Apomixis is not developmentally conserved in related, genetically characterized Hieracium plants of varying ploidy |
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Authors: | A M Koltunow S D Johnson R A Bicknell |
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Institution: | (1) C.S.I.R.O. Plant Industry, PO Box 350, Glen Osmond, South Australia 5064, Australia, e-mail: anna.koltunow@pi.csiro.au Fax: +61-8-83038601, AU;(2) Crop and Food Research, Private Bag 4704, Christchurch, New Zealand, NZ |
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Abstract: | Apomixis is facultative in characterized members of the genus Hieracium. The three components that comprise the apomictic mechanism include apospory followed by autonomous embryo and endosperm
formation. The time of aposporous embryo sac initiation and mode of embryo sac formation are different in Hieracium piloselloides (D3) and Hieracium aurantiacum (A3.4). Genetic studies have shown that a single dominant locus encodes all three components of apomixis in both species
(Bicknell et al. 2000). We histologically examined a range of related, genetically characterized apomictic Hieracium plants derived from D3 and A3.4 to assess conservation of the apomictic mechanism in different genetic backgrounds. The plants
varied in ploidy, and also in the amount of DNA introduced from sexual Hieracium pilosella (P4). An apomictic hybrid from a cross between the two apomicts was also examined. The developmental processes observed in
the parental apomicts were not conserved in the examined plants and alterations occurred in the components of apomixis. One
plant also exhibited adventitious embryony. The results show that other genetic factors can modify apomixis with respect to
time of initiation, spatial location, and mode of developmental progression. Both the apomictic locus and the modifiers are
essential for efficient penetrance of the trait in Hieracium. Some of the findings in Hieracium correspond with observations in Ranunculus and this is discussed in terms of models for apomictic development and the control of apomixis in crops.
Received: 21 June 1999 / Revision accepted: 17 November 1999 |
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Keywords: | Apomixis Apospory Hieracium Seed Modifiers Adventitious embryony |
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