Morphological characterisation of two endemic species of Gomphocarpus (Mobydick) in Kenya
The genus Gomphocarpus comprises 25 – 32 species that occur in Africa and the Arabian Peninsula. In Kenya, two common species; Gomphocarpus physocarpa and Gomphocarpus fruticosus are commercially cultivated as a cut flower for its inflated green bolls. As a comparison, Gomphocarpus physocarpa has larger and more rounded bolls whereas Gomphocarpus fruticosus have small bolls with a sharp pointed end. However, these two species can not be differentiated as they easily hybridize. No precise information on morphological or molecular characterization is available locally. The objective of the study was morphological characterization of commercial Gomphocarpus species grown in Kenya. Gomphocarpus germplasm was collected from Juja farm, Thika, Molo, Narok and Chumvi in Machakos. The experiment was laid out as randomized complete block design with three replications and five treatments per block. The collections were characterized for morphological diversity complimenting with principal component analysis (PCA) and cluster characters using the XLSTAT statistical software. The results showed no morphological variation on qualitative characteristics of leaf, growth habit and stem length. The coefficient of variations (CV) and standard deviations (SD) for all qualitative traits were zero. Boll length was positively correlated to boll weight with a factor of 0.355. Leaf length was inversely correlated to leaf width with a factor of negative 0.064. A PCA based on morphological traits of boll weight and length consistently separates populations of Gomphocarpus physocarpa and Gomphocarpus fruticosus and reveals a close relationship between them. All the qualitative characteristics of leaf colour, leaf shape, boll shape and flower shape were all clustered at the origin, displaying zero variations. The hierarchical clustering dendrogram revealed a 99.9% similarity among Gomphocarpus collections. The study showed that Gomphocarpus characteristics did not reveal any significant divergence in morphological qualitative traits observed. This could be an indication of low reproductive isolation in the collections. The two lines also hybridize, creating intermediate forms. Probably, there is need for complimenting similar work with other techniques such as DNA genetic markers to further accurately characterize Gomphocarpus germplasm existing in Kenya.
Key words: Characterisation, cut flower, mobydick, morphology