Reprinted from Proc. Fla. State Hort. Soc. 113:106-111. 2000. PERFORMANCE OF ‘WASHINGTON’ NAVEL TREES IN ROOTSTOCK TRIALS LOCATED IN LAKE AND ST. LUCIE COUNTIES

WILLIAM S. CASTLE, JAMES C. BALDWIN AND JUDE W. GROSSER lines are selections of nucellar navels which became popular when University of , IFAS field studies proved them to be higher yielding than old-line selec- Research and Education Center tions (Pieringer et al., 1978; Youtsey and Bridges, 1979). 700 Experiment Station Road Navel oranges produced in Florida have the typical navel or- Lake Alfred, FL 33850 ange flavor, but the fruit can sometimes be too large, coarse in ap- pearance, and have low acid content. Florida navel trees are Additional index words. Analysis of covariance, fruit size, juice relatively low yielding. Commercial trees often average only about soluble solids, yield efficiency. 1.5 to 2.5 boxes/tree (Fla. Agric. Stat. Services, 2000a). Some of these problems are accentuated by the rootstock, e.g., trees on Abstract. A ‘Washington’ navel (nucellar budline N–S-F-56-11- rough tends to produce unacceptably large fruit with low X-E) orange [Citrus sinensis (L.) Osbeck] rootstock trial involv- juice content. Trees on Cleopatra mandarin produce fruit with ex- ing eight rootstocks was planted in Astatula fine sand soil at cellent quality, but small size. Swingle and Carrizo cit- 116 trees/acre at Mt. Dora. A 1989 freeze damaged most trees range are currently the most popular commercial rootstocks, but except those on Swingle citrumelo [C. paradisi Macf. ´ Poncir- they also have certain limitations (Castle and Tucker, 1998; Castle us trifoliata (L.)Raf.], sour orange (C. aurantium L.), and ´639 and Stover, 2000). Rootstocks also have favorable effects on tree [Cleopatra mandarin (C. reticulata Blanco) ´ P. trifoliata] which and fruit characteristics, but trials to evaluate rootstocks for navel had 78% to 100% survival. A second trial planted in 1991 re- orange are uncommon (Castle, 1987; Davies, 1986). Our objective placed the original one at Mt. Dora along with a third trial plant- was to evaluate various new and standard rootstocks, selected for ed at Ft. Pierce in Pineda sand soil at 167 trees/acre. Trees on Swingle citrumelo, Cleopatra mandarin, and Sun Chu Sha their possible range in effects on tree size, yield, and juice quality, mandarin were common to both 1991 trials with the remaining at two sites where navel orange trees are most commonly grown in rootstocks being mostly citrumelos, [C. sinensis (L.) Florida. Osb. ´ P. trifoliata], somatic hybrids, and other citrus hybrids with . Yield was measured in each of the first Materials and Methods years after the trees began to crop. Fruit samples were collect- ed to determine juice quality. Tree heights at both locations ‘Washington’ navel (nucellar budline N-S-F-56-11-X-E) trees were measured near the end of the experiments and ranged were propagated on a series of rootstocks and planted in 1985 at from about 6 to 11 ft. The smaller trees were those on Rusk ci- Mt. Dora (long. 81°40’W; lat. 28°50’N; elev. 162 ft), Lake County trange and the somatic hybrids; the tallest trees were general- (Table 1). The trees were badly damaged by a freeze in 1989 and ly those on the mandarin rootstocks. Annual yields varied subsequently abandoned. Tree survival was recorded 6 months lat- from about 1 to 2 boxes/tree. The most productive trees (> 4 boxes/tree cumulative yield) in Ft. Pierce were those on W-2 er. A replacement trial was planted in Sept. 1991 with trees spaced citrumelo, C-32 , and x639, and in Mt. Dora they were 15 ´ 25 ft in a randomized complete-block design of three-tree those on W-2 and Swingle citrumelos, sour orange, and Rusk plots with five replications (Table 1). The soil is Astatula fine sand and Koethen ´ Rubidou ´ citranges. (Typic Quartzipsamment). Another trial at Ft. Pierce (long. 80°30’W; lat. 27°50’N; elev. 20 ft.) was planted in Apr.1991 in Navel oranges are one of the most recognized and enjoyed cit- bedded Pineda fine sand soil (Arenic Glossaqualf) (Table 1). There rus fruits worldwide (Davies, 1986). They are a mainstay of the were 12 replications of single-tree plots in a randomized complete- fresh fruit business because of a distinctive flavor and their tenden- block design with trees spaced 13 ´ 20 ft, but generally data were cy to produce fruit larger than other sweet oranges which makes collected from only six replications. This trial was located at the them especially valuable for gift fruit packages. Navel orange trees end of a block adjacent to a small ditch. Calcareous material from are most suited to Mediterranean climates where the fruit achieve the ditch may have been mixed into the soil during the construction their best eating quality and develop an attractive deep-orange peel of the bed on which the trial was planted. To confirm this, 8 inch- color. Navel orange trees are less reliable in their cropping than deep soil samples were collected using a grid to determine the 27 other sweet orange cultivars because of genetic and climatic fac- sampling locations. Soil pH was measured in water (w/v, 1 soil:2 tors; also, they are less tolerant to environmental stresses, and are water). The soil samples were screened to remove any large parti- more subject to various physiological disorders, such as fruit drop, cles of CaCO 3 and assayed by using acetic acid to determine total that are related to the presence of the opening (“navel”) at the stylar carbonates (Loeppert et al., 1984). The pH values were between end of the fruit (Davies, 1986). 6.5 and 7.5, and the carbonate levels were not excessive according The Florida navel orange industry consists of 23,100 acres to recommended standards (Tucker et al., 1995). (Fla. Agric. Stat. Services, 2000b). The largest acreages are in St. The trees in both trials were irrigated with microsprinklers, and Lucie, Polk, Indian River, and Lake Counties which have between fertilized with about 100 (Ft. Pierce) to 150 (Mt. Dora) lbs. N/acre/ about 2,000 and 3,000 acres each. The most commonly used bud- yr. They were otherwise cared for according to local standards of grove management. Yield was measured annually in field boxes through the 1999-2000 season. Samples of about 50 fruit/replica- Florida Agricultural Experiment Station Journal Series No. N-01959. The au- tion were collected in the last three seasons in December at Mt. Do- thors thank Jim Simpson (Lake County) and Stan Carter (St. Lucie County) for ex- cellent cooperation in providing groves sites and tree care, and with harvesting. We ra, and in early November at Ft. Pierce. Juice was extracted and also appreciate the funding received from the Fla. Research Ad- analyzed for soluble solids concentration (SSC) and titratable acid- visory Council, Grant 927-28. ity (not reported) using industry standard test house equipment

106 Proc. Fla. State Hort. Soc. 113: 2000. Table 1. Navel orange tree survival as of June 2000 in rootstock experiments planted in Lake County in 1985 (LC85) and 1991(LC91) and in St. Lucie County in 1991(SLC91). z

Survival (%)

Rootstock LC85 LC91 SLC91

Citranges [Citrus sinensis (L.) Osb. ´ Poncirus trifoliata (L.) Raf]

Benton — z — 100 C-32 — — 92 C-35 — — 100 Carrizo 0 — 75 Koethen sweet orange ´ Rubidoux trifoliate orange — 100 100 Norton — — 83 Rusk — 100 58

Citrumelos (C. paradisi Macf. ´ P. trifoliata)

F80-5 — — 92 F80-9 — — 83 F80-18 — — 100 Swingle 78 100 100 W-2 — 100 100 Mandarins (C. reticulata Blanco)

Changsha — 92 — Citrus amblycarpa Osche (Nasnaran) — — 100 Cleopatra — 100 83 Sun Chu Sha — 83 92 Somatic hybrids

Cleo + Flying Dragon trifoliate orange — 100 — Cleo + Swingle citrumelo — 90 — Hamlin sweet orange + Flying Dragon trifoliate orange — 87 — Others

Calamandarin (possible mandarin ´ calamondin hybrid) — 100 — 1572 Trifoliate orange ´ Milam lemon (possible C. jambhiri hybrid) — — 75 1573-26 Trifoliate orange ´ Ridge Pineapple sweet orange 0 100 0 1575-21 Ridge Pineapple ´ trifoliate orange — — — 1578-173 Ridge Pineapple ´ Milam — 100 92 1578-201 Ridge Pineapple ´ Milam — 78 33 1584 Trifoliate orange ´ Milam 0 — — 1587 Trifoliate orange ´ Milam 0 — — Gou tou (possible hybrid involving sour orange and C. grandis) — — 100 (probable ) — — 92 (C. limonia Osb.) ´ Troyer citrange — 100 — Ridge Pineapple sweet orange 30 — — Sour orange (C. aurantium L.) 100 92 — ´639 Cleo ´ trifoliate orange 80 — 83

zA dash (—) indicates the rootstock was not included in the trial.

available at the Citrus Research and Education Center, Lake Al- Results and Discussion fred. Fruit size is reported as the mean weight of a fruit determined by dividing the total sample weight by the number of fruit in the Mt. Dora (Lake County) 1985. Between 78% and 100% of the sample. Fruit size and juice data are reported for a representative trees on sour orange, ´639, or Swingle citrumelo survived a damag- year (see Fig. 2). Tree height was measured in 2000. ing freeze in 1989, and a few trees lived on sweet orange rootstock Analyses of variance were performed on all data using PROC (Table 1). All trees on the remaining five rootstocks, which included GLM (SAS Inst., Cary, NC) with mean separation by the Least Carrizo citrange, died. These results reconfirm the known relative Significant Difference (LSD) method. Using 1999-2000 data, cold tolerance of trees on sour orange and Swingle citrumelo (Castle yield was also examined after adjustment for differences in tree et al., 1993; Castle and Tucker, 1998), and are encouraging for the height by analysis of covariance. Simple linear correlations were new rootstock, ´639. determined for fruit size versus juice SSC. Mt. Dora 1991. Tree survival was >85% for all rootstocks ex- cept for the trees on the Ridge Pineapple ´ Milam hybrid, 1578-201. A few trees among the rootstocks succumbed to Phythopthora foot rot, and two trees on 1578-201 declined from an unknown cause.

Proc. Fla. State Hort. Soc. 113: 2000. 107 Some trees on the somatic hybrids grew very weakly and eventually mined by taking the 1999-2000 yield data and using a statistical died. There were no blight losses. procedure to adjust the data so that yield among rootstocks could Tree height generally followed the trends established in other be compared independent of the differences in tree height. The re- trials, i.e., in descending order, mandarin>sour orange>Swingle sults showed that there were differences in yield efficiency (Table cirumelo>Rusk citrange (Fig. 1) (Castle et al., 1993). The tallest 2). For example, the trees on K ´ R and Rusk citranges were inter- trees were ca.11 ft including those on calamandarin, a rootstock in- mediate in height, but with high yields, making them very yield ef- troduced from the Philippines by Dr. Bill Bitters (Univ. Calif., Riv- ficient unlike the trees on Cleo and the 1578-173 and 1578-201 erside; retired). The trees on the somatic hybrids, Hamlin + Flying hybrids that were tall, but bore small crops. Dragon and Cleo + Flying Dragon, were about 50% the height of Fruit size ranged from about 0.55 lbs to 0.72 lbs (Fig. 2). There the trees on Cleo. were no rootstock effects on fruit size when compared to the fruit The 5-yr cumulative yields tended to be higher for some of the from the trees on Swingle, except the trees on Sun Chu Sha, Cala- smaller trees (Fig. 1). Trees on Rusk produced 8 boxes which was mandarin, sour orange, and Rusk which produced larger fruit. Juice a significantly higher cumulative yield than that of all rootstocks soluble solids concentration was inversely related to fruit size (r = - except for the trees on Koethen ´ Rubidoux (K ´ R), or W-2 cit- 0.31; P = 0.02), but the relationship was not strong. Fruit from the rumelo. Trees on the mandarin, and most of the hybrid, rootstocks trees on the Ridge Pineapple hybrid 1573-26, and the somatic hy- produced <50% of the Rusk yield. Yield efficiency was deter- brids Cleo + Flying Dragon and Hamlin + Flying Dragon, had the

Figure 1. Tree heights and yields of ‘Washington’ navel orange trees on various rootstocks grown in field trials planted in 1991 at Mt. Dora (Lake County) and Ft. Pierce (St. Lucie County). The Florida field box for measuring yield contains 90 lbs (ca. 40 kg) of fruit. The horizontal bar marked LSD (Least Significant Difference) is a measure used for statistical comparisons. Pairs of mean values must differ by the length of the bar for the difference to be declared real or significant.

108 Proc. Fla. State Hort. Soc. 113: 2000. Figure 2. Weight, and juice characteristics of fruit from ‘Washington’ navel orange trees growing on various rootstocks in field trials planted in 1991 at Mt. Dora (Lake County) and Ft. Pierce (St. Lucie County). Data are from the 1998-99 season at Mt. Dora, and the 1997-98 season at Ft. Pierce. The horizontal bar marked LSD (Least Significant Difference) is a measure used for statistical comparisons. Pairs of mean values must differ by the length of the bar for the difference to be declared real or significant.

Proc. Fla. State Hort. Soc. 113: 2000. 109 Table 2. 1999-2000 yields (boxes/tree) of the Lake County navel orange/rootstock trial (LC91), and the 1998-99 yields of the St. Lucie County trial (SLC91) adjusted for tree heights by analysis of covariance.

LC91 SLC91

Rootstock Mean Adj. Mean Adj.

Benton citrange — z 1.1 1.2 C-32 citrange — 1.3 1.0 C-35 citrange — 0.9 1.0 Carrizo citrange — 0.6 0.7 Koethen swt. orange ´ Rubidoux trif. orange 2.1 2.3 0.7 0.9 Norton citrange — 0.7 0.7 Rusk citrange 2.3 2.5 <0.5y — F80-5 citrumelo — 0.8 0.7 F80-9 citrumelo — 0.7 0.9 F80-18 citrumelo — 0.9 1.1 Swingle citrumelo 1.9 1.9 1.2 1.3 W-2 citrumelo 1.4 1.3 Changsha mandarin 1.9 1.8 — Citrus amblycarpa — 0.9 0.8 Cleopatra mandarin 1.3 1.2 1.0 0.7 Sun Chu Sha mandarin 1.7 1.7 0.4 0.3 Cleo + Flying Dragon trifoliate orange <0.5y — — Cleo + Swingle citrumelo <0.5y — — Hamlin sweet orange + Flying Dragon trifoliate orange <0.1y — — Calamandarin 2.0 1.9 1572 Trifoliate orange ´ Milam lemon — 0.4 0.6 1573-26 Trifoliate orange ´ Ridge Pineapple sweet orange 0 y — 0 y — 1578-173 Ridge Pineapple ´ Milam 1.0 1.2 0.8 0.9 Gou tou — 0.6 0.6 Murcott — 0.6 0.4 Rangpur ´ Troyer citrange 1.3 1.6 — Sour orange 1.8 1.8 — ´639 Cleo ´ trifoliate orange — 1.7 1.5 zA single dash (—) indicates the rootstock was not included in the trial. y Not included in the statistical analyses. highest values (11.25 to 11.5) which were different from those of trees on ´639, Swingle and W-2 citrumelos, and Benton citrange trees on Swingle; otherwise, there were no differences among the re- were among the largest while cropping relatively well. maining rootstocks in which juice SSC ranged from about 9.7 to Fruit from the trees on C-32, ´639, and several other root- 10.7. Juice soluble solids/acid ratios were from 12 to over 30 reflect- stocks were larger than fruit from those on Swingle, but the mean ing the late December time of harvest of the samples. Fruit from the weight of a fruit did not differ among most rootstocks with a typi- trees on the mandarin rootstocks, sour orange, and Rusk had among cal weight being about 0.6 lbs. Juice SSC did not differ among the the lowest ratios indicating that the fruit matured later on these root- fruit from the trees on most rootstocks as compared to Swingle stocks and, thus, could be held longer on the tree. (~12.7) except for Koethen ´ Rubidoux which had the highest val- Ft. Pierce (St. Lucie County) 1991. Tree survival after 9 yrs was ue (nearly 14.5), and the fruit from the trees on Gou tou, ´639, C- generally above 80%. The trees on Carrizo or Rusk citranges, and the 32, Cleo, and Sun Chu Sha which had the lowest values. Unlike at 1572 and 1578-201 hybrids had survival rates <80%, and no trees the Mt. Dora trial, juice SSC was strongly related to fruit size (r = on1573-26 survived. Mean tree height ranged from <6 ft (Rusk) to -0.71; P = 0.0001). Fruit from the trees on most rootstocks did not >10 ft (Cleo, Murcott, and ´639) with the general order of tree height differ in SS/TA ratio from the fruit sampled form the trees on essentially the same as at the Lake County site: mandarins, C-32, Gou Swingle; however, as in the Lake County trial, fruit from the trees tou>citranges, citrumelos>Rusk. However, there was considerable on the mandarin rootstocks had higher juice acidity and, thus, low- variation within certain rootstocks suggesting that there were specific er ratios and were later maturing. (soil?) differences among tree locations within the trial that affected Rootstock performance (1991 trials) between locations. There tree performance. This was particularly apparent with Carrizo citrange were trees on nine rootstocks common to both locations with Swin- trees which were significantly taller than those on Swingle, but three gle, Cleo, and Sun Chu Sha being the only commercial rootstocks. trees on Carrizo were stunted and often displayed leaf micronutrient There were no large location effects when the commercial root- deficiency. Furthermore, the site was apparently unsuitable for nor- stocks are compared. Tree heights were similar at both locations mally low-vigor trees like those on Rusk, and 1573-26. for Sun Chu Sha and Cleo, but the trees on Swingle were about Only the trees on ´639 had a higher 4-yr cumulative yield (5.8 20% smaller at Ft. Pierce than those at Mt. Dora. This difference boxes) than those on Swingle (Fig. 1). There were no differences reflects the broader soil adaptation of the mandarin rootstocks in yield among trees on Swingle, C-32, Benton, C-35, and Cleo; (Castle, 1987). trees on Carrizo, Sun Chu Sha, and Gou tou produced less fruit, If one year of average yield for the Ft. Pierce trees was added and the trees on Rusk yielded nearly no fruit. In this trial, some of to their cumulative yield so that the two locations could be com- the tallest trees tended to be the most yield efficient (Table 2). The pared, then the trees on Swingle, Sun Chu Sha, or Cleo, respective- ly, would likely have had similar yields. The fact that the Mt. Dora

110 Proc. Fla. State Hort. Soc. 113: 2000. trees did not substantially out produce the Ft. Pierce trees, under The trees on Gou tou, Murcott, the series of numbered hybrids conditions more conductive to tree growth and yield, tends to rein- (1572, etc.), and the somatic hybrids had unacceptable performance force the observation that Florida navel orange trees are not heavy primarily because of low yields (e.g., Gou tou) or very small tree cropping. The fruit size and juice quality data are not strictly com- size that limited yield (e.g., somatic hybrids). parable because they are from different seasons, and the fruit sam- ples were not harvested at the same time. Trees on Rusk, which were common to both locations, did not Conclusions grow well at Ft. Pierce and had low yields unlike those at Mt. Dora Considering overall performance, virtually no rootstocks ex- where they had the largest cumulative yield. ceeded Swingle citrumelo. However, at one or both of the trial sites, General rootstock performance in the 1991 trials as compared specific traits such as smaller tree size, higher yield efficiency, or to Swingle citrumelo. Sour orange is considered the standard root- better juice quality of Rusk, K ´ R, and C-32 citranges, W-2 cit- stock of excellence for navel orange, but it is no longer used in rumelo, and the Cleo ´ trifoliate orange hybrid (´639) suggested Florida, having been replaced with Swingle as the most popular that further trials of trees on these rootstocks would be appropriate. rootstock for new propagations (Citrus Budwood Registration Of- The performance of many rootstocks, especially the more vigorous fice, 1999). Sour orange was included only in the Mt. Dora trial ones, did not vary between Mt. Dora and Ft. Pierce. The soil and site where the trees on sour orange were smaller than those on Swingle, conditions at Ft.Pierce were not suitable for trees on low-vigor but with similar fruit quality. rootstocks. A number of mandarin and mandarin hybrid rootstocks were included in the trials. The trees on Cleo and Sun Chu Sha were vir- tually identical in height and fruit characteristics; however, they Literature Cited were taller than those on Swingle, especially at Ft. Pierce, and had lower yields of fruit with higher juice acidity and no difference in Bureau of Citrus Budwood Registration. 1999. Annual report, 1998-99. Winter Ha- SSC. Low navel orange yields and good juice quality are typical of ven, FL. Castle, W. S. 1987. Citrus rootstocks, pp. 361-399. In R. C. Rom and R. F. Carlson trees on Cleo (Youtsey and Bridges, 1979). It appears that no ad- (eds.). Rootstocks for fruit crops. J. Wiley and Sons, New York, NY. vantages over Cleo were provided by Sun Chu Sha, C. amblycar- Castle, W. S. and D. P. H. Tucker. 1998. Florida citrus rootstock selection guide. pa, or Changsha mandarins, or by the mandarin group over Univ. Fla. Coop. Ext. Serv. Publ. SP 248. Swingle rootstock. However, the hybrid, ´639, showed some Castle, W. S. and E. W. Stover. 2000. Rootstock reflections: Swingle citrumelo up- date. Citrus Industry 81(9):18-20. promise. The trees (included only in the Ft. Pierce trial) were vig- Castle, W. S., D. P. H. Tucker, A. H. Krezdorn and C. O. Youtsey. 1993. Rootstocks orous, but they cropped well and produced fruit typical of a man- for Florida citrus. Univ. Fla. Coop. Ext. Ser. Publ. SP 42. darin rootstock. Trees on this rootstock were also among those in Davies, F. S. 1986. The navel orange. Hort Reviews 8:129-180. AVI Press, West- the 1985 Lake County trial that survived a severe freeze. port, CT. Among the citrange rootstocks, Rusk and Carrizo have a com- Fla. Agric. Stat. Services. 2000a. Citrus summary, 1998-99. Orlando, FL. Fla. Agric. Stat. Services. 2000b. Commercial citrus inventory preliminary report. mercial history. Rusk was a minor rootstock in the 1960s and 70s, Orlando, FL. primarily in Lake County where the trees were small most likely Loeppert, R. H., C. T. Hallmark, and M. M. Koshy. 1984. Routine procedure for the because of infection with a viroid, possibly exocortis. Neverthe- rapid determination of soil carbonates. Soil Sci. Soc. Amer. J. 48:1030-1033. less, they were productive, and produced excellent quality fruit Pieringer, A. P., G. D. Bridges and C. O. Youtsey. 1978. Comparison of yield and internal quality of 25 navel orange selections. Proc. Fla. State Hort. Soc. 91:22- (WSC, pers. obs.) as occurred in the Mt. Dora trial. Rusk merits 25. consideration for navel and round oranges (Wheaton et al., 1991; Tucker, D. P. H., A. K. Alva, L. K. Jackson and T. A. Wheaton. 1995. Nutrition of Wheaton et al., 1995) on the Ridge, but the poor results at Ft. Florida citrus trees. Univ. Fla. Coop. Ext. Serv. Publ. SP 169. Pierce were not encouraging for its use in that environment. Carr- Wheaton, T. A., W. S. Castle, J. D. Whitney, and D. P. H. Tucker. 1991. Perfor- izo and Norton were included at Ft. Pierce because of prior perfor- mance of citrus scion cultivars and rootstocks in a high-density planting. Hort- Science 26(7):837-840. mance on the Ridge (Youtsey and Bridges, 1979); K ´ R, C-32, C- Wheaton, T. A., J. D. Whitney, W. S. Castle, R. P. Muraro, H. W. Browning and D. 35, and Benton are relatively new rootstocks showing promise in P. H. Tucker. 1995. Citrus scion and rootstock, topping height, and tree spacing other sweet orange and trials (unreported data, WSC). affect tree size, yield, fruit quality, and economic return. J. Amer. Soc. Hort. sci. Excluding Rusk, the differences among the other citranges do not 120(5):861-870. Youtsey, C. O. and G. D. Bridges. 1979. Yield and growth comparisons of one old- suggest any particular advantage among them as compared to line and eight nucellar ‘Washington’ navel budlines in a demonstration planting Swingle; however, the trees on K ´ R were more consistently sim- on ten rootstocks. Proc. Fla. State Hort. Soc. 92:20-22. ilar to those on Swingle, and the trees on C-32, while large, had higher yields. Of the numbered citrumelo rootstocks, F80-5, 80-18, 80-9, and W-2, only the latter two have been tested previously with navel or- ange, but were not compared to Swingle (Youtsey and Bridges, 1979). In our trials, the differences in tree size, yield, and fruit quality among the trees on these rootstocks including Swingle pro- vided little justification for recommending any citrumelo over Swingle with possible exception of W-2. The trees on W-2 were taller than those on Swingle, but had among the highest yield effi- ciencies. Nevertheless, certain Swingle decline problems are a suf- ficient reason to continue small-scale commercial trials with other citrumelos (Castle and Stover, 2000).

Proc. Fla. State Hort. Soc. 113: 2000. 111