Genetic diversity of tomato (<i>Solanum lycopersicum</i>) accessions using chloroplast DNA and random amplified polymorphic DNA markers

Abstract

Information regarding genetic diversity and genetic relationships among different genotypes is invaluable in crop improvement of which  its success is largely dependent on genetic variability. As molecular markers continue to be an effective tool for localization of a gene to  improvement of plant varieties, the need to establish phylogenetic relationships becomes extremely important for the process of  breeding new cultivars. This study reports genetic diversity for Tomato accessions across Nigeria (Six geo-Political Zones) as revealed by  chloroplast DNA (cpDNA) and Random Amplified Polymorphic DNA (RAPD) markers. cpDNA data showed a Nucleotide diversity for all  accessions of Tomato at 0.302 while the number of segregated sites as well as parsimony informative sites to be 4.0. Data from five  Random Amplified Polymorphic DNA (RAPD) primers showed a low Gene diversity (h) which ranged from 0.10 to 0.28, Percentage  polymorphism (Pp) ranged from 20 % to 84%. The Unweighted Pair Group Method with Arithmetic Mean (UPGMA) dendrogram grouped  the accessions into two groups at similarity coefficient of 72%, with a value of r = 0.98, showing an excellent correlation between the  accessions and the values of the initial distances (similarity matrix). Similar results were seen with the dendrogram constructed for  genetic relationships of Tomato accessions using RAPD or cpDNA (you have mentioned RAPD up) markers. Split tree analysis equally  revealed a 2 structured gene pool for Tomato gene pool in Nigeria. The high homogeneity of species observed in the study signifies a low  genetic diversity and limited variability in tomato species in Nigeria. Amongst the consequences of low genetic diversity is the  absence of unique variants that can possibly combat disease conditions or adapt to unfavourable environmental changes. The use of  both cpDNA and RAPD markers in this study has efficiently shown that continuous cycling/shuffling of species within the narrow gene  pool is expected to lead to a continuous reduction in genetic variability. No addition of new variant into the gene pool and in turn leads to  inbreeding depression, thus suggesting the need to breed with known wild cultivars to increase genetic variability.