However, cross-pollinated species such as the clovers, alfalfa, rye, sugar beets, and many perennial grasses have reduced seed set or no fertility after self pollination. The amount of fertility in interspecific crosses determines how extensively desirable genes from closely related species or genera can be utilized in a recombination plant breeding program. Infertility covers those cases of infertility or barrenness resulting from irregularities in sexual reproduction.
Gametophytic incompatibility is found in clovers, grasses, sugar beets, potato, and tobacco.
Because the pollen nucleus is haploid, it will contain only one of the incompatibility alleles. The stylar tissue, originating from the female plant, is diploid and will contain 2 of the incompatibility alleles. If the incompatibility S allele in the pollen nucleus is identical with either of the S alleles in the stylar tissue pollen tube growth is slowed in the style and fertilization rarely occurs. Conversely, if the incompatibility allele in the pollen is different than the alleles present in the style, normal pollen tube growth and fertilization will normally occur. Rarely do you have homozygous plants for the S alleles.