This document discusses phenotypic and genotypic variation in onions. It notes that onions are highly outcrossing and show strong inbreeding depression. Variation exists in traits like bulb size, sweetness and color, which is inherited through major genes. Quantitative trait loci have been mapped that control soluble solids content. The goals of the studies discussed were to identify genetic regions controlling bulb color and color intensity, and to estimate correlations between anthocyanin concentrations and other traits. Overall the document examines sources of genetic variation in onions and inheritance of traits like bulb color.

1. Phenotypic and genotypic coefficient of variation
and inheritance pattern in Onion
By
15-arid-5095

2. Introduction
Onion is a diploid (2n = 2x = 16) plant with natural
out crossing rates in the field ranging between 70
and 100% and is reported to show strong
inbreeding depression.
Due to its nutraceutical properties, it has been
cultivated for more than 4000 years.
 The primary center of domestication is in
southwestern Asia, while other regions of great
diversity like those in the Mediterranean areas are
considered secondary centers.
 Onions are grown all over the world, under
different agro climatic conditions.
Taxonomically, onions belong to section Cepa.
Villano et al. 2019

3. Genotypic variation in onion
In genotypic Variation
Genetic variability in cultivated onion is strongly
desirable to develop association genetics and to
allow breeders to identify novel alleles or haplotypes
to improve productivity, adaptation, quality, and
nutritional value.
Characteristics
Quantitative trait loci (QTLs) controlling the
concentrations of soluble solids in onion bulbs have
been mapped to chromosomes 3, 4, 5, and 8.
Distilling the molecular diversity and the genetic
structure of 73 onion accessions, which include
cultivated landraces, commercial varieties, and wild
species, using a custom-made KASP assay
consisting of 400-expressed sequence tag (EST)-
derived SNP markers. Duangjit et al. 2014 , Villano et al. 2019

4. Phenotypic variation in onion
In Phenotypic variation
Selection by growers and breeders has produced cultivars with
widely varying adaptation, bulb size, sweetness, storability
and processing quality, with correspondingly large variation in
bulb carbohydrate composition.
Onions are a major source of dietary fructans, contributing
25% of the average American intake.
Characteristics
Inheritance of blub color in onion
Color classes: white, pink, red, or yellow
Dominant basic color factor ‘C’ necessary for either red or
yellow color.
six major genes loci I, C,G, L, L2, and R.
White bulbs are conditioned by a dominant allele at the I locus
which is a color inhibiting factor dominant over I, or the
homozygous recessive genotype at the C locus which is a
basic color factor.
Mccallum et al. 2006

5. Phenotypic variation in onion
Characteristics
A dominant allele at the G locus conditions golden yellow bulbs,
while the iiC-gg genotypes are chartreuse.
 Red bulb color is conditioned by dominant alleles at the R locus
and either the L.
Transcripts of dihydroflavonol 4-reductase (DFR) were observed in
red onion, and it was proposed that blockage of DFR translation
results in lack of anthocyanin production in yellow onion reported
that the L locus encodes anthocyanidin synthase (ANS) and
proposed that at least four alleles exist at this locus conditioning
yellow (ANS-l), pink (ANS-p), conditional-red (ANSh1), and red
(ANS-L) bulbs, given that a dominant allele resides at the R locus
assigned ANS and DFR to chromosomes 4 and 7 of onion.
Demonstrated that DFR co-segregates with the R locus on
chromosome 7 and identified an additional locus (L2) on
chromosome 4 linked to L that also interacts with R to condition
red bulb color. Duangjit et al. 2014

6. Phenotypic variation in onion
Characteristics
Mapping of QTLs (Quantitative trait locus) is an efficient
approach to identifying major genes and increasing the
selection efficiency in a breeding program.
Detection of major QTLs for bulb-quality traits, such as
concentrations of fructans and flavonoids, should
enhance selection for these beneficial compounds.
The goals of this study were to identify chromosome
regions that condition yellow versus red bulb colors, as
well as the intensity of red bulb color, using segregating
haploid progenies.
A second goal was to estimate correlations between
anthocyanin concentrations, visual assessments of red
color, and soluble-solids contents in onion bulbs. The
long-term goal of this research is to breed for increased
anthocyanin concentrations in onion bulbs.
Duangjit et al. 2014

7. References
Sunil, N. Kumar, V. Thirupathi, R., & Kamala, V. (2014). Phenotypic
diversity and variation a collection of onion (Allium Cepa L.) Germplasm
from peninsular India. Electronic journal of plant breeding, 5(4): 743-751
Dangjit, J. Welsh, K. Wise, M.L. Bohanec, B., & Havey, M.J. (2014).
Genticanalyses of anthocyanin concentration and intensity of red bulb
color among sepregating haploid progenies of onion. Mol breeding, 34:
75-85
Villano, C. Esposite, S. Carucci, F. Lorizzo, M. Fruciante, L. Carputo, D.,
& Riccardo, A. (2019). High through put genotyping in onion reveals
structure of genetic diversity and informative SNPs useful for molecular
breeding. Mol breeding, 39: 5
Mccallum, J. Clarke, A. Pither-Joyce, M. Shaw, M. Don Brash, R.D.
Scheffer, J. Sjaak van Heusden, I.S. Michael J., & Havey, M.S. (2006).
Genetic mapping of a major gene affecting onion bulb fructan content.
Theor Appl Genet, 112: 958–967