The cultivar 'Yubeni' was discovered as a mutant of Meiwa kumquat (Fortunella crassifolia Swingle) in Kushima city, Miyazaki. According to the results of flow cytometry analysis and morphological investigation of several tissues and organs, 'Yubeni' was supposed to be a ploidy periclinal chimera with diploid (2n = 2X = 18) in the outermost layer (histogenic layer L-I) and tetraploid (2n = 4X = 36) inner layer (histogenic layer L-II and L-III) in the shoot apical meristem. Compared with the diploid line, it showed similar morphology to the tetraploid line such as larger leaves, flowers and pollen grains. The weight and size of the fruit were both greater than those of the diploid line. Furthermore, this cultivar has desirable traits for kumquat such as smaller number of developed seed and thicker pericarp.
In order to develop new cultivars adaptable to Japan with high quality and functionality, we attempted to produce interspecific hybrids between Vaccinium uliginosum L. (2n = 6x = 72) of the genus Vaccinium, a wild species native to Japan, and some highbush blueberry cultivars (2n = 4x = 48) of the genus Cyanococcus, using reciprocal crossing. Fertile seeds were obtained from 8 of 9 cross combinations, and 13 seedlings were obtained from 5 cross combinations when V. uliginosum were used as a seed parent, but only 7 seedlings from 2 of 9 cross combinations as pollen parent. It was revealed that seeds were easier to obtain when V. uliginosum was used as a seed parent compared with pollen parent, and unilateral cross incompatibility occurred in the reciprocal cross. These seeds germinated in vitro after pretreatment with gibberellin or in a seed bed after stratification. Four resultant seedlings (KB4: KB-2, 7, 9, 10) from the cross of V. uliginosum and 'Bluecrop' were grafted on rootstock and evaluated regarding their hybridity, ploidy level, morphological characteristics of the flower and fruit, and fruit quality. RAPD analysis showed that KB4 was a hybrid between Vaccinium and Cyanococcus. The hybrids were also confirmed to be pentaploid by flow cytometry and observation of the chromosome number in shoot tip cells; however, they produced fertile pollen and set fruits in an open field without artificial pollination. Fruit of all hybrids also had a peduncle with a pair of leaflets differing from one of their parents. Although the contents of anthocyanin and polyphenol and antioxidant capacity of fruit were different among their hybrids, those values of KB-2 were significantly higher than in 'Bluecrop'. In the future, these hybrids may be useful as breeding material to establish new cultivars with high quality and functionality.
In order to establish an in vitro culture model for male self-compatiblity and -incompatibility in Citrus, we assessed the culture environmental condition and optimal constitution of the liquid culture medium using mature pollen of Hyuganatsu (Citrus tamurana hort. ex Tanaka). A basal medium (Hirano・Hoshino, 2009) was used for examination of the optimum constitution. Mature pollen was cultured in a modified medium containing 0.04% (w/v) CaCl 2 , 0.01% (w/v) H 3 BO 3 , 0.0007% (w/v) KH 2 PO 4 , 0.02% (w/v) yeast extract and 10% (w/v) sucrose with the pH adjusted to 7.0, at a density of 1 × 10 5 pollen grains・mL −1 . These were kept at 25°C under dark conditions. In particular, the addition of CaCl 2 , yeast extract and sucrose to the culture medium was essential for an efficient liquid culture system of mature pollen. In this culture, the nomal germination of pollen grains occurred after 4 hours, and the pollen tubes extended approximately 20 µm per hour. The nomal germination rate of mature pollen was highest (73.6%) after 6 hours of culture. Good growth of pollen tubes was maintained, and they reached 200 µm in length after 8 hours of culture.
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