32 FLORIDA STATE HORTICULTURAL SOCIETY, 1971

SWEET LIME, ITS PERFORMANCE AND POTENTIAL AS A ROOTSTOCK IN FLORIDA

A. H. Krezdorn and W. S. Castle Unfortunately, there are only partially tested alternative stocks. It is the purpose of this report IF AS Fruit Crops Department to review the status of the sweet lime, C. limet Gainesville tioides Tan., as a possible replacement for rough lemon, based on results published in the literature Abstract and recent experimental data. The current decline of many trees on rough lemon, Florida's major rootstock, suggests the Materials and Methods need for an alternate stock. A review of the world Review of literature.—A comprehensive re literature on rootstocks and data obtained in view of the world literature on the sweet lime Florida, indicate sweet lime, (C. limettioides Tan.), and its use as a rootstock was conducted. Informa has many ofthe same basic advantages as rough tion has been extracted from the literature and lemon. It is deeply rooted and as well or better ad presented with new data for comparison and dis apted to sandy soils. Trees on sweet lime are large, cussion. yield well and produce large fruit if budwood free New data.—Data on the depth of rooting of damaging viruses, such as xyloporosis and exo- and mineral content of leaves of trees on cortis, is used. Like rough lemon, they also have sweet lime, rough lemon and sour orange were lower juice quality and less resistance to cold than obtained from a previously described experiment trees on sour orange. Certain combinations on sweet (20) and are presented in Tables 1 and 5. Data on lime are susceptible to damage by tristeza, but the influence of rootstock on cold hardiness were less so than sour orange. obtained from a young rootstock planting at Knowledge of this rootstock is imperfect and Gainesville and are presented in Table 4. its use would involve some risk. This is true, how ever, of other stocks and rough lemon itself. Choice Results and Discussion of sweet lime would appear reasonable in some cases, particularly on the deep sands of central Nomenclature and description.—The sweet lime Florida. (C. limettioides Tan.) is distinct from the acid limes (C. aurantifolia Swing, and C. latifolia Tan.). The sweet lime is sometimes called the Indian Introduction sweet lime but more commonly Palestine sweet Many trees of sweet orange, Citrus sinensis lime. The 'Columbian' sweet lime is a clonal selec (L) Osbeck, have declined in recent years, leading tion that appears indistinguishable from seedling to the names of "young tree decline" and "sand sources. Sweet lime is often incorrectly called hill decline." The cause of this disorder is un sweet lemon but it is distinct from true sweet known. It might better be called "rough lemon lemon (C. limetta Risso.). The floral biology has decline" because rough lemon rootstock, C. jamb- been well described by Singh and Dhuria (32). hiri Lush., appears to be implicated. They reported that sweet lime flowers only in the This decline is of great concern to citrus pro spring of the year and produces a single annual ducers because rough lemon has long been the crop, unlike acid limes which flower more or less basic rootstock for Florida's sandy soils. Camp (3) continuously. A sample of 50 sweet lime fruit reported in 1940 that the adequate fruit quality, from a tree in the variety collection at Gainesville ease of handling and greatly superior yields of contained an average of 14 and a range of 10 to 16 trees on rough lemon gave it an advantage over highly polyembryonic seeds per fruit following all other rootstocks tried to that date on sandy open pollination. The fruit is slightly larger and soils. This has remained true until the present and rounded than the Tahiti' lime which it resembles it is only the decline of trees on rough lemon that somewhat. has now made its use questionable and thesearch Bud union.—Mendel (21) presented a classical for an alternate rootstock appropriate. study of the anatomy of the bud union of 'Sham- outi' sweet orange on sweet lime. He did not re University of Florida, I.F.A.S., Journal Series No. 4189. port any abnormalities. Other reports from Israel KREZDORN AND CASTLE: SWEET LIME ROOTSTOCKS 33

Table 1. Mean tree height, depth of rooting, yield, fruit size and fruit quality of 'Orlando1 tangelo on 3 rootstocks. Lake County, Florida. 1969.1

Rootstock Measurement Sweet lime Rough lemon Sour orange

Tree height 12.1 a 12.3 a 10.1 b (ft.)

Root depth2 11.2 ab 15.2 a 11.3 b (ft.)

Yield/tree 4.69 a 3.85 b 2.08 c (90 1b. bxs.)

Soluble solids 9.5 b 9.0 c 10.5 a (X)

Titratable acid .95 b .83 c 1.04 a

Brix/acid 10.0 c 10.9 b 10.1 a rati o

% juice/wt. 55.6 a 54.2 a 53.9 a

Wt./fruit 174 a 167 b 165 b (grams)

Values in each line not followed by like letters are significantly different at the .05 level of probability. ^Data on additional rootstocks in this experiment is available in previous reports (4, 20). ^Mean calculated from 5 trees on each rootstock. All other means calculated from 15 trees per rootstock. 34 FLORIDA STATE HORTICULTURAL SOCIETY, 1971

Table 2. Yield of a 'Shamouti' orange grove budded Table 4. Freeze damage to 'Orlando1 tangelo trees on sweet lime. Israel.1 on sweet lime, rough lemon and sour orange rootstocks. Gainesville, Florida. 1970.

Age of Yield/tree2 Yield/acre2 Year grove (yrs.) (90 lb. bxs.) (90 lb. bxs.) Severity of damage

1954/55 20 1.4 358 Rootstock

1955/56 21 1.7 437

1956/57 22 1.2 324 No. trees damaged

.9 245 1957/58 23 5 Sweet lime 0 16 16 11 1958/59 24 2.1 540 6 Rough lemon 0 16 16 10 1959/60 25 1.7 334 1 0 0 Sour orange 12 3 ^ata extracted from report-by Mendel (24). Planting distances were 13' x 13', 284 trees/acre; 70% of the trees exhibited visible symptoms of xyloporosis. bating of freeze damage: 1, no damage; 2, leaf Converted from kg./tree and tons/acre to 90 lb. boxes. damage only; 3, leaf and small branch damage; 4, killed to major scaffold branches; 5, killed to top of protective soil bank about 2.5 ft. above (16, 22, 29) have described the anatomy of bud the ground level. There were 16 trees on each rootstock. Trees were evaluated 1 month after unions of ' Shamouti' on several rootstocks and growth in the spring. the unions of sweet lime interstocks. Viewed in their entirety, the union of sweet lime is strong effects might be used advantageously, Table 2, and compatible in the absence of damaging viruses. but the use of viruses to control tree size is not Viruses.—Information in the literature clearly recommended. indicates the damaging effects of tristeza, exo- Exocortis effects on sweet lime have not been cortis and xyloporosis to citrus on sweet lime widely noted or discussed in the literature, prob rootstock. ably because of the emphasis placed on xyloporosis Xyloporosis has been commonly associated with damage, but researchers in California (35) and stunted growth of trees on sweet lime. Results Texas (27) have reported a bark splitting dis from both rootstock trials and commercial plant order of sweet lime infected with exocortis. Bud ings on this rootstock have often been invalidated wood free of exocortis is available for most im because xyloporosis-infected budwood was used (1, portant commercial varieties. 7, 21). However, it has been shown xyloporosis In 1951 sweet lime was reported as somewhat is transmitted only through infected budwood (6) susceptible to tristeza by Grant and his co-workers and xyloporosis-free budwood of virtually all im (14). Giacometti (15) reported in 1965 that sweet portant citrus varieties is available. Strains of lime is more tolerant to the severe strain of xyloporosis which produce primarily dwarfing tristeza (seedling yellows) than sour orange and

Table 3. Growth and yield of nucellar and old-line ■Redblush' grapefruit trees on sweet lime Table 5. Mean values of macronutrients in leaves of and rough lemon rootstocks. Texas.1 'Orlando' trees on rough lemon and sweet lime rootstocks. Lake County. 1970.1

Rootstock weight) Measurement Sweet lime Rough lemon Macronutrient (Xdry Old-line Rootstock Nucellar Old-line Nucellar N P K Mg Ca

12.5 9.0 14.0 10.2 Tree height 2.45** .116 2.08 .690 3.14 (ft.) Sweet lime .696 3.51* Yield/tree2 4.1 7.7 5.2 10.2 Rough lemon 2.29 .114 2.11 (90 lb. bxs.) iMeans of samples from each of 15 trees on each root- bata extracted from report by Young and co-workers (38). stock. Trees were 12 years old, having been planted in 1956 but were severely damaged in a freeze in 1962. *Significantly higher at the .05 level of probability. 2Annual average yield 1963-1968. Converted from 70 lb. to **Significantly higher at the .01 level of probability. 90 lb. field boxes. KREZDORN AND CASTLE: SWEET LIME ROOTSTOCKS 35

that neither sour orange nor sweet lime reacted that very hardy varieties such as 'Orlando' were to a mild strain. The most efficient vector of killed to the ground (36) and another contained tristeza, Toxoptera citricidus Kirk., is not in insufficient plants for an accurate evaluation (37). Florida and the strain or strains of tristeza present However, gross observations of old trees near Avon generally cause only mild reactions. Thus, the Park and young trees at Gainesville indicate sweet threat of tristeza appears to be less for sweet lime lime is much hardier to cold than acid limes and than for sour orange. rough lemon. Foot rot—Information on the susceptibility of It is difficult to generalize on the influence of sweet lime to foot rot, Phytophthora sp., is sparse. rootstock on cold hardiness of the scion. Certain There are occasional suggestions that sweet lime citrus, such as 'Mexican' lime, do not go dormant is relatively susceptible to foot rot (5, 19) but regardless of the rootstock and remain sensitive Olson and his co-workers (23) in Texas, where to cold; whereas when some scion varieties be the soils are heavy and foot rot common, reported come fully dormant, rootstock has little influence that none of the trees on sweet lime in a rootstock on their hardiness to cold (39). Evaluations of the experiment with grapefruit tops had succumbed cold hardiness of scion varieties on sweet lime after 10 years, while a large proportion of the have varied from extremely sensitive to cold (1) trees on 9 sweet orange selections had died, largely to moderately sensitive (13). In the winter of from foot rot. No mention was made of foot rot 1968-1969 the trees in a rootstock planting at on rough lemon but 2 trees had succumbed to what Gainesville were subjected to freezing tempera was termed "wet feet." Klotz (18) presented tures of 17°F for several hours. Some of the trees quantitative data on the relative susceptibility of were killed back to the ground or damaged, despite a number of rootstock and scion varieties to Phyto the use of heaters. The damage to 2-year-old trees phthora, rating sweet lime more susceptible than on sweet lime and rough lemon was about equal sour orange but less so than rough lemon. and more severe than that encountered on sour No foot rot has developed in the 'Orlando' root- orange, which was used as a standard for com stock trials reported in this work but neither was parison, Table 4. foot rot noted in trees on any other stock, includ Leaf mineral content,—Mineral content of ing sweet orange. A fairly comprehensive survey leaves is well recognized as a good measure of the of the few commercial plantings on sweet lime in nutritional status of the tree and ability of the Florida failed to disclose any trees with foot rot. root system to obtain mineral elements from the The senior author has made gross observations soil. Rough lemon is recognized as the standard on hundreds of sweet lime, sweet orange and sour against which others are compared (33). A com orange trees in tropical areas where the incidence parison of the macronutrient content of 'Orlando' of Phytophthora is great. These observations, along tangelo on sweet lime and rough lemon respec with data in the literature, lead to the conclusion tively is shown in Table 5. Levels of P, K and Mg sweet lime is more susceptible to foot rot than were similar but leaves from sweet lime plots sour orange but appreciably more resistant than were significantly higher in N and lower in Ca sweet orange and slightly more resistant to this than those from the trees on rough lemon. Cooper's disease than rough lemon. (8) survey of the nutritional status of 'Orlando' Nematodes.—The sweet lime is damaged by trees in Florida in 1968 contained 1 planting on both the citrus nematode (Tylenchulus semipene- sweet lime and 5 on rough lemon, with the great trans Cobb) and the burrowing nematode (Rado- majority on 'Cleopatra' mandarin. Trees on sweet pholus similis (Cobb) Thome). Rough lemon is lime compared very favorably with those on rough similarly susceptible to these nematodes, with the lemon. Mendel (21) reported N and P contents exception of 'Estes', which is rated tolerant to in leaves on 'Shamouti' sweet orange on sweet R. similis (12). Where the burrowing nematode lime and rough lemon respectively were similar. is the limiting factor, the 'Milam' variety appears These limited data, coupled with observations of to be a reasonable replacement stock, but there vigor and yield, support the conclusion that sweet are many acres of land in Florida without nema lime is at least the equal of rough lemon in its tode problems where other rootstocks could be ability to obtain mineral elements from the soil. considered. Tolerance of sweet lime to high concentrations Tolerance to cold,—Tolerance to cold of sweet of salt, boron and lime in the soil was ranked by lime itself is poorly defined in the literature. One Cooper and his co-workers (9, 26) in Texas as report evaluated hardiness in a freeze so severe moderate to poor, poor, and moderate respectively. 36 FLORIDA STATE HORTICULTURAL SOCIETY, 1971

Rough lemon by comparison rated moderate, mod yield evaluation is observational and quantitative erate, and good, indicating a slight superiority to data are not available. sweet lime. The sandy soils of Florida, however, are Yield data from an experiment in Lake County more likely to be deficient in boron than in excess. with xyloporosis-f ree budwood, presented in Table They generally require liming, and salt intrusion 1, and in earlier reports (20), show clearly that is limited to a few coastal areas. yields of trees on sweet lime are excellent and as Tree size,—Trees on sweet lime rootstock have good or better than those on rough lemon. More been reported as stunted or below normal size in over, there are 3 mature 'Orlando' groves on sweet California (1), Texas (25, 26, 38), Florida (7) lime near Avon Park and 1 near Haines City. The and Israel (23, 24), but stunting was the result trees are uniformly large and yielding excellent of infection with xyloporosis. However, trees on crops according to their owners. Cooper's (8) sur sweet lime have been vigorous and equal in size vey of 30 'Orlando' plantings showed that the to those on rough lemon wherever budwood free highest 2-year average yield was 587 boxes per of these viruses has been used (20, 38). Data acre from a planting on 'Cleopatra' mandarin obtained in Florida (20) demonstrates this very with 'Temple' pollinators. The only planting on well, Table 1. Moreover, 'Orlando' trees in com sweet lime had the second highest yield, 575 boxes mercial groves in Florida are extremely vigorous per acre, even though it was only 7 years old and and equal in size to adjacent trees on rough lemon. did not contain a pollinator. The highest yield Depth of rooting.— There are some reports that from the 5 blocks on rough lemon was from a 12- state or imply the sweet lime is shallow rooted year-old planting without pollinators which pro but data are sparse or lacking (23, 30). Data ob duced 397 boxes per acre. The plantings on 'Cleo tained from an extensive sampling of root systems patra' and sour orange under 15 years of age with 'Orlando' tops are contained in Table 1. Rough produced very little fruit in the absence of polli lemon was the deepest rooted of the standard root- nators. Unfortunately, the only yield data available stocks which agrees with previous work by Ford in Florida are from 'Orlando' tangelo but it is (11)—and sweet lime compared very favorably reasonable to assume that the yields of other with it. This is by far the most extensive examina varieties would be good, even though all varieties tion of the root system conducted and it leaves do not perform precisely the same on a given root- little doubt that sweet lime can be very deep rooted stock. in Florida's sandy soils. The type of root system In Texas (26), 12-year-old 'Valencia' orange that would develop in Florida's coastal and flat- trees on sweet lime that were respectively free wood areas where the water table is at 2 to 3 and infected with xyloporosis were compared in a feet would be restricted to the depth at which the trial with several other rootstocks. Trees on rough water table is maintained. This is also true for lemon, both with and without xyloporosis, were rough lemon and other rootstocks. about equal in yield, but those with xyloporosis Yield of fruit.—Rootstock trials in various on sweet lime were stunted and reduced in yield. parts of the world have often indicated low yields In another experiment in Texas (38), nucellar on sweet lime from the use of budwood infected 'Redblush' grapefruit trees without xyloporosis with xyloporosis (1, 7, 23, 24, 25, 26, 38). Actually, were much larger than old-line trees with xylo xyloporosis infected trees on sweet lime may yield porosis and exocortis on rough lemon and sweet well, even though the trees are dwarfed. In 1956 lime, Table 3. Nucellar 'Redblush' yielded slightly Mendel (23) reported satisfactory yields from more fruit on sweet lime than on rough lemon but trees on sweet lime, even though some trees were the old-line trees yielded more on rough lemon affected by xyloporosis. Mendel (24) later sug than on sweet lime. However, the old-line trees gested that the semi-dwarfing effect of xyloporosis yielded more on each stock than did the nucellar can be used to advantage in controlling tree size. selection on either stock. The greater yields of the He presented data of very satisfactory production virus-infected trees undoubtedly resulted from the of sweet orange on sweet lime that contained difference in the nucellar and old-line selections xyloporosis, Table 2. rather than to the viruses per se. Old, commercial grapefruit and sweet orange Much of the past research is clouded with the trees containing xyloporosis in Florida have pre effects of viruses, but there is evidence that trees sented a pattern of erratic tree sizes, ranging from on sweet lime yield as well or better than those pronounced dwarfing to normal sizes, and satis on rough lemon both on the sandy soils of Florida factory fruiting for the respective tree size. The and the fertile alluvial soils of the Texas citrus KREZDORN AND CASTLE: SWEET LIME ROOTSTOCKS 37 area if the trees are free of damaging viruses. 3. Camp, A. F. 1941. The present status of rough lemon rootstock. Proc. Fla. State Hort. Soc. 54:75-81. Fruit size.—Results of some rootstock trials 4. Castle, W. S. 1971. The root distribution of citrus (2, 31) have indicated fruit sizes on sweet lime rootstocks and their influence on the mineral content of 'Orlando' tangelo leaves. Master's Thesis. Univ. of Florida, were smaller than on a number of other root- Gainesville. 86 p. 5. Chadra, K. L. et al. 1970. Citrus decline in India. stocks, including rough lemon; however, the trees Causes and control. Pub. of Punjab Agri. Univ., Ohio were infected with xyloporosis. Fruit sizes of State Univ. and USAID. 97 p. 6. Childs, J. F. L., R. E. Johnson and J. L. Eichhorn. trees on sweet lime have been excellent, Table 1, 1965. The question of seed transmission of cachexia- xylo porosis virus, p. 90-94. In W. C. Price (ed.), Proc. 3rd and comparable to that occurring when rough Conf. Intern. Organization of Citrus Virol. Univ. of Fla. lemon was the rootstock where trees free of dam Press, Gainesville. 7. Cohen, M. and H. J. Reitz. 1963. Rootstocks for aging viruses were used (20, 35). Also, general Valencia orange and Ruby Red grapefruit: Results of a trial initiated at Fort Pierce in 1950 on two different soil observations of growers indicate that large fruit types. Proc. Fla. State Hort. Soc. 76:29-34. size is characteristic of trees on sweet lime free 8. Cooper, T., Jr. 1969. The macronutrient status of 'Orlando' tangelo in relation to fertilizer practices. Master's of viruses. Thesis. Univ of Florida, Gainesville. 61 p. Fruit quality.—The juice quality of citrus on 9. Cooper, W. C. and A. Peynado. 1955. Boron accumula tion in citrus as influenced by rootstock. J. R.io Grande sweet lime has been low regardless of the virus Valley Hort. Soc. 9:86-94. 10. Creel, J. M., Jr. and E. O. Olson. 1963. Cold damage status of the trees. Extensive research in Israel to young navel orange trees on various rootstocks in freezes (23), Florida (7, 20), Texas (35) and California of 1962 and 1963 in the Winter Garden area of Texas. J. Rio Grande Valley Hort. Soc. 17:55-59. (31) all place sweet lime in about the same cate 11. Ford, H. W. 1954. The influence of rootstock and tree age on root distribution of citrus. Proc. Amer. Soc. gory as rough lemon in this respect. Data in Table Hort. Sci. 63:137-142. 1 illustrate the quality of fruit from trees on 12. and W. A. Feder. 1964. Three citrus root- stocks recommended for trial in spreading decline areas. sweet lime as compared to that from fruit on Univ. of Fla. Agr. Exp. Sta. Circ. 71:81-95. rough lemon and sour orange. 13. Gardner, F. E. and G. E. Horanic. 1958. Influence of various rootstocks on the cold resistance of the scion variety. Proc. Fla. State Hort. Soc. 71:81-95. 14. Grant, T. J., A. S. Costa and S. Moreira. 1951. Studies Conclusions of tristeza disease of citrus in Brazil. V. Further information on the reactions of grapefruits, limes and trifoliate hybrids to tristeza. Calif. Citrograph 36:310-311, 324-329. Sweet lime has generally been discarded as a 15. Giacometti, D. C. 1965. Reaction of sweet lime to possible rootstock for Florida because trees in seedling yellows, exocortis and xyloporosis viruses, p. 302-30. In W. C. Price (ed.), Proc. 3rd Conf. Intern. Organization initial rootstock experiments and commercial of Citrus Virol. Univ. of Fla. Press, Gainesville. trials were severely stunted and yielded poorly. 16. Goldschmidt-Blumenthal, S. 1956. Rootstock-scion in fluence in the morphology and anatomy of the bud union of This rootstock deserves a reevaluation in light of Shamouti orange. Bui. Res. Council of Israel 50:143-154. 17. Heymann-Herschberg, L. 1955. Nitrogen and phos the current knowledge of viruses and the excellent phorus content of citrus leaves in Israel: Frequency dis performance of sweet lime on sandy soils. tribution, and influential factors. Israel J. of Agr. Res. 47:19-27. Performance of commercial plantings and data 18. Klotz, L. J. and H. S. Fawcett. 1930. The relative resistance of varieties and species of citrus to Phythiacytis from trees in rootstock experiments utilizing trees -gummosis and other bark diseases. J. Agr. Res. 41(5) :415-425. on sweet lime that are free of damaging varieties 19. Knorr, L. C, R. F. Suit and E. P. Ducharme. 1957. Handbook of citrus diseases in Florida. Univ. of Fla. Agr. are limited. All information indicates, however, that Exp. Sta. Bui. 587. this rootstock is very well adapted to Florida's 20. Krezdorn, A. H. and W. J. Phillips. 1970. The in fluence of rootstocks on fruiting and fruit quality of sandy soils. 'Orlando' tangelo. Proc. Flafl State Hort. Soc. 83:110-116. 21. Mendel, K. 1936. The anatomy and histology of the Knowledge of the performance of trees on bud union in citrus. Palest. J. Bot. Hort. Sci. 1:13-46. sweet lime justifies limited commercial plant 22. 1945. Orange leaf transpiration under orchard conditions. II Bui. Agr. Expl Sta., Rehovot. No. ings even in the absence of rough lemon decline. 37:59-85. 23. 1956. Rootstock-scion relationships in In the presence of rough lemon decline, trial plant Shamouti trees on light soil. Ktavim. 6:35-50. ings on sweet lime appear even more attrac 24. 1961. New concepts in stionic relations of citrus. Proc. First Inter. Citrus Symp. 1:387-390. tive. Of course, there are always risks involved 25. Olson, E. O., W. C. Cooper, N. Maxwell and A. W. Shull. 1962. Survival, size and yield of xyloporosis- and with any new rootstock. There is no guarantee exocortis-infected old.line red grapefruit on 100 rootstocks. sweet lime or any other rootstock will not ulti J. Rio Grande Valley Hort. Soc. 16:44-51. 26. and A. V. Shull. 1962. Size and yield of mately succumb to whatever is causing rough 12-year-old Valencia orange trees on various rootstocks in lemon decline or to something else. These risks will presence or absence of exocortis and xyloporosis viruses. J. Rio Grande Valley Hort. Soc. 16:40-43. always be present. 27. , A. Shull and G. Bufnngton. 1961. Evalua tion of indicators for xyloporosis and exocortis in Texas, p. 159-165. In W. C. Price (ed.), Prod. 2nd Conf. Intern. Organization of Citrus Virol. Univ. of Fla. Press, Gainesville. LITERATURE CITED 28. Peynado, A. and R. Young. 1962. Performance of 1. Bitters, W. P. 1949. Dwarfing citrus rootstocks. Calif nucellar Red Blush grapefruit trees on 13 kinds of rootstocks Citrograph 34:516-517, 539-543. irrigated with saline- and boron-contaminated well water 2. and L. D. Batchelor. 1951. Effects of over a 3-year period. J. Rio Grande Valley Hort. Soc. rootstocks on the size of orange fruits. Proc. Amer. Soc. 16 :52-53. Hort. Sci. 57:-133-141. 29. Safran, H. and A. Bental. 1968. Effects of sour 38 FLORIDA STATE HORTICULTURAL SOCIETY, 1971

orange, rough lemon, and sweet lime in some interstock- varieties, with particular reference to old-line Eureka lemon. rootstock combinations on the performance of Shamouti Plant Disease Rptr. 43:528-533. [C. sinensis (L.) Osbeck] trees. Israel J. Agr. Res. 18: 35. Woodruff, R. E. and E. O. Olson. 1960. Effects of 193-200. rootstocks on physical characteristics and chemical composi 30. Savage, E. M., W. C. Cooper and R. B. Piper. 1945. tion of fruit of six citrus varieties in Texas. J. Rio Grande Root systems of various citrus rootstocks. Proc. Fla. State Valley Hort. Soc. 14:77-83. Hort. Soc. 58:44-48. 36. Young, R. H. 1963. Climate—cold hardiness—citrus. 31. Sinclair, W. B. and E. T. Bartholomew. 1944. Effects J. Rio Grande Valley Hort. Soc. 17:3-14. of rootstock and environment on the composition of oranges 37. 1963. Freeze injury to young seedlings and grapefruit. Hilgardia 16:125-276. of citrus cultivars and related species in the Lower Rio 32. Singh, J. P. and H. S. Dhuria. 1959. Studies on floral Grande Valley. J. Rio Grande Valley Hort. Soc. 17 :37-42. biology of sweet lime (Citrus limettioides Tanaka). Indian 38. , E. O. Olson and A. Shull. 1968. Com J. of Hort. 16:9-20. parative performance of juvenile and old-line Redblush grape 33. Smith, P. F., W. Reuther and A. W. Specht. 1949. fruit. J. Rio Grande Valley Hort. Sos. 22:16-25. The influence of rootstock on the mineral composition of 39. , A. Peynado and W. C. Cooper. 1960. Valencia orange leaves. PI. Physiol. 24:455-461. Effect of rootstock-scion combination and dormancy on cold 34. Weathers, L. G. and E. C. Calavan. 1959. The hardiness of citrus. J. Rio Grande Valley Hort. Soc. 14:58-65. occurrence of cachexia and xyloporosis in California lemon

PROBLEMS ENCOUNTERED IN OVERHEAD IRRIGATION OF CITRUS WITH WATER OF RELATIVELY LOW SALINITY

Ernest C. Ltjndberg In checking neighboring groves we found the same situation present. The worst leaf burn found The Coca-Cola Company Foods Division was in a section of a grove south of the Hodgson Ft. Pierce Grove that had been irrigated with low volume overhead sprinklers operated during daylight hours. Abstract In all of these groves the source of the irrigation water was the St. Lucie Canal. Salt burn symptoms and leaf loss were noticed on citrus trees in the Indiantown area in April, Literature Review 1971. This was after an extended dry period in areas under daytime overhead irrigation (14 irri Calvert (1) observed salt burn symptoms in gations from December 2, 1970, to May 26, 1971). several Indian River citrus groves during the The water for irrigation was drawn from the St. severe spring drought of 1965. He reproduced the Lucie Canal which contained total soluble salts in leaf burn symptoms on Ruby Red grapefruit by a range from 510 ppm to 590 ppm. sprinkling the trees with artesian water containing Leaves were analyzed for Na, Ca, Mg, K and 1,000 ppm. total dissolved solids, at the rate of Cl. Ratios of Ca: K + Na are included and dis 0.8 gallons per minute (equivalent to 0.07 inch of cussed. water per hour) for a period of nine hours. The damage was increased with the increase in evapo ration of water from the leaf surfaces. Introduction Harding and Chapman (5) have suggested Extremely dry conditions were encountered that leaf chloride contents exceeding 0.25% be this past year which necessitated repeated irriga considered indicative of chloride toxicity. They tions to replenish soil moisture in East Coast found even lower level of chlorides (although not groves. always leading to obvious chloride toxicity symp On April 21, 1971, some Marsh grapefruit on toms) may still effect the longevity of leaves, and Macrophylla rootstock in the Hodgson Grove (near perhaps, lead to reduced yields. Indiantown) were noticed to have severe salt burn Ehlig and Bernstein (2) found that although symptoms on the leaves. Irregular brownish areas foliar absorption of sodium and chloride by citrus developed on the leaves, usually near the leaf tips. leaves from sprinkle irrigation is slower than for Considerable leaf drop occurred. In checking other some stone fruits, severe injury can occur within varieties near this location, the salt burn symptoms one season. They also observed that foliar absorp were noted to a lesser degree. In spot checks over tion during the evening was only one-half as rapid the lemon planting on this grove the leaf drop was as during the day. seen to be very heavy and most of the dropped Harding (4) found that even in the absence leaves exhibited a salt burn pattern. of specific injury symptoms resulting from exces-