Electrophoretic techniques for identification and classification have become a very important tool in systematic research. This technique is particularly of taxonomic importance in separating varieties of plants (Folorunso et al., 2012) and also a useful tool in studies of genetic variability in plants (Oladipo et al., 2008). Electrophoretic technique has been employed on a number of plant groups to show that many isoenzymes or polymorphic proteins are widely distributed in higher plants and also to compare protein distribution of the wild relative of plants to the cultivated ones (Folorunso et al., 2012; Oladipo and Illoh, 2012).

This study therefore compares the electrophoretic pattern of protein bands distribution in the Ludwigia species with the aim of providing useful information on classification and identification of Ludwigia species and identifies both intraspecific and interspecific variations that exist among them and the highest protein richness in them.

Four to six (4 – 6) drops of the sample buffer was added to 10 – 12 drops of the protein sample, 0.2% bromophenol blue was added, and the sample was heated in a boiling water bath for 5 min. After boiling, the samples were introduced into each gel tube. 10% 2-mercaptoethanol was added to the sample to reduce the disulphide bonds in the protein so as to expose the protein to SDS action. The 5% SDS in an anionic detergent that distrupts nearly all non-covalent interactions in native proteins, thus the SDS forms a rod-like material with proteins that gives them uniform movement along the electrophoretic column according to their molecular weights. The glycerol added makes the protein sample denser so that it does not mix within the running buffer. The buffers are employed to maintain polyionic character of protein. Bromophenol blue was added to act as a tracer. The level of similarity of protein profile of the species was used to construct the dendrogram showing the coefficient of similarity.

The pattern of protein distribution in the species of Ludwigia studied and their diagrammatic representation are as shown in Figures 1 and 2, respectively. A keen examination of the bands shows that there are different patterns of band distribution in the genus. Marked differences were recorded for number, combination of bands and intensity of bands between species. The relationship between all the species of Ludwigia on the basis of band distribution is as shown in Table 2. The bands range from one to four (Figure 2). Most of the bands were found to be fast moving bands (2.0 to 3.5 cm), followed by the intermediate moving bands (1.0 to 1.9 cm), and slow moving bands (0.0 to 0.9 cm), respectively. Table 3 shows the common band relationship between all the Ludwigia species studied. L. octovalvis var linearis and Ludwigia hysopifolia have similar bands with the same intensity at 1.6 cm; L. octovalvis var linearis, Ludwigia hysopifolia and Ludwigia abysssinica have similar bands at 0.5 cm but with varying intensity.

There are diagnostic bands peculiar to each of the species which makes individuals different from one another: Ludwigia decurrence B shows band at 0.7 cm, L. octovalvis var linearis at 0.8 cm, Ludwigia leptocarpa at 1.0 cm, Ludwigia octovalvis var brevisepala at 1.8 cm, Ludwigia abysssinica at 2.5 cm, Ludwigia erecta, at 2.8 cm and Ludwigia hysopifolia at 3.0 cm. The band at 2.1 cm was found to be common to all the species and occur at different intensities. Inter specific bands were observed between pairs of species in the genus. L. octovalvis var linearis and Ludwigia hysopifolia were found to have the highest number of bands (four), followed by Ludwigia octovalvis var brevisepala and Ludwigia abysssinica with three bands. Ludwigia decurrence B, Ludwigia leptocarpa and Ludwigia erecta have two bands while Ludwigia decurrence A and Ludwigia adscendens have one band (Figure 2).

The dendrogram depicts the similarity coefficient for the Ludwigia species based on protein banding patterns (Figure 3). Three major clusters were formed, the first cluster comprises of L. hyssopifolia, L. decurrence A, L. adscendens and L. erecta at 1.0 similarity level. The second cluster comprises L. decurrence B and L. abyssinica at 0.85 similarity level. These two clusters are similar at 0.7 similarity level. The third cluster comprises of L. leptocarpa and L. octovalvis brevisepala, they are similar to the first two clusters at 0.45 similarity level. L.octovalvis linearis is delimited from the other species of Ludwigia studied at -0.4 similarity level similarity level. An artificial key for the identification of the Ludwigia species studied based on their band relationships is as shown in Table 4.

Bands with identical electrophoretic mobilities represent proteins with identical amino acid sequences and are therefore potentially homologous in their derivations (Scogin, 1972). L. hyssopifolia and L. abyssinica have proteins with higher molecular weights which informs why they have slow moving band at 0.4. This band therefore delimits them from the other species; other diagnostic bands for the identification of each species are reported in the results.

The protein bands are taxonomically distinct as no two species have the same band distribution. This agrees with the opinion of Olsson (1967) as reported by Folorunso et al. (2012) that biogenetic relationships can best be indicated by quantitative results using chemo-taxonomic methods. The band at 2.1 is taxonomic for all the species of Ludwigia studied; this shows evidence of common evolutionary origin in them. Coming from the same parental stock, their evolution is convergent thereby making it possible for character traits to be shared in common. This support the assertion of Gottlieb (1971) that when a band appears in all individuals in a population, it is assumed that the gene which codes enzyme or protein does not vary. Based on the position of protein bands L. octovalvis var linearis, L. octovalvis var brevisepala, L. hyssopifolia and L. abyssinica are more closely related. The band at 1.0 delimits L. leptocarpa from the other species. L. decurrens A and L. adscendens subsp. diffusa are more closely related based on the number of band and the position of band.

Taxonomic bands for Ludwigia species studied have been reported together with the diagnostic bands for their identification. From the Dendrogram, interspecific relationships as well as their intraspecific relationships based on protein bands were reported. An artificial key was generated for the identification of the Ludwigia species studied based on their protein band relationship.

The authors have not declared any conflict of interest.