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PLATE I.—Typical fruits of the Orlando, Minneola, Thornton, and Seminole tangelos.

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Plate II. United States Department of Agriculture standards for determining the

color of Tangelo rind.

solids and a minimum solids-to-acid ratio of 10.50 to 1.

This study is a part of a broad program of research aimed at improving market efficiency, and expanding markets for farm products.

Description of Orlando, Thornton, Minneola, and Seminole Tangelos and Their Rootstocks

Tangelo varieties vary widely in tree and fruit characteristics. The trees are vigorous, usually attaining standard orange tree size. However, it is mainly the fruit characteristics that interest the grower, shipper, and consumer. The different lands of tangelo fruits vary considerably in size, shape, color of rind and flesh, flavor, and date of maturation. Webber (21) points out that in general, tangelo trees produce fruits about the size of the common sweet orange. The fruits exhibit a tendency to be slightly drawn out at the stem end or necked. Tangelo fruits are usually highly colored—the Orlando, Minneola, and Seminole, bright orange; Thornton, bright yellow. They are aromatic, richly flavored, sprightly acid, only slightly bitter, and very juicy. The rind is usually smooth or slightly bumpy, thin, comparatively loose and easily removable like that of the tangerine.

The Orlando tangelo (formerly known as "Lake") is the result of the cross, Bowen grapefruit X Dancv tangerine, with the latter as the pollen parent (17, 18,21). Orlando is one of the earliest maturing tangelos and harvesting usually begins in early November. However, prime eating quality is not reached until January. The fruit is attractive, highly colored, deep orange to almost tangerine red, and has a thin rind, which is slightly pebbly but not rough. They are about the size of tangerines, the average diameter being from 2%e to 3%6 inches. The

to 12 seeds (plate I).

The Thornton tangelo is believed to be a result of crosses between tangerine and grapefruit (16, 17). It dates back to crosses made by Swingle and Webber in 1897-98 at Eustis, Fla. Swingle, Robinson, and Savage state that "the original records of the group of hybrids giving rise to the Thornton tangelo were lost, so that the pollen parent is not definitely known. As many of the sister hybrids show unmistakable tangerine characteristics, however, it is safe to say that this fruit is a tangelo with grapefruit the known seed parent" (17).

The fruit attain prime eating quality in January and February, although harvesting begins in December. The Thornton is unusual in appearance in that the rind is soft and thick, somewhat wrinkled and pebbly, and the color of the rind and flesh is yellow orange. The fruits range in size from about 2%6 to 3%6 inches and are flattened at the blossom end and slightly tapered at the stem end. Seeds range in number from 10 to 25 per fruit (plate I).

The Minneola tangelo is the result of a cross in which the Bowen grapefruit was pollinated with pollen from the Dancy tangerine (17, 21). The fruit reaches prime eating quality in January and February, although harvesting begins in December. The Minneola is probably the most attractive of the tangelos, and when fully ripe the color of the rind is deep reddish orange. The fruits are medium large in size and range from 2%6 to 3%6 inches in diameter or larger. They are somewhat flattened at the blossom end, and the stem end of the fruit is slightly raised but does not form a distinct nipple. The fruit contains 7 to 12 small seeds closely grouped at the center (plate I).

The Seminole tangelo, like the Orlando and Minneola, is a result of crosses between Bowen grapetangerine (17, 21). The fruit reaches prime eating quality in February or March, although harvesting begins in January. This is one of the most attractive of the tangelo fruits, and in general appearance it is more like a highly colored orange. Fruit size averages from about 2%6 to 3$fe inches in diameter. The rind is thin, smooth, and glossy with a tendency to crease. Seeds are numerous, 20 or more, short, plump, and closely grouped at the center (plate I). The flavor of the juice is tart and sprightly which accounts for the late marketability.

Tangelos have been grown chiefly on sour orange {Citrus Aurantium) rootstock. However, because of the susceptibility of sour orange to the virus disease tristeza, this rootstock is losing favor. In recent years there has been fairly largescale planting of tangelos on rootstocks of Cleopatra tangerine (C. reticulata, referred to hereafter as Cleopatra), rough lemon (C. Limon), and sweet orange (C. sinensis). Rusk Citrange (Poncirus trifoliata X Citrus sinensis, referred to hereafter as Rusk) rootstock is also used in a limited way in Florida.

During the 5 months, October through February, marked physical and chemical changes occur in the fruit. Tangelos, like oranges and grapefruit, do not improve in palatability after harvest. Since they contain practically no starch, they do not undergo marked changes in composition after being picked from the tree, as do apples, pears, mangos, and bananas. The degree of maturity of tangelos at the time of harvest is the most important factor determining their eating quality. They owe their sweetness to natural sugars contained when they are picked and it can readily be understood that they should not be harvested until they are ripe. 11 is recognized that other factors, such as weather conditions, soils, fer

dusting, may also affect eating quality. Some observations regarding the effect of rainfall were made in connection with this investigation.

Materials and Methods
Selection of Plots and Samples

The varieties studied were the commercially important ones—Orlando, Thornton, Minneola, and Seminole. The commercial groves used for fruit sampling were selected to represent average tangelo plantings in Florida. They were located in the central and ridge districts on sandy soils relatively low in organic matter, and in the west coast Bradenton-Terra Ceia districts, where the soils have a relatively higher organic matter content. In each of these districts the tangelos in the plots were on the following rootstocks. Six different groves of Orlando tangelos were on rough lemon, 10 on sour orange, 4 on Cleopatra, 3 on Rusk, and 1 on sweet lemon. Three different groves of Thornton tangelos were on rough lemon, and three on Cleopatra. Two different groves of Minneola tangelos were on rough lemon, three on sour orange, two on Cleopatra, and one on sweet orange. Three different Seminole tangelo groves were on sour orange and one on Cleopatra.

The sample groves ranged in age from 5 to approximately 25 years. Most of them were mature but none were considered old for citrus trees. All the groves were in good condition and had received normal culture, fertilizer, and spray treatments. The trees showed no evidence of deficiency disorders. The location of the plots, variety, kinds of rootstock, age of the trees, and the seasons of investigations are given in table 1.

The tests were started the first week in October and continued until January or February, at which time

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Orlando:

Rough lemon 1

2

3

4

5..

6

Sour orange:

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9

10...

11

12_..

13

14

15

16

Cleopatra:

17

18

10-.

20.

Rusk:

21 _..

22

23

Sweet lemon:

24. _

Thornton:

Rough lemon

25

26

27

Cleopatra:

28

29

30

Minneola:

Rough lemon;

31..

32

Sour orange:

33

34...

35

Cleopatra:

36

37

Sweet orange:

38_.

Seminole:

Sour orange:

39

40

41

Cleopatra:
42

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1As of 1953.

Approximate.

some of the fruit was showing signs of senescence as indicated by creasing, puffiness, separation of the flesh from the rind, drying out of segments, and dropping from the trees.

Samples consisting of at least 125 fruits were picked from each plot at intervals of about 4 weeks. Care was taken to pick fruits from only the regular bloom and the fruits were selected to be representative of various parts of the

trees since some of the chemical constituents vary with location of the fruit on the tree (11, 15). Immediately after being picked the samples were taken to the U.S. Department of Agriculture Horticultural Field Station at Orlando, Fla., and placed in storage at 32° F. They were tested as promptly thereafter as was feasible. The sampling continued through four marketing seasons 1952-53 to 1955

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