VERBENA SEED HILUM MORPHOLOGY CONTRIBUTES TO IRREGULAR GERMINATION

The germination of verbena (Verbena x hybrida) seed was found to be sensitive to high substrate moisture content. Cultivars varied in sensitivity to excessive substrate moisture content, with 'Romance Scarlet' having higher total germination (G) in the presence of free water than 'Showtime Blaze' or seedling 'Red A'. Hilum cavity measurements of dry seeds showed larger hilum apertures with reduced depths for seeds of 'Romance Scarlet' than for the others. Seed imbibition resulted in a rapid and extensive thickening of the hilum wall. The extent of hilum aperture closure varied among cultivars and the quantity of water present. Free water reduced hilum apertures 45% for 'Romance Scarlet', 60% for 'Showtime Blaze', and 86% for 'Red A'. Seeds of 'Romance Scarlet' and 'Showtime Blaze' failed to germinate with lanolin covering the hilum, while seeds coated with lanolin, except for the hilum, had 67% to 78% G of nontreated seeds. This difference indicates that essential oxygen for the embryo was obtained through the hilum and micropyle of the seeds. Total germination varied with substrate moisture content, with seeds placed horizontally on 2%, 1%, or 0.5% agar having 80%, 75%, and 65% germination, respectively, for 'Romance Scarlet' and 59%, 41%, and 24%, respectively, for 'Showtime Blaze'.