Genetic variability in tomato germplasm (Solanum lycopersicum L.) using morphological characteristics and simple sequence repeat (SSR) markers

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Tomato is an essential ingredient in the daily diets of majority of Ghanaians and is cultivated in almost all the agro-ecological zones in Ghana, however, not much information is available on the genetic and morphological variability of tomatoes cultivated by farmers. The need for varietal identification of tomato cannot be over-emphasised. It was therefore, necessary to collate information and collect tomato genotypes from the farmers for morphological and molecular evaluation to assess the variations among and within the genotypes. A survey was conducted and semi structured questionnaires administered to obtain information about farmers’ knowledge of varietal differences, preferences and production practices and constraints. Preferred tomatoes were documented and fruits were obtained from the farmers’ field to extract seeds for the study. A pot experiment was conducted to study the genetic variability among and within 12 tomato genotypes obtained from the farmers in three-selected tomato growing areas, namely Afari, Akomadan and Kumawu and their environs in Ashanti Region and planted in a randomised complete block design. DNA was extracted from eight (8) plants per genotype without bulking to check the purity of the genotypes using the CTAB method with modification by Takrama, (2000) CRIG adopted by Kirkhouse Trust Mobile Laboratory. Data taken included 16 qualitative and 16 quantitative traits and scored using AVRDC descriptor list with additions from the IPRGI descriptor list. It was realised that most (65 %) of the farmers saved seeds from previous harvest for the subsequent planting. Analysis of variance revealed highly significant difference (P≤ 0.01) among the genotypes for all quantitative traits studied except plant height and number of diseased and pest damaged fruits. Genotypic (GCV) and phenotypic coefficient of variation (PCV) were high but narrow for most of the traits studied except for days to first flowering, days to 50 percent flowering, 100 percent flowering and plant height which recorded lower phenotypic and genotypic coefficients of variation (PCV and GCV), indicating the little environmental influence and hence, highly heritable. Genotypes with higher fruit yield per plant (PF-AF and PM-AF) were from Afari and its environs. The correlation analysis indicated that number of fruits per plant was highly significant and positive with fruit yield per plant. Similar observation was made with plant height and days to 50 % flowering. The SSR markers were highly informative as generated by the PowerMaker V3.25 software. NTSyS PC software 2.2 grouped the 96 DNA samples of the 12 genotypes into two major groups. The samples were reduced to 48 for clear dendrogram. Samples from DW-KU were all put into one group while the rest were in the other group. The outcome of this study should be useful to manage the germplasm conservation and future tomato genetic improvement. However, all the genotypes may be cultivated over time at different locations on field to ascertain their stability and purity.
A Thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the Degree of Master of Philosophy in Agronomy (Plant Breeding, 2015)