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SUMMARY
Anther-derived rice (Oryza sativa L., ssp. japonica variety Yerua P.A.) plants were obtained after cryopreservation by an encapsulation/dehydration technique. Immature anthers, excised from spikelets pretreated at 8°C for 8d, were encapsulated in calcium alginate beads. The beads were cultured on N6 medium with 11.5 μM naphthaleneacetic acid (NAA) and 2.3 μM 6-furfurylaminopurine (KIN). Fifteen percent of the encapsulated anthers formed calluses when pretreated with sucrose for 3 d in liquid medium, desiccated on silica gel, slowly cooled to - 30°C, immersed in liquid nitrogen (LN), thawed, and recultured. The cryopreserved encapsulated anthers produced 1.67 shoots/callus, in contrast to the control (non-cooled encapsulated anthers), which produced 6 shoots/callus. Eighty percent of the plantlets developed into normal plants after being transferred to greenhouse conditions. Histological observations showed that the origin of the plants was not modified by the cryopreservation process.
Key words: Oryza sativa L; cryopreservation; encapsulation/dehydration; androgenesis.
INTODUCTION
The production of doubled haploid plants has been used to speed up has breeding cycle by achieving homozygosity in one generation. This has allowed an increase in the selection efficiency because of a better discrimination between genotypes within any generation, and the efficient retention of desirable genes in latter generations. The acceleration of the breeding cycle and increase in selection efficiency has made doubled haploid techniques very attractive, not only for conventional breeding but also for plant improvement through mutation induction. The use of anther culture has been limited by many factors (Afza et al., 2000).The dependence on the flowering time has been one of the major constraints in rice-breeding programs, especially in temperate regions, because of the very limited period of lime when this technique can be used. Although a greenhouse may be used during the rest of the year to produce flowering plants, some negative consequences have been observed: (a) anther response to in vitro culture is affected, and (b) the large number of individuals needed to ensure the effectiveness of anther culture inbreeding programs makes the management of F1, F2, or F3 generations difficult. The production of callus and in vitro conservation of haploid cells might be considered as an option to extend the period of use of haploid culture, but when subcultured, cells undergo various chromosomal and ploidy changes that may...