Storey, W.B.

Pacific Science

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Chromosome Numbers of Some Species of PassijloraOccurring in Hawaii'W.B. STOREy 21 Published with the approval of the Director ofthe Un iversity of Hawaii Agricultural Exper imentStation as Techn ical Paper No. 180.~ ~epa:tment of Horticulture, Uni versity of Ha-wall Agricultural Experiment Station. Manuscriptreceived May 24, 1949.PASSIFLORA IS A GENUS of approximately400 species of plants, mostly woody or herba-ceous vines. About 360 species are native to .tropical and subtropical North and SouthAmerica and adjacent islands. The remainderare indigenous to southeastern Asia, a num -ber of south Pacific islands, and Madagascar(Killip, 1938: 9 ). Man has been instru-mental in disseminating many of the specieswith edible fruits or with highly colored, at-tractive flowers, and . representatives of the:genus are now to be found in most tropicallands throughout the world.Several species of Passifiora have been in-troduced into the Hawaiian Islands for culti-vation for their edible fruits ( Pope, 1935 ).Additional species have been introduced forgrowing as garden ornamentals. A numberof species, both edible and ornamental haveescaped from cultivation and are now' to befound in a naturalized wild state along way-sides, on waste lands, and in lower forestregions ( Pope, 1929: 149 ). A total of 22species has recently been reported as occur-ring in Hawaii (Neal, 1948: 522-525).A number of edible species, of which P.edtllis is the most important , are cultivatedas commercial crops in Australia, Ne w Zea-land, and South Africa, where extensive useis made of the fruit . Their culture is prac-ticed to a lesser degree in various other tropical countries, and in Florida, California, andINTRoDucnoN Hawaii . Numerous ornamental species andspecies-hybrids constitute an important itemin the plant nursery business in the Un itedStates and elsewhere. .Nurserymen have enjoyed some success inproducing interspecific hybrid varieties forthe floricultural trade. Fruit breeders onthe other hand, have had little or no successin attempts to improve upon existing edibletypes through interspecific hybridiza tion ,largely because of hybrid sterility.Cytological studies of plants often serve asa useful adjunct to plant breeding problems.Chromosome numbers and chromosome be-havior frequently indicate origins of speciesa~d relationships between species, and pro-. VIde clues as to which species are most likelyto be compatible upon crossing. Despite theamount of breeding which has been doneamong species of Passifiora, in Hawaii andelsewhere, the genus is but poorly understoodfrom the standpoint of cytology. The recently 'published Chromosome Atlas of CtlltivatedPlants lists the chromosome numbers of onlyseven species (Darlington and ]anaki Am-mal , 1945: 114 ).This paper deals principally with reportingthe chromosome numbers of additional spe-cies of Passiftora as well as of a number ofbotanical varieties and forms, interspecifichybrids, and an intraspecific chromosomalrace. Notes on cytological behavior havebeen added where they might be helpful inclarifying origins or relationships.MATERIALS AND METHODSChromosome numbers ' were determinedfor all species of Passiftora of which materi alfor studycould be obtained in Hawaii. Countswere made from root tips of seedling plants[ 37J3S PACIFIC SCIENCE, Vol. IV, January, 1950or rooted cuttings, and, whenever possible,from suitable flowering material. Root tipswe re stained by t h e crystal-violet-iodinemethod following Randolph 's ( 1935 ) sched-ule. Anthers from young buds were exam-ined in smear preparations with the use ofiron-acetocarmine (Belling, 1926).The figures were drawn with the aid of acamera lucida.forms, 4 interspecific hybrids, and a poly-ploidal race of one species.Six of the seven species listed in the chro·mosome atlas of cultiva ted plants (Darling-ton' and ] anaki Ammal, 1945: 114 ) arereported to occur in Hawaii (Neal, 1948 :522-525 ). These species are P. caerulea 1.,P. edulis Sims., P. foetida 1., P. incarnata 1.,P. quadrangularis 1., and P. racemosa Brot.,all of which are reported to have chromo-OBSERVATIONS some numbers of 2n = 18. The seventhAll species and subspecific forms for which species, P. lutea 1., with a chromosome num-chromosome numbers have been determined ber given as "Zn = 84?," is not known to beare listed in Table 1. They are placed in the in the islands. Of the 22 species listed bytable in the order in which they occur in N eal (lac. cit.), the writer was unable toKillip's (1938 ) systematic treatment of the obtain material of the following seven: P.genus. Interspecific hybrids which are not alata Dry., P. coccinea Aubl., P. entioquienszsincluded in Killip's treatment are placed at Karst., P. k erm esina Link and Otto, P. race-the bottom of the table . The list comprises mosa Brot., P. Bank sii Benrh., P. fruti cosa16 species, 1 botanical variety, 4 botanical Killip . !TABLE 1CHROMOSOME NUMBERS OF VARIOUS SPECIES, SUBSPECIFIC FORMS, AND INTERSPECIFIC H YBRIDSOF Passifl oraPASSIFLORA SPECIES CHROMOSOME NUMBERN 2NP. suberosa 1. 12 24P. suberosa ( trip loid) IS" 36P. lutea 1. ~ ~.. S4?-rP. pulchell« HBK . 6 12P. mollissima ( H BK) Bailey---. ISP. manicata (Juss. ) Pers .. -- . ISP. vitifolia HBK 9 ISP. quadrangularis 1.. ..- ISP. ligularis juss,-- -. ISP. Seemanni Griseb. 9 ISP. malifarmis 1. 9 18P. laurifolia 1. 9 18P. incarnata 1.---- 18P. edulis Sims .. 9 18P. edulis form /lavicarpa Degener . 9 18P. caerulea 1. 9t 18tP. subpeltata Ortega 9 18P. [oetid« 1. 10 20:1:P. [oetid« (3 variant forms ) § 10 20P. foetida variety gossypifolia ( D esv.) Mast . 10 20P. Pjordti ( = alata D ry. X caerulea 1. ).. -..- 18P. maliformis 1. X laurifolia 1.---- 18X P. caerulea 1. ( hybrid) ( D egene r, 1934) . . . . ... . .. 18P. princeps-coccinea (= racemosa Brot. X coccinea Aubl. ) 9t 18t* S ome mei oti c Irregularity.t R eported in Chromosome Atlas. (Da rlingto n a,;,d J anaki Ammal, 1945 : 114) ; not seen by autbor.t Rep?rled as 2n = 18 by. J anak , Ammal ( Da rl in gt on and }anaki Am mal, 1945: 114 ).§ Va riet y or form names, If any, not determined by w riter.Chromosome N umbers of Passi/lora- ·STOREYOn the basis of somatic chromosome num-bers ,which are reported in Table 1 and ofnumbers previously reported in the literature,all of the species, hybrids, and varieties in-vestigated to date may be classified into sixchromosome number groups. Thesegronpsand the species belonging to them are asfollows:2n = 12-P. pulchella2n = 18-P. mollissima; P. manicata; P.vitifo lia; P. quadrangularis; P. ligularis; P.Seemanni; P. maliformis; P. laurifolia; P.maliformis X laurif olia; P. racemose; P. coc-cin ea; P. racemose X coccinea; P. in carnata;P. edulis; P. edulis f. fiavicarpa; P. alata; P.caerulea; P. alata X caerulea (Pfordti); XP. caerulea; P. sub peltata; (P. foetida ?).i n = 20-P. [oetida, and 3 variant forms;P. foetida var. gossypifolia.2n = 24- p. suberosa2n = 36-p. suberosa2n = 84?-P. luteaThe 2n = 12 group consists of but a singlespecies, P. pulcbella.The 2n = 18 group comprises 15 species,4 interspecific hybrids, and 1 botanical form,with 1 species doubtful. Janaki Ammal ( loc.cit. ) determined the somatic chromosomenumber of P. foetida to be 18. The writer,on the other hand , has examined considerablematerial of P. [oetida, its botanical varietvgossypifolia, and several variations, all orwhich occur as common wayside weeds in ./OP5FIG. 1. Mitotic metaphase in P. foetida root tipshowing 20 somatic chromosomes.39Hawaii, and has never failed to find 20somatic chromosomes (Fig. 1). Examina-tions of dividing sporocytes have consistentlyrevealed 10 bivalents normally paired ( Fig.2 ) . The writer, therefore, is disposed to placeP. -foetida in a separate group consisting onlyof itself and its varieties. The possibility isnot excluded, however, that the Hawaiianrepresentatives of the species may be aber-rant forms. P. foetida probably was limited~.•••I. _••lOy>FIG. 2. Meiotic metaph ase I in P. j oetida show-ing 10 bivalent chromosomes. . -to a single introduction from which all ofthe plants presently populating the severalislands are derived.Microsporogenesis was observed to pro-ceed along a normal course in all of the spe-cies in the 2n = 18 group. A single excep-tion was noted in P. subpeltata, in which syn-diploidy occurred in one locule of an anther.The sporocytes in this locule were seen atdiakinesis to have 2 large nucleoli and 18pairs of associated chromosomes instead ofthe usual 9 pairs. There seemed to be nostrong tendency to form multivalent config-urations, and it is supposed that such sporo-cyres would have proceeded to give rise todiploid microspores. The condition veryprobably arose through failure of a mitoticanaphase in the meristem from which thesporogenous tissue was derived.Pope ( 1935 : 11 ) proposed a hybrid ori-gin for P. edulis f. fiavicarpa, possibly as across between P. edu lis and P. ligularis. Thesupposition is nor borne out in studies ofcytological behavior, for meiosis -is normalin every respect ( Fig. 3), and both the ovulesand the pollen grains are fully viable. The40 PACIFIC SCIENCE, Vol. IV, January, 1950secondary association between the bivalentsat the first metaphase ( Fig. 4) . Secondaryassociation in meiosis has been regarded asindicative of . an earlier polyploidal origin( Darlington 1932: 219-223).P. suberosa is also the sole representativeof the 2n = 36 group. This 36-memberedform is undoubtedly an autotriploid deriva-tive of the 24.membered form, constitutinga separate chromosomal race within the spe-cies. There are no conspicuous morphologicaldifferences between the two forms. The onlydistinguishable differences are to be found inthe slightly larger leaves and a slight intens i-fication of anthocyanin pigmentation in theyoung stems and on the dorsal surfaces ofthe sepals of the flowers of the triploid form.The species, however , is highly polymorphic,with all degrees of intergradation among itsnumerous variants , so that 'even these differ-ences are not entirely reliable as a means ofdistinguishing the two races in nature. Thetriploid race appeared spontaneously amongwild populations of the diploid race, the firstcollection being made in 1937. It producesfertile seeds, and has continued to reproduceand spread under natural conditions. Exami -nations of all herbarium sheets of collectionsmade prior to 1937 in the Bernice P. BishopMuseum at Honolulu reveal none whichmight conceivably be the triploid form.Contrary to what might be expected of anautotriploid, triploid P. suberosa goes thronghmicrosporogenesis with a fairly high degreeof regularity and produces a preponderanceof normal quartets of microspores. Mega-sporogenesis must be equally little disturbed ,for the fruit produces a complement of seedsmore or less comparable to that produced bythe diploid. Multi valent chromosome con-o figurations were observed in a few micro-sporocytes, indicating that there is some dis-turbance to normal bivalent pairing. In anoccasional sporocyte, all orders of associationfrom univalence to sexivalence have beenobserved. Anaphasic separation into equal>7/ O y/ O,yFIG. 3. Meiotic metaphase I in P. edulis form/lavicarpa showing 9 bivalent chromosomes.FIG. 4. Meiotic metaphase I in P. suberosashowing 12 bivalent chromosomes. Broken linesindicate pairs of bivalents in secondary association.No flowering material of P. Pfordti, P.maliformis X laurifolw, X P. caerulea, or P.princeps-coccinea could be obtained by thewriter for studies of chromosome behavior atmeiosis in these interspecific hybrids. Allfour appear to be completely sterile.P. suberosa is the sole representative of the2n = 24 group. Microsporogenesis is normalin the species, but there is evidence of strong. "....• •--chromosome number of 18 shows that theplant is not a double diploid, and , therefore,in view of irs full fertility, very probably notan interspecific hybrid. A review of the his-tory of fia1licarpa points to a more probableorigin as a mutation of P. edulis. There areseveral notable differences between typicaledulis and form fiavicarpa, however, includ-ing a high degree of cross incompatibility.The two forms of the species deserve morestudy from the standpoints of both cytology.and genetics.Chromosome Numbers of Passi/lora-SrOREY.numbers appea rs to be effected rather un i-formly despite multivalence, however, fordaughter nuclei were rarel y seen to conta inmore than, or fewer than, 18 chromosomes.There are extremely few abnormal micro ·spore quartets, and corresponding ly few abo r-tive po llen grains.DISC USSIONDarlington and ] anaki Ammal ( 1945 :114 ) give x = 9 as the basic chromosomenumber of the genus Passiflora. This num-ber was doubtless assumed on the basis of6 species with 2n = 18 and one specieswhich was reported as "2n = 84 ? " Deter-mination of n = 6 for P. pulchella indicatesthat not 9 but a lower number pro bably isbasic in the genus. W ith the exception ofthe aberrant species. P. foetida (2 n = 20 j ,all of the species examined, including P. lut tJa( 2n = 84?), comprise a polyploid series ofwhich the monoploid number is 6. It is rec-ognized that the total of 29 species and vari-ant forms for which chromosome numbersare known or presumed is but a meager sam-ple from a genus with over 400 known spe-cies so it seems not unreasonable to supposethat other numbers, both euploid and aneu-ploid, may exist among species unreportedhere.It is perhaps sign ificant from the breeders'standpoint that all of the hor ticultural formsstudied occur in the 2n = 18 group. Theseform s exhibit a fairly high degree of inter-specific compatibility, as evidenced by thenumerous hybrids recorded (Bailey, 1935 :2487); but the hybrids themsel ves are almostinvariabl y .sterile. Their compatibility sug-gests closeness in rela tionship and, possibly,a common origin.With an assumed basic number of x = 6for the genus, the species in the 2n = 18group must be regarded as triploids. Tri-ploidy, however, is generally considered to bea hindrance to the origin of fert ile speciesbecause of the high order of meiotic irregu-41larity which it induc es. It seems unlikely,the refore, that the maj ority of species exam-ined, a ll of which are fertile, have origina tedthrough triploidy, An assumed basic numberof x = 3 would afford a number of motenearl y reasonable explanations of the originof 2n = 18 species. These species could thenbe regarded as hexaploids of more or l essancient origin. As has occurred in manypolyploid species of plants, cytological evid-ence of genomic composition has disappearedin the course of speciation and stabilizationexcept in chromosome numbers.H ow speciation within a group could occuris illustrated by the mutation from P. edulisto the form flavicarpa. The nature 'of themutat ion has not been studied, but when itoccurred it must have been drastic. The formdiffers from the species in several foliar andstem characters. The fruit is yellow insteadof purple, and the seeds are brown insteadof black. In addition, the flowering habit hasbeen modified from strictly diurnal to partlynocturnal, and a barri er of almost completeincompatibility seems to have arisen betweenthe mutant form and the species from whichit is presumed to be derived. As mentionedearlier, the hybrid origin which was suspectedby Pope (1935 : 11 ) is not borne out bycytological studies.P. foetida (2 n = 20) and its varietiesmake up a group divergent from the euploidseries to which all other species examinedbelong. Cytological studies to date have pro-vided no clue to its probable origin. The .possibiliti es exist either that it arose as a sec-ondary polyploid from a 2n = 18 species orthat it belongs to a second euploid series, per-haps ~ith a monoploid number of 5, forwhich additional species have yet to be dis-covered. If the plants growing in Hawaii, aretruly representative of the species, ] anakiAmmal's (loc. cit.) determination of 2n =18 as the chromosome number mu st be con-sidered to be in error.42As·noted earlier , strong secondary associa-tion in P. suberosa (2n = 24 ) is taken asindicative of its polyploidal origin. The 36-membered form undoubtedly originated fairlyrecently as an autotriploid as shown by theabsence of marked morphological differencesin plant characters. It is supposed that tri-ploidy resulted in the species through themating of an unreduced gamete with a nor-mal, reduced gamete. How the unreducedgametes might have been produced is. sug-gested by the case of syndiploidy observed inan anther of P. subpeltata.The occasional . occurrence of all degreesof multivalence up to and including sexi-valence lends credence to the supposition thatthe 2n = 24 form is itself polyploid, at leasttetraploid if not of it higher order of poly-ploidy, and that the derived form is at leasthexaploid . The presence of 6 genomes, al-though bringing about some slight degree ofirregularity in meiosis, allows for more orless normal anaphasic separation into twogametic 18-chromosome complements.CONCLUSIONThe study has shown that th~ basic chro-mosome number for the genus is at most x =6, and may possibly be x = 3, rather than x= 9 as indicated by Darlington and janakiAmmal (1945 : 114) . It has also calledattention to the discrepancy in chromosomenumber determinations for P. foetida. It isthought by the writer that the aneuploidnumber of P. foetid a presages the existenceof another euploid series in the genus. Thedeterminations made bring to 29 the numberof species and variant forms for whichchromosome numbers are known or may beassumed from the composition of varioushybrids.It seems highly probable that there mayexist chromosome numbers other than thosereported here among the 300-odd species ofPassiflora which have not been examined.PACIFIC SCIENCE, Vol. IV, January, 1950Studies of a greater number of species morefully representing the recognized taxonomicgroups and of additional interspecific hybridmaterial would aid considerably in determin-ing origins and relationships within the ge~1Us .REFERENCESBAILEY, 1. H. 1935. T he standard cyclo-pedia of borticelture. 3 vols. xxiv + 3639pp., 4056 figs., 120 pls , The MacmillanCompany, New York.BELLING, J . 1926. The iron-acerocarminemethod of fixing and staining chromo-somes. Bioi. Bul. 50 : 160-162.DARLI NGTON, C. D. 1932. R ecent advancesin cytology. xviii + 559 pp., 109 figs. , 8pls, P. Blakiston's Son and Company, Inc., .Phil adelphia.--- and E. J ANAK! A MMAL. 1945 .Chromosom e atlas of cultivated plants.397 pp. George Allen and Unwin, Ltd.,London.DEGENER, O. 1932-1934. Flora Hawaiien-sis. (Looseleaf), illus. Author, Honolulu.KILLIP, E. P. 1938. T he A m erican speciesof Passifloraceae. Field Mus. Nat. H ist.,Bot. Series 19, parts 1 and 2, publ. No.407 and 408, 613 pp~, 2 figs. Chicago.N EAL, MARIE C. 1948. In gardens of Ha-waii. 805 pp ., 312 figs. Bernice P. BishopMus. Honolulu.POPE, W . T. 1929. Manual of waysideplants of Hawaii. 289 pp., 160 pls, Ad-vertiser Publishing Company, Ltd., Hono-lulu.1935. The edible passion fruit inHawaii. · Hawai i Agr. Expt, Sra., Bul. 74.22 pp., 7 figs.RANDOLPH, 1. F. 1935. A new fixing fluidand a revised schedule for the paraffinmeth od in cytology. Stain T ech. 10: 95.

Chromosome Numbers of Some Species of Passiflora Occurring in Hawaii

Storey, W B

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Chromosome Numbers of Some Species of Passiflora Occurring in Hawaii

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