Creation And Genetic Analysis Of Triploid Citrus Germplasm

Seedlessness is an elite trait in citrus and triploid citrus is seedless in nature due to the abnormal meiosis and embryo abortion. The efficient way to create seedless triploid cultivar is to cross the tetraploid somatic hybrids with diploid cultivars. To generate seedless triploids with horticulturally acceptable fruit, some somatic hybrids, which were fused by scion cultivars with elite horticultural character, were used as the female parent to cross with some peculiar diploid citrus landraces in China. Triploid seedlings were obtained through embryo rescue. The main results are as follows:1. During the years of 2001-2003, interploidy crosses between elite allotetraploid somatic hybrids and several diploid cultivars were conducted. Diploid cultivars including Shatian pummelo (Citrus grandis (L.) Osbeck 'Shatian'), Huanong Bendizao tangerine (C. succosa Hort 'Huanong'), Zhongqiu Satsuma (C. unshiu Marc. 'Zhongqiu'), HB pummelo (C. grandis Osbeck 'Hirado Buntan'), Guoqing No.4 Satsuma (C. unshiu Marc. 'Guoqing No.4') were used as the female parents, and tetraploid somatic hybrids such as NS ('Nova' Tangelo + 'Succari' Sweet orange, [C. reticulata Blanco × C. paradisi Macf.] 'Nova' + C. Sinensis (L.) Osbeck 'Succari'), NH ('Nova' Tangelo + HB pummelo, [C. reticulata Blanco x C. paradisi Macf.] 'Nova' + C. Grandis (L.) Osbeck 'Hirado Buntan'), SH ('Succari' Sweet orange + HB pummelo, C. Sinensis (L.) Osbeck 'Succari' + C. Grandis (L.) Osbeck 'Hirado Buntan'), VM (Valencia orange + 'Murcott' Tangor, C. Sinensis (L.) Osbeck 'Valencia' + [C. Sinensis (L.) Osbeck ×C. unshiu Marc] 'Murcott' tangor), HD ('Hamlin' Sweet orange + 'Dancy' Tangerine, C. sinensis 'Hamlin' + C. reticulata 'Dancy') were selected as the male parents. By embryo rescue three months after the pollination, a total of 288 triploid and 10 tetraploid plants were verified by flow cytometry analysis and chromosome counting from 10 crosses; 172 triploid and 4 tetrapliod plants have been transplanted and survived in the field. Out of these combinations, embryo rescue of Shatian pummelo × NS combination in 2002 was the most successful and 184 plantlets were identified as triploid among 225 plantlets; finally 124 triploid plantlets survived. This is the first batch of triploid plantlets which have potential to become scion cultivars and will lay the foundation of new triploid seedless cultivar selection in the future.2. During the embryo rescue of Shatian pummelo × ('Nova' Tangelo + "Succari' Sweet orange) in 2002, calli were initiated from the embryoids and the hypocotyls of...