Growth and Productivity of Virus-Infected Valencia Orange Trees on Twenty-Five Rootstocks

GARDNER, HUTCHINSON, HORANIC, HUTCHINS: VIRUS STUDIES 89

GROWTH AND PRODUCTIVITY OF VIRUS-INFECTED VALENCIA ORANGE TREES ON TWENTY-FIVE ROOTSTOCKS

F. E. Gardner, D. J. Hutchinson, G. E. Horanic is even more impressive than on the heavier AND P.C. HUTCHINS types. The present study is part of a continuing search for rootstocks as productive as Rough Crops Research Division lemon on the light sands but which produce Agricultural Research Service fruit of betterinternal quality. Also, the data U. S. Department of Agriculture is evaluated for the possibility of predicting fu Orlando ture tree growth and production on the basis of the early years of tree growth and production,

Abstract thus shortening the length of time for rootstock evaluation. During the experiment, 23 of the original 43 rootstocks developed symptoms of xyloporosis or exocortis because the old-line Valencia trees, Materials and Methods used as bud sources, were symptomless carriers of the viruses which cause these diseases. Some The test planting,—Seeds of the various root of the most intolerant rootstocks died or declined stocks were obtained from the variety collection and were dropped from the trial. Data on tree at the USDA farm near Orlando, and the nur size, growth trends, fruit production and quality sery trees were grown at this location. The arepresented for 25 rootstocks during a 19-year budded trees were planted June 30, 1948, near period. In Valencia tree size Kalpi lime and Avon Park, Florida, on a typical Lakeland fine Rough lemon rootstocks ranked first and second, sand as a randomized block design with three- respectively. These two rootstocks also produced tree plots of each rootstock and with five replica more fruit by a wide margin than any of the tions. Tree spacing was 25 x 25 feet. others, although the fruit was low in total Budwood source,—Old-line Valencia buds soluble solids. Citrumelo C-4475, a hybrid of were taken from several mature trees selected seedy grapefruit by trifoliate orange (Poncirus only for freedom from psorosis. When the root trifoliata), was the most dwarfing stock in the stocks were budded in 1946, it was not known experiment. Trees on citrumelo C-4475 were that most commercial citrus trees in Florida very productive per unit of tree size, a factor were infected, as symptomless carriers, with which suggests that this stock could be used xyloporosis and exocortis viruses. Most ofthe advantageously in close-spaced plantings. rootstock varieties used in this planting had not Trunk circumference measurements, taken been tested previously. It subsequently developed at frequent intervals, disclosed that, with few that 26 of the 43 rootstocks originally included exceptions, the relative order oftree sizes on developed symptoms of xyloporosis, exocortis, or the various rootstocks did not change rank ap budunion crease. Trees on most of these 26 preciably after the first 6 years. Thus, the stocks died or declined, and data from them ultimate relative tree size on a given rootstock were accordingly excluded. However, eight were was predictable at a fairly early age. The rela retained as stocks of record because they showed tive order of fruit production established during no exterior, visible evidence of disease, although the early fruiting years was also maintained, they had minor gum deposits in the bark char with a few exceptions, during subsequent years. acteristic of xyloporosis. These are designated in the tables. Tree size, yield, and fruit quality measure Introduction ments,—Trunk circumference, 6 inches above The outstanding fruitfulness of Valencia the bud union, were recorded at frequent inter orange trees on Rough lemon rootstock is well vals. A paint mark on the trunk served as the known. The increased production of Rough point of measurement during theearly years. lemon over other common stocks on light soils Later a finishing nail, driven into the trunk, pro- 90 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 vided a permanent measuring point. Yields of tangor C-653, for example, moved up in rank in fruit were expressed in boxes picked per tree. relation to the group as a whole. Dancy tan Percent total soluble solids and total acid of the gerine lost rank, but this change did not occur juice were determined by standard laboratory until after 1956. As a rootstock, Hamlin sweet methods on random samples of 24 fruits from orange produced significantly larger trees than each plot in each replication. Florida sweet seedlings; this was apparently due to diminished growth on the latter stock between 1959 and 1967. In general, however, Results and Discussion relative tree sizes on the various stocks were Relative growth rate and tree size.—Tree essentially established by 1954, 6 years after sizes on 25 of the rootstocks in 1967, 19 years planting. Small changes in rank are meaning after planting, are arrayed in descending order less, in view of the very small differences in of trunk circumference (Table 1). In order to trunk circumferences between adjacent values. show growth trends at various time intervals With regard to vigor of growth on this light the trunk circumferences were ranked periodi sandy soil, sour orange No. 2, an ordinary sour cally since 1951. On this basis, the trees on selection used as a reference stock in most of our Kalpi lime (Webber's Philippine Hybrid), Rough rootstock trials, ranked 15th on the list. Ber- lemon, and Hamlin orange ranked first, second, gamia sour orange and Bittersweet produced and third, respectively, in size throughout the essentially the same sized trees as sour orange experiment. Several rootstocks, Sauvage sour and No. 2. Sauvage sour, an atypical type of sour

Table 1. Relative ? growth rate, tree size, total soluble solids. and acid in iuice o: : Valencia on 25 rootstocks Trunk circ Juice-TSS Juice-acic 1 Trunk circ. rank in 1967 5-21- 59 5-21- '59

Rootstock '51 '34 •56 f 59 '67 cm % Rank % Rank

Kalpi lime 1 1 1 1 1 83.1 a 11.65 ef 23 0.71 c-e 21 Rough lemon 2 2 2 2 2 81.0 ab 11.06 f 25 0.74 a-e 13 Hamlin orange 3 3 3 3 3 79.4 abc 11.84 de 20 0.71 c-e 19 Duncan gft. 7 6 4 4 4 78.9 abed 12.34 b-e 14 0.69 c-e 22 Sampson tangelo 12 3 7 5 5 77.7 a-e 12.70 be 5 0.75 a-e 10 Sauvage sour or. 11 10 9 8 6 76.1 b-o 11.64 ef 24 0.69 d-e 23 Tangor C-653 22 12 11 9 7 76.0 b-e 12.99 b 2 0.78 a-d 5 Oklawaha sour or. 9 11 12 12 3 73.9 c-f 12.45 bed 10 0.74 a-e 12 Cleopatra mand. 6 7 3 10 9 73.7 c-f 12.44 bed 11 0.77 a-e 6 Dancy tangerine* 5 5 5 7 10 73.6 c-f 12.23 b-e 18 0.70 a-e 14 Alamoen gft. 24 15 15 14 11 72.3 def 11.83 de 21 6.74 a-e 11 Fla. sweet or. 4 4 6 6 12 71.9 efg 12.23 b-e 17 0.73 b-e 15 Leonardy gft.* 10 9 10 11 13 71.8 efg 12.15 c-e 19 0.71 c-e IS Sunshine tangelo* 8 14 13 13 14 68.9 fgh 12.63 be 7 0.72 b-e 17 Sour or. No. 2 14 18 17 17 15 68.6 fgh 12.64 be 6 0.75 a-e 9 Watt tangelo * 17 13 14 15 16 68.3 fgh 12.71 be 4 0.79 abc 4 Bittersweet 19 19 18 16 17 68.2 fgh 12.60 bed 8 0.75 a-e 7 Bergamia sour IS 22 19 18 18 66.1 ghi 12.34 b-e 15 0.32 a 1 r> Pina tangelo* 20 21 20 19 19 65.4 hij 12.53 bed 9 0.75 a-e O Suwannee tangelo* 13 16 16 21 20 61.1 ijk 12.35 b-e 13 0.73 b-e 16 Umatilla tangelo* 1!) 17 22 22 21 60.9 ijk 12.95 b 3 0.79 abc 3 Siamese pum. 25 24 23 20 22 60.1 ijk 12.23 b-e 16 0.68 e 25 Thong Dee pum. 23 25 25 25 23 59.9 jk 11.83 d-e 22 0.63 e 24 Yalaha tangelo* 21 23 24 24 24 56.4 k 13.69 a 1 0.80 ab 2 Citrumelo C-4475 16 20 21 23 25 55.6 k 12.37 b-e 12 0.71 c-e 20 Sig. - Means not followed by any letters in common are significantly different at odds of 19 to 1, *No external symptoms of xyloporosis but some gum-staining of phloem. GARDNER, HUTCHINSON, HORANIC, HUTCHINS: VIRUS STUDIES 91 orange, exhibited rather outstanding vigor but However, in 3 of the 4 years in which tests were produced fruit of low solids. These characteris run on fruit from this experiment, Kalpi lime tics of Sauvage sour rootstocks were reported exceeded Rough lemon in solids by an average previously (3), with Marsh grapefruit as the of 0.56 percentage points and equaled Rough top. Trees on citrumelo C-4475 were the most lemon in the 4th year. Kalpi lime, like Rough dwarfed, as mentioned. lemon, has low tolerance of cold (2) and of Fruit yields and quality,—The total cumula the burrowing nematode, Radolpholus sinrilis tive yields of fruit per tree on the various root- Cobb (Thorne) (4), although it has high toler stocks (Table 2) showed a very wide spread. ance of xyloporosis and exocortis viruses, as Kalpi lime and Rough lemon exceeded all other shown in this experiment. The tristeza tolerance stocks by a substantial margin during the two of Kalpi is not known, nor has there yet been periods of divided yield records, as well as for sufficient field testing of this stock to warrant the total period. Rough lemon, again, demon its general use as a Rough lemon substitute. strated its outstanding fruitfulness as a stock The separation of yields into two periods for Valencia orange on light soils. As antici (1956-60, inclusive and 1961-64, inclusive) shows pated, however, it ranked low in juice solids that comparative yields between rootstocks in (Table 1). the early years and later years are rather con Kalpi lime equalled Rough lemon in growth sistent. For the most part the rankings are in and fruitfulness, and also produced low solids. good agreement between the two periods, al-

Table 2. Cumulative periodic and total yields, and yields per unit of tree

Cumulative Cumulative Total Yield per , yields yields yields dm2 trunk

1956-60 incl. 1961-64 incl. 1956-64 incl. cross section Rootstock Boxes Rank Boxes Rank Boxes Rank Boxes5 Rank Kalpi lime 11.64a 1 18.82a 1 30 .46a 1 5.54 1 Rough lemon 11.05a 2 17.01a 2 28 .06a 2 5.37 2 Ham1in orange 7.46b 3 13.09b 3 20 .56b 3 4.10 5 Sauvage sour or. 5.91bc 5 12.21bc 4 18 .10bc 4 3.93 8 Fla. Sweet or. 6.21bc 4 11.37bcd 7 17 .58bcd 5 4.24 4 Cleopatra mand. 5.21c-f 9 11.39bcd 6 16 .60cde 6 3.84 11 Oklawaha sour or. 4.83c-g 10 11.52bcd 5 16 .36cde 7 3.76 13 Dancy tangerine* 5.70bcd 7 10.60cde 9 16 .33cde 8 3.79 12 Duncan gft. 5.89bc 6 10.18c-f 11 16 .06cde 9 3.24 16 Leonardy gft.* 5.61b-e 8 10.45c-f 10 16 .06cde 10 3.92 9 Bergamia sour or. 4.06c-h 16 10.65cde 8 14 ,71c-f 11 4.23 6 Bittersweet 4.44c-h 13 ■ 9.96c-f 12 14 .40c-f 12. 3.89 10 Sampson tangelo 4.82c-g 11 9.39d-g 13 14 •22c-g 13 2.96 20 Sour or. No. 2 4.11c-h 15 9.15d-g 14 13 .26e-h 14 3.54 14 Alamoen gft. 4.21c-h 14 9.14d-g 15 13 .17e-h 15 3.12 18 Citrumelo C-4475 4.59c-g 12 8.85c-h 16 13 .04e-i 16 5.30 3 Siamese pum. 3.36e-hJ 19 8.15c-h 17 U .51f-i 17 4.02 7 Sunshine tangelo* 3.98c-h 17 7.13g-k 20 11 .llf-j 18 2.94 21 Watt tangelo* 3.48fgh 18 7.38g-j 19 10 .S6f-j 19 2.93 22 Tangor C-653 2.61gh 24 7.51g-j 18 10 •12g-j 20 2.20 25 Suwannee tangelo* 3.07fgh 20 6.45h-k 21 9 .69h-j 21 3.25 15 Umatilla tangelo* 3.03fgh 21 6.23h-k 22 9 • 08ij 22 3.14 17 Pina tangelo* 2;76gh 22 5.37j-k 24 8 • 14j 23 2.39 24 Thong Dee pum. 2.17h 25 5.85i-k 23 8 .-02 j 24 2.68 23 Yalaha taneelo* 2.64gh 23 4.94k 25 7 .581 25 2.99 19 Sig. - Means not followed by any letters in common are significantly different at odds of 19 to 1. *No external symptoms of xyloporosis but some gum-staining of phloem*. 92 FLORIDA STATE HORTICULTURAL SOCIETY, 1967 though there are some notable exceptions. For ent tree decline, were included in the data (as example, Cleopatra moved up from 9th rank in noted in the tables), although some trees of the first period to 6th rank in second period, each showed relatively minor gym staining of confirming common observation that Valencia the phloem area of the rootstock. Since this yields on this stock improve as trees advance in experiment was started, the intolerance of most years. The change in rank of Bergamia sour of the above-listed varieties has been reported orange from 16th to 8th rank was even more by Childs (1) and Olson et al. (6). striking but rank in tree size remained con Several reports indicate evidence that some stant. The majority of the stocks, however, so-called "tolerant" rootstocks can be adversely maintained an even rank in production with in affected by xyloporosis and exocortis viruses creased age which suggests that a rootstock's even though no symptoms are evident (5, 7. 8). productivenenss can usually be assessed in a On this basis, the relative performance of at shorter time than generally believed. In this least some of the "tolerant" stocks in this ex experiment, the yield rank of most of the stocks periment would have been different if virus- did not change materially after the first 12 free buds had been used. It is unlikely, however, years. that the major findings of this report on the Yield per unit of tree size.—Yields in boxes tolerant stocks would have been altered by the of fruit per unit of trunk cross-sectional area use of clean budwood. Nevertheless, since more are presented in order to show which rootstocks than half of the 43 miscellaneous rootstocks were most productive for their size (Column 4 assembled for this experiment showed virus- of Table 2). Kalpi lime and Rough lemon pro intolerance, it is evident that the use of virus- duced not only the largest trees but were also free budwood sources greatly expands the list of the most productive per unit of size. Citrumelo potentially useful rootstocks. C-4475, smallest in tree size, was very produc tive (in 3rd rank in fruit per unit of tree size) Acknowledgements and would qualify as a dwarfing stock for close- We wish to thank the Digiorgio and the Min spaced plantings. Based on area of trunk cross ute Maid Corporations for their care of this section, the trees on citrumelo C-4475 were less experimental planting and for making possible than half as large as those on Rough lemon the yield records; also E. James Koch of the (2.46 dm2 vs. 5.22 dm2). In theory, doubling Biometrical Services Division, Plant Industry the number of the citrumelo-rooted trees per Station, Beltsville, Maryland, for statistical an acre would provide the same total yields as alyses of the data. one-half the number on Rough lemon. In addi tion to greater ease of harvesting from smaller LITERATURE CITED trees, the advantages would include appreciably 1. Childs, J. F. L. 1951. Cachexia, a bud-transmitted disease and the manifestations of phloem symptoms in cer higher solids than from Rough lemon. tain varieties of citrus, citrus relatives, and hybrids. Proc. Fla. State Hort. Soc. 64: 47-51. Rootstocks intolerant of exocortis or xylopo- 2. Gardner, F. E., and George E. Horanic. 1963. Cold rosis.—The following stocks were omitted from tolerance and vigor of young citrus trees on various root stocks. Proc. Fla. Hort. Soc. 76: 105-110. the foregoing tables because of obvious virus 3. Gardner, F. E., and George E. Horanic. 1966. Growth yield anrl fruit quality of Marsh grapefruit on various root symptoms and, in many cases, decline or death stocks on the Florida east coast—a preliminary report. Proc. of the trees. Intolerant of exocortis virus— Fla. State Hort. Soc. 79: 109-114. 4. Ford, H. W., W. A. Feder, and P. C. Hutchins. 1960. Cuban shaddock, Morton citrange, P. trifoliatat Citrus varieties, hybrids, species, and relatives evaluated for resistance to the burrowing nematode Radopholus similis. Rangpur lime, Sunki mandarin. Intolerant of Citrus Experiment Station Mimeo Series 60-13, p. 1-26, Lake xyloporosis virus—Clementine tangerine, King Alfred, Florida. 5. Olson, E. O., and A. V. Shull. 1962. Size and yield mandarin, Nagami and Nippon kumquats, Swa- of 12-year-old Valencia orange trees on various rootstocks in presence or absence of exocortis and xyloporosis viruses. tow mandarin, Temple orange and Orlando, Min- Jour. Rio Grande Valley Hort. Soc. 16: 40-43. neola, Thornton, and Williams tangelos. In addi 6. Olson, E. O., W. C. Cooper, N. Maxwell and A. V. Shull. 1962. Survival, size and yield of xyloporosis- and tion, calamondin and Lakeland and Tavares lime- exocortis-infected old-line red grapefruit trees on 100 root stocks. Jour. Rio Grande Valley Hort. Soc. 16: 44-51. quats were dropped because of death or decline 7. Sinclair, J. B., and R. T. Brown. 1960. Effect of from budunion crease. Dancy tangerine, Leon- exocortis disease on four citrus rootstocks. Plant Disease Reptr. 44: 180-183. ardy grapefruit and six tangelo varieties, with 8. Sleeth, Bailey. 1903. Effect of exocortis and xylo porosis viruses on growth of nucellar grapefruit on different out exterior symptoms of xyloporosis or appar rootstock. Jour. Rio Grande Valley Hort. Soc. 17: 108-111.