All causes inbreeding depression except:

Continued self-pollination result in inbreeding depression. Bud pollination, cleistogamous (closed) flowers and homogamy (Male and female sex organs matures at the same time) promotes self-pollination and causes inbreeding depression. In heterostyly there is difference in between the length of the filaments of stamens and length of style in flowers of some plants. Some of the plants having long stamens and short style, and some of the plants bear long style and short stamens, because anther and stigma are placed in different positions so that the pollen cannot come in contact with the stigma of same flower. Due to this reason, self-pollination is not possible in these plants.