Floral biology of Torilis ieptophylla (L.) Reichenb. f.

Transcription

1 Proc. lndian Acad. Sci. (Plant Sci.), Vol. 93, No. 4, September 1984, pp Printed in India. Floral biology of Torilis ieptophylla (L.) Reichenb. f. PUSHPA KOUL, A K KOUL and I A HAMAL Department ofbiosciences, University of Jammu, Jammu , India MS received 13 June 1983; revised 14 February 1984 Abstract. Torilis leptophylla, an andromonoecious umbellifer, practises a blend of geitonogamy and outbreeding. Although it exhibits strong dichogamy at the level of individual flowers, in the full plant, pistillate and staminate phases overlap. The ratio of hermaphrodite to staminate flowers is 0.37 which is intermediate to those recorded for other andromonoecious umbellifers. Keywords. Torilis leptophylla; andromonoecious; geitonogamy. 1. lntroduction To understand patterns of genetic variation in natural populations, knowledge of breeding system biology is necessary. While some plant families exhibit uniformity in breeding system, others such as Umbelliferae (Apiaceae) include hermaphrodite, andromonoecious, gynodioecious and dioecious taxa which follow varied modes of reproduction. Braak and Kho (1958), Bell (1971), Kumar (1977), Lovett Doust (1980) and Webb and Lloyd (1980) have studied some umbellifers from this angle but the majority still await investigation. The present communication describes certain aspects of the breeding system of Torilis leptophylla, a common weed in Kashmir Himalayas from 1600 to 1900m. 2. Material and methods Floral biology and umbel constitution was determined from live plants from June to August The proportion of hermaphrodite and staminate flowers was determined for whole plants as well as at the level of um[jel orders. The percentage of hermaphrodite and staminate flowers and the ratio between them have been worked out according to Lovett Doust (1980). Fruits formed in umbels of different orders were counted and percentage fruit set calculated. Floral biology, flower morphology and anthesis were studied at different time intervals. The number of pollen grains produced per anther was counted using aniline blue and lactophenol. Pollen-ovule ratios were then calculated for hermaphrodite flowers (which have 5 anthers and two ovules) and for individual plants when the pouen cont of male flowers was also included in the estimation. 3. Results Plants cm tall, hispid, annual herbs; leaves two pinnate, segments linearlanceolate; peduncles short, 2-4 cm in length, involucel of several linear bractlets. The p~ 4 449

2 450 Pushpa Koul, A K Koul and I A Hamal plants are andromonoecious with hermaphrodite and staminate flowers borne within the same umbel. 3.1 Inflorescence The ultimate branches as wetl as the main stem terminate in ah umbel which consists of 3-7 umbellets. Umbels up to third (tertiary) and rarely fourth (quarternary) order are produced. The percentage of umbels of different orders in an individual are: p 8.51, secondary: 31-91, tertiary: and quarternary: Each umbellet bears hermaphrodite flowers at periphery and staminate flowers in the centre (figures 1, 2). 3.2 Floral morphology The hermaphrodite flowers have a zygomorphic corolla. Of the petals in a flower, one is large, two are small and other two are intermediate in size. The five stamens alternate with the petals. Anthers are dorsifixed. Pistil is bicarpellary and syncarpous. The ovary is infe bilocular and bears a pendulous ovule in each locule. The ovary is capped by a bulbous stylopodium from which emerge two styles (figures 3, 4). Except for their smaller size and the absence of pistil and petal symmetry, the staminate flowers resemble their hermaphrodite counterparts in all respects (fgures 5, 6). 3.3 Anthesis The inflorescence differentiates within the leaf sheath. As it emerges, the umbellets fan out in sequence. Flowers of the primary umbel are first to bloom, followed by those of the secondary, tertiary and quarternary umbels. In each umbellet, the hermaphrodite flowers mature earlier than the staminate flowers. An umbel takes 4-6 days (mean ) to bloom. In hermaphrodite flowers, the stamens mature earlier than the pistil so that the species is protandrous. The stigrna becomes receptive much later, when all anthers have dehisced. The anther dehisces through two longitudinal slits. When flowers in second order umbel start opening, the stigmas of the flowers of order umbel are still receptive. The same sequence is repeated in subsequent umbel orders as well. 3.4 Proportion of hermaphrodite and staminate flowers In a mature plant, the number of staminate flowers exceeds that of hermaphrodite flowers (table 1); the average ratio is 0.37 (1 hermaphrodite: 2.73 staminate). The proportion of staminate and flowers va in umbels of different orders and this variation is reflected in fruit set as well (table 2). The percentage fruit set is maximum in primary umbel and it progressively decreases in umbels oflower orders. 3.5 Pollen-ovule ratio In andromonoecious species, pollen grains are formed in both flower types, but ovules are produced by hermaphrodite flowers only. The mean total number of pouen grains produced per hermaphrodite flower is 5,301 ( ) against a total of 2 ovules. The

3 Floral biolo9y of T. leptophylla 451 I 3 ~st 4 5 ' Imm 6 Figures Diagrammatic representation of the arrangement of hermaphrodite flowers (blank circles) and staminate flowers (solid eireles) in (1) umbel, and (2) umbellet; 3. Hermaphrodite flower bud with ineurved stamens; 4. Hermaphrodite flower with its parts exposed; 5. Staminate flower bud; 6. Staminate flower showing redueed stylopodium and relatively smaller petals (St = Stylopodium). pouen-ovule ratio for a hermaphrodite flower is ; but, for whole plant, the ratio averages to Discussion Like other andromonoeeious umbellifers, Torilis leptophylla too exhibits variation in the proportion of hermaphrodite and staminate flowers in umbels of different orders.

4 452 Pushpa Koul, A K Koul and I A Hamal Table 1. Mean values for staminate and hermaphrodite flowers and fruit set in a plant. * Character Total no. of flowers No. of hermaphrodite flowers Percentage of hermaphrodite flowers No. of staminate flowers Percentage of staminate flowers Ratio of +~ : c~ flowers Total no. of fruits formed Percr fruit set of +~ flowers Frequency ( ) l ( ) ( ) ( ) ( ) ( ) ( ) * Mean of 20 determinations; values in parentheses represent ranges. Table 2. Quantitative data (mean +sd) on stammate and hermaphrodite flowers and fruit set in umbels of different orders. Umbel order Character Primary Secondary Tertiary Quarternary No. of umbr studied Total no. of flowers (94-124) ( ) ( ) (29-60) No. of hermaphrodite flowers (34-59) ( ) (91-195) (5-19) Pementage of hermaphrodite flowers ( ) ( ) ( ) ( ) No. of staminate flowers (60-76) ( ) ( ) (24-41) Percentage of staminate " flowers ( ) ( ) ( ) ( ) Ratio of ~ ~ flowers Total no. of fruits formed (34-59) (97-160) (83-160) (0-8) Percent fruit set of ~ flowers ( ) ( ) ( ) Values in parentheses represent the rangos.

5 Floral biology of T. leptophylla 453 In some taxa such as Daucus carota there is a gradual decrease in frequency of hermaphrodite flowers in lower order umbels (Bell 1971). Others like Scandix pectenveneris show a decrease in second order umbels fouowed by an increase in umbels of lower orders, the last formed umbel again showing der (author's unpublished data). In Anthriscus sylvestris, Pastinaca sativa and Smyrnium olusatrum, there is gradual but continued decrease with the last formed umbels producing only male flowers (Lovett Doust 1980). In T. leptophylla, the highest pereentage of hermaphrodite flowers exists in primary, followed by a gradual decrease in lower order umbels. In each umbel order, the male or polliniferous flowers outnumber their bisexual eounterparts. The proportion of staminate and hermaphrodite flowers in an umbel bears a relationship to pouen loss caused by inseet visits to an infloreseence. Large-sized umbels of A. sylvestris and P. sativa possess a much higher percentage of staminate flowers in their inflorescences (1 hermaphrodite: 4 staminate). These inflorescences attract inseets in large numbers. On the contrary, small and generally simple umbels of S. pecten-veneris have a significantly low frequency of polliniferous flowers (1 hermaphrodite: t.2 staminate). On account of their poor visual impact, these umbels ate not frequented by insects. Umbels of T. leptophylla ate medium sized which gets reflected even in the proportion of staminate and hermaphrodite flowers per umbel (I hermaphrodite: 2.73 staminate). Plants of this species suffer some amount of pollen loss due to inseet visitors but this loss is eompensated by the nearly three-fold frequeney of staminate flowers. A higher number of male flowers in the umbel boosts pollen production and promotes insect visits during which pollination is effected. It also ensures the availability of male sex cells for fertilization. Paternal fitness is limited by access of male sex ceus to female (Bateman 1948). Stagge in the maturation time of pollen increases the period for which the pollen becomes available for fertilization (Lloyd 1979). Another significant feature in plant breeding systems is the proportion in which pollen grains and ovules ate produced by ah individual. Low pollen-ovule ratios charactefise autogamous species (Cruden 1977). In Torilis leptophylla, the pollen-ovule ratio per herrnaphrodite flower is around 2650, but at the level of the whole plant the ratio works out to 9883 which conforms to the figures compiled for xenogamous or outbreeding taxa by Cruden (1977). Such structural features of Torilis flower as the zygomorphic corolla (in hermaphrodite flowers), exposed nectar, prominent stylopodium and co-existence of perfect and staminate flowers are suggestive of its outbreeding nature. Moreover, the plants show diehogamy which is also a contravance for outbreeding. However, sinee staminate and pistillate phases overlap when the plant is considered in totality, obligate outcrossing is ruled out. Although umbellifers are in general self-compatible (Bell 1971), selfing is not possible within individual flowers of Torilis leptophylta because they are protandrous. Evidences such as umbel constitution, structural adaptation of flower, pollen-ovule ratio and relative maturation of male and female sex-eells suggest that Torilis leptophylta experiences both geitonogamy as well as out-crossing. Acknowledgements Authors are thankful to the Head of the Department for laboratory facilities. Financial assistance received from csm, New Delhi is thankfully acknowledged.

6 454 Pushpa Koul, A K Koul and I A Hamal References Batcman A J 1948 Intra-sexual sr162 in Droaophila; Heredity Br C R 1971 Brer systems and floral biology of the Umbr in the Biology and Chemistry of the UmbeUiferae (ed.) V H Heywood (London: Acadernic Press) pp Braak J P and Kho Y O 1958 Somr obsr on the floral biology of the carrot (Daucus carota L.); Euphytica 7 I Cruden R W 1977 Pollen-ovule ratios: a con~rvative indicator of br~,,ding systems in flowcring plants; Evolution Kumar C R 1977 Floral biology and brer systems of Bulgarian coriand r (Coriandrum sativum L.); New Botanist IV Lloyd D G 1979 Parental stratr162 of angiospr N.Z.J. Bot Lovett Doust J N 1980 Floral sr ratios in andromonor Umbr162 New Phytol. ti Webb C J and Lloyd D G 1980 Sr ratios in Ncw Zr apioid Umbr162 N.Z.J. Bot