Formation of unreduced pollen by an Impatiens hawkeri x platypetala interspecific hybrid

The Impatiens hawkeri Bull. x I. platypetala Lindl. hybrid 7851-1 was studied for characteristics of unreduced pollen. When I. hawkeri x platypetala 7851-1 (2n = 24) was crossed as a pollen parent to I. hawkeri x aurantiaca Tangeglow (2n = 24), offspring contained somatic chromosome numbers ranging from 2n = 30 to 2n = 36. In root-tip cells of each of these offspring, there were 4 I. aurantiaca chromosomes, as expected after normal meiosis of the seed parent Tangeglow. This result showed that unreduced pollen was contributed by 7851-1. Additionally, a study of 7851-1 micropores showed that. at the tetrad stage, 76 % of cells were dyads, and microspores forming from dyads of 7851-1 were noticeably larger than microspores forming the tetrads. An examination of pollen meiosis in 7851-1 showed that the meiotic mechanism for unreduced pollen formation was parallel spindles in the second meiotic division. As a seed parent, 7851-1 was sterile both in crosses and by self pollination. As a pollen parent, 7851-1 was successfully crossed only to seed parents containing I. aurantiaca chromosomes, indicating that I. aurantiaca is a bridging species in interspecific crosses involving I. kawkeri and I. platypetala. The implications for breeding New Guinea Impatiens (I. hawkeri) cultivars using interspecific hybridization are discussed.