Pollen Stainability and Seed Production of 32 Lantana Camara and 2 Lantana Montevidensis Cultivars

While it is a popular ornamental plant well known for its attraction to butterflies, tolerance to abiotic stresses, and adaptation to environmental conditions, Lantana camara has been listed as an invasive species in south and central Florida and in a number of countries in the world.  L. camara's invasive potential comes primarily from its ability to produce large amounts of seed and/or its ability to cross-pollinate native Lantana species.  The objectives of this study were to assess the pollen stainability and seed set of 32 Lantana camara cultivars and compare them to Lantana montividensis cultivars and to understand the relationships between ploidy levels and pollen stainability and seed set.  For pollen stainability assessment, anthers were collected before flower dehiscence and stained in aniline blue for 24 hours at 60°C.  Over 160,000 pollen grains were then examined and scored as stained or unstained.  For seed set assessment, 20 seed heads on a plant were randomly selected and seeds were counted.  Seed collection and counting were repeated every 5 weeks for four times.  Pollen stainability among the L. camara cultivars ranged from 0.8% ('New Gold') to 75.9% ('Pink Caprice'), i.e. nearly 100-fold difference between cultivars.  An even greater difference (>1000-fold) was observed among cultivars in seed set, from 0.13 seeds in 'Athens Rose' to 143.5 seeds in 'Pink Caprice'.  L. camara cultivars showed higher pollen stainability and seed set than L. montividensis cultivars.  Among the various ploidy levels in L. camara, triploids were the most sterile, with an average pollen stainability of 10.0% and an average seed set of 14.5.  However, some triploids had rather high pollen stainability (e.g. 21.8% in 'Landmark Peach Sunrise Improved') or produced quite a number of seeds (e.g. 27.6 in 'Samson Lantana').  Tetraploids were found to be quite fertile: pollen stainability ranged from 31.0% in 'Gold' to 75.9% in 'Pink Caprice', with an average of 48.6%, and seed set from 11.5 in 'Dallas Red' to 143.5 in Pink Caprice', with an average of 47.4.  In pollen stainability, diploids averaged slightly higher than tetraploids (76.8%), but in seed set, diploids produced fewer (7.6) than tetraploids.  These results indicate that there are a wide range of variation among cultivars and ploidy levels in pollen stainability and seed set and highly sterile cultivars can be found and used as alternative to replace those highly fertile, invasive cultivars.