Pollen Morphology of Selected Taxa of the Genus Solanum from Southern Western Ghats, Kerala, India
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Rheedea Vol. 25(2) 128-145 2015 ISSN: 0971 - 2313 Pollen morphology of selected taxa of the genus Solanum from Southern Western Ghats, Kerala, India Anil Kumar V.S., Maya Nair C.1 and Murugan K.* Department of Botany, University College, (University of Kerala), Thiruvananthapuram, Kerala – 695 034, India. 1Department of Botany, Govt. Victoria College (University of Calicut), Palakkad, Kerala – 678 001 , India. *E-mail: [email protected] Abstract Pollen morphology of 18 taxa of Solanum from Kerala has been analyzed on an evolutionary perspective on palynological relationship shared by the wild taxa and the cultivated ones. The exine ornamentation in wild germplasm ranges from spinulose (S. mauritianum Scop. and S. wendlandii Hook.f) to granulose (S. giganteum Jacq. and S. trilobatum L.), from synechinulate to striate echinulate in shrubby taxa and from echinulose to granulose in herbaceous forms. But the cultivar germplasm uniformly showed a mammilate – echinulate exine ornamentation with lax distribution of projecting elements. The stragglers and lianas of the germplasm viz. S. trilobatum, S. seaforthianum Andr. and S. wendlandii showed a tendency for multi-bridging at the colpi region and the trees, viz. S. giganteum, S. mauritianum and S. erianthum D.Don. showed ornamented colpi with slight tendency for bridging at the region of apertures. Traits like multibridging, compact exine ornamentation and prominent operculum characterize the wild species which makes them better adapted against environmental and biotic stresses. While the wild taxa have well developed aspis and operculum, the domesticated species such as S. melongena L. ‘Neelima’, S. mammosum L., S. macrocarpon L. and S. melongena L. var. insanum (L.) Praine. were having only a feebly developed aspis and operculum as an indication of less protection which in turn is an indication for secondary evolution. Keywords: Pollen morphology; Solanaceae, Solanum, Western Ghats, Kerala Introduction With great diversity of habitats, morphology and morphology found in the family and the striking ecological adaptations, the family Solanaceae variations being assigned to the shape class, consists of about 100 genera together with c. apertural types and tectal surface (Lashin, 2012). 2500 representative species (Olmstead & Bohs, 2007) in tropical and temperate regions with the The pollen morphology of Solanum species had major dispersal centres being Australia and Latin been a subject of interest for various researchers America (Barroso et al., 1991). Plant taxonomic across the globe from time to time (Perveen & studies successfully incorporate microspore Qaiser, 2007; Al-Wadi & Lashin, 2007; Franklim morphology, as the traits of pollen are under the & Esteves, 2008; Lashin, 2012). Palynological selective forces coupled with the processes of approaches have also been attempted in various pollination, dispersal and germination (Moore genera under the family Solanaceae (Punt & Monna- et al., 1991; Stuessy, 1990). Pollen morphology of Brands, 1977; Barth & Duarte, 2008; Martins et al., various members of the family Solanaceae has 2013). The investigations on the palynomorphs of been studied by different workers from time to genus Solanum, (Salgado- Labouriau et al., 1969; time (Natarajan, 1957; Murray & Eshbaug, 1971; Sharma, 1974; Anderson & Gensel, 1976; Symon, Raghuvanshi, 1974; Sharma, 1974; Anderson & 1981; Edmond, 1984; Roubik & Moreno, 1991) Gensel, 1976; Palri & Koch, 1976; Anderson, 1977; suggest a homogeneous morphological pattern to Srivastava, 1977; Edmonds, 1984; Gentry, 1986; the pollen grains of this genus. Edmonds (1984) Plowman, 1998; Persson et al., 1999). Early reports made significant contributions to the knowledge suggest the distribution of tricolporate pollen of infrageneric taxonomic groups for section grains with scabrate tectum as the most common Solanum. V.S. Anil Kumar et al. 129 However, a detailed phylogenetic approach has contrast to the negligent ornamentation patterns not been attempted on the pollen morphology displayed by cultivar taxa as well as domesticated of various species of Solanum. Indian Solanum germplasm . species have not been given any comprehensive treatment after Clarke (1883) despite the significant Domesticated vs Wild genetic resources of contributions on these plants from other parts of the Solanum world. Except for the preliminary investigations on the comparative analysis of the size of the The domesticated germplasm under consideration grains of six medicinally important species of the include the edible Solanum melongena ‘Neelima’ and genus (Vijayakumari & Vilasini, 2005), very few S. macrocarpon, the medicinally potent S. melongena palynological studies have been carried out in the var. insanum and one ornamental taxa S. mammosum Solanum species of Kerala. It is in this background L.. The wild taxa included are S. capsicoides All., S. the present study has been undertaken with a view exarmatum Anil et al., S. mauritianum, S. giganteum, that the results of pollen analysis could be utilized S. erianthum, S. pseudocapsicum L., S. trilobatum, S. in clarifying infraspecific taxonomic disputes of wendlandii, S. seaforthianum, S. violaceum Ortega the taxa as well as for extracting the evolutionary subsp. violaceum, S. violaceum Ortega subsp. tendencies with other species or subspecies. The multiflorum (Clarke) Matthew., S. aculeatissimum morphological and palynological analysis of Jacq., S. torvum Sw. and S. americanum Mill. Solanum species have proved to be of immense assistance in interpreting problems related to Pollen morphology of wild genetic resources taxonomy of different species. 1. Solanum aculeatissimum Jacq. Materials and Methods Grains prolate spheroidal, 19.3‒20.4 × 17.8‒18.3 The polliniferous materials of 14 species of µm in polar view, 16.8‒17.4 × 15.9‒16.8 µm in Solanum, 2 subspecies and 1 variety, along with equatorial view, trizonocolporate, operculate, the cultivated S. melongena ‘Neelima’ were aspis raised, arch-like and connate. Ornamentation collected from Southern Western Ghat region of echinate, with ornamented operculum and aspis the state of Kerala, India between 8o30’0”latitude/ (Fig. 1. a–d). 76o55’12” longitude and 9o51’0” latitude / 76o56’24” longitude. Collections were made during the 2. Solanum americanum Mill. flowering seasons from April to January and mature unopened flower buds were fixed in 70% Grains prolate spheroidal, ranging between alcohol. The anthers were carefully removed, 12.1‒12.44 × 12.2‒12.56 µm in polar view and crushed in distilled water, centrifuged at 1000 12.9‒13.42 × 12.9‒13.15 µm in equatorial view, rpm and filtered through fine mesh. The pollen trizonocolporate with granulose - micro echinate grains were acetolysed (Erdtman, 1958) and exine ornamentation. Grains operculate and colpi were subjected for ultra structural analysis under with minute granules. Ridges are absent (Fig.1. e Scanning Electron Microscope (SU6600, Hitachi –h). and Zeiss EVO 18). Pollen descriptions were made following Punt et al., (2007) and Hesse et al., (2007) 3. Solanum capsicoides All. by observing 75 grains under SEM at different magnifications. Grains heteromorphic, exhibiting trimorphism, triangular obtuse convex and trizonocolporate. Results Type 1: Grains suboblate, in polar view it ranges The analysis of the pollen morphology of selected between 20-21.9 µm and equatorially between species of Solanum from Western Ghat region of 19‒20.5 × 24.2‒25.1 µm, brevicolporate, ora region Kerala revealed inter - specific and intra specific aspidate, ornamentation echinate. The apocolpium pollen morphological variations. The results region is with lax echinae. Operculum and aspis showed inter relationships among different species feebly developed (Fig. 2. a–c). with respect to operculum, multibridging at the colpi and ora as well as ornamentations in the colpi Type 2: Grains subprolate, equatorially elongated region. Further, an evolutionary tendency in exine ranging between 21‒22.7 × 18.5‒19.1 µm, sculpturing can also be deduced as there is intense brevicolporate, with lax echinate ornamentation excrescence patterns in the wild germplasm in without prominent operculum (Fig. 2. d). 130 Pollen morphology of selected taxa of Solanum Fig.1. a–d. Solanum aculeatissimum Jacq.: a. Polar view; b. Equitorial view; c. Ornamented operculum; d. Exine ornamentation; e–h. Solanum americanum Mill.: e. Polar view; f. Microechinate exine; g. Equitorial view; h. Colpus showing minute granules. V.S. Anil Kumar et al. 131 Fig. 2. a–f. Solanum capsicoides All.: a. Polar view of large grain; b. Equitorial view of large grain; c. Exine ornamentation of large grain; d. Medium sized grain in equitorial view; e. Equitorial view of small grain; f. Ornamented operculum of the small grain; g & h. Solanum erianthum D. Don.: g. Equitorial view; h. Colpus region showing ridges and bridging at ora. 132 Pollen morphology of selected taxa of Solanum Type 3: Grains prolate spheroidal, ranging 9. Solanum seaforthianum Andr. between 18‒18.7 × 15.5‒16.5 µm with compact echinules, brevicolporate, having prominent Grains spheroidal and monomorphic, measures finger like operculum with dense micro echinate between 13.8‒14.2 × 13‒13.3 µm in polar view ornamentation (Fig.2. e – f). and 15.8‒16.2 × 15.9‒16.2 µm in equatorial view, tetrazonocolporate, colpi fused in pairs, semi 4. Solanum erianthum D.Don. syncolpate, ornamentation micro echinate, bridge partial and adnate (Fig. 5. c & d). Grains prolate, equatorially elongated ranging between