Effect of Generation Advancement by Inbreeding on Inbreeding Depression and Seed Germination in Strawberry

A problem associated with inbred line breeding of strawberry (Fragaria × ananassa) is that the plant's vigor becomes weak as to selfing repeats itself and as a consequence further, selfing can be impossible. To solve this problem, inbreeding depression and percent germination, categorized by generation to be selected individuals with non-inbreeding depression and to be eliminated individuals with inbreeding depression has been researched. As a result, F₂ lines which originated from 'Akihime' variety had 36.3% germination, and F₃, F₄, and F∧5 had 13.5, 55.9, and 65.8%, respectively. As generation progressed, the percent of germination increased. Also, it had same result by the lines originated from 'Johong' and 'Sachinoka' variety. However, there was a difference of lines on percent germination within the same variety. The investigation of inbreeding depression according to the selfing was; for F₂ generation originated from 'Akhime' variety was 25.0%, F₃ was 48.5%, F₄ was 21.1%, and F∧5 was 14.4%. That of originated from 'Johong' variety was 25, 12.5, 6.2, 5.3%, respectively. Also, for 'Sachinoka' variety was 33, 74.8, 26.4, 14.7%, respectively. When the percent germination of the inbreeding depression plant and non-inbreeding depression plant in lines originated from 'Akihime' variety were compared, there was not a difference. However in lines originated from 'Johong' and 'Sachinoka' variety, the percent germination of inbreeding depression plant was remarkably lower. In the next generation of lines occurred inbreeding depression, we also found the condition of inbreeding depression; although the degree of inbreeding depression varies. As follows, inbreeding depression and percent germination, which has been depicted as a problem on inbred line breeding of strawberry, can be solved by selecting vigorous and productive plant from the early selection.