Evaluation location: Minnesota, United States
In 2019, seeds were grown from 38 populations in Louisiana, Georgia, and Alabama. Seed was germinated in a greenhouse in Chanhassen, Minnesota. Seed from each maternal parent was surface-sown onto a soilless germination mix (Sungrow Horticulture, Agawam, MA). In the greenhouse, flats were placed on heat mats (Hydrofarm Horticulture, Petaluma, CA) and covered with clear plastic domes to maintain high relative humidity. Greenhouse temperatures were maintained between 25 and 30°C with natural daylength. After germination, seedlings were transplanted into 7.62-cm square pots holding a soilless potting medium (Sungrow Horticulture, Agawam, MA) and grown in the greenhouse until June. Seedlings were transplanted into 186.7-cm3 square pots with peat:pine bark (1:1) potting mix and transferred to an outdoor container nursery with overhead irrigation. Plants were watered as needed throughout the growing season. Because plants were completely randomized within the container nursery, random sampling was achieved by measuring the first 100 seedlings located in each population. After terminal buds were set, plants were measured from the top of the soil to the top of the apical bud on the tallest shoot, and nodes were counted on the same shoots. Internode length was estimated by dividing the total height by the number of nodes. See citations for additional details.