Insights into the Heritability and Genetic Basis of Carrot Shoot Growth Using Bayesian Diallel Analysis

Crop establishment in carrot (Daucus carota L.) is limited by slow seedling growth, and delayed canopy closure, resulting in high management costs for weed control. Varieties with improved growth habit (i.e. larger canopy, increased shoot biomass) may help mitigate weed control, but the genetics of these traits in carrot is unknown. This project used a diallel mating design coupled with Bayesian analytical methods to determine the genetic basis of carrot shoot growth. Six diverse carrot inbred lines with variable shoot size were crossed in WI in 2014. F1 hybrids, reciprocal crosses, and parental selfs were grown in a randomized complete block design (RCBD) with two blocks in CA (2014, 2015) and in WI (2015). Measurements included canopy height and width (midseason and at harvest) and biomass. Griffing’s Method I, Model I was used to determine the influence of general (GCA) and specific combining ability (SCA), which correspond to the additive and non-additive gene action, respectively. In parallel analyses, the additive, inbreeding, epistatic, and maternal effects were estimated using a Bayesian linear mixed model, which is more robust to missing data, outliers, and theoretical constraints than traditional biometric methods. Results suggest that additive and non-additive effects significantly influence shoot traits, with a greater influence of non-additive effects at midseason. Narrow sense heritability ranged from 0.12 for root biomass to 0.42 for final canopy height. Additionally, a discriminating tester line and improved hybrids were identified. The outcomes of this project will help facilitate breeding efforts and inform selection strategies for carrot improvement.