Identification of a major QTL controlling onion bulb shape

Onion (Allium cepa L.) has considerable variation in bulb shape, one of the important breeding traits to cater to consumer preference and demand in different markets.
The bulb shape varies from flat to globe to torpedo and has a relatively high heritability trait.
However, the genetic factors controlling the bulb shape have not been investigated yet.
To identify these genetic factors, the two F₂ populations (Pop1 and Pop2) obtained by crossing different shaped cultivars were analyzed.
The bulb shape was evaluated using the SHAPE program package, in which the bulb contour was extracted from photographed images.
This information was translated to the standardized elliptic Fourier descriptors, and the coefficients were summarized by principal component analysis (PCA) scores used as quantitative phenotypic values.
The first PCA score (PC1) explained 74 and 80% of the total variance of the bulb shape in Pop1 and Pop2, respectively.
PC1 was highly correlated to the ratio of height to diameter of the bulb in both populations (r=0.83 in Pop1 and 0.85 in Pop2). Quantitative trait locus (QTL) for PC1 was detected by composite interval mapping using the genotype data obtained from genome-wide 348 and 341 single nucleotide polymorphism markers.
Three and four PC1 QTLs were detected in Pop1 and Pop2, respectively, among which the QTL on chr5 was the highest with logarithm of the odds score in each population.
This major QTL explained 32.4 and 23.9% of total variance in Pop1 and Pop2 and showed an incomplete dominant effect.
The results indicated that the QTL is novel and useful for efficient breeding with improved bulb shape in onion.

IV Asian Horticultural Congress – AHC2023

D. Sekine, H. Tsukazaki, S. Oku

shape evaluation, genetic analysis, quantitative trait, segregating populations, breeding

https://doi.org/10.17660/ActaHortic.2024.1404.77