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 pla typetala 7851-1 (2n = 24) was crossed as a pollen parent to I. hawkeri x aurantiaca Tangeglow (2n = 24), offspring contained somatic chromos ome numbers ranging from 2n = 30 to 2n = 36. In root-tip cells of each of these offspring, there were 4 I. aurantiaca chromosomes, as expect ed after normal meiosis of the seed parent Tangeglow. This result show ed that unreduced pollen was contributed by 7851-1. Additionally, a st udy of 7851-1 micropores showed that. at the tetrad stage, 76 % of cel ls were dyads, and microspores forming from dyads of 7851-1 were notic eably larger than microspores forming the tetrads. An examination of p ollen meiosis in 7851-1 showed that the meiotic mechanism for unreduce d pollen formation was parallel spindles in the second meiotic divisio n. As a seed parent, 7851-1 was sterile both in crosses and by self po llination. 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 ar e discussed.