'Nishiuchi Konatsu', a Bud Mutation of Hyuganatsu

HORTSCIENCE 44(6):1547–1551. 2009. et al., 1990) have been successfully used to reduce the number of seeds in the fruit. Although some Hyuganatsu growers have Reproductive Characteristics adopted these techniques, it is desirable to develop a seedless cultivar for reducing costs for Self-compatibility and and labor. A bud mutation of Hyuganatsu, known as Seedlessness in ‘Nishiuchi Konatsu’, ‘Nishiuchi Konatsu’, was found 25 years ago in Kochi Prefecture. ‘Nishiuchi Konatsu’ bears fruit in an orchard of monoculture a Bud Mutation of Hyuganatsu and produces almost no seeds inside the fruit; thus, it is regarded as a favorable cultivar for (Citrus tamurana hort. ex Tanaka) introduction into Miyazaki Prefecture. 1 Kitajima et al. (2001) researched both pollen Chitose Honsho , Masami Kotsubo, Yuri Fukuda, and Yosui Hamabata tube growth and seed development of ‘Nish- Faculty of Agriculture, University of Miyazaki, 1-1 Gakuenkibanadai-nishi, iuchi Konatsu’, which was mainly used as a Miyazaki 889-2192, Japan seed parent. Tanioka et al. (2001) found an interesting phenomenon; a common variety of Yoshikazu Kurogi and Aya Nishiwaki Hyuganatsu showed a decrease in the number Field Science Center, Faculty of Agriculture, University of Miyazaki, 1-1 of seeds when pollinated with ‘Nishiuchi Gakuenkibanadai-nishi, Miyazaki 889-2192, Japan Konatsu’ pollen. However, little basic infor- mation is available on the reproductive char- Takuya Tetsumura acteristics of ‘Nishiuchi Konatsu’, especially Faculty of Agriculture, University of Miyazaki, 1-1 Gakuenkibanadai-nishi, as a pollenizer. In this study, to elucidate the Miyazaki 889-2192, Japan reproductive characteristics of ‘Nishiuchi Konatsu’, especially its pollen, a pollination Additional index words. citrus, Hyuganatsu, pollination, seed abortion, seed type, self- experiment was conducted using the com- incompatibility monly found variety of Hyuganatsu, Hassaku (Citrus hassaku hort. ex Tanaka), ‘Sweet Abstract. The reproductive characteristics of ‘Nishiuchi Konatsu’, a bud mutation of Spring’, which is a hybrid between Satsuma Hyuganatsu that is self-incompatible, were examined. A pollination experiment resulted mandarin (Citrus unshiu Marc. cv. Ueda in Hyuganatsu · ‘Nishiuchi Konatsu’ and ‘Nishiuchi Konatsu’ self-pollination produced unshu) and Hassaku, and ‘Nishiuchi Konatsu’ their fruit, whereas ‘Nishiuchi Konatsu’ · Hyuganatsu cannot produce fruit as a result and traced their fruit setting and fruit devel- of early dropping of premature fruits within the first 10 weeks after pollination. opment. Finally, the characteristics of the Considering the self-incompatible nature of Hyuganatsu, this result implies a mutation harvested fruits were investigated. of the pollen-expressed gene(s) associated with the self-incompatibility occurring in ‘Nishiuchi Konatsu’. When ‘Nishiuchi Konatsu’ pollen was used for several citrus Materials and Methods accessions (Hyuganatsu, ‘Nishiuchi Konatsu’, Hassaku, and ‘Sweet Spring’), it was observed that the number of normal seeds decreased and that of aborted seeds increased. Plant materials. The following plant mate- Interestingly, the extent of seed abortion differed among seed parents. Hyuganatsu and rials were used: the commonly found variety ‘Nishiuchi Konatsu’ lost most of their normal seeds. In contrast, Hassaku lost relatively of Hyuganatsu (hereafter, Hyuganatsu); its lesser seeds, and ‘Sweet Spring’ lost only a few seeds. Moreover, Hassaku fruits obtained bud-mutated cultivar Nishiuchi Konatsu; Has- by pollination with ‘Nishiuchi Konatsu’ pollen showed various proportions of normal saku cv. Nomabeni Hassaku, which is a bud and aborted seeds even among individual fruits. ‘Nishiuchi Konatsu’ pollen did not affect sport of a commonly used type of Hassaku the fruit characteristics, with some exceptions in Hyuganatsu, ‘Nishiuchi Konatsu’, and (hereafter, Hassaku); and ‘Sweet Spring’. All Hassaku. All the characteristics were superior in Hyuganatsu-pollinated fruits compared accessions used in this study produced mono- with ‘Nishiuchi Konatsu’-pollinated ones in ‘Sweet Spring’. In conclusion, it was demon- embryonic seeds. Hyuganatsu, Hassaku, and strated that ‘Nishiuchi Konatsu’ has two agriculturally important traits: self-compati- ‘Sweet Spring’ were grown at the Field bility and seed abortion. It can be useful for elucidating the mechanisms and as the Science Center, University of Miyazaki, and genetic resources that introduce these traits. ‘Nishiuchi Konatsu’ was grown in a commercial orchard in Kiyotake Town, Miyazaki Prefecture. All trees in each strain were clones Hyuganatsu (Citrus tamurana hort. ex 150 years ago, is a late-season citrus plant. with identical genetic background. Tanaka), which happened to be found as a It is unique to prepare eating this fruit for The flowers of each accession at the chance seedling in Miyazaki Prefecture eating; with a knife, the fruit is peeled off balloon stage were collected from the pre- only the flavedo and the segment and albedo viously mentioned fields, except for ‘Nishiu- are tasted together. Hyuganatsu is now pro- chi Konatsu’ because it bloomed at the Received for publication 26 May 2009. Accepted duced as a special product in Miyazaki, beginning to middle of May, a little bit later for publication 21 July 2009. Kochi Prefecture, and elsewhere. Hyuga- than others that bloomed at the end of April This work was supported, in part, by Grants in Aid natsu is substantially self-incompatible with- to the beginning of May. Thus, the flowers for Young Scientists (B) (19780021 and 21780024) out parthenocarpic traits (Miwa, 1951). As of ‘Nishiuchi Konatsu’, which were grown given to C.H. from the Ministry of Education, a result of these characteristics, a pollenizer in a greenhouse, were supplied from the Culture, Sports, Science and Technology (MEXT), is required to set the fruits, which ultimately Fruit Tree Station at the Kochi Agricultural and the Japan Society for the Promotion of Science contain many seeds (Yamamoto et al., 1995). Research Center. Anthers were excised from (JSPS). However, in citriculture, seedlessness is one the flowers and dehisced by overnight incu- We are grateful to Mitsutoshi Tanaka at the Kochi of the most important factors in determining bation at 30 °C. They were then sieved with a Agricultural Research Center for providing us with ‘Nishiuchi Konatsu’ pollen. We also thank Makoto the commercial value of a fruit. Gibberellic tea strainer to recover pollen grains, which Nakamura for allowing us to use ‘Nishiuchi acid during the early stages of fruit develop- were maintained at 4 °C in a refrigerator until Konatsu’ trees for our pollination experiments. ment (Yamamoto and Iwasaki, 1994) and pollination time. 1To whom reprint requests should be addressed; pollination with pollens from 4· citrus trees Pollinationexperiment.A pollinationexperi- e-mail [email protected]. (Imai et al., 2007; Yamashita, 1976; Yamashita ment was conducted with nine combinations. HORTSCIENCE VOL. 44(6) OCTOBER 2009 1547 The pollination combinations and the numbers pletely within 10 weeks without any mature traits compared with fruits obtained by pol- of flowers pollinated are summarized in Table fruits being harvested (Fig. 1). When Has- lination with ‘Nishiuchi Konatsu’ pollen. 1. The numbers of trees used as seed parent saku and ‘Sweet Spring’ were used as seed Seed weight was considerably influenced were three, three, two, and three for Hyuga- parents, although physiological drop was by pollen source (Table 2). It was demon- natsu, ‘Nishiuchi Konatsu’, Hassaku, and observed, fruits were set by whatever pollen strated that the total seed weight of the fruits ‘Sweet Spring’, respectively. For each seed was used in this study (data not shown). grown by ‘Nishiuchi Konatsu’ pollination parent, the numbers of flowers used for each There was no significant difference in significantly decreased for all seed parents. combination were equalized within acces- fruit growth among pollen sources at each The numbers of seeds obtained for Hyuga- sions. All the pollination processes were measurement date for Hyuganatsu, Hassaku natsu and ‘Nishiuchi Konatsu’ clearly showed performed in May 2007. However, an addi- (data not shown), and ‘Nishiuchi Konatsu’ the effect of the pollen source (Fig. 3). When tional pollination was performed in 2008 only (Fig. 2). ‘Nishiuchi Konatsu’ fruits pollinated ‘Nishiuchi Konatsu’ pollen was used, normal for Hyuganatsu · Hassaku, because the num- with Hyuganatsu pollen showed apparently seeds were almost completely missing, ber of fruits harvested in 2007 was not enough inferior growth compared with the other whereas many aborted seeds were observed. for the analysis. Inflorescences with leaves fruits. It was shown that the ‘Sweet Spring’ In contrast, most of seeds in the fruits were were selected for pollination; excess flowers fruits pollinated with Hyuganatsu pollen had normal when Hassaku pollen was used. and leafless inflorescences were removed so significantly superior growth compared with When Hassaku and ‘Sweet Spring’ were used that one flower remained in a bearing shoot. fruits obtained from ‘Nishiuchi Konatsu’ as seed parents, the use of ‘Nishiuchi Flowers at the balloon stage were emasculated pollen (Fig. 2). The first statistical signifi- Konatsu’ pollen significantly decreased the with forceps and pollinated by a brush. Polli- cances of the longitudinal and horizontal number of normal seeds but increased nated flowers were immediately paper-bagged diameters appeared at 8 and 6 weeks

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