They also point out some problems with some gametic seedlings of Marsh grapefruit and Washington navel on trifoliate. In Japan, Miyakawa and Miyakawa and Matsui report on a bud union abnormality of Satsuma on trifoliate orange. There is a swelling of the scion variety above the union, and bud union crease at the union . When inoculated into Valencia, Hassaku, and Yuzu on trifoliate, the inoculation also caused the disorder. When the author visited Japan in 1976 and observed some of Miyakawa’s work, there was also a similar problem of Ponkan on trifoliate. The causal agent appears to be tatter leaf virus, most Ponkan mandarin trees in Japan are infected, and it has been spread somewhat indiscriminately to other scion varieties through top working operations. The disease also appears to affect Satsuma mandarins on Troyer citrange in Japan. In California, virus-free Meyer lemon on Troyer citrange displays bud union crease . However, if the tatter leaf virus is introduced, the abnormal swelling of the scion above the union also occurs . During the author’s tenure in California, he has examined hundreds of bud unions with trifoliate orange root stock. Except with lemon scions there have been no bud union abnormalities other than the usual compression girdling on older trees . Recently , however, there has been a delayed incompatibility of Washington navels on trifoliate. The trees began to display bud union crease before they were 20 years old. The disorder is described by Schneider and Pehrson . The trees examined were at Lindcove Field Station and were planted by the author in 1963. The planting consisted of Frost navel on 24 trifoliate orange selections. A progress report on the orchard performance of the plot was made by Bitters, McCarty, and Cole after which the plot was discontinued, but not for orchard health reasons.

The trees were thus 20 years old when examined by Schneider,vertical growing towers and bud union crease was already quite evident on most trifoliate strains except the Rich 16-6. It is not known when the bud union crease first began to appear. Later examinations of the union by Schneider revealed that the Rich 16-6 also was developing creasing. Thus, the creasing develops sooner and more rapidly on the more vigorous growing trifoliate selections, but none appear to be immune. As of 1987, [text incomplete] All of the trees examined were Frost navel. One must presume that all navel strains would probably provide similar results, but trees of Parent navel, Atwood navel, etc. were not examined. The fact that the Thomson Improved navel is the only navel strain described as declining on Rough lemon root stock by Ohr et al. could, however, raise some questions. Shannon, Frolich, and Cameron in California gathered a large selection of trifoliate orange strains. I quote, “The authors have observed many large and productive Valencia oranges, Marsh grapefruit, and Washington navel oranges on Poncirus trifoliate in old orchards in Southern California.” The navels had to be parent navels, and the authors categorized the trifoliate selections into largeand small-flowered types. Of the more than 30 selections, at least four had navel scions. They were the Christiansen , Taylor, Davis A, and Davis B. It would have been interesting to know the age and condition of these navel orchards, or if any of the orchards still exist. At Riverside, 33-year-old parent navel trees on Rubidoux trifoliate in the 1927-1930 root stock plots showed no bud union crease when the plots were terminated in 1960, but did show compression girdling. With orchard trees over 30 years of age, the only ones the author has observed with breakage at the union in the removal operations were some on trifoliate orange root stock . There has been no bud union problem with either navels or Valencias on Troyer or Carrizo citranges up to the present time. Recently, however, there has been a delayed incompatibility of Satsuma mandarin on Troyer citrange, but not on trifoliate. The trees begin to show stress at 16-18 years of age and while there is no bud union crease, there is compression girdling of the root stock .

Other scion combinations on Troyer citrange will also show bud union crease. In the Citrus Variety Collection at Riverside, trees of Chironja show this disorder as do some of the mandarin varieties like C. erythorosa, Richard’s Special mandarin , Solid Scarlet mandarin, and others . Washington navel on Coleman citrange also shows severe bud union crease . In the tristeza trials at South Coast Field Station where nearly 200 trifoliate hybrids were tested as root stocks, approximately 10 per cent of the combinations showed bud union crease. Price and Cook Eureka shows severe problems on #1452 Citrumelo , Kirkpatrick, Bitters, and Foote . In the 1970’s, in Tulare County of central California, trees of Minneola tangelo top worked on Clementine mandarin on Troyer citrange root stock developed bud union crease at the Clementine-Troyer interface. Most likely this is an incompatibility of Clementine on Troyer, since in an orchard formerly owned by the author, Minneola and Orlando tangelo planted in 1960 have, as of 1987, not shown any bud union problems. Problems with both Eureka and Lisbon lemons on trifoliate, Troyer, and Carrizo citrange have been clearly pointed out by Bitters , Weathers et al. , Salibe , Nauriyal, Shannon, and Frolich , McClean , and others. In California, it has long been recognized that lemons, especially Eurekas and some Lisbons, were characterized by the scion severely overgrowing the root stocks, and that such trees declined at rather an early age. Budunions on sweet orange, Rough lemon and grapefruit were relatively smooth and the trees were longer lived . Ruggieri reported that in Italy, Monachello lemon on sour orange stock also suffered from severe scion overgrowth, and that such trees declined at an early age and some trees died at 20 years of age. With the expansion of lemon plantings in California in the 1950’s, several new root stocks were tried commercially, and others placed in experimental root stock trials. Some older lemon plantings on Sampson tangelo still had smooth bud unions in the 1970’s. However, bud union overgrowths were common with all Eureka strains and with some Lisbon strains. Bitters et al. attempted to associate the bud union overgrowth with the height of budding , but while there was some correlation, the overgrowth generally occurred regardless of the height of budding.

The problem was reemphasized by Kirkpatrick, Bitters, and Foote , Kirkpatrick , and Kirkpatrick and Bitters . Severe over-growths and subsequent decline were observed in commercial plantings on Sampson tangelo and Cleopatra mandarin and in experimental plantings on Ponkan mandarin, San Jacinto tangelo, Thornton tangelo, a tangelo ‘Willial’ , Seminole tangelo, Marlow tangelo , Orlando tangelo, Williams tangelo, Minneola tangelo, Mency tangor, Calushu, and Clement tangelo. While Salibe in Brazil reports some bud union crease with Eurekas on C. taiwanica, in California, trees of Limoneira 8A Lisbon on C. taiwanica broke off at the union, as did the Frost Lisbon on Ponkan,container vertical farming and Prior Lisbon on Cleopatra mandarin . Some trees of both Eureka and Lisbon showed slight overgrowth on sweet orange, C. macrophylla, and Stow grapefruit. No overgrowths were noted with either scion on Rough lemon and #1449 citremon, or with Lisbons on Troyer citrange. Russo in Italy reemphasizes the overgrowth problem with Monachello lemon on sour orange, but points out that the nucellar line of Monachello at 16 years of age, although it shows some overgrowth, has not shown a deleterious affect. Russo points out that varieties of sweet orange behave differently when used as inter stocks with Monachello. An Ovale sandwich produces almost smooth unions with the sour orange stock and the lemon scion. Many trees of this combination show no decline after 25 years. A Moro blood orange sandwich behaves differently, producing a smooth union with the sour orange stock, but does not avoid the overgrowth of the lemon scion. When Russo inter stocked with an Avana mandarin, the sandwich grew more slowly than either the stock or the scion and consequently there is a constriction, but at 25 years of age the trees were still without any symptoms of decline. Russo also found that trees of Monachello on C. volkameriana have a smooth union and do not show any symptoms of decline. The root stock problem for lemons in California is extremely critical and it is difficult, because of the bud union overgrowth problem and phloem necrosis, to select a suitable root stock. Some growers are reverting to using sweet orange, and there is some interest in an unidentified cultivar called the Yuma Ponderosa Lemon, which is not a Ponderosa lemon but closely resembles the Cuban shaddock. In Egypt, Nour-Eldin observed a bud union overgrowth of Beladi sweet orange budded on Beladi sweet orange root stock in 40 per cent of the trees examined, which exhibited discoloration of the phloem and stem pitting.

Frolich and Hodgson report on an apparently new virus disease of Rangpur lime and citron on sweet orange, including an infectious agent. Reciprocals are not affected.It does not affect Rangpur lime or sweet orange alone. Symptoms are dwarfing, chlorosis, sparse foliage, early and heavy blossoming and repression of stem thickening of the root stock. In Argentina, Fernández Valiela reported a constricted bud union on about 8% of six year old trees of Selecta sweet orange budded on sweet orange. In Brazil, Moreira reported symptoms of a bud union disorder in trees of Pera sweet orange and Selete de Itaborai orange on sour orange root. Salibe budded old-line and nucellar lines of both on Florida Rough lemon and trifoliate orange, and two years later observed abnormal bud union and bud union crease at the union. In Israel, Reichert, Bental, and Ginsburg describes affected trees of Marsh seedless grapefruit on sour orange which also had abnormal bud unions and constrictions or creasing at the union with no gumming, but inverse pitting in the sour orange. This condition could possibly have been xyloporosis. Salibe also reports a bud union disorder of Lue Gim Gong on extensive stock-scion combinations in which the possibility of incompatibility is an unknown factor. 1978). Commonly they may occur more when the root zone is compacted by soil stratification and root density is high. They may occur more commonly within the same cultivar such as Rough lemon to Rough lemon, and less commonly between two different cultivars such as Rough lemon and Cleopatra mandarin. The highest concentration of root grafts observed by the author in California was in a Valencia orange cutting where more than 12 grafts were noted in an area of 60-100 cm. There has always been the question of bench-rooted seedlings and their ultimate performance, also mentioned in this text. They are usually discarded when seedlings are removed from the seedbed and lined out in nursery rows. One of the advantages of bare-rooting nursery trees is that the “bench root” budlings, or those budlings with poor root systems, could be discarded. In balledbudlings there is no such opportunity. In 1944, L. D. Batchelor, at the Citrus Experiment Station, Riverside, planted out 15 Valencia trees on bench-rooted Morton Citrange stock and compared them to 15 comparable adjacent trees with normal root systems. The author did not see the original root systems. But, when the trees were pulled in 1960, 16 years later, the author observed no differences in top appearance, tree size, yield, or the character of the root systems. Perhaps bench roots aren’t as critical a problem in the orchard as growers have assumed. The temperature requirement for root growth appears to be rather specific [“Check” appears here in typescript in the margin of the manuscript – may mean check what the references say, or may mean check the generality in the first sentence]. Wallace and Nauriyal indicate 18°C minimum; 29°C optimum; and 38°C maximum. However, they indicate the optimum temperature is never reached in the root zone in the coastal area of California since the maximum temperature reached is only 21°C. Similar minimum temperatures for root growth have been reported by Cossman , Monselise , Waynick and Walker , Girton and others. Seasonal soil temperature cycles may be an important single factor in behavior and performance of root stocks in varying climates .