T REPRO N DU LA C The International Journal of Reproductive Biology 10(1) Jan., 2018, pp.33-37 P T I F V O E

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S H Andromonoecy in viarum Dunal (): a buzz pollinated taxon T Moumita Saha* and B. K. Datta Plant and Biodiversity Laboratory, Tripura University, Suryamaninagar-799022, Tripura, India *e-mail: [email protected] Received: 10.05.2017; Revised: 01. 06. 2017; Accepted and published on line: 01.08.2017 ABSTRACT Andromonoecy is a plant sexual system in which individual bears both hermaphrodite (bisexual) and staminate (male) flowers. Solanum viarum exhibits continuous flowering pattern with a maximum bloom from February to August and is andromonoecious i.e., they have long-styled hermaphrodite flowers (75%) and short-styled female sterile flowers (25%) which produces fertile pollen. The morphology of the two floral types was compared. The female sterile type is determined prior to the stage at which the flower buds are visible. Self-compatibility and a large number of flowers simultaneously open on the plant suggested that in Solanum viarum the functionally male flowers assist in attracting and sustaining pollinators and ensure high rates of fertilization through an increased pollen/ovule ratio (2984:1).

Keywords : Andromonoecy, Solanum viarum, self-compatibility.

Tremendous variety of reproductive systems are length in is a varietal characteristic. Bobadi and van exhibited by i.e., andromonoecy, which is a plant sexual Damme (2003) stated that nitrogen failed to influence style system where individuals bear both hermaphrodite (bisexual) length and type of flowers of eggplant. According to and staminate (male) flower (Diggle 1994). This reproductive Kowalska (2003), eggplant formed the highest number of system is one of the main focuses of evolutionary biologists flowers with a long pistil and much less flowers with medium (Barrett 2002). Andromonoecy has developed freely from and short pistils regardless of the pollination method (self several times (Miller and Diggle 2003) and is found in pollination, using bumble bees) and flower hormonization. approximately 4000 species of 33 angiosperm families (Bertin The production of short-styled flowers with a small and highly 1982, Yampolsky and Yampolsky 1922, Miller and Diggle reduced gynoecium, often infertile or with small possibilities 2003). Andromonoecy is widespread in the genus Solanum. of setting fruits, seems to be the first step to functional The genus Solanum L. generally bears hermaphrodite and andromonoecy- the production of staminate and homomorphic flowers (Hossain 1973). The variation in style hermaphroditic flowers. length and its position towards stamens was widely described Solanum viarum commonly referred as tropical soda in eggplant (Kowalska 2008). Long styled flowers are always apple is a serious invasive weed species in pastures, more appreciable in the number than short-styled flowers. vegetable crops, row crops, and forests, urban and natural Sometimes flowers with the stigma on the same level as the areas (Coile 1993, Hall et al. 1998, Mullahey and Colvin stamen are defined as medium styled ones. Krishnamurthi and 1993). However, Solanum viarum is an economically Subramaniam (1954) described four types of flowers: long important medicinal plant with a rich source of solasodine, styled with large ovary, medium styled with medium sized an alkaloid used in the synthesis of steroid hormones for ovary, pseudoshort-styled with rudimentary ovary and true- treating cancer, Addison’s disease, rheumatic, arthritis, and short-styled with very rudimentary ovary. Pseudo and short- for producing contraceptives (Chandra and Srivastava 1978, styled flowers fail to set fruits, whereas long and medium Satyabrata et al. 2000). According to Budavari (1989), the styled flowers produce fruits. Fruit set rates are higher for glycoalkaloid present in the fruit of Solanum viarum is a long-styled flowers compared to short-styled flowers, so precursor for the steroid diosgenin and is used as short-styled are not totally sterile (Chen 2001). In long-styled contraceptives. Though S. viarum has been investigated flowers, the stigma may project beyond the anthers, what from the standpoint of its medicinal and economic favours cross-pollination (Nothmann et al. 1983). The importance, its andromonoecious nature has not been proximity of the stigma to the anther pores at anthesis studied yet. In this paper description of the different flower influences fruit set, fruit size and seed content, but not seed types and data on their fertility are presented. The breeding quality of eggplant. Fruit weight and seed formation were system and possible functions of the female sterile flowers maximal in flowers with the stigmata at maturity situated close are discussed. to the anther pores. There are some investigations designed to determine the influence of agronomical and environmental MATERIAL AND METHODS factors on the occurrence of different types of flowers in Seeds of Solanum viarum were sown during 2015, and 5 eggplant. Passam and Bolmatis (1997) showed that the style month old seedlings were transplanted to sandy loam on an 34 The International Journal of Plant Reproductive Biology 10(1) Jan. 2018, pp.33-37

experimental plot at Tripura University. Solanum viarum or styled flowers produce considerably fewer grains than long- tropical soda apple flowers almost throughout the year but styled flowers (Table 1). Pollen grains produced by the two maximum bloom is concentrated from February to August. To types of flowers had the same shape. Pollen ovule ratio is determine variation in size, floral parts were measured in 2984:1. The density and length of the spines on the pedicel flowers of the first five of several plants. In and calyx tube decrease from the first flower to the succeeding each of three floral types, 20 flowers were examined. Pollen ones. The flowers open early in the morning. As soon as grains were counted with a haemocytometer (Ornduff 1970). flowers open, several pollinators like thrips, bees, wasps, The number of grains was determined in the anthers of ten ants and few members of Diptera and Coleoptera visit flowers flowers of each type. To observe pollen germination and to collect forage materials Foraging activity started from pollen-tube growth, hand-pollinated styles were processed for 05:30 hours. During the entire foraging period in a day (05:30- fluorescence microscopy (Martin 1959). Artificial 14:00 h), 7-8 insects visited the flowers. The peak time of pollinations were conducted both to compare fruit-set in visitation was between 07:00-09:00 hrs and 11:00-12:00 h, different floral types and fruit-set after self and cross during which 5-6 insects were recorded. A total of 5 insect pollinations. Floral visitors and their rate of visitation were species were identified as regularly foraging on the flowers of observed during the peak activity period (0530 to1400 hrs). S. viarum. Among them, Amegilla sp. and Xylocopa sp. were the most effective pollinators and they were also found in RESULTS buzzing the flowers of S. viarum. They release pollen which is In the experimental plot, plants of S. viarum attained a more or less strongly held by their anthers, that makes height of 3.5 m and a diameter of about 3.5 m. The extra- pollination more efficient. This type of pollination is known as axillary inflorescences produce two to four flowers. The white buzz pollination. In most other species of Solanum, only large corolla is usually five lobed, but four lobes may also occur. insects capable of buzzing can remove pollen from the anthers There are as many stamens as corolla lobes. The anthers and function as pollen vectors (Symon 1979). Few insects and dehisce by two apical pores each. small beetles (Scarabaeidae beetle) were also observed on the Floral types—Two types of flowers could be distinguished by anthers, possibly searching for pollen. However, they did not style length (Fig 1). The first formed flower of an buzz, nor did they touch the stigma of long-styled flowers, and invariably has a long style extending well thus they were not effective pollinators. beyond the anther tips. In the succeeding flowers have short Fertility—To study the fertilities of the floral types, fruit styles between the bases of the stamen filaments; their development was traced in differently treated inflorescences. rudimentary stigmas never reach the base of the anthers. The Altogether 50 inflorescences from 10 plants were taken. 8 of sequence of the two flower types was observed in 80% of the which had two long-styled flowers. inflorescences on hundreds of plants. Artificial pollinations were conducted to determine if Style length in the two types of flowers is correlated with short-styled flowers failed to produce fruits because of lack of features of the stigma and other floral characters (Table 1). The pollination. Unbagged flowers of 50 inflorescences were hand diameter of the pedicel and both the length and diameter of the pollinated with a mixture of self and foreign pollens. The ovary decrease considerably from long-styled to short-styled number of fruit did not exceed the number of long-styled flowers. The diameter of the corolla is largest in long-styled flowers indicating that, by both artificial and natural flowers. Stamens in short-styled flowers are a little shorter pollination, short-styled flowers do not produce any fruit even than in long-styled ones. Pollen-grain counts reveal that short- if pollen is deposited on their stigmas. Such flowers drop 2-3

Table 1-Characters of floral parts in the two flower types of Solanum viarum Floral Characters Flower types (Mean ± SEM) Long styled Short styled t (long: short)

Length of pedicel 5.5 ± 0.06a(5.4-5.6) 4.5 ± 0.06b(4.4-4.6) 0.0065 Diameter of corolla 7.64 ± 0.15a(7.4-7.9) 5 ± 0.50b(4-5.6) 0.0270 Stamen length 7.13 ± 0.07a(7-7.2) 6.23± 0.15b(6-6.5) 0.0247 Number of pollens per flower 2,98,350 ± 1650a 2,72,537 ± 2143b 0.0060 (2,96,700 - 3,00,000) (2,70,394 - 2,74,680) Style length 12.6 ± 0.11a(12.4-12.8) 2.33± 0.07b(2.2-2.4) 2.10815E-05 Stigma Hairy at the baseBright Hair absentLight green greenPartially lobed Rudimentary Ovary diameter 1.17 ± 0.03a(1.1-1.2) 0.57±0.02b(0.54-0.6) 0.0007 2018 Andromonoecy in Solanum viarum Dunal (Solanaceae): a buzz pollinated taxon 35

A B

C D

E F

Fig. 1–Solanum viarum Dunal A. Long styled flower; B. Short styled flower; C. Stigma of long styled flower; D. Stigma of short styled flower; E. Amegilla sp.; F. Drosophila melanogaster. 36 The International Journal of Plant Reproductive Biology 10(1) Jan. 2018, pp.33-37

days after anthesis. In first set of experiment 50 long styled Heithaus et al. (1974) have suggested for flowers had been emasculated and bagged before anthesis and andromonoecious Baukinia pauletia that another were pollinated with pollen from short-styled flowers. 20 possible role of functionally male flowers could be to raise the fruits were produced from 50 flowers that were pollinated with pollen/ovule ratio. In other words, the large number of pollens from short styled flowers showing that short-styled ovules awaiting fertilization may require a higher flowers contain fertile pollens. To determine whether female pollen/ovule ratio than that occurring in the hermaphrodite sterility of short-styled flowers is caused due to barriers of flower alone. The data for S. marginatum indicate that a pollen germination, flowers were hand-pollinated and hermaphrodite flower produces 184 pollen grains per seed. observed for pollen tubes. Masses of pollen grains were found This ratio is low compared with ratios of pollen grains on the stigmas of long-styled flowers 24 h after pollination, per seed in other nectarless plants in which all the flowers are and pollen tubes were observed within the style. In contrast, hermaphroditic, and which are foraged by vibrating only a few pollen grains were found on the stigmas of short- pollinators (Dulberger et al. 1981). In four species of styled flowers. Thus, the lack of fruit-set in short styled Cyanella (Tecophilaeaceae) the ratios vary from 1,780 to flowers were clearly due to the failure of pollen grains to 33,000 (Dulberger and Ornduff 1980). The functionally germinate and of pollen tubes to grow. male flowers may fulfill a manifold role in different Solanum species, depending on the proportion of hermaphrodite to DISCUSSION male flowers (8%-80%), the degree of attractiveness of Wakhloo (1975) and Martin (1972) found a relationship flowers, and the pollen/ovule ratio necessary for effective between the degree of development of ovules, ovary size, fertilization. and the length of the style at anthesis in each of the three Acknowledgement—Moumita Saha is thankful to the floral types in S. sisymbriifolium and S. mammosum from Department of Science and Technology (DST), New Delhi, embryological observations. In S. mammosum, Martin (1972) Govt. of India for providing INSPIRE (Innovation in Science observed that flower buds 6-8 days prior to anthesis already Pursuit for Inspired Research) Fellowship (No. DST/ showed normal or reduced styles. 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