Preliminary Integrated Phenotypic Characterization of Nine Commercial Marigold Cultivars in a Single-Plot Greenhouse Trial

Marigold (Tagetes spp.) is an ornamental and functional crop valued for flower form and carotenoids. This preliminary single-season study characterized nine commercial cultivars of the Taishan (T. erecta), Durango, and Super Boy (T. patula) series grown in one greenhouse (one plot per cultivar; ten plants). Growth, biomass, flower morphology, color, and an absorbance-based lutein-equivalent index were combined with correlation analysis, principal component analysis (PCA), and clustering. Cultivars differed in all plant traits (descriptive Welch ANOVA, p ≤ 0.003) and height trajectories (cultivar × date, p < 0.001), but because plot and cultivar were confounded, these tests are descriptive only. Durango Yellow had the largest height increment between 8 and 22 June (10.25 cm versus ≤ 4.03 cm in the others). The lutein-equivalent index (one pooled sample per cultivar; not HPLC-validated) was highest in Super Boy Orange (46.88 mg g−1 DW) and near the quantification limit in three cultivars. PCA of 12 traits explained 51.57% and 22.57% of the variance in PC1 and PC2, separating size and biomass from pigment, color, and architecture. PC1 was unchanged without the pigment index, whereas cluster composition depended on it. The data provide a descriptive baseline for replicated, multi-environment experiments with HPLC-validated pigment analysis.