Partitioning the Genetic Variability for Seedling Growth in Sand Bluestem into Its Seed Size and Seedling Vigor Components1

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Abstract
Spaced plants of ‘Goldstrike’ sand bluestem (Andropogon hallii Hack.) were used to obtain estimates of the genetic variances for caryopsis weight, seedling weight at 8 weeks which was used as a measure of seedling growth, and 1st year forage yields. Since caryopsis weight has a positive effect on seedling weight, seedling weights were adjusted for caryopsis weight using regression analyses. Adjusted seedling weights are a measure of seedling growth with the effect of seed size excluded and as such were used as an estimate of seedling vigor. Heritability estimates were calculated using variance components. The broad‐sense heritability estimate for caryopsis weight was 0.87 while the narrowsense heritability estimates for seedling weight, adjusted seedling weight (seedling vigor), and 1st year forage yield were 0.37, 0.22, and 0.63, respectively. As indicated by the heritability estimates, almost half of the genetic variability for seedling weight was due to variation for caryopsis weight while the remaining genetic variability was due to seedling vigor. The genetic correlation of caryopsis weight and seedling weight was 0.70. Selection for seedling weight by indirect selection for caryopsis weight would result in expected gains from selection almost as large as those for direct selection for seedling weight. However, the genotypes selected by the two methods would not be identical. Selection for seedling weight involves selection for both seed weight and seedling vigor and should optimize breeding gains for improved seedling vigor. The correlations of caryopsis weight and seedling weight with post‐establishment 1st year forage yield were small (r ≤ 0.15).