Pre-Fertilization Crossing Barriers on Culture Techniques
The pre-fertilization barriers include situations or events before the fertilization and therefore, may be due to (i) differences in flowering times of the two parents, (ii) lack of stigma receptivity or pollen viability, (iii) failure of pollen tube to reach the ovule due to slow growth, (iv) cross-incompatibility due to any other unknown reason.

The above crossing barriers can be overcome by collecting pollen at the appropriate state of development and using them for in vitro pollination. The pollination may be carried out on stigma, placenta or ovules of an excised ovary cultured on an artificial medium (under aseptic conditions).

The choice between the organs used for pollination is made through a details study of crossing barrier. Fo instance, if lack of stigma receptivity or slow pollen tube growth are the crossing barriers, pollination can not be carried out on stigma, but instead placenta or ovules will have to be used for pollination. The bisexual flowers need to be emasculated and bagged before ovaries are excised for in vitro operations. After fertilization, the ovules or ovaries are transferred to a fresh medium for seed development.

The technique of in vitro pollination and fertilization is also useful in overcoming self incompatibility, where selfing is desired but can not be achieved by conventional method of bagging bisexual flowers. As we know elf incompatibility does not allow fusion of male and female gametes from the same plant, even though the gametes are fertile. It is attributed to barriers at the level of pollen germination and/or pollen tube growth, so that fertilization can be affected, if in vitro pollination is carried out directly on the ovule or on the ovary after removing the stigma and style.