Research Information System
in: Floriculture, ornamental and plant biotechnology, Jaime A. Teixeira da Silva, Editor, Global Science Books, Ltd, Manila, pp.376-384, 2006
Pure lines, i.e., 100% homozygous lines, are invaluable in plant breeding programs and can be produced gynogenetically. Use of irradiated pollen in pollinations induces parthenogenetic haploids in various vegetable and ornamental plants. Following irradiation of pollen using X or gamma rays, the pollen successfully germinate and tube growth takes place reaching ovules. If fertilization does not take place, however, the egg cell is induced to develop giving rise to haploid embryos which can be rescued at the globular or heart stage, i.e., two to three weeks after pollination. The haploid embryos following culture readily germinate producing haploid plantlets. Chromosome number of the plantlets recovered is doubled via in vitro or in vivo techniques using colchicine. The doubled plantlets, dihaploids, following acclimatization are used successfully in breeding programs. The chromosome number of the plants recovered or doubled can be checked/confirmed via direct or indirect methods such as chromosome counting in the root and shoot tips. Morphological observations of whole plants or organs may be used to differentiate between the haploid and dihaploid plants. In general, haploid plants and organs are smaller. Size of stomata is also another indication of the ploidy level as the haploid plantlets contain smaller stomata. Flow cytometry, an indirect method for ploidy level determination, also gives accurate results. The parthenogenetic induction of haploidy, in some vegetable crops such as melon, watermelon, squash and cucumber – several of which are also produced for ornamental fruits and decoration – is now an established technique. However the technique is open to further improvement to increase the frequency of haploids induced. An important drawback of the technique is that an irradiation source is a must therefore hinders its much wider use. An alternative method to obtain the same irradiation effect would facilitate its use both in research and in commercial breeding