Genetic influences on shoot architecture in carrot (Daucus carota L.)

Crop establishment in carrot is limited by erratic germination, slow seedling growth, and delayed canopy closure. This growth habit competes ineffectively with weeds, resulting in high management costs and reduced yields. One strategy to mitigate this challenge is the development of weed suppressive varieties. However, the underlying environmental and genetic control of these traits in carrot is not well understood. This work aimed to provide the groundwork for future investigation and improvement of shoot architecture in carrot. First, a general Bayesian model was used to estimate the relative contributions of additive, inbreeding, epistatic, and parent-of-origin effects to shoot phenotypes in a six-parent diallel. Dominance effects were more influential early in the growing season, while additive effects were more important at harvest. Additionally, a discriminating tester line and high-performing hybrid combinations were identified. Next, a platform for high-throughput phenotyping of carrot shoot and root morphology was developed. Image analysis provided reliable estimates for traits with agronomic importance, including height, root length, and biomass, in addition to root shape, which does not have a hand measurement equivalent. This platform decreased the time needed to collect phenotypic data, enabling more precise estimates of carrot phenotypes for larger population sizes. Finally, the genetic basis of carrot shoot architecture was investigated in L8708 x Z020, an F₂ population that segregated for shoot architecture and root shape. Large effect quantitative trait loci (QTL) for shoot and root morphology co-localized to the distal region of chromosome 2, which is also a hypothesized domestication locus. Findings support applied breeding efforts for carrot shoot architecture by estimating inheritance, establishing a high-throughput phenotyping platform, and identifying genetic regions of interest.