Genet Resour Crop Evol (2015) 62:1037–1053
DOI 10.1007/s10722-014-0207-1
RESEARCH ARTICLE
Diversity in 198 Ethiopian linseed (Linum usitatissimum)
accessions based on morphological characterization
and seed oil characteristics
Negash Worku • J. S. Heslop-Harrison
Wakjira Adugna
•
Received: 24 July 2014 / Accepted: 8 December 2014 / Published online: 20 January 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract Morphological and molecular characterization of germplasm is important for the sustainable
exploitation of crops. Linseed or flax (Linum
usitatissimum) is a multipurpose crop grown in many
environments for food, feed, fibre and industry. In
Ethiopia, a centre of diversity for linseed, it is valued for
food and export. Here, we aimed to develop and use a
set of morphological descriptors to determine levels
and patterns of diversity in Ethiopian germplasm from
the tropical highlands (3–15°N, [ 2,000 m a.s.l.) in
198 Ethiopian traditional varieties. The Ethiopian
traditional varieties included plants with both fibre
and oil-seed stem-branching morphotypes, although
most were relatively small-seeded. Traditional variety
oil quality was assessed; oil content was as low as 30 %
compared to 47 % reported elsewhere. Days-to-flowering and days-to-maturity varied widely and were
Electronic supplementary material The online version of
this article (doi:10.1007/s10722-014-0207-1) contains supplementary material, which is available to authorized users.
N. Worku (&) J. S. Heslop-Harrison
Department of Biology, University of Leicester,
Leicester LE1 7RH, UK
e-mail: mhiret3@gmail.com
N. Worku
University of Gondar, Gondar, Ethiopia
W. Adugna
Ethiopian Institute of Agricultural Research,
Addis Ababa, Ethiopia
highly heritable. Ethiopian linseed had dominant and
recessive yellow seed genotypes; some had a recessive
conjoined or conjoined-seed character. The descriptors
developed here will be useful for genetic mapping and
selection of breeding lines. The results show the range
of characters which can be exploited in breeding lines
appropriate for smallholder and commercial farmers in
Ethiopia, producing a sustainable, secure, high-value
crop meeting agricultural, economic and cultural needs.
Keywords Biodiversity Descriptors Ethiopia
Flax/Linseed Landraces Linum usitatissimum
Varieties
Introduction
Linseed or flax (Linum usitatissimum) is an important
crop for seed oil, stem fibre, and, to a lesser extent,
flour. Linseed oil is used for paints, inks, varnish and
other wood treatments, soap, linoleum, putty and
pharmaceuticals. The fibre from flax is a widely used
and valuable raw material for textiles, thread/rope and
packaging materials; the straw and short fibre for pulp
to produce special papers: for cigarettes, currency
notes and artwork; and the wooden part serves
as biomass energy or litter in cattle farming
(Mackiewicz-Talarczyk et al. 2008; Rowland 1998).
The strength, non-elasticity, repeated flexibility, and
its recyclable nature, with a low density, was very
attractive for use as a rope and thread; interest in its use
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is increasing (Jhala and Hall 2010) after many years of
decline. Flax is a bast fibre consisting of the stem
phloem, contrasting with fibres such as cotton that are
from fibre cells. Linseed oil comprises five fatty acids:
alpha linolenic acid (ALA), an omega-3 fatty acid,
represents up to 61 % of the whole fatty acid
composition. It hardens in air (oxidizes), contrasting
with other solvents for paints or putties which
evaporate. Linseed meal and seed oil has many
reported health benefits (Ayad et al. 2013). Although
formerly a dual-purpose crop, most varieties are now
specialized. Linseed grows in temperate, subtropical
regions and tropical highlands.
Linum usitatissimum, the only cultivated species
from the genus Linum, has been cultivated for oil from
the start of agriculture (Zohary and Hopf 2000)
8,000 years ago, and slightly later for fibre. The whole
genome sequence (Wang et al. 2012) is enabling more
detailed study of the genes and diversity in commercially important accessions. Allaby et al. (2005)
suggest that the cultivated species arose from a single
domestication event from L. bienne, and the first
domestication characters involved selection for annual
habit, non-shattering of capsules and more efficient
self-fertilization (Fu 2011; Durrant 1976; Hammer
1984). Currently the fibre type is the third largest
textile fibre crop, and the oil-type is fifth oil crop in the
world (Ottai et al. 2011), although with a magnitude
lower production than the major fibres (cotton and
jute) or other oil crops (maize, soybean, palm and
Brassica). Of the 2,000,000 t annual world production,
China, the Russian Federation and Canada account for
more than half; Kazakhstan, USA, India and Ethiopia
produce 120,000–160,000 t each.
Linseed is well utilized and valued for food in
Ethiopia, the focus of the current work: for cooking
oil; to make a beverage especially during fasting
periods and visiting friends and relatives for cultural
occasions; for stew or ‘‘Wot’’ substituting pluses
(Geleta et al. 2002; Vaisey-Genser and Morris 2003;
Worku et al. 2012); for export (women at family level
use it as a cash crop); and medicine. However, its use
for fibre in Ethiopia is hardly known (Engels and
Hawkes 1991; Vavilov 1951; FAOstat 2014). Westphal (1975) suggests linseed has been cultivated for
3,000 years by the Agaw in Ethiopia (Abyssinia),
although this is not supported by archaeobotanical
finds of Linum from Axum before 500 BC (Boardman
1999). Edwards (1991) reported that L. strictum L., L.
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Genet Resour Crop Evol (2015) 62:1037–1053
keniense Fries, L. holstii Engl. (may also be L.
volkenssii Engl.) and L. trigynum L. var. sieberi
(Planch.) Cuf. are found in Ethiopia; Vavilov (1951)
and Harlan (1969) have proposed Ethiopia as one of
the origins and centres of diversity of linseed. In
Ethiopia, linseed is part of a crop rotation of 5–7 years
with cereals and maize as good preceding crops
(Worku et al. 2012; Rowland 1998; Seegeler 1983).
Under intensive conditions, linseed seed yield ranges
up to 3,000 kg/ha, compared to a world average of
1,000 kg/ha, similar to average yields in Ethiopia. It is
cultivated by small holders only, both for home
consumption and as a cash crop, and linseed is the
second oil crop, next to Noug (niger, Guizotia
abyssinica Cass., Asteraceae; Geleta and Ortiz
2013), being cultivated in areas where noug and
safflower are not cultivated (Seegeler 1983).
Low productivity of the crop, sensitivity to fungal
diseases, damage by pests, poor response to chemical
fertilizers and competition with weeds are major
constraints on cultivation of the linseed crop in
Ethiopia (Worku et al. 2012; Belayneh et al. 1990;
Seegeler 1983). Plant genetic resources are represented by cultivars and wild relatives which breeders
can exploit to improve agricultural production
(Heslop-Harrison and Schwarzacher 2012; Diederichsen and Fu 2008). In world germplasm collections,
there are 46,513 linseed/flax accessions reported (with
perhaps 10,000–15,000 unique accessions; Lund et al.
2013), of which only 1 % are from wild species
(Diederichsen 2007). There is some evidence that fibre
flax is over-represented compared to seed-oil collections (Diederichsen 2007). The Ethiopian Institute of
Biodiversity Conservation (IBC/ETH; formerly The
Plant Genetic Resources Centre Ethiopia, PGRC/E)
was established in 1976 to promote collection, evaluation, documentation and scientific studies; preserve
and provide germplasm for researchers; and repatriate
and introduce new germplasm into Ethiopia (Worede
1991) and has 3,433 linseed accessions (no wild
species).
Describing the characteristics of a crop species
based on standard descriptors is effective for better
utilization and conservation of germplasm (Diederichsen and Richards 2003; Bioversity International
2007). Descriptors used in genetic resources documentation can be morphological or molecular molecular, and may also include contain passport,
management, environment and site, characterisation
Genet Resour Crop Evol (2015) 62:1037–1053
and evaluation descriptions. Different researchers and
gene bank curators characterized their linseed holdings using nationally developed guidelines (UPOV
TG/57/7 2011; Maggioni et al. 2002). Descriptors,
including those used for gene mapping and heritability
studies, and understanding influence of environment
on characters, are well developed for crops such as
maize (Zea mays) (IBPGR 1991), sesame (Sesamum
indicum) (IPGRI and NBPGR 2004), Brassica (Brassica spp.) (IBPGR 1990) and tea (Camellia sinensis)
(IPGRI 1997), but linseed has variable descriptors, not
all appropriate for the full range of diversity in
cultivated and wild accessions. Robust descriptors are
required for defining ‘Distinctness, Uniformity and
Stability’ (DUS) of a variety (UPOV TG/57/7 2011).
In the present work, we aimed to generate a list of
descriptors and identify benchmark genotypes for
some morphological characters; to characterise Ethiopian linseed accessions, and determine the levels and
patterns of morphological diversity; and survey agronomic characters of the linseed crop and the status of
germplasm collection in Ethiopia.
Materials and methods
Plant materials
Two hundred linseed accessions (including a small
number of segregating traditional varieties which were
divided during the study) were used: 130 from the
Institute of Biodiversity Conservation-Ethiopia (IBC/
ETH); 21 accessions (‘‘lines’’) from Ethiopian Agricultural Research Centres; and 49 collections from
local farmers on-farm holdings. Selection of accessions acquired from IBC/ETH took into consideration
their spatial distributions to represent the different
parts of the country and agro-ecosystems as well as the
times of collections. The altitude, longitude and
latitude ranges were from 1,410 to 3440 m, 05o170 to
14o380 N, and 34o570 to 42o400 E directions, lying in
different former administrative regional divisions of
Ethiopia (Fig. 1a). Samples collected from local
farmers were also from different parts of the country.
Sites for field studies
Two environmentally different research field sites
were used to grow the linseed crop: the University of
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Gondar campus located at 12°350 0700 N 37°260 0800 E
and 2,108 m a.s.l.; and Amhara National Regional
State Agricultural Research Centre Gondar branch
Dabat site located at 12°570 5300 N 37°440 5800 E and
2,593 m a.s.l. Annual average rainfall, relative humidity and monthly average temperature of Gondar site
are 1,216 mm, 49.28 % and 20.42 °C, respectively. A
plastic house was used to study seedling characteristics, with some other laboratory-based germination
tests.
Field trials
Field studies were conducted in five cropping seasons
from 2009 to 2012 to characterize the germplasm and
to study their agro-morphological characters and
diversity under both rainfed and irrigated conditions.
The 200 accessions were grown from July to December in 2009 in the main cropping season at both sites
using a randomized complete block design (RCBD)
field layout. Qualitative and quantitative characteristics were scored for 44 traits adopted from UPOV TG/
57/7 (2011) and Maggioni et al. (2002) (IFDB). For
spatial diversity analysis altitude information grouped
into eight classes using Agarwal (1996) formula:
I ¼ LK S; where I is class width; L is the largest and S is
the smallest values from altitude records, respectively;
K is number of classes obtained from K = 1 ?
3.322logn10; and n is total number of observations,
which is 130.
Cotyledon leaf, boll and seed sizes were measured
using Photoshop software from pictures scanned on a
scaled computer flat-bed scanner (mean of five
measurements). Seed coat colours were scored by
comparison with standards by multiple observers. Boll
dehiscence status from hybrid plants was measured by
heating matured and dry bolls from 22 to 80 °C for
40 min on an electrically heated clay disc (‘‘Mitad’’)
and then kept at room temperature for 15 min before
scoring the degree of dehiscence. Oil content was
measured from oven-dried and intact seed by continuous-wave nuclear magnetic resonance spectroscopy
(NMR; Newport 4000NMR Analyzer, Oxford Analytical Instruments, UK) as an average of three
readings from three samples. Fatty acids compositions
from intact seed samples were analyzed by using NIR
System model 5,000 (Foss NIRsystem Inc., MD, USA)
in the reflectance mode at 1,108–2,492 nm with an
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Genet Resour Crop Evol (2015) 62:1037–1053
Fig. 1 Ethiopian linseed collections sites and diversity between
accessions. A Former administrative regions (1–13) of Ethiopia
with locations of collections (symbols), overlaid with topographic map (green \250 m a.s.l. through brown to white
[3,000 m). Numbers of on-farm collections are show in a light
box while those from ARC are shown in light boxes. B Plots
(1.5 m 9 1.5 m) show extensive variation in characters that
were measured including plant height, growth habit, branching,
colour (on-line version) and flowering date (days to flowering).
(Color figure online)
8 nm step. Each sample was scanned five times and the
mean composition of each fatty acid in a sample seeds
determined. Fifty seeds from each of 198 accessions
were planted on compressed and levelled bed soil with
two centimetres depth furrows in plastic house. The
soil was kept wet constantly. Germination time (days),
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Genet Resour Crop Evol (2015) 62:1037–1053
germination percentage, cotyledon leaf size, seedling
stem colour, length of hypocotyl, and primary branch
development were determined as seedling characteristics and vigour. Germination time (GT) was deterðN xT ÞþðN xT ÞþðN 3xT Þþ...þðN xT
1
2
2
3
3
n
nÞ
mined using: GT ¼ 1 Total
number of seeds germinated
where: Nn = number of seedlings emerged at the
prescribed time (day); and Tn- = the prescribed time
(day) used to score germinated seeds. Germination
Number of seeds germinated
percentage ðGPÞ ¼ Number
of seeds used for the study 100.
From the 198 sample germplasm accessions grown
for characterization and diversity studies, 44 accessions were selected as core samples to conduct tests for
DUS in the next growing season and then to develop
descriptors. Quantitative and qualitative characters
were examined using measurements from a single
plant or its part (MS), or from groups of plants or their
parts (MG); visual assessments from single plant or its
part (VS), or from groups of plants or their parts (VG)
depend on the element used to characterize the
accession. Mean values with standard deviations were
used to describe characters from accessions with a
heterogeneous plant population. The Royal Horticultural Society (RHS) colour chart was used in natural
daylight to determine colour. Most scores of characters
were grouped into classes between one and nine.
Where use of a 9 point scale was not appropriate, some
of the numbers were omitted to fit the number of
classes. Seeds from plants of an accession showing
different expressions for subclasses of a trait were
harvested separately and grown on separate plots for
further characterization for uniformity and stability.
These characters were scored in three generations both
at the same and different field sites from June 2009 to
December 2012, with rows typically 20 cm apart with
10 cm distance between plants, with three replications.
Descriptive statistics, correlation, principal component analysis and analysis of variances were conducted on different groups of genotypes by using SAS
Version 9.1. and PAST Version 1.18.
Results
Descriptors for linseed germplasm
Table 1 details the nature and range of agronomic
and morphological descriptors and classifiers that we
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defined for the linseed germplasm grown in field plots
(Fig. 1). Ranges reported below refer to the 198
accessions of Ethiopian material except where noted.
Seedling characters: For germination time (GT),
only two accessions (1 %) took 7 days or more for
germination. For germination percentage (GP), the
total number of seedlings emerging from 19,800 seeds
was 18,878 (overall germination 95 %): in two
samples seed quality was notably lower than others,
with c. 30 % of seed having either a concave, slightly
shrivelled testa, or uneven matt coloration. In seedlings, cotyledon leaf size (CL) was variable in surface
area (Fig. 2). Many accessions (132 or 67 %) had
seedlings with heterogeneous sizes of cotyledons. The
timing of basal branch development (BD) was scored
as a measure of seedling vigour at 17 days old
(Table 1; Fig. 3); 79 accessions were heterogeneous
(fast ? medium: 27; fast ? medium ? late: 6; medium ? late: 46), although, whether this was a consequence of genetic heterogeneity or environment is not
clear. As a general characteristic, linseed plants
showed the development of lateral shoots on the
epigeal stem when the first shoot including the
cotyledon leaves was removed by the researchers or
by rabbits in the field. When the lower part of a mature
plant stem is damaged and approaches the ground,
adventitious roots developed on the upper and healed
part of the stem.
Plant characters: Days to flowering (DF) showed
continuous variation from 37 to 86 days. Days to
maturity (DM) ranged continuously from 88 to
159 days, in a selection from the tallest line. The
flowering to maturity period (FM; the length of the
time between 50 % of the plants flowering and 90 %
of the bolls maturing period) ranged from 36 to
89 days. Plant natural height (NH) was measured in
5,940 individual plants and ranged from 27 to 112 cm
in the first generation (Fig. 4). Averages for accessions
(measured in 30 plants and excluding two heteromorphic lines discussed below) ranged from 29 ± 1 to
82 ± 5 cm. Only two accessions were described as
very short, also characterized by early maturity and
conjoined seeds (Figs. 6, 7). Systemic/technical stem
height (SH), a discriminator of the branched oilseedtype varieties and strong, long-stemmed fibre types
divided the Ethiopian germplasm between the two
categories. Growth habit and leaf colour (GH, LC)
were also measured (Table 1).
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Table 1 Agronomic and morphological descriptors, descriptor scales or states, and frequency distribution for linseed accessions
The trait/descriptor
Descriptor state
Class or scale
of descriptor
Distribution by classes
of descriptor (%)
Seedling
1. Germination time (GT)
2. Germination percentage (GP)
3. Cotyledon leaf size (CL)
4. Basal branch development (BD)
7th day of sowing
3 = slow
6th day of sowing
5 = medium
2 (1.01)
12 (6.06)
5th day of sowing
7 = fast
\75 %
1 = very poor
184 (92.93)
2 (1.01)
75–85 %
3 = poor
5 (2.52)
86–90 %
5 = intermediate
13 (6.56)
91–95 %
7 = efficient
63 (31.81)
d [ 95 %
9 = very efficient
\14.7 mm
3 = small
115 (58.08)
14.7–20.1 mm
5 = medium
[20.1 mm
7 = large
Late
3 = late
Medium
5 = medium
30 (15.14)
Fast
Heterogeneous
7 = fast
3, 5, 7
79 (39.90)
79 (39.90)
3,014 (15.96)
12,064 (63.91)
3,800 (20.13)
10 (5.05)
Plant
5. Days to flowering (DF)
6. Days to maturity (DM)
7. Flowering to maturity period (FM)
8. Leaf colour (LC)
9. Growth habit (GH)
10. Plant natural height (NH)
123
\47 days
1 = very early flowering
48–57 days
3 = early flowering
58–67 days
5 = medium flowering
68–77 days
7 = late flowering
[77 days
9 = vey late flowering
\100 days
1 = very early maturing
101–112 days
3 = early maturing
2 (1.01)
57 (28.79)
119 (60.10)
16 (8.12)
4 (2.02)
3 (1.52)
27 (13.64)
113–124 days
5 = medium maturing
71 (35.86)
125–136 days
7 = late maturing
68 (34.34)
[137 days
9 = very late maturing
29 (9.59)
\47 days
1 = very soon matured
47–57 days
3 = soon matured
51 (25.76)
3 (1.52)
58–68 days
69–79 days
5 = medium matured
7 = late matured
75 (37.88)
53 (26.77)
[79 days
9 = very late matured
16 (8.08)
Dark green
3 = dark green
Green
5 = green
Light green
7 = light green
Bushy type
3 = bushy type
14 (7.07)
Semi-erect
5 = semi-erect
176 (88.89)
Erect
7 = erect
\40 cm
1 = very short
41–51 cm
3 = short
19 (9.60)
162 (81.82)
17 (8.58)
8 (4.04)
2 (1.01)
43 (21.71)
52–62 cm
5 = medium
73 (36.86)
63–73 cm
7 = tall
68 (34.34)
[73 cm
9 = very tall
12 (6.06)
Genet Resour Crop Evol (2015) 62:1037–1053
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Table 1 continued
The trait/descriptor
11. Systemic/technical stem height (SH)
Descriptor state
Class or scale
of descriptor
Distribution by classes
of descriptor (%)
\26.00 cm
1 = very short
26.00–36.50 cm
3 = short
43 (21.71)
2 (1.01)
36.51–47.5 cm
5 = medium length
85 (42.92)
66 (33.33)
47.51–58.50 cm
7 = long
[58.5 cm
9 = very long
12. SH:NH (S/N)
\0.75
1 = oil type
C0.75
9 = fibre type
13. Primary branches (PB)
\18.0
3 = some
109 (55.05)
18.1–23.0
5 = many
84 (42.42)
[23.0
7 = too many
5 (2.53)
Zero/1
1 = no or one
0 (0.0)
1.1–3.0
3.1–7.0
3 = few
5 = some
0 (0.0)
11 (5.55)
7.1–11.0
7 = many
168 (84.85)
[11
9 = very many
14. Secondary branches (SB)
2 (1.01)
113 (57.07)
85 (42.93)
19 (9.609)
Flower/boll
15. Crown stage petal colour (CP)
16. Petal aestivation (PA)
17. Corolla/petal colour (CC)
18. Corolla or flower diameter (CD)
19. Anther colour (AC)
20. Boll size/diameter (BS)
White
1 = white
Pale–blue
2 = pale-blue
Blue
3 = blue
3 (1.48)
2 (0.98)
189 (93.10)
Blue–violet
4 = blue-violet
4 (1.97)
Violet
5 = violet
3 (1.48)
Red–violet
6 = red-violet
1(0.49)
Pink
7 = pink
1(0.49)
Valvate
3 = valvate
Semi-twisted
5 = Semi-twisted
7 (3.41)
Twisted
7 = twisted
White
Pale–blue
1 = white
2 = pale-blue
Blue
3 = blue
Blue–violet
4 = blue-violet
5 (2.39)
5 (2.39)
162 (79.02)
36 (17.56)
3 (1.43)
195 (93.30)
10 (4.78)
Red–violet
5 = red-violet
Pink
6 = pink
1(0.48)
\20 mm
3 = small
34 (17.17)
20–25 mm
5 = medium
[25 mm
7 = large
134 (67.67)
30 (15.15)
Yellowish
1 = yellowish
14 (5.11)
Salmon pink
3 = salmon pink
39 (14.60)
Silver/Azure
5 = silver/Azure
Greenish
7 = greenish
4(1.46)
19 (6.93)
Bluish
9 = bluish
197 (71.90)
\5.58 mm
3 = small
19 (9.60)
5.58–6.32 mm
5 = medium
[6.32 mm
7 = large
137 (69.19)
42 (21.21)
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Table 1 continued
The trait/descriptor
21. Boll number (BN)
22. Seed number (SN)*
Descriptor state
Class or scale
of descriptor
Distribution by classes
of descriptor (%)
\83.0
3 = some
84 (42.42)
83.1–99.0
5 = many
108 (54.55)
[99.0
7 = too many
16 (8.08)
\8.0
3 = less
2 (1.01)
8.1–9.0
5 = high
1 (0.51)
[9.0
7 = maximum
195 (98.48)
Seed
23. Seed length (SL)
24. Seed width (SW)
25. Thousand-seed weight (TW)
26. Conjoining of seeds (CS)
27. Seed coat colour (SC)
Oil
28. Oil content (OC)
29. Palmitic fatty acid (PF)
30. Stearic fatty acid (SF)
31. Oleic fatty acid (OF)
32. Linoleic fatty acid (LF)
123
\4.0 mm
3 = short
4.0–5.0 mm
5 = medium
80 (40.40)
115 (58.08)
[5.0 mm
7 = long
\2.0 mm
3 = narrow
71 (35.86)
3 (15.15)
2.0–2.5 mm
[2.5 mm
5 = medium
7 = wide
122 (61.62)
5 (2.52)
\4.01 g
1 = very low weight
89 (44.95)
4.01–5.00 g
3 = low weight
65 (32.83)
5.01–6.00 g
5 = medium weight
29 (14.65)
11 (5.56)
6.01–7.00 g
7 = high weight
[7.01 g
9 = very high weight
Single
1 = single
Conjoined
9 = conjoined
2 (1.01)
Yellow
1 = yellow
7 (3.29)
Light-brown
2 = light brown
Medium brown
3 = medium brown
4 (2.02)
196 (98.99)
6 (2.82)
95 (44.60)
Dark brown
4 = dark brown
Olive
5 = olive
None
105 (49.30)
Others
6 = variegated
None
\35.00 %
1 = very low
81 (40.91)
35.00–37.00 %
3 = low
60 (30.30)
37.01–39.00 %
5 = medium
43 (21.72)
13 (6.56)
39.01–42.00 %
7 = high
[42.00 %
9 = very high
1 (0.51)
\5.62 %
3 = low
9 (4.54)
5.62–6.21 %
5 = medium
[6.21 %
7 = high
\4.81 %
3 = low
4.81–5.43 %
5 = medium
63 (31.82)
126 (63.64)
40 (20.20)
132 (66.67)
[5.43 %
7 = high
26 (13.13)
\16.90
3 = low
20 (10.10)
16.90–19.83 %
5 = medium
[19.83 %
7 = high
\14.50 %
3 = low
14.50–15.30 %
[5.30 %
5 = medium
7 = high
159 (80.30)
19 (9.60)
29 (14.65)
159 (80.30)
10 (5.05)
Genet Resour Crop Evol (2015) 62:1037–1053
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Table 1 continued
The trait/descriptor
33. Linolenic fatty acid (LnF)
Descriptor state
Class or scale
of descriptor
\54 %
3 = low
55–58 %
5 = medium
[57 %
7 = high
Distribution by classes
of descriptor (%)
35 (17.68)
138 (69.70)
25 (12.63)
* Character 22 SN: variation is only found in three accessions where late maturity extends into the main rainy season
One group of plants segregating from a heteromorphic accession, PGRC/E13610, was characterized by
early maturity, large boll size, more productivity,
fewer tillers, and a thick and erect stem. The second
group was characterized by very late maturity, small
boll size, less productivity, more tillers and a weak and
thin stem. From accession PGRC/E13535 the two
groups of plants developed into two different groups:
one very tall and late; and the second tall and medium
maturing type. They were differentiated only in these
characters. In the fourth generation all groups of plants
from the two accessions became uniform and stable.
Flower and boll characters: Floral characters were
highly polymorphic and provided a useful group of
five descriptors. Crown stage petal colour (CP) were
well differentiated among white and pink, although
more crown colours like pale–blue and yellowish–
white from blue–violet, blue and white flower origin
plants were observed during the development of the
advanced generations (Fig. 5). Corolla/petal colour
(CC), scored in fully opened flowers (Fig. 5), did not
entirely match crown colour in the ‘blue’ group; white
and pink crown colours developed to white and pink
petal/corollas. Open-flower petal colour showed
higher polymorphism than crown colour. Petal aestivation (PA) (Fig. 5), describing overlapping of petals,
ranged from twisted to valvate flowers. Flower shape
(FS; not scored in Table 1) included disk shaped,
funnel shaped and four accessions with star shaped
flowers. Anther colour (AC) (Fig. 5) showed a
continuous range of colour variation between yellowish through pink to blue. About a third of accessions
showed polymorphism for anther colour. Filament/
stamen colour (FC) had a narrower range of colour
than anthers and petals (Fig. 5). Colour of style (CS) is
shown in Fig. 5. Corolla or flower diameter (CD) was
measured from fully opened flowers. All white petal
flower accessions had a large corolla diameter. More
than half of the studied accessions were characterized
by medium size corolla.
Boll size/diameter (BS) is associated with seed size,
itself associated with yield. Boll size/diameter is used
as a trait to distinguish one genotype from others since
it is not much affected by environmental factors.
Seed characters: Seed size—length and width (SL,
SW), were generally proportional to each other; there
was little difference in seed shape (Fig. 6; some
variation was seen in having blunt to sharp points).
Scanning seeds to measure their thickness was difficult
so that seed size was measured from the two dimensions; although not scored formally, no genotype with
conspicuously thick (a flattened ovoid to spherical,
giving a tendency to roll on glass or out-of-focus edges
when scanned) or thin seeds were noted during
measurement. Thousand-seed weight (TW), an important yield character, varied extensively from 2.30 g
(11 accessions less than 3 g) to 7.54 g. Seed colour
(SC), was classified into yellow, light brown, medium
brown and dark brown. ‘Yellow’ was variable, with a
distinct bright variant in PGRC/E237001. Fifteen
accessions were dimorphic with segregation of two
different seed colours and 183 accessions were
monomorphic in seed colour.
Conjoining of seeds (CS) was seen in PGRC/
E13538 and PRGC/E13700 (Fig. 6). These genotypes
were also very early maturing, and had a very short
plant height, very low oil content and a spreading
growth habit. Conjoined seeds resulted from much
reduced false septa plants (Fig. 7) so the two seeds are
conjoined. The conjoin seed character is not wellknown by farmers.
Oil content (OC) was measured in two different
seasons but was quite stable, varying from 30.5 % up
to 43.57 %, placing Ethiopian linseed in a low to
medium position compared to international varieties.
Linolenic fatty acid (LnF: 18:3 carbon chain:double
bonds) content ranged from 50 to 60 %, categorizing
them as medium genotypes (Table 1). In the second
growing period the number of samples scored as
greater than 60 % LnF increased from 1 to 7
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Genet Resour Crop Evol (2015) 62:1037–1053
b Fig. 2 Characters in linseed seedlings showing uniformity
within accessions and variation between accessions in vigour
and cotyledon size. A 2-day old germinating seedlings (three
rows each, separated by grey lines); B Variation in size of 5-day
old cotyledons (bar = 10 mm); C 7-day and D 17-day old
seedlings. (Color figure online)
Fig. 3 Linseed seedlings at 17 days old showing variation
between accessions in height and basal branch (axillary bud)
development (descriptor BD, Table 1). A, B are tall with
suppressed buds (descriptor class 2). C is short with bud
development (class 3). D is an intermediate height and has
developed buds (class 3). E is short without buds (class 4). F is
tall and has strong axillary bud development (class 1). Scale bar:
30 mm
Biodiversity and component analysis
accessions. Linoleic fatty acid (LF: 18:2) content
ranged from 13.81 to 15.65 %. Three other fatty acids
(16:0, 18:0 and 18:1) were also measured (Table 1).
123
The descriptors were analysed by both administrative
region-origin (Table S3 and Fig. 1a) and altitude of
collection (Table S4 with ANOVA in Table S5).
Variability of characters within regions was high for
nearly all descriptors and (while sometimes reflecting
number of accessions or perhaps collection strategy)
also showed differences in environment or reflected
agronomic practices in the regions. The non-geographic accessions acquired from ARC showed the
highest mean values for some characters (NH, SH,
BD, CD, SL, SW, and OC), suggesting these were
selected. Excluding the ARC samples, the 14
Genet Resour Crop Evol (2015) 62:1037–1053
1047
with region or altitude; SF and OF showed only
regional variation. Accessions from low altitiude.
A principal component analysis (Table 2, with
correlations and factor analysis in Table S2) showed a
quarter of the total variance was accounted for in the
first axis, and 19 % in the second, confirming the
independence of some characters. For other characters, both positive (e.g. NH and SH, 0.970**; SL and
SW 0.838**; SB and BN 0.818**) and negative (OF
and LnF, -0.936**; SN and TW, -0.764**; SF and
LnF, -0.718**) associations were found.
Discussion
Agronomic and phenotypic characters of linseed
Fig. 4 Variation in height (from 30 to 75 cm), systemic/
technical stem height, and branching as seen in four Ethiopian
linseed accessions
accessions from Wollo had many characters with the
highest mean values (TW, BD, SL, SW, GT and OF).
Descriptor averages among groups with altitude
information (Table S4) showed half of the characters
with the lowest means (NH, SH, SN, DF, DM, CD, SL,
OC and SF) were from altitude class one
(1,410–1,664 m a.s.l.) and 57 % of the characters
with the highest means (NH, SH, TW, BD, CD, SL,
SW, GT, OC, PF and SF) were from altitude class
eight (3,195–3,449 m a.s.l.) and, except for DF, also
showed variation with regional origin. The characters
BN, GP, GT and PF showed no significant variation
A range of descriptors was elaborated for Ethiopian
linseed, and these have uses for both the characterization of germplasm and its evaluation for use by
farmers and breeders. The Ethiopian linseed accessions were shown to be diverse, with a continuous
range of variation; comparison with the international
varieties included in the measurements suggests that,
as for many other species of tropical and sub-tropical
origin, 1) much of the genetic variability present is
underutilized (e.g. Phaseolus: Singh 2001; Meza et al.
2013); and 2) there is considerable potential for
genetic improvement of local varieties. Engels and
Hawkes (1991) considered that there was limited
diversity in Ethiopian linseed and concluded that
serious genetic erosion had occurred. The germplasm
from throughout the country studied here (Fig. 1) was
clearly diverse, but perhaps sampling distortion lead to
reports of lower diversity as noted for diploid wheats
(Moghaddam et al. 2000).
Some additional descriptors were considered and
measured during the first field season. However, many
of these proved difficult to score, or varied within lines
or between years. Primary branching, for example, is an
important agronomic character, but in small-scale trials
was very dependent on plant density: it would need to be
assessed in additional trials that included planting at
multiple densities (seeding rate). Characters where there
is likely to be a strong genetic basis and that can be
evaluated on the small-plot scale were emphasized. A
few characters showed minimal variation: these were
retained in the table since some were used in other
studies, and they may show variation to other Linum
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Genet Resour Crop Evol (2015) 62:1037–1053
Fig. 5 Diversity in linseed flower structures and colour:
A. white petal colour and valvate petal aestivation or star shape;
B. violet petal colour and valvate petal aestivation and star
shape; C & D. blue petal colour and twisted petal aestivation and
disc shape; and E & F. white petal colour and twisted or funnel
shape flowers. (color figure online)
species. Seed characters were partitioned to as many
traits as possible to assist with future genetic analysis. It
was notable that the character with the highest variability (CV = 31.82 %) was 1,000-seed weight (TW), a
key component of yield. Most of the accessions
evaluated were below the values from international or
reference varieties, suggesting that TW is a key target
for improvement. Despite the correlations noted
between some factors scored here (Tables 2 and S4),
some deviations (for example between oil content and
1,000-seed weight) will be very important for breeders
and geneticists to identify lines with novel and important
combinations of characters.
A high rate of quick and uniform germination after
storage are key early characters for domestication
(Hammer 1984; Vaughan et al. 2007; Fu 2011;
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Genet Resour Crop Evol (2015) 62:1037–1053
1049
Fig. 6 Variation in linseed seed size and colour. Lower panel, centre right shows conjoined seeds; cf Fig. 7. (Bar: 10 mm)
Table 2 Principal component (PC) analysis of 198 linseed
accessions for 22 morphological variables/characters (Table 1).
Tables S2 and S3 give the Factor Analysis, correlations and
component weights
PC
Eigen value
% variance
% cumulative variance
1
5.49
26.08
26.08
2
3.96
18.83
44.91
3
2.75
13.09
58.00
4
1.80
8.56
66.56
5
1.39
6.61
73.17
\1.00
\5.00
6–22
Heslop-Harrison and Schwarzacher 2012), where crop
seeds often differ from their closet wild ancestors:
seed samples from wild species may show germination
over several years or require special conditions
(vernalization, light wavelengths, imbibition rounds,
or even smoke). The results here suggest that the
accessions carry the desirable traits regarding germination: Lu et al. (2004) reported that linseed seed has
97 % germination percentage, similar to that found
here.
Ethiopian linseed traditional varieties have high
variation in seedling vigour, some but not all or which
may be from heterogeneity (Mezghani et al. 2014).
Plant establishment is an increasingly seen as an
important character for crops: rapid establishment
exploits available soil moisture efficiently, and prevents soil loss through run-off or wind. The range of
cotyledon sizes was notable here and the impact on
crop establishment should be investigated. Seedling
basal branch development (BD, Figs. 2 and 3) from
axillary meristems, leading to variation in apical
dominance (Darwin 1880), was also highly variable,
and the basis of this will be interesting to study since it
is likely to be caused by mutations in auxin production
or receptors. Two other characters noted here, conjoined-seeds (Figs. 6 and 7) and sprouting in the stem
when the seedling is decapitated below the cotyledons
will also be amenable to further study with functional
genetics and hormonal studies: Ishikawa et al. (1997,
reviewing also Adams 1924), reported that most plants
die when their seedlings are cut below the cotyledons.
The accessions varied widely in both time to
flowering (DF) and time to maturity (DM): indeed,
the longest flowering to maturity FM period, 89 days,
equalled the total lifespan of the fastest accessions
from seedling to maturity. These characters are of
adaptive significance. Yield (not measured here) has a
relationship to length of the developmental stages
allowing accumulation of biological products. Development times must also be matched to growth season
conditions to ensure efficient use of moisture, and the
time to maturity must be appropriate for the crop
cycles, including perhaps future multiple crops per
year. In Punjab, India, much of the area is now doublecropped each year, meaning shorter life cycles are
required. Changes in linseed agronomy, for better
water conservation or multiple cropping seasons each
year may change genetic requirements, and the variation found here will be able to meet these challenges.
Flax fibre-types of plants have a higher systemic to
natural stem height ratio (S/N) compared to oilseed
varieties, a ratio that is also reflected in absolute values
of SH and NH. Despite mostly being used for oil,
many of the Ethiopian accessions had a high S/N ratio.
Some of the varieties are segregating for height, and
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1050
Fig. 7 Cross-section of bolls of linseed with A normal; and
B conjoined-seeds (bar = 3 mm), showing the difference in
development with much reduced false septum resulting in
conjoined (paired) seeds (cf. Fig. 6) or conjoining
one selected line of 143 cm was obtained (outside the
17–130 cm range reported by Diederichsen et al.
2013). As with the bud development, study of the
genes involved in phytohormone effects (production,
transport and receptors) on height will be important to
study.
Seed size, which has direct relationship with
endosperm amount, can also contribute for seedling
vigour by providing enough nutrients to the growing
embryo (although in domesticated crops where seeds
123
Genet Resour Crop Evol (2015) 62:1037–1053
are produced, seeds are normally selected to be larger
than the wild relatives). Seed weight is a complex
genetic trait and one of the most important indicators
used to rate linseed cultivars. SSR (simple sequence
repeated)—based clustering of linseed germplasm
showed correlation with thousand seed weight (Wiesnerova and Wiesner 2004).
Although showing less diversity than other characters, there were some differences between lines in
content of the various oil types (LnF, a product of
desaturation of LF derived from OF, and also SF and
PF, each with different carbon chain lengths and
double bonds, Table 1). Time between the beginning
of flowering (starting synthesizing LF) and boll
maturity (accumulation of LnF) thus influences oil
type ratios (Rao et al. 2008), and there is a positive
association between DM and LnF percentage. Breeders have variation available and can selected complex
inherited traits (Jain 2011) based on oil needs from the
crop.
All the floral structures had different subclasses of
colour as colour trait characters (Figs. 5 and 6). The
number and type of petal colour reported by Hayes and
Immer (1942) are similar to petal colour scored in the
present study: Flax Council of Canada (1995) and
Hayes and Immer (1942) reported linseed anther only
as blue and yellow, different from the range of anther
colours found here, although we did not find the
yellow and lavender (26 %) colour petals scored
from world core collections (Diederichsen 2007).
Diederichsen and Fu (2008) reported three anther
colours: white, blue and yellow. Results from the
present study indicate that several genes interact in the
control of anther, stamen and petal colours: Hayes and
Immer (1942) were able to find eight interacting
genes. Although Linum flowers are rarely visited by
insects occasional cross-pollination is important for
gene-flow, small flowers can exclude pollinators while
insects can slip past anthers and stigmas without
pollinating large flowers (Armbruster 2014). Ethiopian linseed germplasm has diversified genetic structure regarding genes controlling floral and seed coat
colours (see also Yurkevich et al. 2013). This shows
the presence of wide range of genotypes for these
scored characters. Worku et al. (2012) reported 17
varieties identified by local farmers although some of
them were duplication as a matter of differences in
language from different ethnic groups.
Genet Resour Crop Evol (2015) 62:1037–1053
The existing diversity of linseed in Ethiopia reflects
regional and altitudinal (Fig. 1 and Tables S3 and S4)
variation (including edaphoclimatic parameters), as
well as the agroecological systems, the cultural history
of the people and farmers knowledge (Engels and
Hawkes 1991). Bekele (1996) reported high diversity
in the Ethiopian crop tef (Eragrostis tef), with some
association between regions where farmers have
migrated. When DNA genotyping arrays or appropriate sequencing technologies become available based
on genomic sequences (Wang et al. 2012), it will be
important to analyse linseed germplasm and hybrid
populations for signatures of selection involving loss
of heterozygosity, fixation of alleles, and linkage
disequilibrium or segregation distortion as has been
shown in many minor crops such as carrot (Daucus
carota; Grzebelus et al. 2014).
The association between high altitude, tall plants,
and long times to flowering and maturity could be due
to the cooler and wetter growing season. In the oil crop
Guizotia abyssinica, Geleta and Ortiz (2013) have
considered late maturity and factors leading to
increases in oil content. Here, there was some
association between higher altitude and oil, presumably a result of longer maturity times whereas faster
maturity lowers oil content. Positive correlations
between commercially important characters are rare
and this is one of the problems of selection for
breeding (Kearsey and Pooni 1996): any outliers
where there is less correlation will be important to
identify and follow.
In conclusion, there is substantial morphological
variation within the linseed germplasm pool in Ethiopia, and reflecting both regional and altitude differences. It is important to ensure that the full diversity
present in the country has been assessed and collected
for preservation and use, perhaps emphasizing lower
and higher altitude extremes, and also the minor
linseed producing regions like Sidamo, Illubabor and
Kefa. Measurements of morphological variation will
be helpful in the selection of suitable parents for
breeding programs, while knowing the population
structure of crop genotypes from morphological and
DNA markers will be helpful for association studies
through linkage disequilibrium in populations for
identifying particular alleles associated with a given
phenotype (Anhalt et al. 2008). Breeding aims
regarding oil, linen fibre or dual use need to be
considered, and integrated with the regional ways that
1051
the crop is used, including as animal feed-meal and
bedding, or whole-seed and flour use as human food. It
will be an ongoing challenge to develop improved
varieties and disseminate these as appropriate to
smallholders, at the same time aiming to conserve all
diversity in traditional varieties: morphological,
genetic and marker based studies will assist in
reaching these aims.
Acknowledgments Holetta and Adiet Agriculture Research
Centres, Institute of Biodiversity and Conservation, and local
farmers from Ethiopia are acknowledged for your kind and
generous provision of us with linseed germplasm, as research
materials for the studies. The Amhara Agricultural Research
Centre, Gondar branch was providing us research field and we
thank the Centre for that. The University of Gondar and
University of Leicester, GENIE project, Holetta Agricultural
Research Centre, Prof. Pat Heslop-Harrison and Dr Trude
Schwarzacher’s miscellaneous projects fund were the sources of
funds for the research.
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