Stevia rebaudiana is a member of the Asteraceae family that produces sweet compounds in its leaves called steviol glycosides that are 300 times sweeter than sucrose. Steviol glycosides are non-toxic and non-caloric, making them a healthy alternative to replace artificial sweeteners and part of the sucrose market.  Stevia is a new crop in the United States and is well-suited to replace tobacco because it can be grown using some of the same production methods and equipment. Growers looking for alternative crops will be interested as researchers develop adapted cultivars and suitable methods for production. Plant breeding efforts are primarily directed at increasing the concentration of steviol glycosides and maximizing yield (Mg/ha). The studies conducted during this dissertation aimed at estimating heritability using parent-offspring regression and evaluating seed longevity under two temperature regimes to aid future researchers in improving the crop.

Stevia seed lots were harvested from field pollination cages in 2016 and used in routine germination experiments. Seed lots were evaluated for the effect of cold and room temperature storage conditions on seed longevity over a 53-month period. Twelve seed lots were selected for the seed longevity study and germinated in 3 replications over 24 time periods (quarterly) to identity optimum storage temperature and determine viability over time. Seed lots with low initial viability were not able to withstand long-term seed storage and deteriorate at a faster rate than seed lots with higher initial viability. For maximum viability, seeds should be used within 1 year if stored at room temperature (21°C), and within 1.5 or 2 years if stored in cold temperature (4°C).

Field trials were conducted in 2015 and 2016 to assess diversity and heritability in stevia populations developed by intercrossing off-patent cultivars and landraces. Analysis of variance showed wide variation among genotypes in two locations for phenotypic, agronomic, and steviol glycoside traits. Narrow-sense heritability was highest for reb-A (0.56), reb-C (0.50), Reb-D (0.40), and stem height (0.30). Pearson correlations comparing plant densities (6-plant and 30-plant plots) were high for early subjective ratings of stem height (0.72). A positive correlation was observed for early subjective branch width ratings in 6-plant and 30-plant plots (0.62). Early season subjective branch width ratings of 6-plant plots were correlated with early season stem height ratings in 30-plant plots (0.66).  Early season subjective stem height of 30-plant plots was correlated with branch width ratings of 6-plant plots (0.63). These results indicate plant density played a role in the plants’ phenotype for measured traits. Overall, the results from these studies provide stevia breeders insight to estimating heritability as well as provide guidance for storing seeds semi-long term.