The 2012 ASHS Annual Conference

Interploid sexual hybridization of mandarins, via 28 (diploid x tetraploid) and 2 reciprocal (tetraploid x diploid) crosses was carried out during the 2011 season on different locations in central Florida. The main breeding objectives were: seedlessness, easy-peel fruit, and extending the season of availability (early and late); also, improved juice quality, shelf life, cold hardiness, and disease resistance. In diploid x tetraploid (2X x 4X) crosses, the female (seed) breeding progenitors were the following diploids: ‘Ellendale’ tangor, ‘Fortune’ mandarin, ‘Marisol Clemenetine’ mandarin, ‘Nules Clementine’ mandarin, ‘Monreal Clementine’ mandarin, ‘Lee’ tangelo, ‘Fallglo’ tangelo-tangor, ‘Sugar Belle’ tangelo, and ‘Ambersweet’ tangor. The pollen progenitors were the following allotetraploid somatic hybrids: [‘Page’ tangelo + ‘Ortanique’ tangor], [‘Page’ tangelo + (‘Clementine’ mandarin x ‘Satsuma’ mandarin)], [‘Succari’ orange + ‘Murcott’ tangor], [‘Succari’ orange + ‘Changsha’ mandarin], [‘Succari’ orange + ‘Page’ tangelo], [‘Murcott’ tangor + ‘LB8-8’ tangelo], [‘Rhode Red’ orange + ‘Dancy’ mandarin], [‘Hamlin’ orange + ‘Dancy’ mandarin], [‘Valencia’ orange + ‘Page’ tangelo], and [‘Valencia’ orange + ‘Minneola’ tangelo]. Two allotetraploid somatic hybrids [‘Page’ tangelo + ‘Ortanique’ tangor] and [‘Murcott’ tangor + ‘LB8-8’ tangelo] were also included as female parents in tetraploid x diploid (4X x 2X) crosses while diploid ‘Furr’ tangor was the pollen progenitor in both crosses. Immature fruits were collected 100–120 days after hand-pollination. No fruits were observed in six (2X x 4X) crosses, as well as two (4X x 2X) crosses. In other 26 (2X x 4X) crosses, zygotic embryos were recovered from seeds using an embryo rescue method (embryos were carefully excised under the stereomicroscope and plated on a modified MT medium for 1–3 months to induce germination). Germinating embryos were cultured on different growth media (B+, DBA3, and RMAN) for 4–6 months, and ploidy levels of fully developed seedlings were determined by flow cytometry. The analysis of nuclear DNA content in the progenies revealed variation in ploidy level among produced seedlings. From the total number of generated plants (747), majority were sexual hybrids (582 - 77.9%).  Triploids (3X) represented the highest percentage of sexual hybrids (557 - 95.7%); 24 seedlings (4.1%) were found to be tetraploids (4X), and only 1 (0.2%) to be hexaploid (6X). All sexual hybrids that survived in vitro manipulation were grafted on citrus rootstocks for subsequent field evaluation.