POLLEN FLOW IN DIMORPHIC TURNERA SUBULATA (TURNERACEAE)

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1 New Phytol. (1984) 98, POLLEN FLOW IN DIMORPHIC TURNERA SUBULATA (TURNERACEAE) BY N. RAMA SWAMY AND BIR BAHADUR Department of Botany, Kakatiya University, Warangal , India (Accepted 23 April 1984) SUMMARY Turner a subulata J. E. Smith is heterostylous with pin and thrum flower forms and is self-incompatible but cross-compatible. Pin and thrum flowers produce the same number of grains. Only 3-07 % of the produced participates in the pollination. Pin stigmas receive an average of 425 grains and thrums 327. Stigmas of pin flowers receive more thrum than pin grains. Thus in compatible pollinations, flow from the thrum to the pin form was greater than in the reverse direction. Key words: Pollen flow, heterostyly; Turnera subulata. INTRODUCTION Darw^in (1862) hypothesized that the seed production in the two floral morphs of distylous plants might be related to the number of grains that reach the stigmas. In recent years, investigations have been carried out on flow in several di- and tri-stylous species to test the Darwinian (1862) hypothesis [Lithospermum caroliniense (J. F. Gmelin) MacM. (Levin, 1968; Weller, 1980), Amsinckia grandifiora Kleeberger (OrnduflF, 1976), Pulmonaria obscura Dumort (Olesen, 1979), Hypericum aegypticum L. (Ornduff, 1975), Hedyotis caerulea (L.) Hooker (OrnduflF, 1980a), Jfepsonia parryi Torr. (OrnduflF, 1975), Primula veris L. (OrnduflF, 1980b), Lythrum salicaria L. (Mulcahy and Caporello, 1970) and Cratoxylum formosum (Jack) Dyer (Lewis, 1982)]. Although some work has been done on various aspects of heterostyly and incompatibility in Turnera subulata J. E. Smith (Rama Swamy & Bahadur, 1981; Bahadur & Rama Swamy, 1982; Rama Swamy, Bahadur & Arthi, 1983a, b; Rama Swamy & Bahadur, 1983; 1984a), T. ulmifolia L. (Martin, 1965; Barrett, 1978), T. trioniflora Sims (Bentley, 1979) and Piriqueta caroliniana (Walt.) Urban (OrnduflF & Perry, 1964) to date there is no study that deals with flow in any distyious species of Turneraceae. In this paper, we report flow within a natural population of T. subulata. MATERIALS AND METHODS The present investigations were carried out on a natural population of T. subulata growing in Kakatiya University Campus, Warangal, India, in October Total production of the two flower forms was determined by acetolysing undehisced anthers and estimating the total number of grains per flower by the use of a haemocytometer. Observations were made 0 h after flower opening (06 to 07 h). To study the at diflferent times the excised stigmas were collected separately from pin and thrum flower forms at diflferent time X/84/ $03.00/ The New Phytologist

2 2o6 N. R A M A S W A M Y AND B. BAHADUR intervals (0" to 4 h) and stored in aceto-alcohol (1:3 mixture). The stigmas were mounted in lacto-phenol and lightly stained with aniline blue. The total number of grains that had been transferred to the stigmas (i.e. whether from pin/thrum flowers) were determined since the grains from both the flower forms exhibit strong size dimorphism as well as distinct exine characters (Rama Swamy & Bahadur, 1983). RESULTS AND D I S C U S S I O N Pin flowers produce an average of grains and thrums an average of grains per flower. Thus production in both the flower forms of T. subulata is equal despite the fact that the thrum anthers and the grains are larger than those of pin (Rama Swamy & Bahadur, 1981). Ornduflf (1970), however, observed more pins than in thrums oijepsonia heteranda Eastw. The total production in both the forms of T. subulata is 28845, but the stigmas of the two flower forms together receive an average of 1079 grains (Tables 1 and 2). From this it is obvious that only 3-07 % of produced in the pin/thrum population is transferred to pin/thrum stigmas and % of is removed by the insects and used either for food or smeared on the body of vectors. The data on s of thrum and pin stigmas at various time intervals (see Tables 1 and 2) show that the total number of grains on both the flower forms steadily increased from the time of opening. This was related to the number of insect visits which increased steadily during the day. The active floral visitors and pollinators are Apis cerana indica, Calliphora erythrocephala and Bombus sp. 4 h after flower opening the maximum number of grains observed on thrum and pin stigmas, respectively, were 145 (44%) and 0 (40%), The data in Tables 1 and 2 also show that the pin stigmas of T. subulata bore 61 % (460) thrum grains and 39% (292) pin grains whereas thrum stigmas bore 40-5 % (150) pin grains and 59-5 % (177) thrum grains. Similar differences were observed in Jepsonia parryi (Ornduff, 1970), J. heteranda, (Ornduff, 1971; Ganders, 1974), Hypericumaegypticum{Ornduf[, 197S),Amsinckia grandiflora (Ornduflf, 1976), Lithospermum caroliniense (Levin, 1968) and Pulmonaria obscura (Olesen, 1979). The only study where more pin grains (94%) were found on pin than on thrum stigmas is that of OrndufT (1980a) in Hedyotis caerulea (Rubiaceae). A large proportion of incompatible (illegitimate) grains (54%) has been recorded on thrum stigmas of T. subulata. These findings are different from those in J. parryi where Ornduff (1970) observed a higher percentage of incompatible grains (77-8%) on the pin than on the thrum stigmas (27-1 %). Ornduff (1980a) has also noted in Hedyotis caerulea that 11 of the 13 pin s contained more pin grains (53 to 80%) and nine of the 13 thrum s contained a predominance (54 to 73 %) of pin grain. Weller (1980), however, observed that more incompatible is deposited by pollinators on both pin and thrum stigmas of Lithospermum caroliniense. Thus the s on pin stigmas of T. subulata exceeded those on thrum stigmas in the ratio of 1:2, i.e. 327:752. This excess has been attributed to the greater accessibility of pin stigmas to pollinators. The ample supply of compatible (legitimate) which the pin stigmas receive possibly accounts for their good seed production (for details Rama Swamy & Bahadur, 1981).

3 Pollen flow in Turnera subulata 207 Table 1. Composition of s observed on stigmas of pin flowers of Turnera subulata Time (h) Number of flowers sampled Total size of stigmatic of pin of thrum Percentage of thrum grains Total Table 2. Composition of s observed on stigmas of thrum flowers of Turnera subulata Time (h) Number of flowers sampled Total size of stigmatic of pin of thrum Percentage of thrum grains Total The present study clearly suggests that the pollinators preferentially remove thrum from the population of thrum plants of T. subulata. This could well be related to the greater accessibility of thrum anthers of T. subulata to pollinators than those of the pin which are located at the base of the flower (Fig. 1) (see also OrnduflF, 1975). However, only 46% of the pin is involved in legitimate pollinations in comparison to 61 % of the thrum in T. subulata. Weller (1980), however, found a low percentage of involved in legitimate pollinations and stated, ' This perhaps accounts for lack of participation in legitimate crosses'. Thus, it is evident that the heterostyly in T. subulata prevents self-pollination within flowers and therefore is advantageous not only in promoting flow within the two floral morphs but in maintaining the balanced polymorphism which is controlled by an 5-gene complex (Rama Swamy, 1982). Although only a small percentage of the total produced by T. subulata actually becomes available for fertilization; it is more than suflficient to produce a large number of seeds per flower (Rama Swamy & Bahadur, 1981; Rama Swamy, 1982).

4 2O8 N. RAMA SWAMY AND B. BAHADUR Fig. 1. Camera lucida drawings showing thrum (a) and pin (b) forms of Turnera subulata after the removal of sepals and petals. The pollination relationship between thrum and pin flowers is also shown. Arrows with solid lines indicate compatible pollinations and the figures in the unshaded sector of the circles indicate the percentage of participating in these pollinations. Arrows with broken lines indicate incompatible pollination and the flgures in the shaded sector of the circles indicate the percentage of participating in these pollinations. Scale = 9 mm. ACKNOWLEDGEMENT We are grateful to Professor D. Lew^is, FRS for his interest and encouragement. N.R.S. is grateful to the Council of Scientific and Industrial Research for the award of a Post-Doctoral Fellowship. REFERENCES BAHADUR, B. & RAMA SWAMY, N. (1982). Biochemical changes in the pistils of distylous Turnera subulata J. E. Smith (Turneraceae) following self- and cross-pollinations. Journal of Palynology 18, BARRETT, S. C. H. (1978). Heterostyly in a tropical weed: the reproductive biology of the Turnera ulmifolia complex (Turneraceae). Canadian Journal of Botany, 56, BENTLEY, L. B. (1979). Heterostyly in Turnera trioniflora, a roadside weed of the Amazon Basin. Biotropica, 11, DARWIN, CH. (1862). On the two forms, or dimorphic conditions in the species of Primula and on their remarkable sexual relations. Botanical Journal of Linnean Society, 6, GANDERS, F. R. (1974). Disassortative pollination in the distylous plant Jepsonia heteranda. Canadian Journal of Botany, 52, LEVIN, D. A. (1968). The breeding system of Lithospermum caroliniense : Adaption and counter adaption. American Naturalist, 102, LEWIS, D. (1982). Incompatibility, stamen movement and economy in a heterostyled tropical tree, Cratoxylum formosum (Guttiferae). Proceedings of the Royal Society of London, B, Biological Sciences, 214, MARTIN, F. W. (1965). Distyly and incompatibility in Turnera ulmifolia. Bulletin of the Torrey Botanical Club. 92, MuLCAHY, L. D. & CAPORELLO, D. (1970). Pollen flow within a tristylous species: Lythrum salicaria. American Journal of Botany, 57, OLESEN, J. M. (1979). Floral morphology and flow in the heterostylous species Pulmonaria obscura Dumort. (Boraginaceae). New Phytologist, 82,

5 Pollen flow in Turnera subulata 209 ORNDUFF, R. (1970). Incompatibility and the economy of jfepsonia parryi. American Journal of Botany 57, ORNDUFF, R. (1971). The reproductive system of Jfepsonia heteranda. Evolution, 25, ORNDUFF, R. (1975). Heterostyly and flow in Hypericum aegypticum (Guttiferae). Botanical Journal of Linnean Society, 71, ORNDUFF, R. (1976). The reproductive system of Amsinckia grandifiora, a distylous species. Systematic Botany, 1, ORNDUFF, R. (1980a). Heterostyly, population composition, and flow in Hedyotis caerulea. American Journal of Botay, 67, ORNDUFF, R. (1980b). Pollen flow in Primula veris (Primulaceae). Plant Systematics and Evolution ORNDUFF, R. & PERRY, J. D. (1964). Reproductive biology of Piriqueta caroliniana (Turneraceae). Rhodora 66, RAMA SWAMY, N. & BAHADUR, B. (1981). Heterostyly and incompatibility in Turnera subulata J. E. Smith (Turneraceae). Incompatibility Newsletter {Netherlands), 13, RAMA SWAMY, N. (1982). Studies on Heterostyly and Incompatibility in Distylous Turnera subulata^ E. Smith (Turneraceae). Ph.D. thesis, Kakatiya University, Warangal {A.P.), India. RAMA SWAMY, N., & BAHADUR, B. (1983). Pollen tube growth studies in self- and cross-pollinated pistils of distylous Turnera subulata J. E. Smith (Turneraceae). Journal of Biological Research, 3, RAMA SWAMY, N. & BAHADUR, B. (1984a). Unilateral interspecific hybridization between Turnera ulmifolia (9) X T. subulata (Turneraceae). Indian Journal of Botany, 7 (in press). RAMA SWAMY, N. & BAHADUR, B. (1984b). LM and SEM studies of in distylous Turnera subulata J. E. Smith (Turneraceae). Proceedings of 3rd Indian Palynological Conference, HAU (Hissar), Allied Publishers (in press). RAMA SWAMY, N., BAHADUR, B. & ARTHI, C. (1983a). Effect of mentor on self-incompatibility in heterostylous Turnera subulata J. E. Smith (Turneraceae). Incompatibility Newsletter {USA), 15, 7-8. RAMA SWAMY, N., BAHADUR, B. & ARTHI, C. (1983b). Overcoming self-incompatibility in distylous Turnera subulata J. E. Smith (Turneraceae): Bud pollinations and tube growth studies. Incompatibility Newsletter {USA), 15, 8-9. WELLER, S. G. (1980). Pollen flow and fecundity in populations of Lithospermum caroliniense. American Journal of Botany, 67,

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