Lagerstroemia indica L. is a favored landscape plant in mild-climate regions, cherished for its easy propagation and cultivation, prolonged blooming period, and variety of plant forms. The majority of new cultivars are the result of cross hybridization. However, compatibility issues arise with some cultivars and species. To enhance our understanding of the cross-compatibility of our elite cultivars, we selected four plants (C14-35, C14-39, D03-29, and D03-34) for reciprocal crosses and for crossing with other elite plants, chosen for their clean foliage and extended summer bloom periods. A total of 3126 crosses were made in the summer of 2023. By the season's end, 731 fruits were harvested to assess seed set, and viable seeds were counted in winter 2023. From these efforts, 20,862 seeds were harvested, with 5,470 identified as viable. Interspecific crosses with L. speciosa revealed that C14-35 and C14-39 had significantly better fruit set percentages (40% and 35.2%, respectively) compared to D03-29 and D03-34 (6.3% and 0%, respectively). Thus, C14-35 and C14-39 exhibit greater compatibility with L. speciosa. For reciprocal crosses, C14-39 and D03-34, when used as pollen donors, resulted in much lower fruit set percentages and seed sets than C14-35 and D03-29. Pollen studies of the four cultivars indicated that both C14-39 and D03-34 produced little to no pollen, while C14-35 and D03-29 were prolific pollen producers. Future cross hybridization studies will therefore avoid using C14-39 and D03-34 as pollen donors. A seed germination study is planned for spring 2024 to further assess the various cross combinations and confirm interspecific hybrids.
