PALMS Sudhersan e t a l . : Haoaxan th i c Da te Pa lm Shoo ts Volume 45(2) 2001

HapaxanthicAxillary Shootsin Date PalmPlants Grownin vivo and in

Date palms are propagated sexually by seeds andvegetatively by offshoots or t issue cultureplantlets. Both the tissue culture plantlets and theseedling palms resemble each other in growth anddevelopment in the field except that seedlingsstart with juvenile leaves while the offshoot-derived palms start with adult leaves. Axillaryshoots are produced during the early vegetativephase prior to the onset of flowering in the fourthyear. However, axillary shoots may develop duringthe reproductive phase in certain cultivars. Theseaxillary shoots are called racoobs, and they develophigher up on the tree.

During our 15 years of experience with in vitro andin vivo date palm growth and development, weobserved a third type of axillary shoot in additionto the offshoots and racoobs. These peculiaraxillary shoots are morphoJogically different fromthe normal offshoots and racoobs. These axillarv

C. SuournsAN, M. AsoEL-N[

AND J. HUSSem

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shoots are hapaxanthic, i.e., they produce terminalinflorescences after one or two years of growthand die. This phenomenon is common in bothtissue culture palms and seedling palms duringtheir second or third year of growth in the field.

Vegetative proliferations from inflorescences orfrom floral sites has been reported in many palms:Cocos (Davis 1948,1967; Balaga 1975; Sudasrip etaI.1978), Elaeis (Hemy & Scheidecker t953), Arecacatechu (Davis 1968) and Borassus (Davis & Basu1969).ln rare instances, the apical meristein of theflower bud proliferates to form floral or vegetativeorgans (Eames 1961; Padmanabhan et al. 7987).Recently Mohamed (1997) reported on axillaryshoots that terminated in inflorescences in thedate palm cultivar 'Mishring wad-khatib.' Weobserved hapaxanthic shoots of several date palmcultivars in vitro and in vivo. The details of ourobservations are presented in this paper.

vitroDate palm (Phoenix dactylifera L.) produces axillary shoots from axillary shoot meristems

and inflorescences from floral meristems. Axillary shoots are produced during the early

vegetative growth period and cease when flowering starts after three years. A few axillary

shoots produce terminal inflorescences and die. These flowering shoots are termed

hapaxanthic axillary shoots and appear in seedling palms and tissue culture palms

during the second or third year of vegetative growth. The production of hapaxanthic

shoots does not affect the normal growth of the mother tree.

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PALMS Sudhersan e t a l . : Hapaxan th i c Da te Pa lm Shoo ts Vo lume 45 (2 ) 2001

Observations

Hapaxanthic axillary shoots (HAS) were observedin tissue culture date palm (Figs. 1, 2) cultivars'Maktoomi,' 'Nebut-seif, ' 'Succari, ' 'Barhi, ' 'Munifi '

and 'Sheshi' Oable 1). The same ohenomenon wasalso observed in several seedling palms (both maleand female) grown for landscaping. Thesehapaxanthic axil lary shoots (Fig. 3) wereperiodically removed from the mother plant anddissected out in the laboratory for observation(Figs. 3-12).

Morphologically, these axil lary shoots weredistinct from offshoots andracoobs. They produced2-8 basal leaves with a full complement of leaflets,followed by 2-3 leaves with few leaflets at the tipfollowed by 3-5 cataphylls (Fig. 5). These shootsgrew for a yeat or two and produced terminalinflorescences (Figs. 7, 8). Some of them producedinflorescences at their basal leaf axils (Fig. 9). Theinflorescence axis was cylindrical and taperingtowards the end (Figs. 7, 8). There was no prophyllcovering the inflorescence at the early devel-opmental stage. Each inflorescence axis had severalnodes with bracts or scale leaves (Figs. 10-12). Thebasal bracts were larger, and the upper ones weregradually reduced to a smaller size. Some of theinflorescence axes produced flowers at all thenodes (Figs. II, 72), some flowered only at basalnodes and some did not produce any flowers (Figs.7, 8). There was no rachilla development, but someinflorescences showed small branches with flowerbuds at the basal nodes (Fig. 10). The inflor-escences emerged with 4-15 flowers. The flowerswere normal and produced parthenocarpic fruits.Some of the poll inated ones produced normalfruits with seeds.

Terminal inflorescences were induced to form ondate palm seedlings in vitro, when cultures weresupplemented with indole acetic acid (IAA), benzylaminopurine (BAP) and sucrose (Ammar et al.1987). The same growth regulators (IAA and BAP)and sucrose did not induce floral bud formationin plantlets induced via embryogenesis in calluscultures (personal observations). Among the datepalm plantlets produced in cultute, 0.1olo producedflowers (Fig. 13). Some of the in yltro floweredplantlets were hapaxanthic (Figs. 14, 15). A fewplantlets produced terminal inflorescences and

some with axillary shoots terminated in inflor-escences. After producing flowers the plantletslived for a month or two and then died.

Discussion

Hapaxanthic axillary shoots (HAS) were observedas a common phenomenon among seedlings andtissue culture derived palms growing underregularly irrigated soil conditions. None of theplants that we observed produced this type ofshoot during the reproductive phase. Occurrenceof HAS during the juvenile stage in both tissuecultured and seedling palms indicated that it ishighly related to the juvenile stage. Each palmproduced one or two such shoots during thesecond or third year of the vegetative Srowth. HASwere rare among the palms developed from theoffshoots.

The developmental pattern of HAS was similar tothe development of terminal inflorescences inbanana. After one year of vegetative growth, thenumber of leaflets per leaf diminished, and theleaflets finally became cataphylls (without leaflets).Later the meristem terminated in an infloresencewithout bracts or rachillae. Since the earlier growthwas similar to the normal offshoot growth, it isclear that the shoot meristem later converted intoa floral meristem. This developmental pattern wasalso confirmed by the plantlets growing in cultureshowing the similar HAS phenomenon. Ourpresent study confirmed that HAS productionoccurs not only in tissue culture plants but alsoin seedling palms. These shoots died after thedevelopment of terminal inflorescences withoutaffecting the growth of the mother plant. Furtherdetailed study is needed to find out the real causeof the development of hapaxanthic axillary shootsin date palm.

LrrERaruRE Crrp,l

Anavan, S., A. BrNsaDrs AND B.K. Tnrp.qrut. 1987.Floral induction in date palm seedlings (Phoenixdactylifera L. Var. Deglet Nour) cultured in vitro.Canadian Jour. Bot. 65: 737-742.

BALAGA, H.Y. 1975. Induction of branching incoconut. Philippine Jour. Biol. 4: 35-74O.

D.wrs, T.A. 1948. Abnormal palms of TravancoreIII. A bulbilliferous coconut palm Cocos nucifera

Thble 1. Different date palm cultivars and percentage of hapaxanthic axillary shoots (HAS).

Cultivar'Maktoomi''Nebut-seif''Barhi''Shesi''Munifi'

Seedling palms

No. of plants observed303020207 Z170

No. of plants with HAS27241 nL L

zo8

78

o/o of plants with HAS90806010066.745.9

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P A L M S Sudhersan e t a l . : Hapaxan th i c Da te Pa lm Shoo ts Volume 45(2) 2001

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1. Tissue culture date palm showing hapaxanthic axi l lary shoot. 2. Hapaxanthic axi l lary shoot showing inf lorescenceoroduced at the basal leaf axil.

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PALMS Sudhersan e t a l . : Hapaxan th i c Da te Pa lm Shoo ts Vo lume 45 (2 ) 2001

3. lsolated hapaxanthic axillary shoot. 4. Partly dissected out hapaxanthic shoot. 5. Dissected out leaves.

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6. Seedling date palm with hapaxanthic axi l lary shoot. 7. Hapaxanthic axi l lary shoot with terminal inf lorescence. 8.Dissected out shoot with terminal inf lorescence. 9. Hapaxanthic axi l lary shoot with inf lorescence at i ts basal leaf axi l . 10.Inf lorescence axis scale leaf and a small inf lorescence branch with f lower bud. 1 1 . Inf lorescence axis showinq female f lowerat its basal swollen node. 'l 2. Terminal inflorescence with flowers.

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13. Date palm plantlet showing normal inf lorescence produced in culture. 14. ln vitro grown plantlet with terminalinflorescence. 15. Dissected out in vitro plantlet showinq terminal inflorescence with flowers.

L.) Jour. Bombay Nat. Hist. Soc. 47: 527-529.

Davrs, T.A. 1967.Foliation in coconut spadices andfl owers. Ol6agineux 22:79-23.

Davrs, T.A. 1968., Phyllody of the spadix in Arecacatechu L. Sci. Cult. 34: 456-458.

Davrs, T.A. aNo S.K. B,q,su. 1969. Two cases of butbitbearing Borasus flabellifer L. Jour. Ind. Bot. Soc.48:798-201.

HrNnv, P. .qNr D, ScHEIlpcrEn. 1953. Nouvellecontribution d l '6tude de Elaeis vivipares.Ol6agineux 8: 681-688.

MoH,qnrD, M.E. 1.997. Observations of abnormaldevelopmental patterns of axillary buds in datepalm (Phoenix dactylifera). Principes 4\: 52-53.

PanNraNasr{aN, D., C. SurHERsaN AND A.Ra.JavanreNoav. 1987. Floral proliferation infruits of Borassus flabell ifer L. Jour. SwamyBotanical. Club 4: 97-98.

Eeltls, AJ. 1961. Morphology of Angiosperms. Suo,+snlr', H., H. Ka,u aNl A. Davrs. 1978. ClonalTata McGraw-Hill luUtistring Co. Ltd., New : propagation of the coconut via bulbils.Delhi, pp. 257. Phil ippine Jour. Coc' 3: 865-879.

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