and Yapwattanaphun, 2001; Zee Off-season Flower Induction of Longan with et al., 1998). Inconsistent floral Potassium Chlorate, Sodium Chlorite, and induction and alternate bearing in longan production has been alleviated Sodium Hypochlorite by the discovery of potassium chlo- rate (KClO3) to induce off-season 1,4 2 3 flowers and fruits worldwide (Choo, Tracie K. Matsumoto , Mike A. Nagao , and Bruce Mackey 2000; Manochai et al., 2005; Nagao and Ho-a, 2000; Sabhadrabandhu
ADDITIONAL INDEX WORDS. Dimocarpus longan, bleach, subtropical fruit tree, and Yapwattanaphun, 2001; Yen dragon eye, Sapindaceae et al., 2001). Application of KClO3 as a soil drench (10% to 20% chlorate SUMMARY. Flower induction of longan (Dimocarpus longan) with potassium solution), broadcast under the can- chlorate has improved the availability of longan fruit, but potassium chlorate is opy (200 to 400 g/tree), foliar spray potentially explosive and often difficult to purchase, transport, and store. Previous (1 to 2 gÁL–1), or branch or stem reports suggested that hypochlorite enhances natural longan flower induction. This –1 study is the first to demonstrate that chlorite- and hypochlorite- (bleach) induced injection (0.05 to 0.25 gÁcm off-season longan flowering is similar to chlorate-treated trees. Hypochlorite branch) is effective for promoting induction of flowering with bleach was likely the result of chlorate in the bleach flowering (Manochai et al., 2005; solution. Chlorate was present in the leachate from potted longan trees treated with Yen, 2000; Yen et al., 2001). For bleach and was detected in bleach before soil application. The quantity of chlorate optimal flowering, KClO3 should be found in bleach induced flowering to the same or greater extent as equivalent applied to trees with mature leaf quantities of potassium chlorate, suggesting chlorate is an a.i. responsible for flushes 40 to 45 d old (Manochai longan flowering. et al., 2005). Although KClO3 indu- ces flowering regardless of the geno- ongan is in the Sapindaceae production occurs in Florida, Hawaii, type, the flowering response of each family along with its other and California. In 1998, the United cultivar may vary with 100% flower- better known relatives, lychee States produced 1.4 million lb of ing observed in ‘Si-Chompoo’ after L –2 (Litchi chinensis) and rambutan longan with an estimated value of application of 1.0 gÁm , whereas ‘E- (Nephelium lappaceum). Commonly $2.8 million (Mossler and Nesheim, Daw’ required 8.0 gÁm–2 (Manochai referred to as dragon eye, the longan 2002). In Hawaii, production was et al., 2005). Fruits obtained from fruit is smooth, round, and yellowish valued at $438,000 for 142,000 lb KClO3-treated plants do not contain brown at harvest with a translucent of longan sold in 2005. Future chlorate, chlorite, or hypochlorite and crispy edible aril surrounding a longan production is expected to residues in the aril, and the size, round, brown–black seed. Although increase with current fruit production weight, exocarp color, fruit pole usually consumed fresh, the dried based on only 47% of the total strength, fruit volume, total soluble longan fruit is used for medicinal acreage planted in longan trees [U.S. sugars, and sulfur dioxide residues purposes or as a tea during special Department of Agriculture (USDA), from postharvest treatment are unaf- occasions (Zee et al., 1998). National Agricultural Statistics Serv- fected (Kanaree and Pankasemsuk, Longan trees are commonly ice and Hawaii Department of Agri- 2005a, 2005b). grown in many subtropical and trop- culture, 2006]. Originally discovered as the a.i. ical countries with the majority of Floral initiation in longan is in fireworks gunpowder, KClO3 is a the production in Thailand, Taiwan, dependent on cool and dry envi- strong oxidizing agent responsible China, and Australia (Menzel et al., ronmental conditions with flower- for the explosive nature of fireworks 2002). In the United States, major ing occurring during March to (Yen, 2000; Yen et al., 2001). Potas- May in Hawaii (Sabhadrabandhu sium chlorate is an extremely useful Mention of trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and Units does not imply its approval to the exclusion of other products or vendors that also may be suitable. To convert U.S. to SI, To convert SI to U.S., multiply by U.S. unit SI unit multiply by We thank Richard and Jenny Johnson of Onomea Orchards for kindly donating use of the longan trees, 29.5735 fl oz mL 0.0338 Tsuyoshi Tsumura for his excellent technical assis- 318.3268 fl oz/ft2 mLÁm–2 0.0031 tance, and Dr. Francis Zee for technical discussion 0.3048 ft m 3.2808 and critical review of the manuscript. 0.0929 ft2 m2 10.7639 1USDA, ARS, Pacific Basin Agricultural Research 3.7854 gal L 0.2642 Center, Tropical Plant Genetic Resource Manage- 2.5400 inch(es) cm 0.3937 ment Unit, P.O. Box 4487, Hilo, HI 96720 0.4536 lb kg 2.2046 2Department of Tropical Plant and Soil Sciences, 1 micron mm1 College of Tropical Agriculture and Human Resour- 28.3495 oz g 0.0353 ces, University of Hawaii at Manoa, Komohana 305.1517 oz/ft2 gÁm–2 0.0033 Agricultural Complex, 875 Komohana Street, Hilo, 7.4892 oz/gal gÁL–1 0.1335 HI 96720 11.1612 oz/inch gÁcm–1 0.0896 3USDA, ARS, Pacific West Area, 800 Buchanan 1 ppb mgÁL–1 1 Street, Albany, CA 94710 1 ppm mgÁL–1 1 3 4Corresponding author. E-mail: tmatsumoto@ 14.7868 tablespoon cm 0.0676 pbarc.ars.usda.gov. ( F – 32) O 1.8 F C (1.8 · C) + 32
296 • July–September 2007 17(3) tool to effectively plan flowering and was calculated by recording the num- On 10 Aug. 2005, three potted fruiting of longan trees for market. ber of flowering terminals divided by trees were irrigated with either 1) 0.5 However, the dangers associated with the total number of terminals in the L water, 2) 0.5 L bleach (26.25 g large quantities of this chemical make tree canopy. NaOCl), or 3) 26.25 g KClO3 gran- it difficult to obtain and store; a EXPT.2.The experiment was ular broadcast with 0.5 L water. mixture of KClO3 and sulfur was conducted in a well-drained silty clay Plants were irrigated to maintain responsible for an explosion at a loam soil in Onomea, Hawaii, where adequate soil moisture for growth longan processing plant in Chiang mean maximum and minimum tem- but avoiding excess water leaching Mai, Thailand, killing 35 workers peratures were 26 and 19 C, respec- through the pot. One month after and injuring over 100. Lack of per- tively, and annual rainfall was 3781 application, the pots were uniformly sonal protection equipment during mm. The experiment was repeated irrigated with 10 L of water. Grav- prolonged use of KClO3 by Thai twice (18 May 2005 and 16 Sept. itation water from the soil was col- longan workers resulted in increased 2005). Three-year-old ‘Biew Kiew’ lected and volume recorded. The levels of anemia, thrombocytopenia, trees were selected for uniformity in water samples were filtered with a high serum creatinine, and methemo- vegetative flushing, and each treat- 0.2-mm filter to remove soil particles globinemia, which are hypothesized ment was randomly assigned to three and sent to NovaChem Laboratories to be related to KClO3 toxicity trees (May application) or five trees Inc. (Oxford, Ohio) and analyzed for (Wiwatanadate et al., 2001). (September application). Plants were chlorate and chlorite according to the Sodium hypochlorite (NaOCl) is treated as follows: no treatment con- National Environmental Laboratory the a.i. in bleach and has been shown trol; 300 g/tree (May) or 250 g/tree Accreditation Conference standard to increase flowering of ‘Do’ longan KClO3 (September) broadcasted using ion chromatography (Environ- trees (53.7% flower emergence in under the canopy; 45 g/tree (May) mental Protection Agency Method untreated trees versus 96.2% flower or 50 g/tree KClO3 (September) 300.1). Commercial bleach (5.25% emergence in treated trees) (Sritontip broadcasted under the canopy; and NaOCl) samples were diluted 1:10 et al., 2005a). However, it is not clear 2 gal bleach (May and September) with distilled, deionized water and if NaOCl can induce off-season flow- applied as a soil drench under the tree also analyzed for chlorate (NovaChem ering because soil drenches with canopy. After the KClO3 applications, Laboratories). NaOCl at 50 mLÁm–2 of canopy pro- 2 gal of water was applied on the soil SOIL ANALYSIS. Soil samples from duced only 5% flower emergence surface. Flowering was monitored three ‘Biew Kiew’ trees treated with –2 compared with KClO3 5gÁm can- biweekly by counting the number of 2 gal bleach and three untreated trees opy, which produced 75% of flower flowering and nonflowering terminals grown at the Onomea site were ana- emergence (Sritontip et al., 2005b). on two sides (north and south) of the lyzed for salinity and sodium (Na+) The objective of this experiment was tree and determining the percentage content. Fourteen weeks and 1 year to determine if NaOCl can be used as of flowering terminals. after treatment, four 16-cm core sam- an alternative to potassium chlorate STATISTICAL ANALYSIS. SAS (SAS ples were taken 50 cm from the trunk. for off-season longan flower induc- Institute, Cary, N.C.) PROC GLIM- Subsamples from each tree were tion in Hawaii. MIX was used for a generalized linear pooled and sent to the University of models approach with a logit link for Hawaii, College of Tropical Agricul- Materials and methods the binomial responses (Littell et al., ture and Human Resources, Agricul- EXPT.1.Four-year-old ‘Egami’ 2002). Treatment means were tested tural Diagnostic Service Center, and ‘Biew Kiew’ longan trees on the for a decrease from the KClO3 stand- Honolulu. University of Hawaii, Waiakea Agri- ard using Dunnett’s adjustment for culture Research Station (WRS), were multiplicity. In Expt. 2, test of effects used for this study. The soil consisted slices were used to compare the Results and discussion of an extremely stony Papai muck north and south tree faces within EXPT.1.Flowering of trees at the with organic soils formed over mostly treatments. WRS treated with KClO3, NaClO2, fragmented a’a lava. On 15 Sept. CHLORATE ANALYSIS. Two-year- bleach, and bleach plus CuCl2 began 2004, the longan trees were un- old ‘Biew Kiew’ plants were grown at 5 weeks (22 Oct. 2004) after treat- treated or treated with 300 g/tree the USDA, Agricultural Research ment. By 12 weeks after treatment, KClO3 or 300 g/tree NaClO2 Service, Pacific Basin Agricultural trees stopped production of panicles applied as a granular broadcast under Research Center, Tropical Plant and the number of flowering termi- the tree canopy or 2 gal/tree liquid Genetic Resource Management Unit nals was determined. Nontreated NaOCl bleach solution [397 mL at WRS in 15-gal pots containing a control trees did not flower and (397 g) NaOCl a.i.] or 2 gal/tree 1:1:1 (by volume) mixture of soil, KClO3, NaClO2, bleach, and bleach bleach plus 0.5 g copper chloride composted macadamia husks, and plus CuCl2-treated trees exhibited (CuCl2) applied as a soil drench under volcanic cinder. Plants were kept in 97.8% (484 flowering/495 total ter- the tree canopy. The experiment was a covered greenhouse and fertilized minals), 91.8% (462 flowering/503 a completely randomized design with bimonthly with 1 tablespoon of total terminals), 84.7% (326 flower- three trees per treatment. Two 16N–7P–13.3K plus micronutrients ing/385 total terminals), and 96.9% ‘Egami’ trees and one ‘Biew Kiew’ and monthly with 1 tablespoon/L (493 flowering/509 total terminals) tree were randomly assigned to each of 30N–4.4P–8.4K foliar fertilizer. flowering, respectively. The means treatment. On 10 Dec. 2004, flower- Plants were watered three times for each treatment were not signifi- ing stopped and percent flowering weekly with 19 L water. cantly less than the KClO3 treatment
• July–September 2007 17(3) 297 RESEARCH REPORTS
(P > 0.27) for NaClO2, bleach (P > Gordon, 1999). The incorporation such as bleach may be exposed to 2+ 0.18), and bleach plus CuCl2 (P > of copper (Cu ) to the bleach sol- elevated temperatures during trans- 0.43) as analyzed by SAS PROC ution, an ion that catalyzes both portation and storage, which could GLIMMIX using Dunnett’s adjust- degradation pathways of hypochlorite account for the presence of chlorate ment for multiplicity. This demon- to chlorate or oxygen (Adam and in the bleach. Chemical analysis of the strates that chlorate, chlorite, and Gordon, 1999), appeared to induce bleach resulted in 3.97 ± 0.65 gÁL–1 hypochlorite can effectively induce flowering to the same degree as sodium chlorate, which is equivalent off-season flowering of longan. KClO3 treatment or bleach treat- to 25 to 35 g of chlorate contained Investigation into the mecha- ments alone, suggesting chlorate in in the 2 gal of bleach applied to nism of chlorate toxicity by A˚ berg bleach contributed to the promotion the trees. suggested that the chlorate toxicity of longan flowering. EXPT.2.To determine if the is incited by reduction of chlorate to CHLORATE ANALYSIS. To apply amount of chlorate found in bleach chlorite and hypochlorite by nitrate equivalent quantities used in field could induce longan flowering to the reductase (reviewed by LaBrie et al., applications of 300 g KClO3 broad- same extent as bleach, ‘Biew Kiew’ trees 1991). As predicted by A˚ berg, the casted in a 5-ft diameter (19.63 ft2) in Onomea, Hawaii, were left untreated majority of plant nitrate reductase under the tree canopy, 26.25 g or treated with 300 g KClO3,45g enzymes reduce chlorate to the toxic KClO3 and 500 mL (26.25 g of KClO3, or 2 gal of bleach. The 300-g chlorite. Chlorate was used exten- NaOCl) bleach were applied to pot- treatment was previously shown to be sively in the past as an herbicide to ted longan plants in a 17-3/4-inch- effective for inducing flowering in control problematic weeds such as diameter (1.72 ft2) pot. Leachate Hawaii (Nagao and Ho-a, 2000), and bindweed (Latshaw and Zahnley, collected 4 weeks after treatment 45gofKClO3 is a high estimate of the 1927; Loomis et al., 1933; Neller, contained 173.3 ± 7.1 mgÁL–1 of amount of chlorate present in 2 gal of 1930) and is the a.i. in many herbi- chlorate from pots treated with bleach applied onto the soil. –1 cides used today (Bennett and Shaw, 26.25 g KClO3 and 8.3 ± 2.3 mgÁL Trees treated on 18 May 2005 2000). Chlorate has also been useful of chlorate from pots treated with began flowering 8 weeks after treat- in the isolation of mutants with 0.5 L bleach. Leachate from control ment (8 Aug. 2005) and produced reduced nitrate uptake or impaired pots contained negligible chlorate new panicles until 16 weeks after nitrate reductase activity (Crawford (less than 50 mgÁL–1). Presence of treatment. No significant differences and Forde, 2002; Crawford and chlorate in the leachate from the in flowering were found between the Glass, 1998; LaBrie et al., 1991; bleach treatments suggests that hypo- north and south tree faces for all Meyer and Stitt, 2001). Nitrate chlorite was converted to chlorate in treatments. Bleach-treated trees flow- reductase activity in leaves is reduced the soil or before the application. ered at 54.9% (118 flowering/215 in longan trees treated with soil appli- Decomposition of bleach to chlo- total), which is significantly less (P = cations of KClO3, NaClO2, and rate is also catalyzed by higher tem- 0.048) than the 300 g KClO3 treat- bleach (Matsumoto et al., in press). peratures. Nonperishable products ments in which 94.0% (221 Reduced nitrogen levels in foli- age is hypothesized to be an impor- tant factor in determining the receptiveness of the terminals to nat- ural flower induction conditions in lychee, a related species in the family Sapindaceae. Nitrogen levels in excess of 1.85% results in vegetative flush- ing, whereas levels of 1.75% to 1.85% are conducive to flowering (Menzel et al., 1988). Optimal lychee flower- ing and fruit set have been correlated with 1.3% to 1.5% nitrogen in leaf dry matter in Hawaii, South Africa, India, and Australia (Davenport and Stern, 2005), thus suggesting a possible link between low nitrogen levels and flow- ering in these Sapindaceae crops. Hypochlorite enhances flower- ing in longan similar to potassium chlorate (Sritontip et al., 2005a), and we demonstrate that it can also effectively induce off-season flower- ing. NaOCl degradation occurs through two pathways. The first path- Fig. 1. Percentage of ‘Biew Kiew’ longan trees with panicles after treatment with way leads to the production of oxy- 2 gal (7.6 L) bleach, 50 g (1.8 oz) potassium chlorate (KClO3), or 250 g (8.8 oz) gen, whereas the second leads to KClO3 on 16 Sept. 2005. Trees were monitored every 1 to 2 weeks from 3 Nov. chlorate formation (Adam and 2005 to 6 Jan. 2006.
298 • July–September 2007 17(3) flowering/235 total) of the terminals In addition to hypochlorite and and G.K. Waite (eds.). The lychee and flowered, but the bleach treatment chlorate, sodium was also added to longan: Botany, production and uses. was not significantly different (P = the soil during the bleach treatment. CABI Publishing, Wallingford, U.K. 0.406) compared with 67.9% (142 Soil analyses from trees treated with flowering/209 total) of the terminals bleach and control trees at Onomea Kanaree, W. and T. Pankasemsuk. 2005a. Determination of potassium chlorate res- flowering in trees treated with 45 g showed that at 14 weeks after treat- idues in ‘Do’ longan fruit. Acta Hort. KClO3. This suggests that the chlo- ment, soil from bleach-treated trees 665:249–254. rate in the bleach may be responsible contained 151.3 ± 36.8 ppm of Na+, for flower induction in longan. whereas soil from untreated control Kanaree, W. and T. Pankasemsuk. 2005b. Trees treated on 16 Sept. 2005 trees contained 37.7 ± 2.9 ppm of Effect of potassium chlorate on fruit qual- began flowering 7 weeks after treat- Na+. Soil pH and salinity were not ity of ‘Do’ longan. Acta Hort. 665:281– ments (4 Nov. 2005) and actively significantly different in soil samples 283. produced new panicles until 12 weeks from bleach-treated and untreated LaBrie, S.T., J.Q. Wilkinson, and N.M. (8 Dec. 2005) after treatment (Fig. trees and no visible signs of sodium Crawford. 1991. Effect of chlorate treat- 1). Flowering on the north and south toxicity could be detected. One year ment on nitrate reductase and faces of the trees was not significantly after bleach treatment, there was no nitrate reductase gene expression in Ara- bidopsis thaliana. Plant Physiol. 97:873– different for 250 g KClO3 (P = 0.926) significant difference between soil or 2 gal bleach (P = 0.783); however, samples of bleach-treated trees, 24.4 ± 879. flowering was significantly different 2.9 ppm, and untreated trees, 24.3 ± Latshaw, W.L. and J.W. Zahnley. 1927. for the 50 g KClO3 treatment (P = 4.8 ppm, suggesting that sodium did Experiments with sodium chlorate and 0.003). This difference in the flower- not accumulate in the soil. other chemicals as herbicides for field ing observed between the different Therefore, we conclude that bindweed. J. Agr. Res. 35:757–767. faces of the trees treated with 50 g chlorate, chlorite, and bleach are able Littell, R.C., W.W. Stroup, and R.J. KClO3 may be attributed to the to induce flowering in longan. Bleach Freund. 2002. SAS for linear models. uneven distribution of chlorate on is an effective alternative to potassium 4th ed. SAS Institute Inc., Cary, N.C. the soil under the tree canopy. Overall chlorate for producing off-season flowering of the trees treated with longan fruits. The decomposition of Loomis, W.E., E.V. Smith, R. Bissey, and bleach was 97.1% (297 flowering/ hypochlorite to chlorate in the bleach L.E. Arnold. 1933. The absorption and movement of sodium chlorate when used 306 total terminals), which was not contributes to the floral induction as a herbicide. J. Amer. Soc. Agron. significantly different (P = 0.501) without sodium accumulation in soil 25:724–739. than trees treated with 250 g KClO3 1 year after application in a high rain- in which 96.4% (318 flowering/330 fall environment. Manochai, P., P. Sruamsiri, W. Wiriya- total) of the terminals flowered but alongkorn, D. Naphrom, M. Hegele, and was significantly greater (P = 0.004) F. Bangerth. 2005. Year around off season than flowering on trees treated with flower induction in longan (Dimocarpus Literature cited longan, Lour.) trees by KClO3 applica- 50 g KClO3 in which 68.7% (237 tions: Potentials and problems. Scientia flowering/345 total) of the terminal Adam, L.C. and G. Gordon. 1999. Hypo- chlorite ion decomposition: Effects Hort. 104:379–390. flowered. of temperature, ionic strength and Matsumoto, T., T. Tsumura, and F. Zee. Comparing longan flowering chloride ion. Inorg. Chem. 38:1299– observed in trees treated in May and Exploring the mechanism of potassium 1304. chlorate induced flowering in Dimocarpus September, KClO3 at the higher (250 or 300 g) application rate consistently Bennett, A.C. and D.R. Shaw. 2000. longan. Acta Hort. (in press). resulted in over 90% flowering and Effect of preharvest desiccants on weed Menzel, C.M., M.L. Carseldine, and D.R. the lower (45 or 50 g) KClO appli- seed production and viability. Weed Simpson. 1988. Crop development and 3 Technol. 14:530–538. cation rate resulted in 70% flower- leaf nitrogen in lychee in subtropical ing. Flowering of longan trees treated Choo, W.K. 2000. Longan production in Queensland. Austral. J. Expt. Agr. 28: with bleach varied between the two Asia. Regional Office for Asia and the 793–800. Pacific (RAP) Publication 2000/20. applications dates with 54.9% flower- Menzel, C.M., B.J. Watson, and D.R. Food and Agriculture Organization of ing observed after the 18 May 2005 Simpson. 2002. Longan, p. 259–292. the United Nations Regional Office for application and 97.1% flowering In: T.K. Bose, S.K. Mitra, and S. Sanyal Asia and the Pacific, Bangkok, Thailand. observed after the 16 Sept. 2005 (eds.). Fruits: Tropical and subtropical application. This increase in flowering Crawford, N.M. and B.G. Forde. 2002. Vol. 2. Partha Sankar Basu, Calcutta, may be attributed to the conversion Molecular and developmental biology of India. inorganic nitrogen nutrition. 26 Aug. of NaOCl to chlorate possibly by Meyer, C. and M. Stitt. 2001. Nitrate 2003.
• July–September 2007 17(3) 299 RESEARCH REPORTS
Nagao, M.A. and E.B. Ho-a. 2000. Stim- Sritontip, C., Y. Khaosumain, S. Chang- exposed longan growers. Internal Medi- ulating longan flowering in Hawaii with jaraja, and R. Poruksa. 2005b. Effect of cine J. Thailand 17:94–97. potassium chlorate. J. Hawaiian Pacific potassium chlorate, potassium nitrate, Yen, C.-R. 2000. From boom to bloom. Agr. 11:23–27. sodium hypochlorite and thiourea on Agr. Hawaii 3:26–27. Neller, J.R. 1930. Effect of chlorates off-season flowering and photosynthesis upon the catalase activity of the roots of of ‘Do’ longan. Acta Hort. 665:291–296. Yen, C.-R., C.-N. Chau, J.-W. Chang, bindweed. J. Agr. Res. 43:183–189. U.S. Department of Agriculture, National and J.-C. Tzeng. 2001. Effects of chem- Sabhadrabandhu, S. and C. Yapwattana- Agriculture Statistics Service and State of icals on flowering in longan. J. Chinese phun. 2001. Regulation off-season flow- Hawaii Department of Agriculture. 2006. Soc. Hort. Sci. 47:195–200. ering of longan in Thailand. Acta Hort. Hawaii tropical specialty fruits.8 Aug. Zee, F.T.P., H.T. Chan, Jr., and C.-R. 558:193–198. 2006.
300 • July–September 2007 17(3)