Morphological and molecular characterization of nerium (Nerium oleander L.)

Abstract

The study entitled "Morphological and molecular characterization of nerium (Nerium oleander L.) genotypes" was conducted at the Department of Floriculture and Landscaping, College of Agriculture, Vellayani, Thiruvananthapuram, during the period 2022-2024. The primary objective was to evaluate the performance of fifteen nerium genotypes and to characterize them using morphological descriptors and molecular markers for assessing their genetic variability and diversity. Analysis of variance revealed significant differences among the genotypes for all morphological traits, including plant height, leaf blade length, and leaf blade width. Among the fifteen genotypes, twelve (T1, T2, T3, T4, T5, T6, T8, T9, T10, T11, T13 and T15) flowered during the experimental period. Floral characteristics, such as the number of flowers per plant at full flowering stage (i.e. two months after first flowering), flower diameter, corolla throat length, corolla throat diameter, corolline appendage length, and sepal length, also showed significant variations among the genotypes. Leaf blade width showed the highest phenotypic and genotypic coefficients of variation (PCV and GCV) among the plant traits, while the number of flowers per plant at the full flowering stage (i.e., two months after flower initiation) showed maximum variation among the floral traits. Heritability was high across all traits (69.6%–100%), with leaf blade length and single flower weight recording the maximum values. Notable genetic advance was observed, especially in the number of flowers per plant and corolla throat diameter. Traits with high heritability and genetic advance indicate strong genetic control, making them ideal for selection in breeding programmes. Correlation analysis revealed that flower diameter exhibited a significant positive genotypic correlation with plant height, length and width of leaf blade, corolla throat diameter, single flower weight, and shelf life. However, a negative correlation was observed between flower diameter and both the number of flowers per plant and overall flower yield. Additionally, plant height showed a significant 126 positive phenotypic correlation with flower diameter, corolla throat diameter, and single flower weight. Although flower diameter was negatively correlated with the number of flowers per plant, it displayed a strong positive correlation with plant height, corolla throat diameter, and single flower weight, making it a crucial trait for selecting loose flowers. Genetic diversity analysis using the ‘Average method’ and ‘Euclidean distance measures’ clustered the genotypes into four groups based on floral characteristics. The maximum inter-cluster distance was observed between cluster 3 and cluster 4, suggesting that hybridization between these clusters would be most effective. Scoring based on DUS guidelines revealed the highest score for genotype T13 and it was followed by T1 and T4. Molecular characterization of the fifteen genotypes was carried out using ten ISSR primers, all of which generated polymorphic bands. Among the 98 amplicons obtained, 81 exhibited polymorphism, whereas 17 were found to be monomorphic. Among the primers, UBC 826 yielded the highest number of alleles (14), while UBC 814 produced the fewest (3). The primer UBC 855 exhibited the highest polymorphic information content (PIC) value of 0.38, whereas UBC 814 showed the lowest PIC value of 0.15. Based on the cluster analysis of the molecular data, the genotypes were grouped into three distinct clusters: Cluster 1 consisting of seven genotypes (T1, T2, T4, T7, T8, T9, T12), Cluster 2 also containing seven (T3, T6, T10, T11, T13, T14, T15) and Cluster 3, comprising a single genotype (T5). Among the genotypes, T3 exhibited the highest yield of fragrant flowers, followed by T1, making them ideal for loose flower production and potential parental genotypes for breeding programmes. T5 was identified as a dwarf genotype, suitable for potted plant applications. Seasonal variations in flower production were observed across all the genotypes which flowered during the experimental period. These findings provide valuable insights into the morphological and genetic diversity of nerium genotypes, aiding in the selection of superior genotypes for floriculture and breeding purposes.