Rootstocks With Dwarfing Effect investigations indicate some citrus rootstocks exert dwarfing effect on scions budded to them W. P. Bitters Several of 60-odd rootstocks used in trifoliate root were 43% as large as trees ous trials, the Rusk, the Coleman, the an extensive citrus rootstock trial of the on sweet root but produced 79% as much Cunningham, and others, while they had Citrus Experiment Station at Riverside fruit. The Kumquat also does well on tri- a dwarfing effect on the top, resulted exerted a dwarfing effect on scions bud- foliate. The trees are healthy and fruitful. in combinations which were unhealthy ded onto them. The trifoliate orange is slow growing. in appearance and unproductive. They Dwarfed types of citrus trees might be Budded combinations in the orchard should probably not be used as rootstocks a desirable type for people having limited have been precocious and have produced under California conditions. space in which to grow trees and limited well in proportion to the size of the trees. Severinia buxifolia markedly dwarfed tree care facilities. The fruit is early to mature and is of high the various scions budded onto it. At 17 Citrus rootstocks which have a dwarf- quality. The trees have been disease- years of age, grapefruit trees on this stock ing effect on the scion are used in com- resistant, and have shown a greater hardi- are nine feet tall, whereas comparable mercial plantings in the citrus areas of ness than some other rootstocks. If the trees on sweet root are 14 feet high. These China, Japan, and Palestine. factor of exocortis can be avoided it is a trees are uniform and healthy. They an- rootstock well worthy of consideration. nually produced about three boxes of The Savage citrange has definite merit average quality fruit, or about 45% as Trifoliate Orange Citranges for dwarfing grapefruit trees, but is not much as check trees on sweet root for the Different top varieties may be dwarfed recommended for other combinations ex- first 10 years. Results with Valencia or- to varying degrees when budded upon the cept with mandarin tops. Grapefruit tops anges are more variable than with Marsh same source of rootstock. Included in the on this root after 19 years of age are 5876 grapefruit, but such trees are now around rootstocks tested which showed dwarfing as large as trees on sweet root the same 12 feet in height, as compared to trees tendencies in the Riverside investigation ageZ and average about 76% as much on sweet root, which are 16 feet high. In were the trifoliate orange citranges-tri- fruit. The fruit is of excellent quality. the first 10 years they produced 52% as foliate orange crossed with sweet orange In the case of the Satsuma oranges, the much fruit as the checks. Washington -Severinia, Cuban Shaddock, Palestine trees on Savage citrange at eight years Navels on this stock after 17 years are sweet lime, and Eureka lemon cuttings. of age were 55% as large as trees the same nine feet in height, compared to 14 feet Grapefruit tops on trifoliate orange age on sweet root, but were yielding 84% high on sweet root. They have fairly open roots at 20 years of age are 28% as large as much fruit. This rootstock is resistant tops, are chlorotic, and annually yield as comparable trees on sweet root. The to gummosis and the combinations are only about one box of fruit, or 27% as trees are healthy. From 1942-47 they more hardy than similar tops on conven- much as trees on sweet root. Eureka produced 58% as much fruit as the trees tional stocks. lemons budded on this root produced on sweet root. Navel oranges on trifoliate The Morton citrange, while it has not 33% as much fruit as trees on sweet root are 54% the size of trees on sweet root effected extreme dwarfing on tops budded during the first 10 years. In practice at 20 years of age and are producing 94% to it, results in a very heavy producing probably only grapefruit should be bud- as much fruit. The Valencia trees on tri- tree yielding excellent quality fruit. ded on this stock. foliate orange averaged 58% as large as Washington Navels budded upon it pro- trees on sweet root and for the first 10- duced 63% more fruit during the first year period have yielded 94% as much 10-year period than trees the same age Palestine Sweet lime fruit. For the last six-year period, 1942- on sweet root, although the trees on Mor- Trees on the Palestine sweet lime are 47, the production was equal to that on ton were only 72% as large. From 1942- very markedly dwarfed. Washington sweet root. 47 the combination produced 24% more Navels on this combination 18 years old Eureka lemons on trifoliate orange all fruit than trees on sweet root. The Sat- are 9yz feet tall and 37% as large as trees developed exocortis on the trifoliate roots. suma oranges budded on Morton citrange on sweet root which are one year older. The trifoliate orange is a very satisfac- were 91 % as large as trees on sweet root, They annually yield about 3Vz boxes of tory root for the mandarin group of or- but have produced 40% more fruit. As a fruit. Eighteen-year-old Valencia trees are anges. Eight-year-old Satsuma trees on rootstock it is worthy of consideration 58% as large as check trees one year for home plantings. Its biggest drawback older. They are about 11 feet tall and an- is the difficulty of obtaining seeds for nually produce about four boxes of fruit. rootstock purposes. Fruit size of Wash- The grapefruit trees are about 10 feet ington Navels on this root tend to be small high at 18 years of age and produce an but not too small to be undesirable for annual yield of four boxes of fruit. Eu- Left: Effect of dwarfing rootstocks upon tree sire of oranges and grapefruit. 1. Grapefruit on home usage. reka lemons on Palestine sweet lime are trifoliate orang-21 years. 2. Grapefruit on The Troyer citrange has only recently 55% the size of trees on sweet root and Severinia buxifolia-17 years. 3. Grapefruit on Savage citrange-21 years. 4. Navel on trifoliate been included in rootstock trials. Pre- produce about 50% as much fruit. This orange-21 years. 5. Navel on Palestine sweet liminary observations on this rootstock stock has a tendency to heavy production lime-18 years. 6. Navel on Cuban shaddock- 16 years. 7. Valencia on Severinia buxifolia-17 indicate that it is very promising and in early years and that is one of the rea- years. 8. Valencia on Palestine sweet lime-18 possesses sufficient merit to warrant fur- sons its use is preferred in some coun- years. 9. Valencia on Eureka lemon cuttings-18 years. The measuring standard is a 12-foot rod ther plantings with it. tries. Trees budded on this combination calibrated in feet. Other citranges included in the vari- Continued on page 14 CALIF ORNI A AGRICULTURE, FEBRUARY, 1950 5 DROP have produced 60% as much fruit in the tion starting in the cuts. Also the girdling first 10 years, but only 42% as much in knives should be dipped after each cut in Continued from page 6 the last six. Fruit quality is below average a disinfectant to.prevent spread of the teresting to speculate on even how much and the combination is easily damaged d'Isease. more effective 2,4,5-T in the amine form by low temperatures. In addition to being 4. To determine accurately whether the might be. susceptible to gummosis this rootstock is girdling has been beneficial it is desirable susceptible to shellbark. It may also be to obtain yield records during harvest Wm. S. Stewart is Associate Plant Physiolo- gist in the Experim.ent Station, Riverside. another source of psorosis if the parent from the girdled trees and from adjacent H. Z. Hield is Senior Laboratory Technician lemoq trees were carrying the disease. trees of comparable size. .As a rootstock it has little to recommend in the Experiment Station, Riverside. H. T. Hartmunn is Assistant Professor of Po- Cooperating in these studies were B. L. Bran- it other than the dwarfing tendency. mology and Assistant Pomologist in the Experi- naman, Senior Laboratory Technician, in the Most citrus growers in California pre- ment Station, Davis. Experiment Station, Riverside; F. Arnold fer those combinations which produce R. M. Hoffman is Farm Advisor, Tehama White, Farm Advisor, Santa Barbara County; County. and C. P. Teague, Farm Advisor, Riverside large or standard sized orchard trees. County. While in general tree size and fruitfulness The above progress report is based on Re- search Project No. 1301. The above progress report is based on Re- are associated, they are not always cor- search Project No. 1346. related. Long-lived, healthy, and produc- tive dwarfed combinations may have a definite place in plantings made by the INJECTIONS home grower and perhaps the orchardist. DWARFING Continued from page 10 Continued from page 5 Iv. P. Bitters is Assistant Horticulturist in the Citrus Experiment Station, Riverside. tity of dilute acid soluble phosphorus and potassium in this soil is very low and are very sensitive to cold and at Riverside The above progress report is based on Re- have shown more damage from cold than search Project No. 193C. correlates well with the low phosphorus any of the other combinations. Fruit pro- and potassium content of the leaves. duced on this stock is very low in acid and Lemon orchards with the leaf spotting has a tendency to be somewhat insipid.