Impatiens crosses were made between Plant Introduction (P.I.) 349629 (2n = 16) and cultivar Tangerine (2n = 8), producing a hybrid (2n = 12) that seemed sterile. A large number of pollinations of the hybrid with 'Tangerine' pollen, however, produced only three progeny with 2n numbers of 8, 9, and 12. The backcross with hybrid pollen on P.I. 349629 produced five progeny, all of which were 2n = 20. None of these backcross progeny has shown fertility at present. Backcrosses involving the hybrids between 32 chromosome P.I. accessions and 'Tangerine' have been unproductive. Eleven of the hybrids (2n = 24) between P.I. 349629 and several of the 32-chromosome P.I. accessions occasionally produced viable pollen. When used on a 'Tange-glow' female, which is a 24-chromosome amphidiploid, numerous progeny resulted, some of which proved to be fertile in subsequent crosses.
Viable pollen-producing hybrids were obtained from the crosses New Guinea Impatiens Plant Introductions (P.I.'s) (2n = 32) × Java Impatiens P.I. 349629(2n = 16). The hybrids were crossed with a 24-chromosome amphidiploid ‘Tangeglow,’ resulting in 2n = 34-chromosome hybrids. One of these 34-chromosome hybrids was crossed with P.I. 349692 (2n = 16), producing two offspring having chromosome counts of 2n = 24 and 2n = 30. Subsequent crosses using the 30-chromosome hybrid showed a continuing tendency for production of viable partly unreduced gametes.
Pollen germination on 2% agar medium was investigated as a method of screening pollen viability, using ISU 7851-1, a Java × New Guinea Impatiens interspecific hybrid. A chi-square test showed that percentage pollen germination was related to corresponding seed set. However, some pollinations yielded seeds from pollen that tested in vitro as low as 0.5% germination. Other Impatiens genotypes were screened rapidly for pollen viability by microscopically scanning for pollen germination in vitro. ISU 7851-1 pollen diameter sizes ranged from 18 to 81 μm on agar medium, but only pollen grains of 45 μm and larger were capable of in vitro germination.
Impatiens crosses were made among the following: P.I. 349629 (Java), P.I. 349586 (New Guinea), I. Itolstii, and "Tangerine." All crosses were successful except those made with I. Itolstii. Chromosome counts were as follows: P.I. 349629 = 16, P.I. 349586 = 32, I. Itolstii = 16, and "Tangerine" = 8. Chromosome counts of the hybrids were midway between the respective parents. Cytological studies indicated a similarity in chromosome morphology and size among all parents except I. holslii. A new genome count of 4 is reported for the genus Impatiens indicating a ploidy series in which x = 4.
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