Successful sexual hybridization involves a series of events including
pollen germination, pollen tube growth, fertilization, embryo and
endosperm development, and seed maturation. Stebbins [2] divided
hybridization barriers into two broad groups, namely pre-fertilization
and post-fertilization barriers. The pre-fertilization category
includes those mechanisms which prevent fertilization and includes
geographical isolation, apomixes, and pollen-pistil incompatibilities.
Post-fertilization barriers are a greater hindrance to hybridization and
can be a result of ploidy differences, chromosome elimination, seed
dormancy and hybrid breakdown of particular importance is the need
to get hybrids that are fertile.