Mutation in Citrus

MASAO NISHIURA

Chief, 1st Laboratory of Fruit Tree, Okitsu Branch, Horticultural Research Station

Most of the present commercial citrus varie­ concerning bud variations, and as a matter of ties cultivated in the world are said to have course. the more the Citrus variety is widely arisen through some kind of natural mutation. planted. the more variations are found in it. Methods of artificial vegetative propagation. In addition. certain chromosomal' changes such as grafting, cutting and layering. which were observed in some citrus. In this paper. are popularly used in fruit trees. facilitate the the bud variations found in Satsuma mandarin, conservation and accumulation of mutation. sweet orange, grapefruit. Natsudaidai and other particularly such a mutation followed by steril­ varieties will be mentioned in the main. ity. as it must be destined to be eliminated under sexual reproduction. Natural Gene Mutation Moreover. nucellar embryony- extra embryos. derived not from the egg cell but from somatic 1) Variation in Satsuma mandarin cells of the nucellus. are developed in the ovules Unshu-mikan or Satsuma mandarin replaced in most varieties of Citrus. and also in For­ the older varieties about 100 years ago, because tunella and Poncirus. This phenomenon is con­ of its early ripening character, superior quality sidered to have been of great advantage in and seedlessness. As Satsuma culture increas­ maintaining natural mutation. since early man­ ed, growers soon began to distinguish differences kind had no technique of vegetative propaga­ between Satsumas grown in various localities. tion. Pomological studies of the various Satsuma In ancient times. Citrus may have secured types by Dr. T. TANAKA in 1918 confirmed the character of poly-embryony, and this phe­ the existence of at least five varieties: "Zail'ai". nomenon in Citrus poses particularly interesting "Ikeda", "Ikiriki", "Owari". and "Wase." problems which deserve consideration. for the The Zairai has large, flattened. coarse. inferior discussion of the evolutionary pattern in citrus quality and late-maturing fruit. The Ikeda has and the utilization of natural and artificial small spherical fruit of excellent quality which mutations. matures later than the Zairai. The Ikiriki has In Citrus. visible variations arise in the body very large fruits of excellent quality and has or somatic tissues of the plant rather frequently, a rather dwarf growth habit. and genetical differences called "bud variation" The Owari has large. flattened fruit of good may be small or great but they are visible. quality and is early maturing. The W ase has measurable and consistent. In the appearance a thin rind, earlier maturing fruit, and has a of the variation, there are two cases in which dwarf growth habit when compared with the the tree was affected. The exact point of origin Owari. is not known but the differences are visible or Old trees of the Zairai. Ikeda. and Ikiriki measurable from parent clone. and the differ­ varieties still exist but they are no longer prop­ ences are visible and affecting only on a branch agated and are not recommended for com­ or a limb. The latter is called "limb sport" mercial planting. or "bud sport". There is much information The Owari variety is the most commonly

10 grown variety. The Aoe-Wase was first found mature from late November to middle Decem­ around 1895 as a limb sport on a tree of the ber. Many bud variations of Wase character common Satsuma in Oita Prefecture. This were found in trees of the Owarl and Zairai discovery of the Wase as a bud mutation was varieties. Among them. the "Miyagawa-Wase" an epochal finding in the citrus industry of appeared as a limb sport from the Zairai Japan. Search for limb sports has attracted Satsuma in 1915 and was introduced by Dr. citrus researchers' and growers' attention and T. Tanaka in 1923. It was the best strain many new bud variations we1·e discovered of the early Satsumas until 1·ecently. among all of the Satsuma varieties. Through A large number of limb sports from the the years. many strains of Satsuma have devel­ Owari variety were found and have given rise oped th.rough limb sports or bud variations to selections superior to the original Owari. and the superior ones have become the main Among the best are the "Sugiyama" and source of Japanese cltdculture today. "Hayashi". At present. each citrus producing In these selections from natural mutation, a prefecture recommends superior strains for very wide range of variations including a range commercial planting. This situation is shown of early to late maturing types have been ob­ in Table 1. More recently, several limb sports tained; namely. Wase Satsumas ripen in early of Owari have been selected for cold hardiness October. several Satsuma strains ripen in early and are being tested. to middle November, and common Satsumas

Table 1. Varietal dlfl'erentlation in Unshu-mlkan through natural mutation Season of Name of variety and strain matw·ity

- Zairai Ikeda In Fukuoka~(in Osaka ) ( Prefectul'e Pl'efecture - Okitsu-Wase (N. S.) E. Oct. Miyagawa-Wase -l- Miho-Wase (N. s.) E. Oct. - Mochimaru-Wase E , Oct.

Matsuyama-Wase E. Oct. Tachima-Wase E. Oct. Original - Yonezawa-Unshu E. M. Nov. Unsh.u-mikan - - Nagahashi-Unshu E. M, Nov. In Kagoshima - Nankan No. 20 E. M . Nov. Prefecture - Shigeta-Un.shu E. M . Nov. Iklrlkl ----- Owari ----1-Sugiyama-Unshu L. Nov. in Nagasaki) in Aichi ) - Silver-hill (N. S.) L. Nov. ( ( Prefectu1·e Prefecture -Tan!kawa-Unshu (N. S.) L. Nov. -Nankan No. 4 L . Nov. Tomono-Unshu L. Nov. Hayashl-Unshu E. Dec. Ooiwa No. 5 E. Dec. - lshlkawa-Unshu l\'I . Dec. - Juman-Unshu M. Dec.

Abbreviations: N. s. = Nucellar seedling E. = Early, M. = Middle, L. = Late

- 11 - On the other hand, systematic citrus breed­ septa, and juice vesicles. were arisen in the ing was projected and conducted at the Horti­ Mediterranean rngion. The Washington Navel cultural Experiment Station. Okitsu (present orange was found in Brazil as a limb sport Okitsu Branch. Horticultural Research Station. from "Laranja Selecta" of ordinary sweet orange Ministry of Agriculture and Forestry) since type. 1937. In our breeding program. it is emphasized Within the Washington Navel and Valencia that selection work among nucellar seedling which are the most world-wide varieties at lines has been conducted on a large scale for p1·esent. many different strains are selected from improving strains of Satsuma by Dr. M. Ka­ its bud variation or limb spod, 1·espectively. jiura. And the effectiveness of breeding Recently. in our country. three strains such through nucellar seedling selection. being ob­ as Ukumori. Tange and Suzuki originating as tained from such superior strains as "Okitsu­ limb sports from Washington Navel wei·e select­ Wase" and "Miho-Wase". was akeady mentioned ed and patented. These strains are rather pro­ in this periodical (cf. JARQ Vol. 2. No. 1. 1967 ). ductive even in our unfavourable climatic 2) Variation in sweet orange conditions and are promising. At present, there are many different varieties The Trovita orange was believed to have or strains of sweet orange in the world. how­ originated from nucellar seedling of Washington ever. they are said to have derived from natural Navel orange in California, and it is non-navel mutations through asexual propagation. regard­ orange which has viable pollen and a few seeds. less of gene recombination through hybridiza­ It was introduced into Japan in 1935 and is tion. Though the sweet orange has an ultimate promising for trial in om· citrus regions where origin in India. it may have been introduced the Washington Navel often fails to set a crop. into China for a long time ago. and also was 3) Variation in Grapefruit impo1-ted into Europe around the 15th century. The grapefruit was introduced into Florida where many varieties originated from natural in 1823. At present. Florida has the largest mutations. Fo1· example. the Shamouti. a production of grapefruit, but the world output famous Palestine 01·ange. originated probably of this kind is only about one-sixth the pro­ as a bud sport from the Belladi. the ordinary duction of sweet oranges. Since the Duncan or common orange of Palestine. variety was a seedling of the original tree in­ The blood oranges such as Maltese blood troduced into Florida in 1823. all other varieties orange which have anthocyanins in the rind, of today may be considered to have arisen from

Table 2, Seedless and flesh color mutations in grapefruit

Flesh colo1·

White Pink Red

Seedy Duncan Vv'alters _ _ ___,.., Foste1· - --,;o,. Hudson (red) (red) (Rind color) ~(wltlte)

Seedless Marsh a. (Rind color) (white) ;,:::;on~ R;,:) Webb Red Blush (red)

- 12 - it by natural mutations. The Duncan has yellow and many selections have been obtained. rind at maturity, flesh of pale ivory-yellew, Among them. the "Kawano Natsudaidai" was usually spoken of as white, and has from 30 found as a limb sport about 60 years ago in to 50 seeds. The seedless condition has arisen Oita Prefecture and was patented in 1950. in later days. however. in this case not by bud This selection is early-ripening (March to April) mutation but by seed mutation. Namely. the and is much less acid than the standard Natsu­ Marsh seedless may originate from seedy daidai. More recently. the "Tajima Natsudai­ Duncan through nucellar seedling. And at dai" was found as a limb sport. It is a late least three instances, including Marsh. are strain. ripens in midsummer and is very juicy. known of seeds from normal seedy grapefruit In addition, two seedless mutants have been producing trees with seedless fruits. The color found from common Natsudaidai. mutation is quite independent of mutation for Iyo: The Iyo originated as a chance seedling seedless condition. and pink and red forms are in Yamaguchi Prefecture and was introduced grown of both seedy and seedless types. in 1886. It is judged to be a tangor and ripens As shown in Table 2. seedy W alte1's of nor­ in January to February. Recently. a limb sport mal type was selected from Duncan through a of the Iyo was found that ripened earlier than nucellar seedling. and the Foster originated as the parent variety and was seedless. It was a limb sport from it in 1906. The Foster has patented in 1966. flushed pink rind, pink flesh and contains seeds. Hyuganatsu : The Hyuganatsu originated as The Hudson. red and seedy grapefruit, was a chance seedling about 1820 in Miyazaki discovered as a limb sport on a Foster tree in Prefecture. and is valuable as a late maturing the mid 1930's at San Benito. Texas. In the variety with excellent aroma, tender flesh and seedless varieties the sequence is clearly very juicy for use as fresh fruit. But the severe established. fruit drop in cold winters reduces its value for The Thompson originated as a pink- fleshed commercial planting generally. It ripens in bud sport of a Marsh tree in 1913. It is seed­ May to June and has a tendency for regreen­ less. just as Marsh is. and of the same external ing. Recently. a limb sport of this variety appearance, for no pink shows on the rind. was found that had a deeper color in rind than The Ruby is the first grapefruit with deep red the parent Hyuganatsu and had excellent flesh arisen as a Jimb sport of the Thompson quality in later season. It was patented in at Texas in 1926. It is also seecliess and the 1965. rind is crimson blush.

Lycopene and associated carotenes are the Refernnces colori'ng compounds present in the sports. From about 1935 there was the vogue for 1) Iwasaki, T., Nishiura, iVI., Shichijo, T., Okuclai, planting pink, seedless grapefruit, followed N., ancl Zaizen, T. : Studies on the Strains of about 1945 \.vith similar heavy planting of red. Early Satsuma Orange (2nd Rep.). Bull. Hort. seedless forms in Florida. It is a quite interest­ Res. Sta., Japan, Se1·. B, No. 1, 37-47 (1962) ing phenomenon that the color mutations (in Japanese with English summary) occuned in parallel in both of the seedy and 2) Nishiura, M. : Citrus Bt·eecling ancl Bud Selection seedless groups. in Japan. Proc. Fla. State Hort. Soc., 77, 79-83 (1964) 4) Variation in Natsudaidai and other 3) Nishiura, 1vI. : Natmal Mutation and Its Utiliza­ citrus fruits of Japan tion in the Selection of Citrus Fruits. Gamma Field Symposia, No. 4, 27-42 (1965) Natsudaidai: The Natsudaidai is the second 4) Nishiura, M. : Citrus Breeding Tht·ough Nucellar most popular citrus fruit in Japan and is the Seedling Selection. JARQ, Vol. 2, No. 1, 15-19 most common late-maturing (May to June) (1967) variety at present. In Natsudaidai. search for 5) Nishiura, M., Shichijo, T., Iwasaki, T., Jozukuri, limb sports has been continued extensively, A., and Kihara, T. : Studies on the Strains of

13 - Satsuma Orange (3rd report). Bull. Hol't. Res. Vol. 4 (1932) Sta., Japan, Ser. B, No. 3, 11- 26 (1964) (in 7) Webber, H. J. and Batchelor, L. o.: The Japanese with English summary) Citrus Industry. Vol. 1, Univ. of Calif. Press 6) Tanaka, T. : A Monograph of the Satsuma (1948) Orange, With Special Reference to the Occur­ 8) Ziegler, L. w. and Wolfe, H. s.: Citrus Grow· rence of New Varieties Through Bud Variation. ing in Florida. Univ. of F la. Press (1961) Mem. Fae. Sci. & Agr. Taihoku Imp. Univ.,

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