Unreduced Gametes and Polyploidization In Lantana Camara

Polyploidization is common in plants and has been one of the major driving forces in plant evolution.  A wide range of ploidy levels, ranging from diploid to hexaploid, exists in Lantana camara, and tetraploids are more frequently found in naturalized lantana populations than native ones.  It has been an important, but yet to be addressed, question what was the mechanism of polyploidization in lantana.  The distribution of ploidy levels in more than 500 progeny from self-pollination of 'Gold', 'Lola', and 'Pink Caprice' and more than 350 progeny from open-pollination of 'Carlos', 'Cream', 'Dallas Red', 'Gold', 'Irene', 'Lola', and 'Pink Caprice' were analyzed in this study, and the results showed occurrence of unreduced gametes in some cultivars while absence in other cultivars.  More than 40 controlled crosses were made between these two groups of cultivars over four seasons, and the ploidy level distribution in these progeny confirmed the variation among cultivars in their ability to produce unreduced gametes.  Further studies showed that the trait could be transmitted from one generation to the next and it appeared to be controlled by nuclear genes.  When unreduced gamete-forming cultivars were present, we observed a wide range of polyploidy levels (triploid to hexaploid) in open-pollinated progeny, which strongly suggests that the occurrence of unreduced gametes contributed to polyploidization in lantana.  This phenomenon may also explain the unexpected fertility of some lantana triploids.  Additionally, it indicates a need to avoid unreduced gamete-producing diploids and tetraploids in inter-ploidy crosses designed to produce triploid lantana for genetic sterilization and invasiveness control.