The Breeding Behavior of the 'Clementine' Tangerine

76 FLORIDA STATE HORTICULTURAL SOCIETY, 1964

Table 10

True-To-Type Seed Source Trees For Propagation From Seeds Or Buds

Citrange: Rangpur Lime(Brazilian)4 Carrizo 8 Rangpur Lime(Florida) 14 Morton 3 Sweet lime 23 Troyer 10 Citrus Taiwanica 4 P. trifoliata: Cleopatra Mandarin 20 Rubidoux 9 Rough Lemon 25 Wacissa strain 32 RoughLemon (Red) 20 Windermere strain 4 Sour Orange 20 Unnamed trifoliata hybrids: Citrange 6 Citrumelo 41

Average Age 4 years.

thorniness, and poor fruit quality. Cameron (1) budeyes or less) may be obtained without charge and others found that young Valencia lines, 24 upon written application to the Budwood Regis years removed from seed, showed extreme alterna tration Program, Drawer A, Florence Villa Sta tion in yield due to juvenility. The Budwood tion, Winter Haven. Foundation Grove, with large numbers of old-

line clones selected for their high quality and LITERATURE CITED with equal numbers of nucellar lines brought to 1. Cameron, J. W., R. K. Soost, and H. B. Frost. 1959. gether under a common environment under Flor The horticultural significance of nucellar embryony in citrus, p. 191-196. IN J. M. Wallace (ed.), Citrus virus diseases, ida conditions, may resolve the question of which Univ. Calif. Div. Agr. Sci., Berkeley. type Florida growers should use. 2. Frost, H. B. 1943. Seed reproduction: Development of gametes and embryos, p. 767-815; Genetics and breeding, p. The Tables which follow summarize the 817-913. IN H. J. Webber and L. D. Batchelor (ed.)f The citrus industry, vol. 1. Univ. Calif. Press, Berkeley. sources of budwood available from the Founda 8. Strasburger, E. 1878. Ueber Polyembryonie. Jenai- tion Grove. Limited quantities of each clone (25 sche Z. Naturw. 12: 647-670.

THE BREEDING BEHAVIOR OF THE 'CLEMENTINE' TANGERINE

Philip C. Reecb and C. Jack Hearn "false-hybrids," as Swingle termed them, were later understood to be zygotic and nucellar seed Crops Research Division lings. The nucellar seedlings are a major ob Agricultural Research Service stacle encountered in citrus breeding. Great diffi culties arise in distinguishing between the two U. S. Department of Agriculture types unless some easily recognized characteristic Orlando is introduced into the hybrid or zygotic seedling by the male parent. When the cross involves When W. T. Swingle began the first known parents with similar characteristics, much time, attempts at breeding of Citrus, the complexities money, and land may be wasted by growing un of the problem were not fully realized. The ap recognized, unwanted nucellar seedlings. This pearance in the F1 population of hybrids and is generally the case unless the cross is between REECE AND HEARN: "CLEMENTINE" TANGERINE 77 different genera or at least different species. citrange (C sinensis X P. trifoliata), 'Moti' and In 1909, Swingle introduced budwood of the 'Davis' grapefruit, 'Hamlin' orange (C. sinensis), Clementine into the United States. The variety, Tangor No. 653 (C. sinensis X C. reticulata), and which originated in the garden of an orphanage 'Minneola' and 'Orlando' tangelos. Twenty-six in Algeria, was named by L. Trabut of the Al crosses of other types were also made; and in gerian Botanical Garden in honor of Brother an attempt to identify 3851 hybrid and nucellar Clement who was in charge of the orphanage gar seedlings, Furr and Reece (1) developed a modi den (7). Trabut considered that the Clementine fication of the rootstock color test of Halma and was an accidental hybrid of some mandarin and Haas. That test indicated that all Clementine a sour orange. Tanaka (6) gives it the rank of seedlings were hybrid. Such a situation seemed species. Both views seem extremely doubtful in doubtful because of the very high percentage of the light of breeding performances to be brought apomictic seedlings known to occur in other va out later. rieties. However, their hybridity was confirmed The Clementine was first used in the breeding by pollinating Clementine blossoms with Poncirus program in 1913-14 in a cross listed as 'Bowen' trifoliata (L.) Raf. pollen. The genes that con grapefruit (C. paradisi Macf.) X Clementine (5). trol the development of trifoliate leaves in P. The Bowen is referred to in literature concerning trifoliata seem to be present in a double dominant the early work of the U.S.D.A., but E. M. Savage, condition because all Clementine X P. trifoliata who was associated with Swingle and Robinson seedlings had trifoliate leaves. Later, when the in the breeding program for 40 years, reports trees in question bore fruit, observations substan that the variety was actually a Duncan grape tiated the earlier evaluations of their hybrid fruit which they had selected on the property nature by the color test (1). of Mr. Bowen. The records indicate that Clem It must be remembered in any discussion of entine was used as the male in this cross, but the breeding behavior of a citrus variety that in because Swingle was in the habit of listing the most cases the observations have perforce been male first in any cross, this is open to doubt. made on small populations. No hard and fast The Duncan grapefruit is a very highly apomictic conclusions concerning their genetics can be variety. These facts, together with the fact that drawn with safety from such limited data. 163 hybrids were obtained (one of which, the Clement tangelo was released) indicate that the Clementine X Citrangor cross was probably Clementine X Duncan. In a population of 31 seedlings from a cross of In 1918, the cross of 'Thornton' tangelo (C. Clementine X Citrangor, 16 hybrids could easily reticulata X C. paradisi) X Clementine and its be identified by their trifoliate leaves (1). All reciprocal were made and 33 hybrids were pro plants produced exceptionally strong, handsome duced (5). The records do not show from which and compact trees but they were completely cross the hybrids were secured, but in the light worthless from the standpoint of fruit quality of what we know today, they probably were from because of their unpalatable flavor. the cross of Clementine X Thornton. A note was Ten seedlings in a population of 12 from a made that in 1923 Clementine was pollinated by cross of Clementine X Morton citrange had tri a number of males from which a few probable foliate leaves and in general characteristics they hybrids were secured; however, this statement were very similar to those in the cross of Clemen was probably based on a later misinterpretation tine X Citrangor. of Swingle's notation system. During the fol lowing decade, methods of notation were changed Clementine X Hamlin orange and improved. In 1934 three tangelo varieties were pollinated Only two seedlings of a population of 25 from by Clementine and 51 hybrids were produced; this cross a could be identified by morphological when Clementine was pollinated by 14 males, characteristics (1). Later, they all produced fruits 482 hybrid seedlings were produced and tested that were predominantly mandarin in general (5). None was released. Data are lacking con character. Thin skinned, flat fruits with open cerning the characteristics of all these plants. centers were the rule. They ripen in the early After some years of inactivity, citrus breeding fall; this might be expected in hybrids whose was resumed by the U.S.D.A. in 1942. Clemen parents both ripen early. Flesh of these fruits tine was pollinated by 'Citrangor' (C. sinensis is peculiarly tender and melting. Their flavor is Osbeck X (C. sinensis X P. trifoliata)), Morton not outstanding and quickly cloys the taste. 78 FLORIDA STATE HORTICULTURAL SOCIETY, 1964

Clementine X Tangor No. 653 ceola and Lee, tangerine hybrids were released (3). Six others are undergoing extensive root- Five hybrids from a population of 359 were stock and variety tests. One or more of them will considered worthy of second tests. All seedlings probably be released in a few years. had strong mandarin characteristics with dark In some of the selections the progeny showed a orange colored thin rind and dark orange flesh. wide range in size, color, seediness, thickness of The tangor flavor, easily recognizable by those rind, and the frequent appearance of naveled who are familiar with tangors, seemed to be fruit. dominant over other flavors. On the basis of the many good Clementine hybrids observed, Clementine has been crossed Clementine X Mott grapefruit with 5 orange varieties, 5 grapefruit, 2 tangelos, Fifty-seven out of 253 hybrid seedlings from 11 mandarin and mandarin hybrids, and with 4 the cross of Clementine X Mott grapefruit could intergeneric hybrids. Over 1,300 Clementine hy be recognized by general morphological character brids have reached a fruiting stage. Many hun istics (1). Five seedlings from the total popula dreds of additional hybrids are not old enough tion were considered worth second testing. The to be evaluated. others were characterized by a yellow rind color Our observations on the behavior of Clemen that was apparently dominant over orange in a tine seedlings confirm the opinion of Dr. H. J. ratio of 9 to 3. Pear-shaped, necked fruit, to Webber who said, in discussing the cultivated round fruit appeared in a 1 to 1 ratio. Rind varieties of Citrus in the Citrus Industry (7), thickness ratios were approximately 8 thick, to that "most of the variations (in seedlings grows 2 medium to 1 thin. Flavors were mostly acid and from the seeds of unguarded flowers) seemed to poor. Sometimes, the flavor was like garlic. Some be merely ranges within the ordinary mandarin times, it was fishy. A few had a sickeningly sweet types; a few of the seedlings had foliage ap perfumed quality. They are monoembryonic and proaching that of the sweet orange (C. sinensis) have been used in backcrosses to grapefruit, be in form and character, but none examined had cause grapefruit X grapefruit crosses are virtu foliage suggesting that of sour orange (C. au- ally unattainable. rantium) in shape, color or odor." Webber thought that the variety is simply a variant with in the mandarin group; or that if it is a hybrid Clementine X Minneola tangelo between species, its characters in general more These hybrids showed considerable variability. closely suggest a slight mixture with the sweet Flavors ranged from very acid to sweet. Rind orange. thickness and shape were also variable. A large, In addition to those breeding characteristics very acid, naveled, mandarin type is characteris already mentioned, two other qualities stand out tic of one tree. A sister hybrid is pear-shaped, in the population; first, cold hardiness, a de early ripening, and sweet and firm fleshed like cidedly advantageous characteristic; second, their a navel orange. susceptibility to foot rot, is disadvantageous. The reciprocal cross produced mostly nucellar In addition to the breeding work with this seedlings. Fruits of most hybrids were pear- type in Florida, the Clementine is an important shaped like the female parent. One of the hybrids parent in many citrus crosses in California (2). was released under the name of Page. It pro duces fruits that are early, sweet, highly colored LITERATURE CITED and of excellent quality. The trees, leaves and 1. Furr, J. R., and P. C. Reece. 1946. Identification of fruit of Page resemble an orange in most charac hybrid and nucellar citrus seedlings by a modification of the rootstock color test. Amer. Soc. Hort. Sci. 48: 141-146. teristics (4). It is interesting to note that Web 2. , J. B. Carpenter and A. A. Hewitt. 1963. ber (7) reported that some of the several hun Breeding new varieties of citrus fruits and rootstocks for the southwest. Jour. Rio Grande Hort. Soc. 17: 90-107. dred Clementine seedlings which he observed had 3. Reece, P. C, and F. E. Gardner. 1959. Robinson, Osceola and Lee—New early-maturing tangerine hybrids. leaves approaching those of the sweet orange. Proc. Fla. State Hort. Soc. 72: 48-51. 4. Reece, P. C, F. E. Gardner, and C. J. Hearn. 1963. Page orange—a promising variety. Proc. Fla. State Hort Clementine X Orlando Soc 76: 53-54. 5. Swingle, W. T. [Unpublished records of citrus crosses as compiled by T. Ralph Robinson.] Three hundred and twenty-seven hybrids of 6. Tanaka, Tyozaburo. 1954. Species problem in Citrus. Japanese Soc. for the Promotion of Science, Ueno, Tokyo. this cross were evaluated. Thirty-seven were 7. Webber, H. J. 1948. Cultivated varieties of citrus. selected for second tests. Three, Robinson, Os- Vol. I, Chap. V, The Citrus Industry. Edited by L. D. Batchelor and H. J. Webber; Univ. Calif. Press, pp. 475-913.