one-fourth of that in 1975. To maintain and develop the citrus industry in Japan, it is indispensable to develop new mandarin cultivars with large fruits and high sugar content in addition to ease of eating. The citrus breeding program in Japan began
Hiroko Hamada, Keisuke Nonaka, Terutaka Yoshioka, and Masahiko Yamada
Jude W. Grosser, Hyun Joo An, Milica Calovic, Dong H. Lee, Chunxian Chen, Monica Vasconcellos, and Frederick G. Gmitter Jr
-induced polyploidy in citrus embryogenic cultures, somatic embryos, and regenerated plantlets Plant Sci. 74 135 141 Grosser, J.W. Chandler, J.L. 2004 Production of twelve new allotetraploid somatic hybrid citrus breeding
Keisuke Nonaka, Masayuki Kita, Yoshinori Ikoma, Hiroshi Fukamachi, Atsushi Imai, Terutaka Yoshioka, and Masahiko Yamada
repeatedly used as parents in the NIFTS citrus breeding program were chosen ( Table 1 ). Five fruit were sampled from one tree of each cultivar and selection (genotype) at both Kuchinotsu Citrus Research Station in Nagasaki, Japan (lat. 32°59′N, long. 130
Catherine J. Westbrook, David G. Hall, Ed Stover, Yong Ping Duan, and Richard F. Lee
study would be a worthwhile investment because of the important role of P. trifoliata in citrus breeding programs. Poncirus trifoliata is graft-compatible and hybridizes with Citrus , is the dominant rootstock in China, and since 1892 in Florida has
Sharon Inch, Ed Stover, Randall Driggers, and Richard F. Lee
increase cold tolerance, although the fruit of Poncirus itself is inedible ( Barrett, 1990 ; Gmitter, 1994 ; Tignor et al., 1998 ). The USDA citrus breeding program has been using Poncirus in some hybridizations for many years, specifically to enhance
Francisco A. A. Mourão Fo, Jude W. Grosser, and Frederick G. Gmitter Jr.
Protoplast culture following polyethylene glycol (PEG)-induced fusion resulted in the regeneration of somatic hybrid plants from the following combinations: `Succari' sweet orange (C. sinensis L. Osbeck) + `Ponkan' mandarin (C. reticulata Blanco), `Succari' sweet orange + `Dancy' mandarin (C. reticulata), `Succari' sweet orange + `Page' tangelo [a sexual hybrid between `Minneola' tangelo (C. reticulata × C. paradisi Mcf.) × `Clementine' mandarin (C. reticulata)], `Valencia' sweet orange (C. sinensis) + `Page' tangelo. `Succari' and `Valencia' protoplasts were isolated -from ovule-derived embryogenic cell suspension cultures and from seedling leaves for the other parents. Somatic hybrid plants were Identified on the basis of leaf morphology and electrophoretic analysis of isozyme banding patterns. Root tip cell chromosome counting is being performed on all plants. Other putative somatic hybrids Include: `Succari' sweet orange + `Minneola' tangelo; `Succari' sweet orange + `Murcott' tangos (C. sinensis × C. reticulata); `Valencia' sweet orange + `Murcott' tangor; and `Valencia' sweet orange + `Dancy' mandarin. These plants may have direct cultivar potential, but there primary use will be for interploid hybridization with selected monoembryonic scions to produce improved seedless triploids.
S. Kobayashi, I. Oiyama, K. Yoshinaga, T. Ohgawara, and S. Ishii
Iwao Oiyama and Shozo Kobayashi
Seedlings from some small seeds of diploid × diploid crosses using `Miyauchi iyokan' (Citrus iyo Hort. ex Tanaka) as the seed parent were found to be pentaploid (2n = 5x = 45). The growth of pentaploid seedlings was extremely weak on their own roots, but was much more vigorous when micrografted on seedlings of tetraploid trifoliate orange [Poncirus trifoliata (L.) Raf.]. Diploid `Miyauchi iyokan' produced hexaploid seedlings from small seeds in addition to triploid and tetraploid seedlings from normal seeds when crossed with tetraploid `Funadoko' (C. funadoko Hort. ex Y. Tanaka) and `Trovita' sweet orange [C. sinensis (L.) Osbeck]. Based on this phenomenon, the origin of pentaploids is discussed.