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Heritability estimates of traits assist breeders in optimizing cultivar development and can help predict gain from selection in breeding programs. Narrow‐sense heritabilities were measured in agronomic traits and glycoside concentration in four elite stevia (Stevia rebaudiana Bertoni) populations using half‐sib family analysis. Gain from selection at 20% selection intensity was estimated for morphological, yield, and glycoside traits. Experiments were conducted in two field locations in North Carolina. Variation was observed across cultigens for agronomic traits including stem height, branch width, and leaf size, for both subjective and objective measurements. Yield, lodging resistance, disease resistance, and percent survival showed a high genetic variation across cultigens. In addition, glycosides including Reb A, Reb C, and Reb D also showed high variation by cultigen. Heritability estimates for plant morphological traits were highest for stem height, and moderate for yield and branch width. However, other traits such as leaf area and lodging resistance showed low heritability (0.10). Glycosides including Reb A, Reb C, Reb D, stevioside and total steviol glycosides (TSG) showed high heritability. The estimated gain from selection per year for stem height (24 mm/year), leaf area (131 mm2/year) and yield (dry weight) (1.2 Mg/ha per year) suggest significant improvements are possible per breeding cycle. The estimated gain for glycoside concentration and percent of TSG of Reb A (26.44 mg/g, 14.51%), Reb C (20.20 mg/g, 20.17%), Reb D (1.70 mg/g, 1.49%), stevioside (6.73 mg/g, 10.72%), and TSG (20.90 mg/g), similarly, indicate significant gains are possible per breeding cycle. Core Ideas: The stevia cultigens evaluated showed high variability for yield and glycoside traits.Heritability estimates for morphological traits were medium to high for plant height, width, and yield.Heritability estimates for Reb A, Reb C, Reb D, stevioside, and total steviol glycosides showed high heritability.Estimated gain from selection for yield and glycosides suggest significant improvement are possible. [ABSTRACT FROM AUTHOR]

The watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus) has high variability for fruit size, shape, rind pattern, and flesh color. This study was designed to measure the qualitative inheritance of rind phenotypes (solid dark green vs. light green). For each of the 2 families, “Mountain Hoosier” × “Minilee” and “Early Arizona” × “Minilee,” 6 generations (PaS1, PbS1, F1, F2, BC1Pa, BC1Pb) were developed. Each family was tested in summer 2008 in 3 environments in North Carolina. Phenotypic data were analyzed with the χ2 method to test the segregation of Mendelian genes. Deviations from the expected segregation ratios based on hypothesized single dominant gene for solid dark green versus light green rind pattern were recorded, raising questions on the inheritance of this trait. Inheritance of solid dark green rind versus light (gray) rind showed duplicate dominant epistasis. Duplicate dominant epistasis gives rise to a 15:1 ratio (solid dark green:light rind pattern) in F2 generation. When both the loci are homozygous recessive, we observe light rind pattern. The g-1 and g-2 genes were identified to control light green rind when in homozygous recessive form. [ABSTRACT FROM PUBLISHER]

Fruit weight in the cultivated watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] ranges from 1 kg to over 100 kg. In recent years, preference of consumers has shifted toward fruit of smaller sizes than the large sizes traditionally used for parties and picnics. This has produced increased interest in the genetics of fruit weight, especially among watermelon breeders. The objectives of this study were to determine the inheritance of fruit weight. Six adapted cultivars having very large or very small fruit weight were crossed in a half diallel. Field trials were conducted at two locations in North Carolina (Clinton and Kinston). Large-fruited parents had higher phenotypic variance than small-fruited parents. Environmental variance was higher than genetic variance (mean, 7.58 and 3.82, respectively) at Kinston, NC. At Clinton, NC, genetic and environmental variances were similar (mean, 9.45 and 8.99, respectively) for 67% of the families. Narrow- and broad-sense heritability estimates were low to intermediate (mean, 0.59 and 0.41, respectively). A high number of effective factors (mean, 5.4) was found to influence fruit weight in watermelon. Watermelon breeders should use quantitative methods such as recurrent selection for population improvement to change fruit weight in the development of new cultivars. [ABSTRACT FROM AUTHOR]

High yield is a major goal for watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] breeders. The objective of this study was to measure yield in a diverse set of watermelon cultivars to identify high-yielding germplasm for use in breeding programs. Phenotypic variation for fruit yield in a diverse set of 80 watermelon cultivars was studied in the field in North Carolina. Yield was evaluated in replicated experiments of three environments (combinations of 2 yr and two locations), and two to four replications per environment. Plots were hare vested one to two times, depending on the average maturity of the fruits at the first harvest. The highest yield overall was obtained from 'Mountain Hoosier' and 'Starbrite'. Some of the new, elite hybrid cultivars were in the top-yielding group, but there were old, inbred cultivars in the top group as well. Consistent and significant yield differences among the 80 cultivars across environments indicates genetic variation for the trait. In addition, high-yielding cultivars for use in breeding programs were identified. Watermelon breeders interested in developing new, high-yielding cultivars should make use of top performers in this study in their breeding programs. [ABSTRACT FROM AUTHOR]

Presents a study which evaluates all available cultigens of cucumber for downy mildew resistance under field conditions in North Carolina. Methodology used to conduct the results of the study; Results of the study; Discussion surrounding the results of the study.

• Superior cultigens were identified using publicly accessible seed lines. • Genetic diversity of cultigens impacted biomass and yield of steviol glycosides. • Steviol glycosides are also influenced by environment and G x E interactions. • Plant height and width are important considerations in screening for yield. • Leaf size was not an effective indicator of yield. Currently, stevia (Stevia rebaudiana Bertoni) seeds are available to growers from many sources, but the origin of these populations is often unknown. Since stevia is a natural outcrosser, populations are heterozygous and heterogeneous. We were interested to characterize germplasm from 16 sources of stevia seeds for traits including yield, glycosides, and plant morphology, and then identify trait correlations. The cultigens evaluated were obtained from garden seed companies and commercial sources, and the trials were conducted for two years at two field locations. To quantify plant morphological traits, objective measurements were collected at two intervals to determine stem height, branching width, and leaf area. In addition, we screened for lodging and disease resistance, and yield before flowering stage. The cultigens tested were highly variable for yield and steviol glycosides, suggesting that a diverse genetic base is found among the population which is readily available to growers and breeders. High-yielding cultigens for biomass and glycoside concentration were identified. Cultigens with the highest yield and stability over years were seed-derived progeny from 'Katupyry', sourced from Stevia Store, and represent genetics useful in breeding for increased biomass. Cultigens with the highest glycoside level were NC-1003 and NC-1022, seed grown from Seed Savers, and could be used to improve desirable glycosides. This study highlights readily available seed cultigens that can be used to develop elite breeding populations. [ABSTRACT FROM AUTHOR]

Downy mildew, a foliar disease caused by the oomycete Pseudoperonospora cubensis (Berk. and Curt.) Rostow, is one of the most destructive pathogens of cucurbits. From 1961 to 2003, resistant cucumber cultivars in the United States had sufficient resistance to grow a successful crop without the use of fungicides. The pathogen resurged as a major problem in 2004. Since then, the dm-I gene has not been effective against the new strain of downy mildew, and yield losses are high without the use of fungicides. The objective of this experiment was to identify cultivars having high yield and resistance to the new downy mildew. The experiment had 86 cultivars and breeding lines (hereafter collectively referred to as cultigens) and was conducted in Clinton, NC, in 2007 and 2009, in Castle Hayne, NC, in 2008 and 2009, and in Bath, MI, in 2007 to 2009. Plots were rated weekly on a 0 to 9 scale (0 = none, 1-2 = trace, 3-4 = slight, 5-6 = moderate, 7-8 = severe, and 9 = dead). Mean ratings for downy mildew leaf damage ranged from 2.9 to 5.7 in Michigan in 2008 and 2009 and from 3.8 to 6.8 in North Carolina in 2007 to 2009. None of the cultigens tested in this study showed a high level of resistance, although differences in resistance were detected. Lines WI 2757 and M 21 and cultivar Picklet were consistently among the top resistant lines in North Carolina and Michigan. The cultivars Coolgreen, Wis. SMR 18, and Straight 8 were identified as moderately to highly susceptible. An unreleased hybrid, 'Nun 5053 Fi', and the cuitivar Cates were the top yielding lines overall. The highest yield in a single year and location was from the cultivar Cates in Clinton, NC, in 2009, with 25.6 Mg ⋅ ha-1. The best cultivars in this study were only moderately resistant and would likely require fungicide applications to achieve high yield and quality in the presence of downy mildew. Until high resistance becomes available, growers would benefit by using fungicides in combination with tolerant and moderately resistant cultigens. [ABSTRACT FROM AUTHOR]