Triploid Formation and Heat Tolerance of Angelonia angustifolia with Various Ploidy Levels

Angelonia ( Angelonia angustifolia ), a popular potted flower and bedding plant, often experiences severe wilting or leaf drying during hot summers in tropical and subtropical regions. Polyploidization may enhance the heat tolerance of angelonia plants. In this study, diploid (2 x ) angelonia ‘Serena Purple’ and ‘Serena White’ were crossed with tetraploid (4 x ) lines to produce interploidy plants. More seed production was observed from 4 x × 2 x crosses than from 2 x × 4 x crosses. Despite observing triploid block in interploidy hybridization, triploid plants were successfully obtained from the interploidy seeds. Growth, flowering, and photosynthesis of diploid, triploid, and tetraploid plants were assessed at day/night temperatures of 30/25 °C and 25/20 °C. All angelonia plants exhibited increased height and stem diameter as well as reduced leaf SPAD-502 value, leaf thickness, flower number, flower length, net photosynthetic rate, and stomatal conductance at 30/25 °C compared with those at 25/20 °C. At 30/25 °C, triploid and tetraploid plants had higher leaf SPAD-502 values, leaf thickness, and net photosynthetic rates than those of diploid plants. Diploid plants had the most branches at 25/20 °C, but their branch and flower numbers decreased the most at 30/25 °C compared with those of triploid and tetraploid plants. Notably, at 30/25 °C, triploid plants exhibited the earliest f lowering and produced the most branches and flowers compared with those of diploid and tetraploid plants.