Abstract
The investigation was carried out to study the genetic diversity and molecular characterization of lemon at "Collection, Evaluation, Conservation and Utilization of Land races and Wild relatives of some Important Vegetables and Fruits of Bangladesh (CVFB)" project, Department of Horticulture, the Bangladesh Agricultural University, Mymensingh during 2005-2007. Evaluation and morphological characterization of 69 lemon accessions were performed using different qualitative and quantitative characters and found a wide range of variations among the accessions. Considering morphological characters, 6 promising accessions, viz. CL 03, CL 07, CL 08, CL 16, CL 18 and CL 53 were selected for further evaluation. Genetic diversity was estimated using 10 morphological characters based on multivariate (D2) analysis and 69 lemon accessions were grouped into eight clusters. Principal component analysis revealed that the first five axes were accounted for 88% of total variation, and the rest five axes for 12% variation. From the principal coordinate analysis it was revealed that the inter-cluster distance was higher than the intra- cluster distance, the highest inter-cluster distance (10.99) was estimated between cluster IV and cluster VIII. Three isoenzymes, viz. GOT, MDH and PER were used to investigate genetic diversity of 73 lemon accessions. Eight zymotypes with GOT, 10 with MDH and 7 with PER were formed by 22, 39 and 12 bands at different Rf values, respectively. Based on three isozyme banding patterns, the 73 accessions were grouped into nine clusters. RAPD analysis of 73 lemon accessions was done to detect genetic diversity at the DNA level. Among the 39 primers tested, 5 decamer primers amplified 44 bands of which 32 (73%) were polymorphic. Nei's gene diversity was 0.309 and Shannon's information index was 0.443 across all loci. According to UPGMA dendogram based on Nei's genetic distances revealed that the 73 accessions were grouped into nine clusters. It was evident from morphological, isozyme and RAPD analyses that there was no relationship between genetic divergence and geographical distribution of accessions. Correlation studies between yield and yield components indicated that plant height, percent fruit set, diameter of fruit and number of fruits per plant had significant positive correlation with yield. Parameters, like, length of fruit, diameter of fruit, average weight of fruit and number of seeds per fruit were found to have significant negative correlation with ascorbic acid content. For most of the cases, genotypic, correlation coefficient was higher than phenotypic ones. Crossing between 7 selected parents was performed in diallel method without reciprocal. Success of crossing was 20 to 56%. Intra-specific hybrids were characterized using GOT and MDH isozyme analyses. Thirteen hybrid specific bands were formed, six with GOT and six with MDH, none of which was present in their respective parents. For more confirmation, RAPD analysis was used to detect 21 hybrids of lemon. With three primers, 14 amplified bands were found in F, but not from that of either parent indicating hybrid specificity. None of three primers alone was able to detect all 21 hybrids.