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Systematic Analysis of Morphological Characters and Their Value in the Taxonomy of Solanum

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Systematic Analysis of Morphological Characters and Their Value in the Taxonomy of Solanum Tanzania Journal of Science 44(1): 37-51, 2018 ISSN 0856-1761, e-ISSN 2507-7961 © College of Natural and Applied Sciences, University of Dar es Salaam, 2018 THE POWER OF COEFFICIENTS AND METHODS OF CODING IN DELIMITING SPECIES USING PHENETIC APPROACH: THE CASE OF AFRICAN SOLANUM SECTION SOLANUM SENSU EDMONDS Mkabwa LK Manoko University of Dar es Salaam, College of Agricultural Sciences and Fisheries Technology Department of Crop Sciences and Beekeeping Technology, P.O. Box 60091, Dar es Salaam. Tanzania. [email protected] ABSTRACT Phenetics is one of approaches used to delimit species in plant classification. Conclusion in phenetics is based on overall similarity often of morphological data. The approach uses coded data that are analyzed using coefficients to create similarity matrices that are analyzed using clustering analysis to create the classification. Exists different similarity coefficients and coding methods though in practice are used intuitively sometimes giving results that have been challenged. Though similarity coefficients and coding methods have some times been blamed, studies to analyze their influences are limited. The trend however is to avoid morphological data in favor of DNA markers. The current study assessed the power of eight similarity coefficients to recover ten known section Solanum species that have also been delimited using AFLPs. Each similarity coefficient was used to analyze two similarity matrices created using two Pledji’s binary or conventional methods of coding multistate characteristics. Analysis used clustering option of PAST’s software. The ten species were recovered from each matrix only when Gower’s or Hamming’s coefficients were used. Jaccard’s and Dice coefficients recovered ten species only with binary coding. Other coefficients recovered zero to five species. Coefficients of similarity and coding method thus influences species level classification in phenetic approach. Key words: Phenetic approach, similarity coefficients, UPGMA, Section Solanum, cophenetic coefficient, morphology. INTRODUCTION epidemiology, pest management and Botanical classification remains to be one of quarantine, human health, pathogens and the most important undertaking that serve their biological control agents, protection of mankind. It finds its use in all sciences and useful plants and insects (http://www.bionet- traditions that use plants though often intl.org/opencms/opencms/caseStudies/defau underestimated. The basic unit of lt.jsp). Species identification is only possible classification is the species based on which if the boundaries between and among all other more inclusive ranks are formed. species of the same genus are clear. Proper delimitation of species is key to understanding of biodiversity and develop Traditionally morphological characteristics strategy for the conservation. Proper have been used to delimit species though identification which can only be done based recently use of DNA markers is at increase on descriptions of species have saved (Hebert et al. 2003, Hebert et al. 2004, Pons humanity. BioNET lists 48 case studies et al. 2006, Clement and Donoghue 2012). where correct identification of species was This trend however has led to a debate on the key to success. The notable areas were the suitability of DNA markers over 37 www.tjs.udsm.ac.tz www.ajol.info/index.php/tjs/ Manoko -The power of coefficients and methods of coding in delimiting species … morphology and vice versa (Hebert et al. methods of coding. It has also been said that, 2004, Brower 2006, Sass et al. 2007, phenetic results are influenced by the Taberlet et al. 2007, Spooner, 2009, Liu et subjective choice of coefficient of similarity al. 2010). Although this debate is beyond the (Jackson et al. 1989, Sokal 1986, Finch scope of this study, it is necessary to 2005). Nevertheless, though there are many mention here that in plant classification coefficients, only a few are commonly used morphological characteristics are still intuitively. The frequently used coefficients extremely important. All taxa are practically are Simple Matching, Jaccard’s and identified, descriptions are written and keys Euclidean (Sokal 1986, Finch 2005). are constructed using morphology. Jackson et al. (1989) compared six similarity According to the International Code of coefficients namely Jaccard’s, Dice, Rusell Botanical Nomenclature a plant species has and Rao, Simple Matching, Rogers- only one correct name. A botanical name is Tanimoto, Ochiai, Phi and Yule. These given to a group of individuals that can be authors concluded that the dendrograms described using morphology and is different obtained provided little evidence of group from other related groups. Thus even when structure and some coefficients provided DNA markers have been used, the practice more or less similar information. Edmonds is to correlate the groups defined by (1978) studied member of the sect. Solanum molecular markers to morphology (Bohs and using phenetic approach. The author found Olmstead 1997, Bohs 2005, Levin et al. that nine different sets of morphological data 2005, Levin et al. 2006, Weese and Bohs sampled from the same individuals depicted 2007). Morphological data also allows the different classifications. Similarly, Olet interpretation of the observed features of (2004) failed to separate eight known plants and the formation of hypotheses on species of sect. Solanum from each other. adaptation and evolution (Knapp 2001). Whether or not this confusion could be explained by the used similarity coefficients Phenetic taxonomy is a system of or method of coding has never been classification based on the overall similarity assessed. Sokal (1986) called for studies to of the organisms being classified in which compare usefulness of different coefficients the relationship is based on all available data of similarity but such studies are limited. characters without any weighting (Sokal What is however evident currently is 1986). At each level members of each taxon avoidance to use morphological data in are on the average more similar to each classification in favor of DNA markers. other than they are to members of other taxon at corresponding levels. At species Section Solanum is one of the most level classification therefore individuals that taxonomically complex groups in the genus fall in the same cluster constitute the same Solanum when it comes to species species whereas those that exhibit delimitation. The complication is attributed morphological or genetic gaps they fall in to existence of genetically determined different clusters and they are thus different variations coupled with environmentally species. Clustering pattern in phenetic induced phenotypic plasticity, existence of approach and even in phylogenetic different ploidy levels and polymorphism. reconstruction, is influenced by among Others are occurrence of natural others method of coding of multistate hybridization between certain diploid taxa characteristic (Sokal 1986, Jackson et al. with various stages of pre- and post- 1989, Wiens 2000, Datwyler and Wolfe fertilization isolating mechanisms (Edmonds 2004, Simmons and Geisler 2002). Pledji’s and Chweya 1997). Current taxonomic (in Forey and Kitching 2000) described four treatment pulls together sections Solanum 38 Tanz. J. Sci. Vol. 44(1), 2018 Episarcophyllum, Campanulisolanum, and analysis? (3) Whether or not phenetic Parasolanum into one Morelloid clade classifications based on morphology lead to (Bohs 2005, Bohs and Wiens 2007). grouping unrelated forms into paraphyletic Section Solanum forms one of the most or even polyphyletic taxa making it possible important groups of leafy vegetable in to recognize multiple species? Usefulness of Africa. Members of the section are known cophenetic coefficient measures was also for their medicinal, mollucidal or larvicidal assessed. properties and some carry resistance genes against Phytophthora infestans an important MATERIAL AND METHODS disease for cultivated Solanaceous crops Plant materials used in this study were such as Tomato and Irish potato (Roddick, grown at Radboud University Botanical 1991, Edmonds and Chweya1997, Kamoun garden from seeds obtained mainly from et al. 1999, Singh et al. 2001, Zengfu, 2001, African countries. Table 1 summarizes seed Heo et al. 2005). Solanum nigrum is accession numbers, the code used during the poisonous and hyperaccumulates heavy analysis and number of individuals per metals (Perez et al. 1998, Xu et al. 2009). species. Morphological data were collected Such a taxonomically complicated but based on a descriptors list of 33 economically useful group makes a good characteristics (both qualitative and candidate to assess of delimitation of species quantitative) modified from Edmonds and using morphology. Chweya (1997). Data were collected from plant of same age. Nomenclature was based This study answers the following questions: on species recognized based on AFLP (1) how does coefficient of similarity markers (Manoko 2007, Manoko et al. 2007, influences clustering pattern thus Olet et al. 2011, Manoko et al. 2012, delimitation of species under phenetic Edmonds 2012). approach? (2) Do method of coding multistate characteristics matter in phenetics Table 1: List of species Botanical name Acronym Individuals Solanum villosum Mill. vill/VILL 24 Solanum nigrum L. nigr/NIGR 12 Solanum nodiflorum Jacq. nod/NOD 14 Solanum scabrum Mill. scab/SCAB 31 Solanum chenopodioides Lam. chen/CHEN 5 Solanum memphiticum Gmel. sensu Manoko 2007 non mem/MEM 7 Edmonds 2007; 2012
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