I

Ih3t (1~)

ve

sacs. Linear ~ola') of the .3 to 90.9% i-numbered. the 6 major

3. 'Osceola', Ie similar to 13). 'Nova' of tangelos, )', its tange­ar monoene h other and

Nere 1.8 for l' and from j-numbered e 5 hybrids. 1eir low iso 0.8% ('Cle­i monoenes

comprised . the total N the value :entage dis­.mbered > at for iSO­. all citrus nged from

61 -t \'Robinson') to 76.0% ('Lee'). The 4 major anteiso mono­enes of the 5 hybrids were C24, C26, C27 and C28.

In the previous discussion of Tables 1-3, data were presented which showed that generally the 5 'Clementine' x tangelo hy­brids have hydrocarbon profIles intermediate between those of their parents. In some instances the hybrid profIles tended to mirror their mandarin parent rather than their tangelo parent while in others the reverse was evident. These profIles indicate

hybrids subscribe to a "hybridization dilution effect" Further studies are being conducted, based on this obser­

[GO, in which each of the nine major alkanes (> 79% of total) 3[C correlated with each other. Preliminary results show that the 5 hybrids have a mean "citrus alkane index" value of 35.5 which is in contrast and intermediate between their parents: 'Orlando' (19.9), 'Minneola' (21.0) and 'Clementine' (51.6). The individual hybrid alkane index values, which varied over a 26% range, are being correlated with the hybrid fruits' organo­leptic and morphological characteristics. Further studies are being conducted on other hybrids to substantiate the potential usefulness and reliability of this index system in chemically s: o;omatizing citrus fruit.

Literature Cited

1. Albach, R. F. and G. H. Redman. 1969. Composition and inheritance of flavanones in citrus fruit. Phytoch~mistry 8:127-143.

2. Hearn, C. J. 1973. Development of Scion cultivars of citrus in Flor­ida. Proc. Fla. Hart. Soc. 86: 84-88.

3. Hodgson, R. W. 1967. Horticultural varieties in citrus. p. 496-505. In H. 1. Webber and L. D. Batchelor (eds.), The citrus industry, vol. 1. Univ. of Calif. Press, Berkeley, Cali f.

4. Kamiyama, S. 1967. Studies on the leaf oils of citrus species. Agr. iJial. Ch~m. 31:1091-1096.

J. Amer. Soc. Hart. Sci. 101(3):265-267. 1976.

Salt Tolerance of Some Citrus Species, Relatives, and Hybrids Tested as Rootstocks!

C. L. Ream and J. R. Furr2

U. S. Date and Citrus Station, U. S. Department ofAgriculture, Indio, CA 92201

Additional index words. rootstock breeding

A bstract. Although some selections of the sour orange (c. aurantium L.) differed in salt tolerance, none was as salt tolerant as Cleopatra mandarin (c. reticulata Blanco). Twenty hybrids were as salt tolerant as Cleopatra and have characters desirable for use in breeding improved rootstocks.

In most areas where citrus is irrigated with water saline enough for measurable effect on growth and yield, the main salts causing injury are chlorides. Cooper et al. (2) found that the rootstock largely controlled uptake and accumulation of CI in citrus trees. At salinity levels at which it is feasible to grow citrus, some rootstocks are much more tolerant to chlorides than others because, to a considerable degree, they can exclude CI. The work of Hewitt et al. (5) indicatoo that to screen young citrus trees for salt tolerance, the leaves could be analyzed for CI after 3 or 4 weeks of treatment with highly saline irrigation water. Furr and Ream (3, 4) reported that inheritance of salt tolerance in citrus was quantitative, that most of the progeny from crosses between 2 highly salt-tolerant parents were highly salt tolerant, and that only a few of the progeny of crosses be­

lReceived for publication April 22, 1975. 2Research Horticulturist and Collaborator, respectively, Agricultural Research Service.

tween tolerant and intolerant parents were highly tolerant. The objective of this work was to screen some species, culti­

vars, selections, and hybrids of citrus and citrus relatives for salt tolerance and for their potential use in a rootstock breeding program.

Materials and Methods Clones with valid cultivar names are designated by single

quotes, and other names assigned to selections for convenience are without quotes as follows: C aurantium 1., 'African', Algerian, Baladi, Bergamia, Bittersweet, 'Brazilian', Ceylon, Cuban, Egyptian, Glenn, Karun Jamir, Keen, Merritt Island, Nansho Daidai, Naranja de Tierra, Olivelands, Palermo, Pales­tine, Rehoboth, Rhodesia, 'Rubidoux', Sespe, Sicilian, Sicily, Sauvage, 'Standard', Tel Aviv, Tunis; C Celebica Kourd. x C. grandis (1.) Osb. (?), 'Alemow'; C. grandis (1.) Osb., 'Kao Ruan Tia', Red shaddock; C. limon (1.) Burm. f. x (?), 'Kama', Rough lemon; C. paradisi Macr., Grapefr~it, 12509, '~arsh'. 'Redblush'; C. reticulata Blanco, 'Changsha, Cleopatra, 'WII­

5. Nagy, S. and H. E. Nordby. 1971. Comparative long-chain hydro­carbon profiles of orange and tangor juice sacs. Phytochemistry 10:2763-2768.

6. and . 1972. Saturated and mono-unsaturatec long-ehain hydrocarbon profIles of lipids from orange, grapefruit. mandarin and lemon juice sacs. Lipids 7 :666-670.

7. and . 1972. Long-chain hydrocarbon profile· of grapefruit juice sacs. Phytochemistry 11 :2789-2794.

8. and . 1972. Saturated and mono-unsaturatec long-ehain hydrocarbons of lime juice sacs. Phytochemistry 11 :2865­2869.

9. and . 1972. Long-chain hydrocarbon profile' of Duncan grapefruit, Dancy mandarin and their hybrids. Lipids 7' 722-727.

10. and . 1973. Saturated and mono-unsaturatec long-ehain hydrocarbon profiles of sweet orange. Phytochemistr... 12:801-805.

11. Nordby, H. E. and S. Nagy. 1972. Saturated and mono-unsaturatec long-chain hydrocarbons from lemon juice sacs. Phytochemistr., 11:3249-3254.

12. and . 1975. Saturated and mono-unsaturated long-chain hydrocarbon profiles from Citrus Unshiu juice sacs. Phytochemistry 14:183-187.

13. and . 1975. Saturated and mono-unsaturated long·chain hydrocarbon profIles from mandarin juice sacs. Phyta­ch~mistry 14: 1777-1782.

14. Reece, P. C. and F. E. Gardner. 1959. Robinson, Osceola and Lee ­new early maturing tangerine hybrids. Proc. Fla. State Hart. Soc. 72:48-51.

15. Reece, P. C., F. E. Gardner and C. 1. Hearn. 1963. Page orange - a promising variety. Proc. Fla. Stat~ Hart. Soc. 76 :53-54.

16. Reece, P. c., C. J. Hearn and F. E. Gardner. 1964. Nova tangelo - an early ripening hybrid. Proc. Fla. State Hort. Soc. 77: 109-110.

17. Scora, R. W. and M. N. Malik. 1970. Chemical characterization of Citrus as a tool in phylogeny. Taxon 19:215-228.

Ll Tot 1 eve

11.26 14.14

8.50 9.22

14.60 11.70 11.01 14.10 12.50

0.29 1.95 0.36 1.03 1.20 1.84 1.11 1.96 1.18

3.64 7.75 2.14 5.63 5.95 6.42 5.04 7.39 8.07

5.56 12.48 3.11 7.41 . 9.69 9.04 7.31

11.80 11.83

1. Amer. Soc. Hort. Sci. 101(3):265-267. 1976. 265

-Table 1. Mean Cl content of dried leaves of 'Redblush' grapefruit scions

grown on various rootstocks in plots irrigated with salinized water, 5,000 ppmz.

Cl Rootstock (%)

Rough lemon Willowleaf mandarin Glenn sour orange 58-83-3x Sauvage sour orange 57 -297 Carrizo citrange 55 -81-3 Bergamia sour orange Rubidoux sour orange Nansho Daidai 55 -82-3 Bittersweet sour orange Troyer citrange Uvalde citrange Changsha mandarin Keen sour orange Palestine sour orange Algerian sour orange Merritt Island sour orange African sour orange 55 -47-8 Sicilian sour orange Olivelands sour orange Brazilian sour orange Standard sour orange Tunis sour orange Sespe sour orange Yuma citrange seedling Alemow Bergamia sour orange Yuma citrange 55 -47 -1 Sicilian sour orange Cleopatra mandarin 55 -6 -I 07 (Rangpur x Brazilian sour orange) F I

2.63 AY 2.53 AB 2.36 ABC 2.31 ABCD 2.03 BCDE 1.96 CDE 1.88 CDE 1.87 CDE 1.84 CDE 1.82 CDE 1.80 CDE 1.76 DEF 1.74 DEF 1.74 DEF 1.73 DEF 1.70 EF 1.70EF 1.68 EF 1.68 EF 1.54 EFG 1.53 EFG 1.52 EFG 1.52 EFG 1.50 EFG 1.48 EFG 1.48 EFG 1.18 FGH 1.03 GH 0.71 HI 0.32 I

zTreatment started July 6, 1966 leaves were sampled Aug. 15, 1966. YComparable mean separation by Duncan's multiple range test, 1% level. xU. S. Date and Citrus Station accession number.

lowleaf; C. reticulata var. austera Swing., 'Sunki', 'Rangpur' lime; C. sinensis (L.) Osb., 'Hamlin', Seville; C. tachibana (Mak.) Tan. x C. reticulata Blanco (?), Shekwasha; Eremocitrus glauca (Lind!.) Swing., 'Australian desert lime' hybrid (pollen parent unknown); Poncirus trifoliota (L.) Raf., Barnes, Chris­tiansen, English, Jacobsen, 'Rubidoux', Swingle, P. trifoliata (L.) Raf. x C. sinensis (L.) Osb., 'Carrizo', 'Savage', 'Troyer', 'Uvalde', 'Yuma.'

Open-pollinated seeds of the various citrus species, relatives, and hybrids were planted in flats containing a mixture of peat moss and vermiculite. The seedlings were watered with a com­plete nutrient solution and grown to lining-out size in a green­house. They were then planted in field plots or in a seedling nursery and eventually budded with an appropriate scion.

Budded plants of suitable size were transplanted into ran­domized rows in small field plots with 8 to 12 replications. The plants were grown until well established and 2 to 3 weeks before the start of the salt treatments the trees were pruned to a height of 91 - 102 em and all branches were cut to 3 to 4 buds. The regrowth following the pruning provided leaf samples which were more nearly uniform as to age and exposure than those from unpruned trees. Cleopatra mandarin was used as the standard rootstock.

General procedures of testing the plants for salt tolerance were similar to those described by the U. S. Salinity Laboratory Staff (6). We prepared salinized irrigation water by adding about equal parts (i.e., an equal number of gram equivalents of Cl by weight) of NaCl and CaC12 to Colorado River water, which contained about 700 ppm of total salts. The salinized water used in these tests ranged in concentration from 5,000 ppm to

Table 2. Mean Cl content of dried leaves of lemon scion grown various rootstocks in plots irrigated with salinized waterz.

CIY Rootstock (%)

Rehoboth sour orange 3.36 AX BaIadi sour orange 3.28 A Ceylon sour orange 3.23 A Naranja de Tierra sour orange 3.18 A Rubidoux sour orange 3.08 AB Tel Aviv sour orange 3.05 AB Sespe sour orange 3.03 AB Standard sour orange 3.01 ABC Tunis sour orange 2.99 ABC Merritt Island sour orange 2.99 ABC Algerian sour orange 2.96 ABC Sicily sour orange 2.95 ABC Olivelands sour orange 2.94ABC Seville sour orange 2.94 ABC Cuban sour orange 2.94 ABC African sour orange seedling 2.93 ABC Keen sour orange 2.89 ABC Egyptian sour orange 2.88 ABC Algerian sour orange 2.85 ABC Rhodesia sour orange 2.28 BC Kama 2.21 C Cleopatra mandarin 1.11 D

zTreatment started Aug. 14, 1968 with 5,000 ppm salinized water that was increased to 6,000 ppm Oct. 15, 1968; leaves were sampled Sept. 13, 1968 and Nov. 1,1968. YMean of two sampling dates. xComparable mean separation by Duncan's multiple range test at the 1% level.

6,000 ppm total salts. The moisture content of the soil was kept near field capacity by frequent (usually weekly) irrigation with the saline water.

Samples of 5 to 10 leaves were collected from the midpor­tion of several of the youngest, fully matured shoots on each tree. At that time there was a marked variation in the degree of visible salt injury to the leaves both between and within clones. The range was from no visible injury to a slight marginal burn. These samples were dried in a forced-draft oven at 700 C, ground, and analyzed for Cl by electrometric titration (I).

Results and Discussion In spite of its susceptibility to the tristeza virus, sour orange

is still extensively used as a rootstock. A large number of sour

Table 3. Range of mean Cl content of dried leaves of lemon scion grown on nuceUar seedlings of selections from various sour orange rootstocks in plots irrigated with salinized waterz.

Rootstock

Karun Jamir Palestine Sicilian Brazilian Sicilian 55 -47 -6Y Sicilian 55-47-4 Palermo Cleopatra mandarin

No. selections

tested

5 4 7 1 1 1 1 1

CI range (%)

3.95 - 3.54 3.90 - 3.61 3.84 - 3.48

3.56 3.19 3.05 2.96 0.63

I I I.

zTreatment started Sept. 17, 1968 with 5,000 ppm salinized water that was increased to 6,000 ppm Oct. 15, 1968; leaves were sampled Nov. 1, 1968. YU. S. Date and Citrus Station accession number.

J. Amer. SOC. Hart. Sci. 101(3):265-267. 1976. 266

---CI

AX ,A

3A i8 A ,08 AB 05 AB 03 AB 01 ABC 99 ABC 99 ABC 96 ABC 95 ABC 94ABc 94 ABC 94 ABC 93 ABC 89 ABC 88 ABC 85 ABC 28 BC 21 C lID

Nater that ! Sept. 13,

at the 1%

soil was rrigation

midpor­on each legree of '1 clones. tal burn. t 700 C, 1).

r orange of sour

>n grown lotstocks

range (%)

- 3.54 - 3.61 -3.48

3.56 3.19 3.05 2.96 0.63

r that ov. I,

1976.

ral'.~ 4. Mean CI content of dried leaves of 'Hamlin' sweet orange scions grown on various hybrid rootstocks in plots irrigated with salinized water, 5,000 ppmz.

Cl Rootstock (%)

,6_43-14Y (Cleopatra x SWingle, P. tnfoliata) FI ; 7-149- 2 Seville sweet orange 61-182-6 (Cleopatra x Rubidoux,P. trifoliata) FI ;9 ['25-3 (Rangpur x Savage citrange) FI ~8 _ :9-7 (Cleopatra x Barnes, P. trifoliata) F I ~8 .110-1 (Swingle x Grapefruit 12509) FI ~6-43-9 (Cleopatra x Swingle, P. trifoliata) FI 58-208-2 (Cleopatra x Swingle, P. trifoliata) Fl 54-63-27 (Rangpur x Shekwasha) Fl Cleopatra mandarin 58-206-3 (Cleopatra x Rubidoux, P. trifoliata) F 1 56-43-7 (Cleopatra x Swingle, P. trifoliata) F I 59-130-19 (Sunki x Rangpur) Fl 56-43-13 (Cleopatra x Swingle, P. Trifoliata) Fl 61-54-5 (Christiansen, P. trifoliata x Cleopatra) FI

3.82 AX 3.75 A 2.18 B 2.11 B 2.00 B 1.79 BC 1.53 BCD 1.52 BCD 1.48 BCD 1.07 CDE 1.03 CDE 1.03 CDE 0.87 DE 0.74 DE 0.48 E

Zlreatment started April 23, 1968; leaves were sampled June 18, 1968. YU. S. Date and Citrus Station accession number. xComparable mean separation by Duncan's multiple range test at the 1% level.

Table 5. Mean CI content of dried leaves of lemon scion grown on various rootstocks in a plot irrigated with salinized waterz.

CI Rootstock (%)

58-210-5Y (Cleopatra x Savage citrange) FI 3.67 AX 56-146-2 Australian desert lime hybrid 3.50 A 58-207 -3 (Cleopatra x English, P. trifoliata) F I 2.80 B 60-23 (57-1 Australian desert lime hybrid x Rangpur) Fl 2.56 B 62-116-11 (Sunki x Jacobsen, P, trifoliata) FI 2.00 C 58-143-1 (Rangpur x Savage citrange) Fl 1.43 D 58-207-6 (Cleopatra x English, P. trzfoliata) FI 1.30 D 62-116-7 (Sunki x Jacobsen,P. trifoliata) FI 0.97 DE 53-~ 10-14 (Cleopatra x Savage citrange) Fl 0.55 E Cl,::u,latra mandarin 0.53 E

zTreatment started Sept. 17, 1968 with 5,000 ppm salinized water that was increased to 6,000 ppm Oct. 15, 1968; leaves were sampled Nov. 1, 1968. YU. S. Date and Citrus Station accession number. xComparable mean separation by Duncan's multiple range test at the 1% level.

orange selections were tested to fmd one or more of relatively l:igh salt tolerance. Some of the sour orange selections differed significantly, but none was as salt tolerant as Cleopatra man­darin (Table 1, 2, 3). Sicilian 55-47-1 seemed to be some­what more tolerant than most of the other sour orange selec­tions (Table 1). Accordingly, we selected it for use in the breeding program, although it had not been tested as a root­stock. Brazilian sour, which seemed to be nearly as salt tolerant as Sicilian 55-47-1, had been used in tests at the Univ. of California Citrus Research Center, Riverside and proved to be a

J. Amer. Soc. Hort. Sci. 101(3):265-267. 1976.

Table 6. Mean Cl content of dried leaves of lemon scion grown on various rootstocks in plots irrigated with salinized waterz.

Rootstocks (%)

56-33-18Y (Shekwasha x Rough lemon) FI 2.51 AX 55 -11-81 (Rangpur x Kao Ruan Tia) Fl 1.69 B 56-33-22 (Shekwasha x Rough lemon) Fl 1.26 BC 59-120-36 (Rangpur x Red shaddock) Fl 1.03 BCD 55-11-9 (Rangpur x Kao Ruan Tia) FI 0.99 BCD 57 -44-6 (O.P.S. 54-63 -5 [Rangpur x Shekwasha} Fl)W 0.77 CD 59-120-67 (Rangpur x Red shaddock) Fl 0.45 D 54-63-24 (Rangpur x Shekwasha) Fl 0.34 D 57 -44-7 (O.P.S. 54-63-5 [Rangpur x Shekwasha} FI)Z 0.32 D Cleopatra mandarin 0.26 D

zTreatment started Sept. 17,1968 with 5,000 ppm salinized water that was increased to 6,000 ppm Oct. 15, 1968; leaves were sampled Nov. 1, 1968. YU. S. Date and Citrus Station accession number. xComparable mean separation by Duncan's multiple range test at the 1% level. wTree grown from open-pollinated seed of 54-63-5 (Rangpur x Shek­washa) (pollen parent unknown).

highly satisfactory rootstock (7). Seed from several crosses of Rangpur lime x Cleopatra man­

darin were planted, but nearly all of the plants that morpholo­gical characteristics showed to be hybrids were so weak or cWorotic that few were fruited, and none seemed worth testing for salt tolerance.

Of the 32 hybrid selections tested, 20 were as tolerant as Cleopatra mandarin (Table 1,4,5,6). Cleopatra was one parent of 8 of the tolerant hybrids; and Rangpur lime, also a highly salt-tolerant rootstock, was a parent in 10 of the crosses. Several of the hybrids that appeared to have a lower uptake of C1 than the Cleopatra standard were somewhat dwarfing, but 55-6­107 (Rangpur x Brazilian sour orange) was more severely dwarf­ing than any of the other selections tested. These higWy tolerant hybrids may prove useful in breeding rootstocks that have a high degree of salt tolerance combined with other desirable traits.

Li terature Ci ted

1. Brown, 1. B., and R. K. Jackson. 1955. A note on the pontentio­metric determination of chloride. Proc. Amer. Soc. Hort. Sci. 65: 187.

2. Cooper, William C., B. S. Gorton, and E. O. Olson. 1952. Ionic ac­cumulation in citrus as influenced by rootstock and scion and concen­tration of salts and boron in the substrate. Plant Physiol. 27: 191-203.

3. Furr, J. R., and C. L. Ream. 1968. Breeding and testing rootstocks for salt tolerance. Calif Citrograph 54:30-35.

4. , and . 1969. Breeding citrus rootstocks for salt tolerance. Proc. First Int. Citrus Symp. 1:373-380.

5. Hewitt, A. A., J. R. Furr, and J. B. Carpenter. 1964. Uptake and distribution of chloride in citrus cuttings during a short-term test. Proc. Amer. Soc. Hort. Sci. 84: 165-169.

6. U. S. Salinity Laboratory Staff. 1954. Diagnosis and improvement of saline and alkali soils. U. S. Dept. Agr. Handbook 60.

7. Webber, H. J. 1948. Rootstocks: Their character and reactions. p. 69-168. In L. D. Batchelor and H. J. Webber (eds). The citrus industry, Vol. 2. Univ. Calif. Press, Berkeley.

267