EFFECT OF BORON AND ARSENIC ON JUICE ACIDITY

SMITH: BORON & ARSENIC ON GRAPEFRUIT 95 Fig. 2. Vlenci ornge leves from declining tree showing type of mteril used for electron microscopic study Ar rows point to typicl res long midveins tht were excised, fixed, nd embedded in plstic. Younger leves lso were ex mined. EFFECT OF BORON AND ARSENIC ON JUICE ACIDITY OF GRAPEFRUIT Pul F. Smith U.S. Deprtment of Agriculture, Agriculturl Reserch Service Orlndo, Florid 32803 Abstrct. Vrious combintions of boron nd rsenic were pplied to 'Mrsh' grpefruit trees to determine the effect on cidity of the juice of mturing fruit. Boron incresed the cidity. This occurred with both boric cid or sodium borte nd with soil or folir pplictions. Arsenic con sistently decresed juice cidity by smll mount. This ntgonistic effect ws essentilly the sme when both elements were included in the sme spry, pplied in seprte sprys, seprted by time intervl, or when B ws pplied to the soil nd to the folige. lmention of trdemrk nme or proprietry product does not constitute gurntee or wrrnty of the product by the U.S. Deprtment of Agriculture, nd does not imply its pprovl to the exclusion of other products tht my lso be suitble. Both boron (B) nd rsenic () re used in the culture of grpefruit in Florid. Sodium borte is pplied to the soil or in folir spry to prevent gumming of the peel nd premture fruit drop. Led Arsente is pplied in folir spry to lower the cidity of the juice nd hsten mturity. Unfortuntely, B increses juice cid ity, thus tending to dely mturity, nd induces gumming, thus incresing the need for more B. Dcszyck nd Sites (3) pplied B in postbloom sprys nd in nother spry 3 to 6 weeks lter. The result ws essentilly cn celltion of the effect of in lowering juice cidity. No comprisons hve been mde of other possible combintions, such s spry preced ing B spry or soil pplictions of B versus folir ppliction. Becuse of the growing trend of using highnlysis mixed fertilizers nd stright mterils, B often cn be pplied more conveniently s

96 FLORIDA STATE HORTICULTURAL SOCIETY, 1973 spry. It is sometimes included in pesticidl spry, or in the sme spry with. Experi ments were conducted in 1971 nd 1972 to pro vide dditionl informtion on the use of these two elements. Mterils nd Methods A young commercil grove of 'Mrsh' grpe fruit (Citrus prdisi Mcf.) on 'Rusk* citrnge tx>ck (Poncirus trifolit [L.] Rf. X C. sinensis %.] Osbeck), in Lke County, ws selected. The llees were only 3 yers old, but they were uni- "fpxm in size, fruitful, nd convenient for the ^rpose of pplying lrge number of spry trlaients with smll equipment. The sme mount of B ws pplied per tree when?isbil or spry pplictions were used. In Mrch 1971, 0.3 oz of Solubor* (66% B2O3) ws pplied per tree; in 1972, 0.4 oz ws pplied becuse of incresed tree size. These bse rtes re referred to s IX. When soil pplictions were mde, Solubor ws diluted with snd nd brodcst in brod bnd ner the drip line of the tree. Folir pplictions of nd B were mde with miniml mounts of wter so tht very little dripped off the trees. The min prt of the experiment consisted of 24 tretments in fctoril combintion. Twelve of the tretments re shown in Tble 1. These sme tretments were pplied t two rtes of in the spry (0.5 nd 1.0 lb of led rsente per 100 gl), mking 24 tretments. In ddition, five supplementl tretments nd untreted check trees were included with the intention of clrify ing certin points bout the effect of B on juice cidity. These were: () IX Solubor spry, (b) 2X Solubor spry, (c) 3X Solubor pplied to the soil, (d) IX B spry from boric cid H3BO3), nd (e) sodium crbonte (N2CO3) spry contining the sme mount of N s IX Solubor These tretments were pplied in My of ech Tble 1. Twelve tretment combintions of boron (B) nd rsenic () on spry dte 4/25 6/25 8/25 grpefruit B soil on in Mrch, B pplied in spry 4 weeks before With 4 weeks fter yer, except (c), which ws pplied in Mrch. No ws pplied to the supplementl plots of ;? trees. Ech of the 30 tretments ws pplied to twotree plots tht were rndomized in three replicte blocks. Close observtions were mde fter ech dte of spry ppliction to mke certin tht the mterils were not immeditely wshed off by rin. Fortuntely, in 18 seprte times of sprying during the 2 yers, the closest following rin ws 3 dys in once instnce. For the other pplictions, there ws no rinfll within 5 dys. The trees received good commercil cre in regrd to pest control, fertiliztion, nd weed control. The trees were observed closely for toxicity symptoms from either B or nd for growth behvior. Yields were determined by counting the number of fruit on ech tree in December. Sm ples of 16 rndom fruit were tken ech yer in mid-december from ech of the 90 plots for men size nd qulity determintions. Lef sm ples were collected on August 30, 1972, for gen erl nutritionl ssessment nd especilly for determintion of the B sttus of the folige under the vrious tretments. Results nd Discussion Tree performnce ws excellent. Folige color ws deep green, with only slight trnsient symp toms of Mn deficiency ech spring. These were not ssocited with experimentl tretment. Good crops of fruit were borne. No toxicity symp toms were induced. No B deficiency or toxicity symptoms occurred except on trees receiving 2X Solubor spry. Some of those trees showed mild B toxicity symptoms on few twigs. Yield of fruit ws not ffected by ny tret ment. In 1971, s 3-yer-old trees, there ws n verge of 43 fruit per tree. In 1972, the verge ws 208 fruit. These re pproximtely 0.5 nd 2.5 field boxes per tree respectively. Of the nine fruit-qulity fctors mesured, there ws no tretment effect on men fruit weight, rdil dimeter, xil dimeter, rind thickness, percent juice, totl soluble solids, or vitmin C content. Two fctors were ffected. Degreening of the fruit ws ffected by B. The cidity of the juice nd the solids/cids rtio were effected by both nd B. These spects will be discussed in the following sections. Degreening. Visul rtings of individul fruit in the December smples showed tht complete degreening hd not occurred on the tree. From

SMITH: BORON & ARSENIC ON GRAPEFRUIT 97 5 to 50% of the surfce res were still greenish. Arsenic sprys hd no effect on degreening. There ws slight but definite effect of B tretment on the mount of green color. Fruit from un treted trees were 75% free of green color. Fruit from ll of the numerous B-treted plots ver ged only 65% free of green color. The gretest mount of green ws on fruit with 2X strength Solubor spry tretment (60% free of green color). The time of B ppliction lso ffected de greening. Fruit from trees receiving B in Mrch (either in folige spry or on soil) were less green (70% green-free surfce) thn those re ceiving B spry in August-September (62% greenfree surfce). There ws one seemingly contrdictory obser vtion. Trees spryed with H3B03 nd with high lef B (Tble 2) hd bright fruit. The rt ing ws 75% greenfree surfce. Trees spryed with N2CO3 nd with low B concentrtion in the leves (Tble 2) hd fruit with delyed degreening (65% greenfree surfce). This sug gests tht the N in Solubor might be involved in delyed degreening. Sodium nlysis, however, showed low lef vlues of N (350-450 ppm) nd no reltion t ll to N ppliction. Thus, the reltion between B fertiliztion nd the rte of degreening of fruit is not yet cler. Further experimenttion will be required to eluci dte the sitution. The effect is rther smll nd would be of little consequence except to increse Tble 2. Citric cid concentrtion in the juice of Mrsh grpefruit nd boron (B) content of leves fter vri ous tretments, minly spry pplictions of B nd rsenic () ^ Juice cidity Lef B5 8/30 Tretment 1. Check (none) 2. IX Solubor spry (My) 3. 2X Solubor spry (My) 4. 3X Solubor, soil (Mrch) 5. IX H3BO3 spry (My) 6. N2C<>3 spry (My) 7. Soil B + spry 8. B spry before spry 9. B nd sme spry 10. B spry fter spry 11. in My 12. in July 13. in September 14. 0.5 lb led rsente/100 gl 15. 1.0 lb led rsente/100 gl 16. B on soil (Mrch) + spry 17. B spry (Mrch) t spry 1.20 1.30 1.24 1.19 1.14 1.12 1.13 1.15 1.13 1.08 b d e e d c bc b be c be (ppm) 68 141'ef 216 h 147 f 182 g 57 88 b 122 cd 124 cd 117 c 118 c 132 de 90 b 119 c 116 c 85 b 88 b Sttisticl indices: Vlues in verticl column shring the sme letter do not differ from ech other t odds of 19:1.

98 FLORIDA STATE HOETICULTURAL SOCIETY, 1973 the problem of degreening grpefruit hrvested in September nd October. Effect of rsenic on juice cidity. The effect of sprys on juice cidity ws consistent with the results of erlier studies (1, 2, 3, 4, 6, 7) nd the recommended use of mturity spry on grpefruit. The high rte of reduced cidity more thn the low rte t ll ppliction dtes. Applictions in My nd July were eqully effec tive, showing the long non-criticl spry period tht is vilble. Sprys in September, however, were lrgely ineffective (see Tble 2). These results require little discussion since they confirm existing informtion. It should be pointed out, however, tht the effect of on fruit cidity is reltively slight on 'Mrsh' grpefrui t. The mximum drop in cidity ws from 1.20 to %. This compres fvorbly with the dt of Deszyck nd Sites (3). On mture 'Mrsh* trees, they experienced drop from 1.41 to 1.28% with similr rtes of. Effect of boron on juice cidity. Applictions of B lwys incresed juice cidity slightly (Tble 2). Incresed rtes of B, in the bsence of, incresed cidity somewht proportion tely (compre tretments 1-5). Lef B tends to be directly relted to juice cidity. This result corrobortes the effect of B spry on fruit cid ity found by Deszyck nd Sites (3). In erlier studies, soil ppliction of B ws noted to in crese the cidity of 'Vlenci* ornges (C. sinensis L. Osb.) but not pink or red grpe fruit (8). Mrch ppliction of equl mounts of B to the folige or to the soil resulted in lmost the sme lef level of B in August nd nerly iden ticl levels of cid in the juice (tr. 16 nd 17). These re men vlues from 12 plots tht were ll rsented. Other comprisons re not men ingful becuse B ws only pplied to the soil in Mrch, while the B sprys were pplied t vri ous times from Mrch to September. Boron from boric cid or Solubor hd similr effects on juice cidity, but lef B ws higher from boric cid thn from Solubor (compre tr. 1, 2, nd 5). Sodium lso contributed slightly to juice cidity (tr. 1 nd 6). Lef N ws not ffected by sprys contining N, s noted erlier. However, N is mobile element, nd lef content my not reflect its physiologicl effect on the fruit. The B in the check trees nd the trees in tretment 6 ws pprently residul B in the soil-plnt system from prior usge. Ironiclly, B nd exerted opposite effects on juice cidity, nd the net effect of pplying ws mostly to counterct the cidity tht ws induced by pplying B. This could not be verted by vrious schemes of ppliction (compre tr. 1 nd 7-10). The result ws essentilly the sme regrdless of which element ws pplied first, or pplied simultneously in the sme spry, or widely seprted in time. Boron from the soil hd the sme effect s tht from folige sprys. Even B pplied to the soil in Mrch combined with n spry in September gve results similr to mixing B nd in September spry. Arsenic hd no pprecible effect on lef B concentrtion when pproprite comprisons were mde (compre tr. 8-10; 14 nd 15). Tret ment 2 cnnot be compred with these sme tretments becuse of the vrition in, time of B ppliction in reltion to lef smpling. Some of the tretments used in compiling the mens in 8 through 15 hd not yet received the current yer's B ppliction. Therefore, the vlues re lower thn tht for tretment 2. When only plots tht hd received ny combintion of nd B spry prior to smpling were compred, the ver ge B vlue ws 143 ppm but with no difference due to (dt not shown). The sme expln tion pplies to the vrition in lef B in reltion to time of ppliction (tr. 11-13). Since B is necessry element for growing citrus, there is no possibility of voiding its use. Excessive use of B should be voided where erly mturity is gol. Otherwise, there ppers to be nothing wrong with the prctice of pplying B nd in the sme spry. Bsic reserch is needed to elucidte the mechnism involved in shifting the cidity of the juice by B nd, s this might led to more intelligent mnipultion of mturity con trol thn we now hve. Miller (6) showed tht sprys ffect the respirtion rte of the tree. Metclf nd Vines (5) reported tht inhibited both oxidtive nd phosphoryltive enzymtic processes in mitochondril preprtions from grpefruit. Rtes of commercil use of B were estblished t time when the rtes for were higher thn they re now. Additionl reserch likely could led to some refinement in recommended use of B. Grpefruit trees tht re not rsented, for instnce, would undoubtedly require less B thn those tht re rsented. Miniml rtes of B need

SMITH: BORON & ARSENIC ON GRAPEFRUIT 99 to be estblished for other, vrieties tht hve delyed mturity becuse of excess cidity. Literture Cited 1. Deszyck, E. J. 1954. Effect of vrible rtes of led rsente on mturity nd qulity of Ruby Red grpefruit. Fl. Agr. Exp. St. Ann. Rpt. 156-157. 2.. 1956. Lef nd fruit drop s relted to bo rx nd lef rsente sprys on mture Mrsh grpefruit trees. Fl. Agr. Exp. St. Ann. Rpt. 161-162. 3., nd J. W. Sites. 1953. The effect of borx nd led rsente sprys on the totl cid nd mturity of Mrsh grpefruit. Proc. Fl. Stte Hort. Soc. 6:62-65. 4.. 1954. The effect of led rsente sprys on qulity nd mturity of Ruby Red grpefruit. Proc. Fl. Stte Hort. Soc. 67:38-42. 5. Metclf, J. F., nd H. M. Vines. 1965. Effects of r sente on oxidtive phosphoryltion in grpefruit mitochon dri. Proc. soc. South. Agr. Workers, Inc. 62:242-243. 6. Miller, R. L. 1933. The effect of led rsente insecti cides on citrus fruit. Proc. Fl. Stte Hort. Soc. 46:57-63. 7. Reitz, H. J. 1949. Arsenic sprys on grpefruit in re ltion to the new citrus code. Proc. Fl. Stte Hort. Soc. 62:49-55. 8. Smith, P. F. 1955. Reltion of boron level to produc tion nd fruit qulity of grpefruit nd ornges. Proc. Fl. Stte Hort. Soc. 68:54-59. TOLERANCE OF TRIFOLIATE ORANGE SELECTIONS AND HYBRIDS TO FREEZES AND FLOODING George Yelenosky U.S. Horticulturl Reserch Lbortory Agriculturl Reserch Service U.S. Deprtment of Agriculture Orlndo R. T. Brown Plquemines Prish Experiment Sttion Fort Sulphur, Louisin nd C. J. Hern U.S. Horticulturl Reserch Lbortory Agriculturl Reserch Service U.S. Deprtment of Agriculture Orlndo Abstrct. Freezes nd floods in Louisin, freezes in Georgi, nd controlled-environment studies in Florid indicte seven selections of trifolite ornge (Poncirus trifolite [L.] Rf.), citrdi (C. urntium L. X P. trifolit), nd citrumelo (C. prdisi Mcf. X P. trifolit) re sources of reltively high tolernce of freezes nd flooding. The highest yield of fruit/tree fter d verse conditions ws not lwys directly ssoci ted with the tolernce of freezes nd flooding. The effects of dverse environment on citrus trees sometimes cn be lessened by pproprite rootstocks (1, 3, 5, 8). In continuing studies of cultivr evlutions, we tested citrus rootstock selections s budded nd unbudded trees in the field nd s unbudded plnts in controlled en vironments. Results of controlled-environment tests with young plnts do not pply eqully to mture trees in the field; but the reltive rtings of the cultivrs tend to be similr between field nd controlled-environment tests, even with un budded young trees (14). In this study, the objec tives were to test the rection of citrus-breeding selections to severe freezing nd flooding nd to identify potentil citrus-breeding mteril with cold-hrdiness nd flooding tolernce. Mterils nd Methods Selections of trifolite ornge '(Poncirus try folit [L.] Rf.), trifolite ornge hybrids, nd mndrins (Citrus reticult Blnco) were used in this study. Hybrids included citrnges (C. sinensis [L.] Osbeck X P. trifolit), citrumelo (C. prdisi Mc. X P. trifolt), citrdi CPB 50097 (C.urntium L. X P. trifolit), citrndrin (P. trifolit X C. reticult), citrngedin (citrnge X Clmondin [C. reticult vr. ustsr X Fortunell sp.], nd citrngor ([C. sinen sis X P. trifolit] X C. sinensis). Plnts were from open-pollinted seed, germinted in glss house. One- to 1 1/2-yer-old plnts were trns plnted to the field nd used in controlled-environ ment tests. Field plntings were ner Port Sulphur, Louisin, nd Byron, Georgi. These sites were selected becuse they my hve moderte to severe freezes nd/or floods. Rootstocks were tested s scion-rootstock combintions in Louis in, primrily s unbudded plnts in Georgi, nd s unbudded plnts in controlled-environ ment tests in Florid. In Louisin, budded tops were 'Owri' stsum mndrin (C. reticult) nd Wshington' nvel ornge (C, sinensis,) Buds were from vlidted sources. Test trees