The Chemical Induction of Parthenocarpy in the Calimyrna Fig and Its Physiological Significance' Julian C

606 PLANT PhIYSIOLOGY 14. SCHREVEN-, D. A. \VANT. 1959. Effects of added 18. THORNTON, H. G. AND J. RuDIORF. 1936. The ab- sugars and nitrogen oni nodulationl of legumes. normal structure induced in nodules on lucerne Plant Soil 11: 93-112. (Medicago sativa L.) by the supply of sodium ni- 15. TANNER, J. W. AND I. C. ANDERSON. 1963. Ani trate to the host plant. Proc. Roy. Soc. Lod(lon external effect of inorganic nitrogen in root nio- B 120: 240-52. dulation. Nature 198: 303-04. 16. THIORNTON, H. G. 1936. The actionl of sodium ni- 19. TONHAZY, N. E. AND M. J. PEI.CZAR. JR. 1954. trate upoIn the inifectioii of lucernie root liairs by Oxidation of indoleacetic acid by anl extracellular nodule bacteria. Proc. Roy. Soc. London B 119: enzyme from Polyporus zersicolor anid a similar 474-92. oxidation catalyzed by nitrate. Science 120: 141- 17. THORNTON, H. G. The discovery of the use 42. of dichlorophenoxyacetic acid in controlling plant 20. WILSON, P. W. 1940. The biochemistry of symbio- growth. Rept. Rothamsted Expt. Sta. for 1939- tic nitrogen fixation. University of WViscoisin 1945: 83. Press, Madison.

The Chemical Induction of Parthenocarpy in the Calimyrna Fig and its Physiological Significance' Julian C. Crane Department of Pomology, University of California, Davis, California

Several auxins (1, 4, 5, 6) and a gibberellin (8) Materials and Methods have been found to be effective for inducing parthenocarpy in the Calimnvrna fig. None of the chemi- The investigation was coinducted at the Univer- cals, however, has been adopted by the industry for sity's Wolfskill Experimental Orchards, Winters, commercial application because of the inferior quality California, and the methods used were essentially of the figs produced. In contrast to pollinated fruits the same as those previously reported ( 1, 4). The that contain numerous drupelets with lignified endo- growth regulators were applied as aqueous solutions carp tissue which imparts a seedy texture, no ligni- on June 25, 1964, by spraying the young syconia and fication of this tissue occurs in chemiiicallv induced foliage to the point of slight drip. Each solution also parthenocarpic fruits, except those treate(d with ben- contained 0.05 % Tween 20 (polyoxyethylene sorbitan zothiazol-2-oxyacetic acid (6). The lercent parthe- monolaurate) as the surfactant. Tordon concentra- nocarpic fruit set with the latter chemical, however. tions of 20 mg/liter and below were tused, as severe is so erratic from year to year that it cannliot be relied leaf and wood damage resulted from higher concen- tupon. Conseqtuently, the search has continuied for a trations in 1963. SD 83393, a benzyladenine in which growth regulator that consistently indutces the produc- the hydrogen onl carbon atom 9 is substituted with the tion of large qtuanitities of parthenocarpic figs con- nonpolar ring struicture of tetrahydropyran, was tested taining drupelets with lignified endocarp. Prelimi- narv tests in 1(63 indlicated that the herbicide Tordon 2 (4-amino-3, 5, 6-trichloropicolinic acid) offerecl con- 2 Supplied by the Dow Chemical Company. Tordon is siderable promqise in this respect. The results ob- classified here as an auxin because of its similarity in biological activity to that of the substituted phenoxyacetic tained with this auxin in 1964, together with those acids. of a kinin compound are presented here. 36- (benzylamino) -9- (2-tetrahydropyranyl) -9H-purine, produced in the laboratories of Shell Development Com- pany and supplied by Dr. J. van Overbeek, Modesto, I Received November 27, 1964. California. CRANE-INDUCED PAtTHENOCARPY IN FIG 607 at concentrations of 500 and 1000 mg/liter. This though concentrations of 6 mg'/liter and below pro- new synthetic kinin was not only applied as a spray duced parthenocarpic fruit sets of only 88 to 94 %, but it was also injected with a hypodermic syringe these were considerably greater than those generally through the ostiole and into the central cavitv of the obtained by cross-pollination under commercial or- young fruit. The cavity was filled with 1 to 2 ml chard conditionis ( 1, 4, 5, 6). The percent fruit set of the solution. As a basis for comparison, GA, resulting from cross-pollination in the orchard where (potassium salt of gibberellic acid) and the auxin this investigation was conducted was not determined PCPA (para-chlorophenoxyacetic acid), regulators because the commercial procedure for pollination was proven to be effective for inducing parthenocarpy in not followed. the fig (1,8), were used at acid equivalent concen- Maturity of the parthenocarpic fruits, as judged trations of 25 and 75 mg/liter, respectively. Fifteen by color, firmness, and taste, occurred about a week to 20 fruits were used for each treatment. earlier than that of pollinated ones. Externallv, they At the time of treatment, the female flowers with- appeared identical to fruits that had been pollinated; in the syconia were receptive to polliniation. Cross- internally, however, the pulp was amber as contrasted pollination with the male fig, however, was prevented to the strawberry red that characterized pollinated by covering the branches bearing the fruits to be fruits. Ini contrast to parthenocarpic fruits pro- treated with muslin bags. The bags enclosed the duced with PCPA in which ligniification of the endo- branches for about 2 weeks, the period during which carp in the individual drupelets does niot occur, pollination of unbagged fruits was accomplished by this tissue in fruits produced with Tordon was the insect Blastophaga pseues. Bagged but untreated definitely lignified (fig 1). The degree of lignifi- fruits served as controls. Sinlce previous tests with cation, however, was not as great as that in pollinated the surfactant Tween 20 showed it to have no effect fruits, as (letermiined by mastication, but progressively on the fig, it was not applied in aqueous solution to increased as concentration of Tordon increased. the control fruits. Unless cross-pollination occurs The fruits had a seedy texture similar to pollinated or the syconia are treated with certain growth regu- ones; there was no evidence of embryos within the lators, they cease growth, wither and absciss in about individual drupelets. 2 weeks. No vegetative damage whatsoever was noted from concentrations of Tordon of 6 mg/liter or less. A Results concenitration of 8 mg/liter produced slight chlorosis of the younger leaves: leaf chlorosis and necrotic Tordon is a very effective compound for inducing areas on current-season's shoots increased progressive- parthenocarpy in the fig (table I). This chemical ly as concentration was increased above 8 mg/liter. at a concentration of 8 mg/liter was just as effective Slight leaf chlorosis developed following the applica- as 75 mg/liter of PCPA, the concentration of the tion of PCPA. This symptom did not occur in pre- latter that has been shown to be optimum (5). Al- vious experimentation with PCPA. perhaps because

Table I. The Comiipairative Effectiveness of 2 Auixins, a Gibberellin, and a Kinin for Inducing Parthenocarpy in the Calimyrna Fig Parthenocarpic Treatment fruit set Observations on vegetative growth mg/liter

Control (unpollinated) 0 Auxins: Tordonl 2 94 Like control 4 90 Like control 6 88 l ike control 8 100 Slight leaf chlorosis 10 93 Moderate leaf chlorosis and slight shoot injury 20 100 Severe leaf chlorosis and severe shoot injury PCPA 75 100 Slight leaf chlorosis Gibberellin: GA., 25 100 Rest period of 33 % of terminal vegetative buds was broken with subsequent shoot growth Kinin: SD 8339-sprayed 100 18 Abscission of youngest leaves 500 57 Abscission of youngest leaves SD 8339-inj ected 100 100 Like control 500 100 Like control 6,08 PLANT PHYSIOLOGY for inducing parthenocarpy lut, as shown in talble I, A the rest periodl of 33 % of the buds was broken anld ani average of 4.5 cm of new shoot growth resuilted. SI) 8339 was also very effective for inlduicinig )arthenocarpy, particularyv wheni inijecte(I inlto the younlg svcoinia (table 1). Iinjectioni of either coin- centration resuiltedl in 100 % p)arthenocarpic set and( (levelopmenit to maturity al)out a week earlier thani milatuirity of pollinate(l fruits. \Vhen applied as a 2 spray at conicenitrationis of 100( and(l 500 mg/liter, SD 8339 set onily 18 aln(d 57 % of the fruits, respectively. TI hese results inidicate that the compound is niot rea(Oi- 1v absorbed 1y fig leaves or that it nlax nlot be easily tralislocatedl. Externally, the fruits apleared as pollinated onies, btit internally thev were similar t) frulits prodticedl with PCPA or GA. (fig 1). Abscission of the youn-est leaf on shoots that were sprayed with either conicenitratioll of SI) X33() ,3 d, J was the only vegetative response niote(l. Discussion \'ariotis auxiins, gibberellin-like, and kiinetinll-ike substances have been found to occtcr ill fruits: the seeds are partictilarly rich souirces of these materials (9). This informationi, together with the fact that .0~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...... '| X fruit size an(l shape are positively correlated in sev- .!.N.. ..4.g. eral inistances with see(d number anlCI distribution. le(d to the comiimonly accepted view\ that fruit grow\tll anld development are controlled 1yl hormilolnes emianat- *, ...Q inig fromii the see(ls. However, studies of auxinls in general have revealed positive correlationis between their levels and( the dlevelopmlient of thie eildospermi an(l embryo in the see(d btt little or nlo relationislhip) haS *e~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~. been shown between their leve's an(l fruiit gro\wth. Similarly, relatixrely large qtuanitities of gibberellin-like Fio. 1. 1C)Calumnvria figs by produced cross-pollina- substanices have been extracted from votinig see(ds. tioIn and those l)ro(duce(l by aqueous parthenlocarpically In general, a positive correlation wvas found(l between spray of 2) 6 apI)lication ing/liter of Tordon (4-amino-3, growth of the seed and inlcrease in amounllt of 5. 6-trichloropicolinic aci(l), 3) para-chlorophenoxyacetic gibber- ellim-like substances but, as in the case of atixins, no acidl, 4 ) potassium salt ()f gibberellic acid, and( 6) in- bv relationship between levels of these substances anid jection ')f 500 mgiliter of SI) 8339, a kinin. frtuit growth has been (lenlonistrate(l. Kinetini-like activity also has been detected in extracts of various a stirfactanit was niot inceltu(ld( in the spray soluitionl fruits and( particularly their seeds. In most cases, (1,5 ). the highest levels of these substances have been fotund( GA,, as rel)orte(l previously (8), was also very to occur in voting fruiits and it has been stuggested that effective for inidtucinig l)arthenocar)y (table I). As thev mnay be associated with the period of cell (livi- in the case of fruits p)rodtice(I With Tordloln or PCPA, sioni ( 14). Extracts of uinfertilized apples prior to maturity of those produced with GA., also occurred (Irol), as wvell as those of flower petals anld leaves, also about a week earlier than that of pollinated fruits. have been shown to conitaini substances that exhibit 'rhe skin of the fruits was consi(leral)bv more tenider- kinetin-like activity, in(licatilg- that these substances thani that of pollinate(l frulits or those induce(d 1w are nlot necessarily products of the see(ls but may be PCIPA or I'or(lon anid the necks were somew\ hat synthesized in parts of the plant other thani the fruiit. enlarged (fig 1). The internial color was amber and(1 In fact, Goldacre ( 10) presente(l evidenice for a nlo ligniificationi of the endocarp tissuie occurred. l,inetin-like substance originlatinlg in r1oot miieristeniis An undesirable effect of GA\., on the fig is the anid Loeffler and van Overbeek (15) have demon- breaking of the rest period of the termiinal vegetative strated the presence of 5 kinietiln-like materials iii buds with subsequent shoot growth in proportion to bleeding sap of the grape, which id(licates that they the concentration of GA3 applied (8). A concentra- may have been synthesized in the roots. Thus, coni- tion of 25 mg/liter is about the lowest effective one siderable experimental evidence casts doubt onl the CRANE-INDUCED PARTHENOCARPY IN FIG 609 concept of fruit growth being stimulated by hormones of mobilizing centers and the greater is growth and moving out of the seeds via the vascular system or by development of the fruit. diffusion through the testa. The results presented show that different degrees A lack of precise information on the idenltitv of of drupelet development occur in parthenocarpic fig the hormones that occur in seeds and fruits. their fruits depending upon the regulator applie(l to induce dlistribution within these organs, an(l the sites fromii parthenocarpy. Of the 7 auxins that have been which they originiate enahIcs only speculation in re- found to be effective for inducing parthehnocarpy (1, 4, 5, 6), only benzothiazol-2-oxyacetic acid (6) and( gard to the physiological role they play in fruit Tordon, as reported here, produce figs in which ligni- growth. In view of the ability of auxins, GA,, and fication of the drupelet endocarp is similar to that in a kiiiin to induce parthenocarpy in the fig, together pollinated fruits. The fruits produced with the other with evidence reported concerning the action of these auxins, as well as GA3, and the kinini SD 8339, coIn- substanices individually in other connections, the phvs- tain drupelets in which lignification of the endocarp iological role of hormones in fruit growth cou'd very does not occur. Obviously, the effect of benzothia- well be that of mobilizing metabolites into the fruits zol-2-oxyacetic acid or Tordon more closely duplicates from other parts of the plant where they are pro- that of the endogenous auxins in pollinated figs (7). duced. The fact that parthenocarpic figs similar in Various factors might contribute to the differential gross morphology can be produced by the applicationl development of the drupe'ets. As examples. timiie of an auxin, a gibberelliin, or a kinin. demonstrates inidirectly that each of these hormones, should they of regulator application in relation to stage of ovary be essential for fruit growtlh and development, call developmenit, whether or not translocation of the be supplied by some part of the plant other than the regulator into the ovary occurs, or its effect on seeds. This suggests that, although seeds mav conl- vascular developmelnt or oni enzyme activity asso- tain relatively large quantities of one or more of the ciated with lignification miglht be involved. 3 types of hormone at some time during their development, any individual one can initiate the mobili- Summary zation of essential metabolites including other hormones. This property of bringing about mobilization Since parthenocarpic Calinyrnta figs similar in apparently is not unique with hormones that normally gross morphology were pro(luced by the applicatioll stimulate growth but chemicals classed as growth of either an auxin, a gibberelliin, or a kinin, it was retardants apparently can do the same. Coombe (3) demonstrated indirectly that each of these endogenotus recently reported significant increases in berry set of hormonies, should they be required for fruit growth. both parthenocarpic and nonparthenocarpic grape can be somiie of the other cultivars as a result of dipping the clusters 3 weeks supplied by part plant before anthesis in solutions of either 2-chloroethyl- than the seeds. It is proposed that fruit growth is trimethylammonium chloride (CCC) or tributyl-2. not conitrolled by the hormonies emanating frolml the 4-dichlorobenzylphosphoiniunm chloride (Phosfon-D). seeds but. oln the conitrary, by their capacity to at- A mass of evidence showing the ability of fruits tract metabolites from other regionis of the plailt with to mobilize organic and inorganiic substances even at the fruit tissues surrounding the seeds tapping the the expense of vegetative growth has been reviewed metabolite supply and acting as storage organis. by Leonard (11). While the details of the processes The herbicide Tordon appears to offer promise for of mobilization into the fruit remain obscure, there is commercially producing parthenocarpic figs of ac- a growing body of evidence that hormone-directed ceptable quality. transport may be important in the redistribution of nutrient reserves from various parts of the plant to Acknowledgments growing organs (14). That mobilization of metabolites may be a general feature of hormone effect is The assistance of William N. Lipe and James R. Hicks suggested by evidence of this role of hormones in is greatly appreciated. barley seed germination (17) and such phenomena as apical dominance (2), senescence (12), abscission Literature Cited (16), and fruit growth (18). Seeds are relatively rich in hormones anid by vir- 1. BElONDEAU, R. AND J. C. CRANE. 1950. Furtlher tue of this fact apparently act as mobilizationi ceniters studies onl the chemical induction of parthenocarpy with the surrounding fruit tissues utilizing and storing in the Calimityrnza fig. Plant Physiol. 25: 158-68. some of the metabolites that are attracted from other 2. BOOTH, A., J. MOORBY, C. R. DAVIEs, H. JONES, AND parts of the plant. Thus, the asymmetrical growth as- P. F. WAREING. 1962. Effects of indolyl-3-acetic sociated with partial fertilization or with ovule abor- acid on the movement of nutrients within plants. tion in fruits that contain many potential seeds may Nature 194: 204-05. be ascribed to the lack of centers of mobilization in 3. COOMBE, B. G. 1965. Increase in fruit set of Vitis the underdeveloped portions. Conversely, the larger vinifera by treatment with growth retardants. Na- the number of developing seeds the larger the number ture. (In Press). 610 PLANT PHYSIOLOGY

4. CRANE, J. C. AND R. BLONDEAU. 1949. The use 11. LEONARD, E. R. 1962. Inter-relationis of vegetative of growth-regulatiing chemicals to induce partheno- aInd reproductive growth, with special reference to carpic fruit in the Calimnvr;a fig. Planit Physiol. indeterminate plants. Botan. Rev. 28: 353-410. 24: 44-54. 12. ILEorPo.n), A. C. 1961. Senescenice in plant develop- 5. CRANE, J. C. AND R. BLONDEAU. 1951. Hormoln1e- menit. Scienice 134: 1727-32. induced parthenocarpy in the Calimvrina fig and a 13). LEOPOLD, A. C. AND M. KAWVASE. 1964. Benlzyl- coml)arison of parthenocarpic an(I caprified syconiia. adeninie effects on bean leaf growth an(l seniescenice. Plant Physiol. 26: 136-45. Am. J. Botany 51: 294-98. 6. CRANE, J. C. 1952. Ovary-wall development as in- 14. LETHAM, D. S. 1963. Regulators of cell (livision fluenced by growth-regulators inducing partheno- in plant tissues. I. Inhiibitors and stimulanits of carpy in the (Calimprmi fig. Botan. Gaz. 114: 102- cell division in developing fruits: Their propertics 07. anid activity in relation to the cell divisioi l)eriod. 7. CRANE, J. C., M. V. BRADLEY, ANI) L. C. LUCKWILL. New Zealanld J. Botany 1: 336-50. 1959. Auxins in parthenocarpic and nonipartheno- 1 5. LOEFFLER, J. E. AN.D J. VAN OVERBEEK. 1964. Kinini carpic figs. J. Hort. Sci. 34: 142-53. activity in coconlut milk. In: Regulateurs Naturels 8. CRANE, J. C. AND R. C. CAMPBELL. 1962. Breakinig de la Croissance Vegetale. Colloq. Initerni. Cenltre rest and inducinig partheniocarp)y in the Calimyrna Natl. Rech. Sci. Paris. 123: 77-82. fig wvith gibberellin. In: Advances in Horticultural 16. OSBORNE., D. J. AND S. E. Moss. 1963. Effect of Scienice and their Applications. Pergamon Press, kinietini on seniescenice and( abscission inl exl)lants of Nexx York. Vol. 2: 204-09. Plhascolns vdlyaris. Nature 200: 1299-1301. 9. CRANE, J. C. 1964. Growth substances in fruiit 17. PALEG(, L. G., D. H. B. SPARROoW, AND A. JENNING(S. settinig anld development. Ann. Rev. Plant Pllysiol. 1962. Physiological effects of gibberellic acid. IV. 15: 303-26. Oni barley grain with niormal, x-irradiated, anid 10. GOLDACRE, P. L. 1959. Potenitiation of lateral excised embryos. Plant Physiol. 37: 579-83. root inductioni hy root initials in isolated flax 18. WVEAVER, R. J. AND) J. VAN OVERBEEK. 1963. Kini- roots. Aust. J. Biol. Sci. 12: 388-94. ins stimulate grape growth. Calif. Agr. 17: 12.