Characterization of Morphological Diversity in Marigold (Tagetes spp.) Accessions in Sri Lanka: A Preliminary Study

The study evaluated twenty-five marigolds (Tagetes spp.) accessions in Sri Lanka, identifying them taxonomically as T. erecta (African marigolds). Despite its increasing demand in Sri Lanka, there has been limited scientific assessment of the floral morphological variation in locally available marigold accessions, which is essential for guiding breeding, landscaping, and commercial applications. Marigold accessions were collected from various locations in Sri Lanka and cultivated at the Faculty of Agriculture, University of Ruhuna, Sri Lanka. All together ten traits were considered for the analysis including plant architecture, petal colour, flower diameter measurement, and morphological classification of disc and ray florets; Flowers were categorized into single, semi-double, double, and anemone types based on ray and disc floret arrangements. The accessions displayed a diverse range of flower colours, including ranges of colours in yellow and orange. Flowers were classified into three size categories: small (<3.9 cm), medium (3.9–4.9 cm), and large (>5 cm). Single-type flowers were observed in accessions 2, 8, 15, and 22, while semi-double appeared in accessions 1, 2, 3, 4, 11, 13, 18, 23, and 24. Accession 6 was double type and accessions 5, 6, 7, 10, 14, 17, and 21 were anemone-type flowers (featured prominent disc florets in all colour ranges). The floral trimorphism was recorded in accessions 22 and 24. Principal Component Analysis (PCA) revealed that the first three principal components accounted for 73.38% of the total phenotypic variation. PCA results showed that variation among marigold accessions was primarily influenced by traits related to floral productivity, and branching (PC1), as well as flower size and structure (PC2), highlighting their value as key descriptors for genetic diversity assessment and breeding selection. Hierarchical clustering using Ward’s method grouped the 25 flower accessions into three distinct clusters, reflecting clear phenotypic differentiation based on the evaluated morphological traits. The constructed key can be utilized to distinguish studied marigold accessions in future. This floral diversity supports the development of cultivars suited to consumer preferences. Single and semi-double types can be promoted for biodiversity conservation and ecological sustainability, attracting pollinators in agroecosystems since they have a lot of disc florets for seed production. Meanwhile, double and anemone types can be commercially propagated for premium floriculture markets, enhancing economic value since they have attractive appearance.