescences, number of flowers per inflorescence, fruit yield per plant, fruit number per plant, average fruit weight, weight of leaves per plant and pollen viability. Both positive and negative inbreeding depressions were found in many progenies in terms of the analysed characters. Weight of leaves per plant in S₁, S₂ and S₃ was affected the most (inbreeding depression ID = 62.5, ID = 66.2 and ID = 67.2, respectively). In the second generation (S₂), average fruit number per plant increased in comparison to S₀ (ID was -6.1). Inbreeding depression for average fruit weight per plant decreased in the successive inbreeding generations.

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