Root Systems of Various Citrus Rootstocks

44 FLORIDA STATE HORTICULTURAL SOCIETY was deaerated under 28 indies vacuum and recovery of peel oil. By-products such as flash pasteurized at 190 to 200 degrees F., feeds, alcohol, molasses, etc. were not in cooled and filled into cans at a temperature cluded in the canning program. of 185 degrees F . C-enamel cans were used In conclusion it can be said that unfortu at first but later plain cans were used because nately Australia is in an unfavorable position the high acidity and high amounts of peel oil for her citrus industry due to the following in the* juice caused the enamel to peel off. reasons: (1) lack of efficient rail transporta One lot of grapefruit was tested just prior tion within her borders, (2) her home con to canning and the following results were sumption limited by the 6^ million popula obtained: Brix 12 degrees, acidity 3.8 per tion in an area almost as large as the U. S. cent, ratio 3.16 to 1; when sweetened with with little prospect of increased population sugar to a Brix of 15.5 degrees it had a ratio from heavy immigration, (3) restricted ex of 4.5 to 1 and it was too bitter to drink. An port trade as Australia is a long distance from analysis was made of some Washington Navel world markets and transportation to these oranges September 15, 1943, which is the lat would make the price to the consumer too ter part of the season, with the following high for competition, and (4) the high cost results: Brix 12.59 degrees, acidity 1.14 per of production per unit, with the attitude of cent, ratio 10.85 to 1, pulp of juice 12 percent the trade unions there making competitive and 75 gallons of juice per 2000 pounds of selling almost impractical. It can also be said fruit. Oranges analyzed from 30 to 50 mg. that some of the leaders of the industry and of ascorbic acid per 100 ml. of juice research workers are united in a movement Refuse or waste from citrus canning plants to better educate the grower to the applica was usually thrown away, except in a few tion of scientific work in an attempt to raise plants which converted orange waste into production and lower cost per unit through marmalades. A few plants had equipment for more efficient methods. This I hope succeeds.

ROOT SYSTEMS OF VARIOUS CITRUS ROOTSTOCKS

E. M. SAVAGE, WILLIAM C. COOPER and R. B. PIPER Division of Fruit and Vegetable Crops and Diseases, Bureau of Plant Industry, Soils and Agricultural Engineering, U. S. Dept. of Agriculture, Orlando

INTRODUCTION darin, Morton citrange, Rusk citrange, sweet Fifteen species and varieties of citrus are lime, calamondin, and yuzu (kansu). This now being tested by this station for their value paper presents results of a study of the root as rootstocks for oranges, grapefruit, and systems of these various stocks. tangerines. These rootstocks include seedlings The rootstocks were grown in the nursery of the common sour orange, bittersweet at the experimental farm near Orlando. The orange, Pineapple sweet orange, Parson soil in this nursery is classed as Norfolk fine Brown sweet orange, rough lemon, Duncan sand. The seed were planted in January grapefruit, Bowen grapefruit, trifoliate or 1939, and transplanted to the rootstock nur ange, Cleopatra mandarin, Suen Kat man sery in November of the same year. The FLORIDA STATE HORTICULTURAL SOCIETY 45 plants were spaced 1 foot apart in rows 3 feet bearing trees. Al&o, as is obvious from the apart. They were budded with orange, grape photographs, the ends of many of the roots fruit, and tangerine varieties in May 1941. were clipped on excavation of the tree from The main rootstock plantings were planted the soil. It was almost impossible to obtain out at field spacing in 1942 and 1943. There every root of the plant intact. Accordingly, were, however, a number of the budded root- when a depth of 4 feet and a spread of 5 feet stocks left undisturbed in the original nur are observed in the photograph it is quite sery, and it was with these that the present possible that the actual depth and spread investigation on root systems was made. were slightly greater. The photographs show The root systems of the stocks were ex clearly whenever the roots were clipped and cavated and photographed in January 1945, the results can be interpreted accordingly. six years after planting the seed and nearly When taking the photographs, all plants four years after budding. Inasmuch as this were placed the same distance from 1Sie investigation is concerned primarily with the camera. A measuring stick marked in one comparative character of the root systems foot intervals was placed at the side and top of the various stocks rather than with pos of each plant. sible effects of the scion variety on the roots, Sour Orange (Citrus aurantium L.), Figs. tflie trees selected for study were all budded A 1 and A 2. to one scion variety, namely, Parson Brown This stock, which is widely used in Florida, orange. However, with one rootstock, the is frequently characterized as possessing Morton citrange, root systems of trees budded abundant and deeply penetrating roots. The to Duncan grapefruit and to Dancy tangerine photographs of this variety show three or were also excavated and photographed in more well-developed central tap roots pene order to determine with this one stock if there trating 3 to 4 feet deep in tihe soil. There were any striking scion effects on the char were numerous relatively small and delicate acter of the roots. lateral roots, particularly in the upper foot The stocks, having grown at close spacing of soil. Some of these had a horizontal for six years, had ttieir root systems fairly spread of 5 feet from the trunk to end of well mingled with the adjoining plants, and root. These laterals were well supplied with it was a slow, tedious task to extract the roots many fine, fibrous roots. intact. It was frequently necessary to uproot Bittersweet Orange (possibly sour orange several adjoining trees in order to remove hybrid, Swingle), Figs. B 1 and B 2. the entire root system of a desired plant. The root system of the bittersweet differed Because of these difficulties and because it mainly from that of the regular sour orange had been observed in digging the large num in having fewer laterals and very few fine ber of trees for field planting that the various fibrous roots. The central or tap roots were trees on any -one stock had remarkably uni more vigorous and penetrated slightly deeper form root systems, only two trees of each than the regular sour orange. stock were carefully excavated for detailed Sweet Orange (Citrus sinensis Osbeck study. It is believed that the photographs Figs. C 1, C2, Dl and D 2. shown are typical for these rootstocks under The root systems of both Pineapple and the conditions -of these experiments. Parson Brown sweet orange seedlings, which were very similar in character, showed well RESULTS AND DISCUSSION developed central roots, usually two, which In studying the results presented in figures penetrated the soil to about the same depth 1 to 17, inclusive, it should be kept in mind (3 to 4 feet), as the sour orange. There were that the trees under observation are young, numerous small lateral roots over the full and the depth of penetration and spread of length of the tap roots. The laterals in the the root system are considerably less than upper foot .were not so long as those of the that which undoubtedly occurs in mature sour orange. There was an abundance of 46 FLORIDA STATE HORTICULTURAL SOCIETY

fibrous roots, particularly in the upper foot dwarfs the top of most varieties worked upon of soil. it. Its root system, with Parson Brown sweet These observations are not in agreement orange worked on it, was of fair vigor even with Mills' (1) observations that in California though- the growth of the top was dwarfed. the sweet orange has a shallow root system. It had deeply penetrating central roots and The results are more in agreement with numerous laterals with abundant fibrous roots Hume's (2) statement that the roots of sweet in the upper 1% feet of the soil. The root stock are equal in development to the deep- system was similar to that of the sour orange rooted sour orange stock. Oppenheimer (3), except it had a smaller spread of the laterals. likewise, reports that the sweet orange is Cleopatra or Ponki Mandarin (Citrus reticu- deep-rooted in the sandy soils of Palestine. lata Blanco), Figs. I 1 and 2. Rough Lemon (possibly lemon-citron hy The Cleopatra mandarin has received some brid, Webber), Figs. E 1 and E 2. attention as a possible substitute for rough This stock, which grows so well on the light lemon rootstock, on tiie assumption that it sandy soils of central Florida, had the most is more cold-resistant and produces better- vigorous root system of all fifteen stocks un quality fruit. It had a. cone-shaped root der test and appeared to be well adapted, by system with well developed central roots pene virtue of its root spread, for securing water trating vertically 4 feet or more into the soil. and nutrients from such soils. The stock was The long, fine-textured lateral roots in the characterized by its exceptionally large lateral upper 2 feet of soil were well supplied with roots which had a horizontal spread of 5 or fibrous roots. In general it did not differ more feet from tree trunk to end of root. greatly from the root system of the sour The central tap roots penetrated vertically orange except that its tap root was straight, into the soil as deeply as did the sour orange slightly longer, and less divided. tap roots. The lateral roots of the rough Another variety of mandarin, called Suen lemon had many fine fibrous roots, but they Kat (Citrus reticulata var. austera Swing.) were not so abundant around the crown of has'also been studied and its root system ap the plant as were those of the sour and sweet peared to be identical with that of the Cleo

oranges. patra. Grapefruit (Citrus paradisi Macf.), Figs. F Citrange (Poncirus trifoliataxCitrus sinen- 1, F 2, G 1, and G 2. sis hybrid), Figs. J 1, J 2, K 1, K 2, L 1 and The root systems of both the Duncan and L 2. the Bowen grapefruit seedlings were char The citranges appear to be worthy of more acterized by their abundance of fibrous roots attention as rootstocks than they have received and paucity of vigorous laterals. They had in the past. From their Poncirus trifoliata two or more large, moderately penetrating parent they have inherited a marked degree (approximately 3 feet) tap roots which were of cold hardiness and induce in scion varieties practically hidden from view by a thick mass budded -on them at least some degree of this of fine fibrous roots for a full three-foot depth. resistance. Unlike trifoliata, which is a dwarf There were numerous small delicate lateral grower, the citranges exhibit unusual vigor roots in this mass of fibrous roots, and they and produce vigorous budded trees. tended to descend obliquely through the soil. The root systems of the Morton citrange This abundance of fibrous roots in grape with Parson Brown orange, Duncan grape fruit confirms both Mills' (1) and Oppen- fruit, and Dancy tangerine scions are illus heimer's (3) observations on grapefruit in trated in figures J to L. There appeared to California and in Palestine* respectively. be no marked difference in tita character of Trifoliate Orange (Poncirus trifoliata the roots with the three scion varieties. The, Raf.), Figs. H. 1 and 2. tap root, in most instances, was divided into The trifoliate orange is the most cold-hardy several roots which, instead of penetrating of all stocks commonly used for citrus. It the soil vertically, as was the case with most FLORIDA STATE HORTICULTURAL SOCIET^ 47 of the other stocks, tended to fan out and penetrating tap root system of the varieties descend obliquely. They penetrated ttie soil tested. The marked tendency of the roots to for about 3 feet. The lateral roots were sim grow downward was even expressed in Okie ilar to those of the sour orange. In general lateral roots which sometimes changed their they showed a tendency to descend obliquely horizontal direction and turned downward. in the soil rather than horizontally and were Yuzu (possibly Citrus ichangensis x Citrus well supplied with fine fibrous roots. reticulata var. austera hybrid, Swingle), Figs. The root system of the Rusk citrange was 0 1 and 0 2. found to be similar to that of the Morton The yuzu, sometimes called kansu, has been except that it had fewer fibrous roots. used widely in Japan as a hardy stock for the Sweet Lime (possible lime x lemon hybrid, satsuma, and it is also the stock on which, in Webber), Figs. M 1 and M 2. Japan, Thompson navel orange succeeds best. The sweet lime, sometimes referred to as The root system was the smallest of the the sweet lemon, is the principal rootstock fifteen stocks tested. It penetrated the soil used for citrus in Palestine. The vigor of the deeply but there was a scarcity of laterals growth of Parson Brown tops obtained on and, what few there were appeared to grow this stock exceeded that on rough lemon. The mainly in a vertical rather than horizontal root system is composed of many slender direction. It produced less top growth- of the laterals covered witii a mass «of fine fibrous iParson Brown scion than any -of the other roots. This stock developed no tap root. The stocks tested. abundant fibrous root system, however, pene Sweet Orange Cuttings, Fig. Q. trated three or more feet deep and had a All of the root systems described above spread of about 2 feet from the trunk. This were derived from seedlings of the rootstock root system resembled the grapefruit some varieties. This is the common method of what in its abundance of fibrous roots. The propagating citrus rootstocks. Many varie grapefruit, however, had a pronounced tap ties of citrus, however, can be readily propa root, while the sweet lime had none. gated from cuttings with the aid of growth Cuban Shaddock (possibly lime x lemon hy substances (Cooper 4). The roots on cuttings brid, Webber), Fig. P. of tflie Pineapple sweet orange after six years' This variety is highly recommended in Cuba growth in the nursery are shown in figure Q as a stock for the Washington Navel orange and may be compared to roots of seedlings, and reputedly grows well on saline soils. figures C 1 and C 2. It is seen that while the The top growth produced by the Parson seedling roots penetrated deeply into the soil, Brown scion grafted on this stock, as on the the cuttings had a shallow root system with sweet lime, greatly exceeded that on tfae rough out a tap root. The root system of the cut lemon. The root system, however, was almost ting consisted of about 10 long, vigorous identical in character with that of the rough lateral roots wtoch did not penetrate the soil lemon, except that it was supplied with more any more deeply than about 2 to 3 feet. As fine fibrous roots. a matter of speculation, the seedling root Calamondin (possibly Citrus retioulata var. system would, therefore, appear better austera x Fortunella hybrid, Swingle), Figs. adapted for foraging f«or water in the deeper N 1 and N 2. layers of light sandy soil than would the The calamondin is reputedly cold-resistant roots from cuttings. The vigorous, shallow and has been mentioned as a promising stock root system of the cuttings might be adapted for tfoe lime in Texas. The outstanding char to the moist hammock or shallow flatwood acteristic of the root system of the calamon soils. din was the group of vigorous central roots, Summary usually 4 or more, which grew vertically down The root systems of 15 different citrus root- to considerable depth. Under the conditions stocks budded to Parson Brown sweet orange of these experiments it had the most deeply have been excavated, photographed, and de- 48 FLORIDA STATE HORTICULTURAL SOCIETY scribed. Many striking differences in the spread as the root system of the sour orange. character of the r-oot systems of the various Literature Cited varieties were observed. The rough lemon 1. Mills, J. M. Citrus fruit culture. Calif. and Cuban shaddock had the most extensive Agr. Expt. Sta. Bull. 138, 1902. root systems, the calamondin the deepest, and 2. Hume, H. H. The cultivation of citrus the sweet lime and grapefruit the greatest fruits. The Macmillan Co., New York. abundance of fine fibrous roots. All stocks 1926. had more or less deeply penetrating tap roots 3. Oppenheimer, H. R. A citrus rootstock except the sweet lime. The root systems of trial on light soil. Hadar 9(2): 3-8, 1936. the bittersweet orange, sweet orange, man 4. Co-oper, William C. Rooting citrus cuttings darin, and citrange penetrated approximately with synthetic growth substances. Proc. as deeply and had nearly the same lateral Fla. State Hort. Soc. 53: 174-177, 1940.

THE FREEZING PRESERVATION OF CITRUS HEARTS

A. L. STAHL Florida Agricultural Experiment Station, Gainesville

The characteristics and nutritional values served by freezing. This paper is a report of fresh foods are more nearly preserved by of these tests. freezing than by any other method of preser Freezing Grapefruit Hearts vation. The bright natural colors are retained The work on grapefruit freezing was started that are destroyed under high temperatures several years ago and the effects of various necessary for canning. In texture and flavor, things were determined, namely, variety, also, the frozen foods are very similar to the method of preparation, syrup concentration, fresh, for freezing preserves the crisp, firm deaeration, inert gases, anti-oxidants, temper texture, the mild, pleasing flavors and most ature, storage temperature and packaging. of the nutritive value of the fresh products. Various varieties of mature grapefruit were Citrus fruits when heated lose their flavor, tried and comparisons made as to their suit texture and nutritive value, more so than do ability for frozen hearts. Taste, color, tex most «other fruits. Cooking does not change ture, quality, acidity, appearance and Vita the taste of most fruits as much as it does min C were determined at intervals over a citrus. Most cooked fruits have a pleasant period of 12 months, the test being made di taste and the taste of some are even improved rectly upon thawing. by cooking but any heat used on citrus fruits Silver Cluster, Duncan, Excelsior, Florida detracts from the appearance and flavor ma Common, Marsh (Seedless) and Thompson terially. We have therefore looked for other (Pink) were tried, and their value for freez means of preserving citrus hearts than can ing as hearts was found to be in the order ning and have found freezing to be ideal for named above. All .of the seedy varieties were the preservation of flavor, texture, appearance far superior to the seedless varieties, the only and quality of all types and varieties of citrus. disadvantage being the labor of removing the For the past several years we have been seeds. investigating methods and procedures by Several methods of preparation of the which citrus hearts could be successfully pre hearts were compared as to the effect on the