An Indoor, Container System for Producing Citrus Nursery Trees

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colored juices, since the color score for U.S. Grade A orange juice is 36-40. About 29% of Florida's orange trees are early- maturing ... USDA Tech. Bull. 988.

postharvest losses were less than those from 'Dancy' or

'Robinson'.

Processing Qualities

'Sunburst' fruit likely will be marketed fresh, but some may be processed for juice. In 1975, fruit samples were pro cessed in a pilot facility and several important factors were evaluated (Table 4). Fruit maturity was earlier than aver age in 1975. The oil content of 'Sunburst' juice was only about 0.01%, preierable to the 0.04% in samples of 'Dancy' juice from the same season (January 1976) (oral communi cation with C. J. Wagner). The ascorbic acid content of 'Sunburst' juice was 26 to 28 mg/100 g of juice in 1975 and 36 mg/100 g in December 1974. These ascorbic acid levels were similar to those reported for 'Dancy' juice (1) and somewhat lower than those in 'Hamlin' orange juice. Table 4. Processing qualities of 'Sunburst' fruit from the 1975 crop.z Sunburst? CLEO

RL

Scion rootstock

Processing date Nov .19,1975 10.6 Total soluble solids % 0.84 Total acids % 12.6 Solids-acids ratio 0.010 Oil % 10.0 Pulp % 26.0 Ascorbic acid mg/100 g 42.5 Color score 0.0 Limonin 47.8 Finished juice yield %

Nov. 19,1975 11.8 0.84 14.0 *• 0.013 11.0 28.0 43.5 0.0

Hamlinx

Dec. 10,1975 11.5 0.73 15.8 0.013 11.5 57.0 35.4

49.2



color scores lower than 36. The absence of limonin in 'Sun

burst' juice is a desirable processing feature. The finished juice percentage from 'Sunburst' fruit was essentially the same as that of 'Hamlin/ The finished juice yield from 'Dancy' fruit in January 1976 was lower than that from 'Sunburst' (oral communication with C. J. Wagner).

Pollination Studies Tests in 1961 showed that 'Robinson* and 'Osceola' gave poor fruit set unless cross-pollinated with pollen from certain other cultivars (3). On the basis of the S-allele gene system, described by Soost (5), it was expected that 'Sun burst' would be self-incompatible and would require crosspollination for fruit set. Screen cages were placed on 2 'Sunburst' trees having abundant flower buds in the spring of 1975. A small colony of honey bees was kept inside one cage during the entire bloom period, and pollinating insects were excluded from the other cage. On completion of bloom, the cages were removed. There was no fruit set on either of the caged trees, suggesting that 'Sunburst' was self-incom patible. During the same season, 'Sunburst' flowers were hand-emasculated and cross-pollinated with pollen from 'Robinson', 'Orlando', 'Nova' (a sibling of 'Robinson'), and 'Temple' (C. reticulata hybrid ?). The fruit set percentages were 35, 52, 51, and 40, respectively. The average numbers of seed per fruit were 29, 19, 14, and 26, respectively. These limited data suggested that 'Sunburst' required crosspollination for good fruit set and that any of the 4 cultivars

listed above could be used effectively as a pollenizer.

50.3

Literature Cited ^Sunburst fruit processing and data by Charles J. Wagner, Jr., Citrus and Subtropical Products Laboratory, AR, SEA, USDA, Winter Haven, FL.

yValues taken from 3 field boxes of Sunburst fruit per rootstock. xHamlin orange fruit were juiced and processed for reference.

The color scores of 'Sunburst' juice (Table 4) are some

what higher than that of 'Hamlin'. At scores of 42.5 and 43.5 'Sunburst' juice can be used in blending to improve poorly colored juices, since the color score for U.S. Grade A orange juice is 36-40. About 29% of Florida's orange trees are earlymaturing cultivars that frequently produce fruit with juice

1. Harding, P. L., and M. B. Sunday. 1949. Seasonal changes in Florida tangerines. USDA Tech. Bull. 988. 59 pp. 2. Reece, P. C, and F. E. Gardner. 1959. Robinson, Osceola, and Leenew early-maturing tangerine hybrids. Proc. Fla. State Hort. Soc. 3#

72:48-51.

t and R. O. Register. 1961. Influence of pollinators on

fruit set on Robinson and Osceola tangerine hybrids. Proc. Fla.

State Hort. Soc. 74:104-106. 4. Ridgeway, R. 1912. Color standards and nomenclature. The Author, Washington, D.C. 43 pp., 53 color plates. 5. Soost, R. K. 1969. The incompatibility gene system in citrus. Proc. First Int. Citrus Symp. 1:189-190. Univ. of Calif., Riverside, CA.

Proc. Fla. State Hort. Soc. 92:3-7. 1979.

AN INDOOR, CONTAINER SYSTEM FOR PRODUCING

CITRUS NURSERY TREES IN ONE YEAR FROM SEED1

W. S. Castle

University of Florida, Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, P. O. Box 1088, Lake Alfred, FL 33850 W. G. Adams and R. L. Dilley Adams Citrus Nursery Inc.,

P. O. Box 1505, Haines City, FL 33844

Additional index words, greenhouse, pregerminated seed, seed sizing, plastic planter bag, seedling tube, microbudding, Speedling tray. iFlorida Agricultural Experiment Stations Journal Series No. 2056.

Proc. Fla. State Hort. Soc. 92: 1979.

Abstract. A production system for citrus nursery trees is being developed based upon reuseable plastic tubes or frays for raising rootstock seedlings, a commercial growing

medium (PRO-MIX BX), plastic bags for the budded trees and

operation within an enclosed heated and cooled production structure. Plants suitable for microbudding can be produced in 3 to 4 months with a finished plant available in about 12 months. The system is flexible and offers advantages in the conservation of time and space. Techniques being studied to further enhance these advantages, the use of presized and pregerminated seed, are described. The production of citrus nursery trees in containers has certain recognized advantages (6, 7). Many of these result from the control afforded over the media used, particularly 3

in regard to fertilization, irrigation, diseases, weeds and other pests. Generally, container-grown trees require less space, the growing site is reuseable, and transplant shock is lessened. When plants are grown indoors, there are the added benefits of reduced cold protection costs and shorter growing cycles (6, 7). Citrus plants in containers are used on a limited basis commercially in Florida despite the advantages in their production. Such plants usually are more expensive and their smaller trunk caliper is not as readily accepted as com pared to the larger field-grown tree. This preference is changing in Florida, however, because growers recognize that container trees are easier to transplant and because nurserymen wish to reduce their costs and risks. The higher plant density associated with a container system, as com pared to a field one, also represents an advantage to the nurseryman in the improved efficiency and possible automa tion of several production practices. The advantages of container production combined with the large movement of nursery trees in Florida (3 to 5 million trees/year) have stimulated the interest of nursery

men in new techniques by which trees can be rapidly pro pagated. This report describes such a production system as presently developed and in operation at Adams' commer cial nursery.

System Description

Components

The fundamental elements of this system are the 2 types of containers used to raise seedlings, the black polyethylene bags (3) for raising the finished plants, a commercial grow ing medium (PRO-MIX BX), and the benefits obtained from growing plants indoors. These components are not new in the production of nursery plants; however, together, they represent a system in which the growing of citrus

nursery trees can be optimized enabling the routine produc

tion of container-grown plants in 12 to 14 months from seed.

The 2 containers are: (a) a Speedling (8) polystyrene tray about 13 x 26 x 5 inches containing 128 cells. Each cell has the shape of an inverted pyramid with one drainage hole at the base and has a volume of about 5 inches3; and, (b) a plastic tube which is available commercially in 3 sizes. The intermediate and largest tubes are 1 x 6.3 inches with a volume of 4 inches3 and 1.5 x 8.5 inches with a volume of 10 inches3, respectively. The tubes (Fig. 1) are constructed with 3 anti-spiral ribs which effectively keep root growth oriented downward. At the base of each tube is a drainage opening with 3 additional ones on the sides. The growing medium used for each step in the system, PROMIX BX, is composed of 60% Canadian peat, 20% perlite and 20% vermiculite with dolomitic limestone, superphos phate, Ca(NO3)2 and fritted trace elements added. A 4-mil, nominal i/% gallon, polyethylene bag with the dimensions 2.5 x 4 x 14 inches is used (Fig. 2). The plants are grown in a quonset shaped plastichouse with an inflated double polyethylene film covering (Fig. 3A) and in a standard Speedling

(8) plastichouse

(Fig. 3B). Both struc

tures have heating and evaporative cooling systems with conventional end-wall air circulation fans. A cooling system is particularly important in order to avoid the detrimental effects which can result from temperatures above 100°F (9). Such greenhouse temperatures are commonly reached during the summer months in Florida. An additional component of the system is a mechanical tube- and bag-filling machine (4). System Operation The first step is the collection of seed. A process was

Fig. 1. The seedling containers being used in an indoor system to produce citrus nursery trees are a large tube (LT), 1.5 x 8.5 inches, and a smaller one (ST), 1 x 6.3 inches, with anti-spiral ribs. The smaller tube is presently preferred. The root system of a 4-month-old rough lemon seedling growing in PRO-MIX BX is illustrated in the plant removed from the tube. Air pruned roots are present on the plant remaining in the tube.

devised to extract seed by crushing the fruit followed by

several washes and an enzyme treatment (1, 2, 11). Seed sowing takes place in a building, separate from

the growing area, where materials are stored and the potting machine is located. One seed is sown in each mechanically filled tube or tray compartment and covered with a shallow layer of coarse vermiculite. The vermiculite seems to help prevent washing out of the seed during irrigation and suppress algae growth. The Speedling trays are transferred to the standard Speedling greenhouse where they are set out on the bench-level "T" rails (Fig. 3B). The tubes are suspended in custom made benches covered with wire which permits the tubes to be placed adjacent to each other (Fig. 3A). Seedlings in the tubes have been grown in the quonset plastichouse. Irrigation and fertilization in both greenhouses are provided by an overhead traveling boom or by hand watering. Pesticides are applied with a small power sprayer.

Germination and emergence, depending upon the rootstock, generally begin in 5 to 7 days with 50% or more

of the seedlings having emerged in about 2 weeks. Aisles between the tube benches permit access for grading. Sort ing of the tube plants has been found to be useful because tubes with an ungerminated seed (blanks) are easily re moved. Also, germination is not uniform in time and those seedlings which emerge first tend to shade and retard the growth of later developing plants, particularly with largeleafed rootstocks. The Speedling house has only a center walkway with no side aisles. Thus, the plants are less accessible and do not readily lend themselves to sorting

or to the removal of extra embryos.

Seedlings are generally suitable for microbudding (10) Proc. Fla. State Hart. Soc. 92: 1979.

Fig. 2. The polyethylene bag currently in use and the extent of root growth in PRO-MIX BX about 6 months after budding of 'Hamlin' sweet orange on Carrizo citrange.

in about 60 to 90 days. At this time, the seedlings are either budded in their original containers (Fig. 4), or, trans planted to a plastic bag for budding about 10 to 14 days later. Presently, the latter procedure is followed. The bags are filled mechanically with the same medium used for growing the seedlings. The entire plant including the medium is removed from the tube or tray and inserted into a hole previously drilled by the potting machine. After budding, the top of the plant is removed, primarily because the handling of lopped plants under the higher density conditions of a greenhouse is inconvenient. When the bud has begun to grow, the new shoot is staked and tied as in a field nursery (Fig. 5). Again, the plants are sorted periodically to keep similar sized plants together. The budded plants generally maintain a single stem be cause of the close spacing and which reach about a one-half inch caliper in 9 months. The tree is induced to branch (headed) by pruning the stem after being transplanted to the field. Modifications, Advantages, Disadvantages The basic goal of this system is efficiency, i.e., how to produce a saleable plant in the shortest time at the lowest

cost. One considerable advantage offered by the system is the conservation of space. One or 2 greenhouses of modest

size (30 x 140 ft) can replace a large field seedbed. Each house of this size can produce 500,000 to 1 million seedlings per year assuming a crop every 3 months. In order for this system to operate at maximum efficiency, however, a high

degree of uniformity in seed germination and plant growth

Proc. Fla. State Hort. Soc. 92: 1979.

Fig. 3. Greenhouses being used for a rapid citrus nursery tree production system: (A) A double polyethylene covered greenhouse containing seedlings in tubes with an overhead irrigation system in operation on the right-hand side; (B) A standard Speedling plastichouse showing recently seeded polystyrene trays.

is necessary. It is essential that at each stage in the system, only useable and/or saleable plants are retained and that all greenhouse spaces are occupied by a desirable plant. The use of pregerminated and/or presized seed is being evaluated to improve plant uniformity. Citrus seed vary in size within each cultivar, some such as Cleopatra mandarin (Citrus reticulata Blanco) being relatively uniform (Fig. 6) as compared to Carrizo citrange [Poncirus trifoliata (L.) Raf. x C. sinensis (L.) Osb.] or Swingle citrumelo (P. trifoliata x C. paradisi Macf.) (Fig. 7). The preliminary results of a study being conducted at the Agricultural Research and Education Center (AREC), Lake Alfred, suggest that larger seeds germinate quicker and produce larger, more vigorous seedlings than smaller seeds of the same cultivar. Pregerminated seed are not precisely defined but would generally include those in the range from the completion of the initial uptake of water (imbibition) to emergence of the primary root. They have 2 important potential advant ages. First, viable seed are identified in advance of sowing; and second, if seeds are being germinated continuously, the normal range in time to germination can be virtually

eliminated by sowing only those seeds which have reached a predetermined germination stage. Seed sizing has not yet been incorporated into the system; however, seed are being pregerminated in a moist chamber maintained at 90° F. Seed are treated to these conditions for several days and then the most advanced ones are sown.

88 100 SEED WEIGHT (ing)

150

Fig. 6. Frequency distribution by weight of 200 Cleopatra mandarin seeds. (X = average seed weight).

500

Fig. 4. Sour orange seedlings in the large tubes with healed in micro-

buds.

This treatment appears to promote seedling emergence and initial growth. A second advantage, that of conservation in time, has been approached primarily through the manipulation of temperature. Temperature conditioned seed to enhance germination were mentioned above. Plant growth has also been stimulated by locating an air distribution tube, similar to the one shown located above the benches in Fig. 3A, underneath each plant bench. Seedlings in the Speedling trays have not responded as well as those in tubes, however,

100

150 SEED

169

200

250

300

WEIGHT (119)

Fig. 7. Frequency distribution by weight of 200 seeds each of Carrizo citrange and Swingle citrumelo. (X" = average seed weight).

primarily because the thin-walled tubes are not as resistant to heat transfer as are the polystyrene trays. Furthermore, air readily passes between the invididual tubes while similar air movement is inhibited by the trays. Seedlings are raised in both tubes and trays. Plants in the tubes are generally easier and more convenient to utilize for the complete indoor system while those in trays lend themselves more readily to bulk handling, an asset useful in raising liners for transfer to a field site for budding and finishing.

The smaller of the 2 tubes (Fig. 1) is presently pre ferred. In growth studies conducted at Adams Nursery and the AREC, the smaller tube did not appear to inhibit plant growth rate for a period of 3 months. Thus, satis factory sized seedlings are produced in 3 months or less

and transplanted to a plastic bag for budding. The larger tubes may be more satisfactory, however, when raising

seedlings for microbudding in the tube. A simple guide for determining the proper time to transplant seedlings grow

ing in either the tubes or trays is the appearance of roots in the drainage holes. Emerging roots will air-prune, but, if the plants remain in the containers too long, a knot of roots forms making it difficult to remove the plant. The decision to use the medium described earlier was based on empirical comparisons made at Adams Nursery. Clearly visible differences in plant growth were observed Fig. 5. Shoot growth in recently budded seedlings in plastic planter bags.

among several commercial and custom mixed media (Fig. 8).

Plants in a water hyacinth preparation outgrew those in the Proc, Fla. State Hort. Sac. 92: 1979.

medium being used, but the hyacinth material had not been obtained from a burrowing nematode [Rhadophohis similis (Cobb) Thorne] approved site.

Modifications and improvements to this basic system are expected. A similar system employing a different growing structure with tubes arranged in trays, which can be pur chased with the tubes, is in operation elsewhere in Florida (Fig. 10). As experience is gained with a wider range of rootstocks and scions, propagation techniques other than budding may be more appropriate (5).

Fig. 8. Seedling growth in tubes demonstrating the effect of different media.

Prognosis

Acceptable citrus nursery trees have been produced in doors in one year from seed using plants grown in tubes

and the plastic planter bag. The performance of the system represents several meaningful advantages which seemingly outweigh the potentially higher costs of establishing this system as compared to a field nursery. The greater flexibility of the indoor system (Fig. 9) is also important as well as the time factor. These advantages may allow the nurseryman to custom-fill orders rather than speculate on the needs of

Fig. 10. A plastichouse for raising seedlings using commercially available trays instead of wire-topped benches. The capacity of this structure is approximately 300,000 plants. (Photographed with the per mission of Coca-Cola—Foods Division.)

One crop of trees has been produced to date and trans planted to a commercial grove. The field behavior of these trees and grower acceptance of smaller caliper container trees will be significant factors in the future successes of this type of system.

the industry.

Literature Cited FLOW DIAGRAM CITRUS NURSERY PROPAGATION CONTAINER

FIELD SEED GERMINATION

Conventional

1. Barmore, C. R., and W. S. Castle. 1979. Separation of citrus seed from fruit pulp for rootstock propagation using a pectolytic en zyme. HortScience 14(4):526-527.

2. Cody, R. 1979. Solution for citrus seed extraction.

Citrus Ind.

6O(7):29-31.

outdoor seedbed

3. Gouin, F. R. 1979. Plastic planter bags, advantages and disadvant ages. Nursery Business 24(7):63-64, 38.

4. Hardy, N. G. 1979. New look for Florida citrus groves. Citrus Ind. LINER STAGE

60(8):4-ll.

5. Maxwell, N. P., and S. D. VanGundy. 1979. A technique for propa gating container-grown citrus on sour orange rootstock in Texas. HortScience 14(l):56-57.

6. Moore, P. W. 1966. Propagation and growing citrus nursery trees in containers. Comb. Proc. Int. PL Prop. Soc. 16:54-61. BUDDING

Liners budded prior to settin q

7. Platt, R. G., and K. W. Opitz. 1973. Propagation of citrus, p. 1-47. In W. Reuther (ed.) The Citrus Ind., Vol. 3. Univ. Calif.,

Liners budded in conventional manner

Riverside.

in the field

DISPOSITION

Sold

Sold with live buds

Fig. 9. Flow diagram comparing the conventional field method, and an indoor container system, to produce citrus nursery trees.

Proc. Fla. State Hort. Soc. 92: 1979.

8. Reilly, A. 1979. The Speedling scene. Nursery Business 24(7):40-43. 9. Reuther, W., E. M. Nauer, and C. N. Roistacher. 1979. Some high temperature effects on citrus growth. /. Amer. Soc. Hort. Sci. 104(3):353-356. 10. Wishert, R. L. 1974. Microbudding citrus. South Australian Dept. Agric. Ext. Bull. 18.74. 11. Woods, C. 1979. How the state's largest nursery produces certified seed and seedlings. Fla. Grower Rancher 72(4):8-10.

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