INDUCTION OF TANGERINE EMBRYOGENIC CALLI FROM UNFERTILIZED OR IMMATURE OVULES

Triploid hybrids may be obtained by interploid crosses between diploid and tetraploid individuals, but it is difficult to generatetetraploid lineages because of the high frequency of chimeric polyploids. It is possible to induce polyploids in embryogenic calli or cell suspensions by using antimitotics. Embryogenic calli may be obtained from unfertilized, or fertilized ovules, or from the nucellus. Aiming to establish suspension-cell cultures for further treatment with antimitotics, ovules of ‘Ponkan’, ‘Montenegrina’, ‘Mexerica-do-Rio’ and ‘Cravo’ tangerines were used. Two experiments were carried out. After asepsis in sodium hypochlorite (3:1) solution, the ovules were inoculated on Petri dishes containing MT basal medium. In the first experiment, the ovules were cultivated on a growth-regulator free basal medium or with growth regulators BAP (5.0 or 10.0 mg L^-1), KIN (5.0 or 10.0 mg L^-1) or 2,4-D (1.0 or 2.0 mg L^-1). The percentage of responsive explants was evaluated after three months. For the second experiment, the ovules were inoculated in MT basal medium supplied with 5.0 mg L^-1 kinetin. After two months, the percentage of embryogenic calli and somatic embryos was recorded. All cultures were subcultivated every four weeks. In the first experiment, the induction of calli from ovules occurred on growth-regulator free basal medium in all studied cultivars. ‘Montenegrina’ ovules showed the largest percentage of responsive explants (35%) on growth-regulator free basal medium. The second experiment of calli and embryo induction occurred in the eighth week. ‘Mexerica-do-Rio’, ‘Cravo’, ‘Ponkan’ and ‘Montenegrina’ presented 25, 35, 15, and 9% calli, respectively. Somatic embryos developed rapidly. ‘Ponkan’ and ‘Montenegrina’ presented the highest percentage of somatic embryos, 45 and 30%, respectively. The type and concentration of plant-growth regulators, and the cultivar used, may have influenced embryogenic callus induction. The different cultivars used presented different responses to the induction of calli and somatic embryos.