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Home , Citrange, Citrus, Citrus rootstock, Grapefruit, Lemon, Severinia buxifolia

With Dwarfing Effect investigations indicate some 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 ous trials, the Rusk, the Coleman, the an extensive citrus trial of the on sweet root but produced 79% as much Cunningham, and others, while they had Citrus Experiment Station at Riverside . The 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 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 conditions. space in which to grow trees and limited well in proportion to the size of the trees. buxifolia markedly dwarfed 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- of age, 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 , , 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 has definite merit average quality fruit, or about 45% as 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 , and Eureka 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. 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 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 -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 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 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 . duced on this stock is very low in acid and Lemon orchards with the spotting has a tendency to be somewhat insipid. OLIVE referred to here have been noted in parts of Santa Barbara, Ventura, Tulare, and The stock itself is very susceptible to gum- Continued from page 3 mosis. It is questionable if this stock has San Diego counties. More recent analyses sufficient merit to warrant its usage in ceding the 1949 only and bore 124 show that the leaves obtained from these California. pounds per tree as compared with 28 same areas are also very.10~in phos- The Cuban Shaddock produces sub- pounds for the check trees. All the 1949 phorus. standard sized trees. Marsh grapefruit girdling in this orchard was done on Feb- Apropos of leaf analysis as a diagnostic trees on this stock after 14 years of age ruary 15. tool, it can be stated that so far, responses are 70% as large as trees 17 years old om There was a reduction in fruit size of to tree injection of phosphorus and po- sweet root. They produced as much fruit the heavier crop on the girdled trees, but tassium have been obtained only where in the first 10 years as the trees on sweet this was offset easily by the greatly in- exceedingly low levels of these elements root, but in the last six years have yielded creased yields. were found in the leaves. Previous tree only 71% as much. Washington Navel Using the yield records and size grades, injection work using mono-calcium phos- orange trees on this stock at 14 years of and computing on an acre basis from the phate and di-potassium phosphate in Ven- age are 45% as large as 17-year-old trees 15 girdled trees in this test orchard the tura, Orange, and Riverside counties on sweet root. Production for the first 10 increase in gross return in 1949 over non- failed to produce response in trees having years is about the same as on sweet root, girdled trees would amount to approxi- phosphorus and potassium levels con- but in the last six years has dropped to mately $620 per acre at 50 trees per acre. sidered adequate by current standards. 80% of the check trees. Eureka lemons Girdling of olive trees is not recom- This is the first time in California that on this stock in 1947 were 48% as large mended at present for use as a genreal citrus trees in the field-with leaves of a as trees on sweet root which were three practice but it may be worthwhile to try- known low phosphorus and potassium years older. They produced 66% as much in an experimental manner-on a limited content-have responded to phosphate fruit for the first 10-year period as trees number of trees in orchards which have and potassium treatment. on sweet root. Unfortunately, there were a habit of blooming heavily but failing This response of citrus to phosphorus no trees on sweet root of the same age for to set good . in southern California is of interest in the comparison, but obviously the difference Under such conditions the following light of previous failures of many field in size and production of the two combi- suggestions are made: trials with citrus to show responses from nations cannot be entirely accounted for 1. The primary scaffold branches these elements. by the three years difference in their ages. should be girdled about the middle of Feb- It remains for future work to determine Trees on this stock tend to have a heavy ruary, with one or two branches on each whether the response of lemons to phos- early production, but this is not main- tree left ungirdled to supply the roots phorus and potassium injections reported tained in later years. -This rootstock ap- with until the girdling cuts in this article can be duplicated by.soi1 pears to be fairly susceptible to footrot. heal over. treatments. In general, its effect on the top is to pro- 2. Girdling cuts are made most easily It seems certain, based on the extensive duce poorer fruit quality and a tendency with a grape-girdling knife in areas with leaf analysis surveys and soil studies of toward greater damage from low tem- smooth bark. The soft bark should be re- phosphate and potash in citrus groves peratures than when conventional root- moved down to the hard inner wood in a made previously, that many groves are stocks are used. strip, not to exceed one fourth inch in amply supplied with these constituents. Eureka lemon cuttings budded to Va- width, completely around the branch. D. G. Aldrich, Jr., is Assistant Chemist in the lencia oranges were also part of the or- 3. The cuts should be covered immedi- Experiment Station at Riverside. ange rootstock trials. After 18 years these ately with either hot wax or with A. R. C. Haas is Plant Physiologist in the Ex- trees approximate 81/2 feet in height as an asphalt emulsion grafting compound. periment Station at Riverside. compared to comparable trees on sweet In orchards infected with Olive Knot pro- The above progress report is based on Re- root which are 16 feet in height. They vision should be made to prevent infec- search Project Nos. 1087 and 1305.

14 CALIF0 R N I A AGRICULTURE, FEBRUARY, 1950