Several trees of Webb Red Blush grapefruit on Tavares limequat also showed problems at the bud union.Olson postulated that since seedlings of calamondin, lemonquat, red grapefruit, and sweet orange grew normally, whereas certain budded combinations showed bud union crease, it would seem possible that the disorder was related to interaction between specific root stock and scion varieties. It seemed desirable, therefore, to determine whether the disorder was of virus origin and other scions were susceptible. He found that old-line grapefruit on sour orange was compatible, but observed bud union crease with the same scion on calamondin and lemonquat. Olson showed that nucellar Red Blush grapefruit, old-line Red Blush grapefruit, nucellar Valencia and old-line Valencia all displayed bud union crease on calamondin root stock within two to three years. However, nucellar Eustis limequat, old-line Eustis, nucellar Lakeland limequat, and Meyer lemon showed no symptoms on calamondin. He also found that calamondin, Cleopatra mandarin, Columbian sweet lime, Sunki mandarin, and Rangpur lime on Eustis limequat showed no bud union problems in two years time, but on sour orange and Sunshine tangelo there were problems. He concluded the problem was not a virus, but rather a localized incompatibility,vertical tower for strawberries and probably could be prevented by the insertions of a proper inter stock. Olson and Frolich reviewed the calamondin bud union problem.
They point out that this disorder was also reported by Salibe in Brazil and also by Salibe in Florida as well. It was also emphasized that while the work of Weathers and Calavan showed that, while six different root stock varieties which produced bud union crease when propagated with old budline calamondin tops grew normally when budded with nucellar calamondin buds, when nucellar calamondin buds were inoculated with old budline calamondin tissue the trees also remained free of bud union crease. However, when Weathers top worked old-line calamondin onto the nucellar calamondin on the same six root stocks so that the old budline calamondin formed the tops and the nucellar calamondin formed the inter stock, the trees developed bud union crease at the lower union between the nucellar calamondin and the root stock. Evidently, something was translocated from the old budline calamondin across the nucellar calamondin inter stock, because nucellar calamondin on the same root stocks failed to show bud union crease when they were eight years old. Weathers suggested that his old budline and nucellar calamondin were different, even though the nucellar line was a seedling from the old budline . Olson and Frolich also report that at Weslaco, Texas, eight trees of old budline calamondin propagated on C. taiwanica had only one tree of the eight show bud union crease. They emphasize that off type seedlings of C. taiwanica are common and may explain this occurrence. At Indio, California , nucellar calamondin trees on Carrizo and Troyer citranges grew vigorously for seven years free of bud union crease. However, nucellar and old budline kumquats on the same root stocks died a few years after budding, and they emphasized that compatibility reactions of kumquat and calamondin are not necessarily identical.
Olson and Frolich budded a large number of varieties on calamondin root stock. Table 13 shows the varieties which were compatible and showed no bud union crease after 2-1/2 years. Table 14 shows a list of those varieties which Olson found to be incompatible on calamondin stock and showed bud union crease at the end of 2-1/2 years. When old budline calamondin was grown on sweet orange root stock in California, or a nucellar grapefruit top was grown on calamondin root stock in Texas, bud union crease developed. However, when Cleopatra mandarin on Rough lemon was used as an inter stock between incompatible components, bud union crease failed to develop within a three-year period, see Table 15. Although Swingle considered calamondin to be a mandarin-kumquat hybrid, the incompatibility reactions of the kumquats were not identical with those of the calamondin. In California, old budline kumquat trees grow well on calamondin and on sweet orange root stocks, and make excellent unions. However, old budline calamondin tops with kumquat inter stock on sweet orange root stock developed mild bud union crease between the sweet orange and kumquat. Also, calamondin grows well on Rough lemon root stock whereas kumquat does not. Old budline kumquat trees on Rough lemon root stock show a swelling like a collar at the bud union. In Florida, this disorder termed “Podagra” was neither infectious nor transmissible according to Knorr . Olson concludes, as do others like Weathers and Calavan , that bud union crease of certain varieties of citrus on calamondin root stock appears to result from tissue incompatibility. Salibe in Brazil budded old-line and nucellar calamondin on Brazilian Rough lemon and Florida Rough lemon. Three years later there was severe creasing and gumming at the bud union of all trees on the Brazilian Rough lemon, but they were normal on Florida Rough lemon except there was stem pitting and wood discoloration similar to xyloporosis. Salibe also found Eureka lemon and old-line Selecta de Itabuna orange incompatible on calamondin, and nucellar line calamondin on Natsumikan, Caipira sweet orange, Coachella Eremocitrus, and Brazilian Rough lemon also showed bud union crease. In the 1927-1930 root stock plantings at the Citrus Experiment Station, described and discussed by Webber and Batchelor and Rounds , various scions budded on the calamondin generally did very poorly.
The poorest results were obtained with the Eureka and Lisbon lemon scions, and those trees were removed from the orchard very early. The Washington navel, Valencia orange and grapefruit scions did slightly better, but such trees were all discarded before the author arrived at Riverside, 20 years later. All of these combinations showed bud union crease. However, as a root stock for Satsuma, results were quite good, the bud unions were normal and there was no bud union crease. Webber shows a picture of the bud union and the root system; however, yields were only average. In the 1948 tristeza plantings at Baldwin Park , the Valencia oranges on calamondin did show bud union crease , but did not react to tristeza. The trees showed little distress up to the time when the experiments were discontinued 13 years later. In the same plantings, the bigaraldin reacted severely to tristeza, but showed no indication of any bud union problem. The calamondin was also included in root stock trials by the author in the desert area of California in 1960. Scions included the marsh grapefruit, Valencia orange, and the Dancy tangerine. The grapefruit and Valencia trees showed a bud union crease problem within a few years, but managed to survive with some distress for at least 20 years. The Dancy tangerine trees did not develop any bud union crease, and were vigorous, healthy trees up to the time of their removal. The Glen citrangedin is incompatible on Carrizo citrange . At South Coast Field Station in California, Valencia oranges on Faustrimedin were incompatible,vertical growing but Eureka and Lisbon lemons on this same stock were still healthy at ten years of age with no sign of bud union problems . Some discrepancy in calamondin performance may be the result of incorrect identification. Even Hodgson on page 531 of volume I of The Citrus Industry, describes the calamondin as “sweet and juicy.” It is juicy, but it definitely is not sweet, possessing an acidity that ranks with commercial lemons and limes. In fact, in the Philippines where commercial lemons and limes are not grown, the calamondin is widely grown and used as a substitute for those varieties. While Swingle suggests that the calamondin “is very probably and orangequat that arose in China by insect cross-pollination of a sour, loose-skinned mandarin orange and a kumquat,” the cultivar in the first place should not have been designated as an “orangequat.” While it has some morphological similarities with the kumquat and some of its physical responses in scion-root stock combinations also resemble certain kumquat reactions, recent unpublished isozyme studies at the Citrus Research Center, Riverside, would seem to confirm that there is no genetic relationship between these two cultivars. As early at 1905, Coit in Florida referring to rebudding frozen trees, stated with reference to the kumquat that one does not bud directly onto the Rough lemon since it is incompatible, but rather buds onto the sprouts of the oranges and grapefruit. This may have been the first report of incompatibility with kumquat and Rough lemon. Hodgson on page 580 of volume I of The Citrus Industry shows a 30-year-old Nagami kumquat on sweet orange root stock. In the old citrus variety collection at Riverside, Nagami did very well on trifoliate orange and sweet orange as root stocks. Later plantings of Nagami on Troyer citrange root stock also did well at Riverside. W. Reuther presented the author with a picture of a 13-year-old Nagami on Swingle in Venezuela. The bud union looks fine . Nagami can also be successfully propagated on calamondin. The problem seems to be more acute with the Meiwa variety. In Japan, the Meiwa is grown exclusively on trifoliate orange root stock. In my many visits to Japan, the author is unaware of any incompatibility problems. The original source of Meiwa at Riverside was on trifoliate orange and was healthy up to the time of the orchard’s removal nearly 30 years later.
The author also has a Meiwa on trifoliate orange in his back yard, which is now 21 years old and showing no bud union problem. In California, Meiwa kumquat is incompatible on Troyer citrange . It is also incompatible on the calamondin and on Citrus shunkokan . Also, in the tristeza trials at South Coast Field Station , Valencia trees on Meiwa, and F. hindsii are incompatible . Eureka and Lisbon lemons on these same stocks are also incompatible . In the Baldwin Park tristeza tests , Valencia oranges on Thomasville citrangequat showed no tristeza problems and no bud union problems after 13 years. Thomasville and Sinton citrangequat at Riverside have also not shown any bud union problems when grafted on several miscellaneous root stocks. In Italy, Russo reports that all trees of seedling Meiwa kumquat budded on sour orange showed decline symptoms within 2-3 years. He also reports observing the same situation in Spain. McClean and Engelbrecht report that Nagami kumquat budded on seedlings of Nagami were incompatible. This is not surprising since Nagami produces only hybrid seedlings. There are many problems of incompatibility of various scions on Rough lemon root stock. Nour-Eldin noted bud union crease on more than 90 per cent of the trees of Baladi sweet orange budded on Rough lemon root stocks. He also observed bud union crease in about 80 per cent of the blood oranges budded on Rough lemon, but doesn’t state specifically the varieties of bloods. Salibe , and Knorr report problems of kumquats budded on Rough lemon. Fernández Valiela also found problems of blood oranges budded on Rough lemon. Salibe found Shamouti and Pera oranges incompatible on Florida Rough lemon, but when he inoculated with Pera buds into nucellar Bahianinha on Florida and Mazoe Rough lemon, the trees were normal; however, buds from the same Pera budded into two other cultivars of Rough lemon showed bud union crease on both. The list of scion root stock combinations exhibiting bud union crease included many sweet orange varieties budded on Rough lemon . Rodriguez in Argentina indicated all Pera sweet oranges budded on Rough lemon showed bud union crease. Bhutani, Bakhshi, and Knorr pointed out that Mosambi sweet orange and Blood red orange showed decline on Rough lemon root stock. In South Africa, McClean found no problem with Marsh seedless and Ruby Red grapefruit on Rough lemon. However, Triumph grapefruit, probably a hybrid, had bud union crease. The same applied to Jackson grapefruit, a seedling sport of the Triumph, and also to a seedling of Jackson. Three Ruby grapefruit seedlings scions on Rough lemon also showed mild symptoms at the union following inoculation with buds from trees of sweet orange on Rough lemon with a faulty union. McClean states that the abnormal union that some sweet oranges make on Rough lemon varies in degree. The most common orange varieties on Rough lemon affected are Valencia and Washington navel. He only found problems in one orchard of Valencia old-line, but most navels were affected.