Factors affecting seed set in the crosses between <Emphasis Type="Italic">Dendranthema grandiflorum</Emphasis> (Ramat.) Kitamura and its wild species |
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Authors: | Chun-Qing Sun Fa-Di Chen Nian-Jun Teng Zhao-Lei Liu Wei-Min Fang Xi-Lin Hou |
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Institution: | (1) College of Horticulture, Nanjing Agricultural University, 210095 Nanjing, China;(2) State Key Laboratory, Laboratory of Crop Genetics and Germplasm Enhancement, 210095 Nanjing, China; |
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Abstract: | Reproductive barriers often exist in the crosses between Dendranthema grandiflorum (Ramat.) Kitamura and its wild species and seriously result in low seed set, consequently reducing breeding efficiency. For
the purpose of revealing the factors leading to low seed set, we investigated pollen viability, germination behavior of pollen
grains on stigmas and embryo development in the crosses between D. grandiflorum and three wild species, D. nankingense (Nakai) Tzvel., D. indicum (L.) Des Moul. and D. zawadskii (Herb.) Tzvel. using technique of paraffin section, and light, fluorescence and scanning electron microscopy. The results
indicated pollen viability of three wild species ranged from 20 to 25%. In the cross between D. grandiflorum and D. nankingense, very few pollen grains germinated on stigmas after pollination and most of them germinated abnormally. In addition, normal
embryos were observed in 12% ovaries at 8 days after pollination and thereafter all the embryos aborted. In other two crosses,
many pollen grains germinated on stigmas and pollen tubes penetrated stigmas normally after pollination. Moreover, normal
embryos were observed in over 50% ovaries from 8 to 15 days after pollination in the cross between D. grandiflorum and D. indicum, and seed set was 59%. In the cross between D. grandiflorum and D. zawadskii, normal embryos were observed in 52% ovaries at 8 days after pollination. After that, however, most embryos degenerated and
seed set was only 9%. These data suggest that pollen viability has no significant effects on seed set of the three crosses.
Very few germinated pollen grains on stigmas and abnormal growth of most pollen tubes before fertilization, and embryo abortion
are the main factors causing failure of the cross between D. grandiflorum and D. nankingense, whereas only embryo abortion is a main factor resulting in low seed set in the cross between D. grandiflorum and D. zawadskii and no barriers occur in the cross between D. grandiflorum and D. indicum. |
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