Morphological And Genetic Characterisation Of Some Lima Bean (Phaseolus Lunatus L.) Cultivars And Their Nodulating Rhizobia

Abstract Three major investigations were carried out to assess the morphological traits and nodulation potential of thirteen lima bean cultivars as well as the genetic diversity of rhizobia nodulating these lima bean cultivars. Thirteen lima bean cultivars obtained from the CSIR-PGGRI and various market centres in Ghana were used. The experiment was conducted in pots filled with natural topsoil and arranged in a randomised complete block design (RCBD) with three replicates at the Biotechnology and Nuclear Agriculture Research Institute (BNARI) of the Ghana Atomic Energy Commission (GAEC). The study aimed at obtaining some relevant information on the morphological traits of the lima bean to be improved upon, to evaluate their nodulation tendencies and determine similarities and differences of their nodulating rhizobia. Significant differences were obtained in quantitative characters (leaflet length, leaflet width, pod length, pod width, seed length, seed width, seed weight per 10 seeds and days to 50% emergence), contributing to divergence among the lima bean cultivars. Qualitative traits, however, were mostly similar, with few exceptions such as the flower wing colour, growth habit, leaf shape, main stem pigmentation, pod beak shape, seed secondary colour and seed pattern colour showing divergence among the lima bean cultivars. Two major clusters were joined at the similarity distance of 0.69. Majority of the lima bean cultivars were identified to be of the same morphotype. with exception in cultivars M4 and A2. There were no significant differences in mean nodule number, mean effective and non-effective nodule counts. The lima bean cultivar GH 1714 showed superior performance with respect to nodule number counts, effective nodules, fresh shoot weight and fresh root weight. Additionally lima bean cultivars, M5 and A2 xxii indicated superior radiation use efficiency with total shoot dry matter of 731kg/ha and 704kg/ha respectively. A positive and high correlation existed between mean nodule number, and mean effective nodules, mean fresh nodule weight and mean fresh shoot weight. Molecular diversity studies indicated that primers RPO1 and RPO4 were effective in differentiating Rhizobium strains compared to the primer ERIC (1 and 2). Cluster analysis identified two major groups of Rhizobium strains at the similarity level of 49%. Inter-cultivar genetic studies identified similarities and differences within and between the lima bean cultivars with respect to nodule bacteria isolates. Possible isolates also existed among the Rhizobium isolates both within and between cultivars.