Field Crops Research 103 (2007) 62–69
www.elsevier.com/locate/fcr
Development of somaclonal variants of wheat (Triticum aestivum L.)
for yield traits and disease resistance suitable for heat
stressed and zero-till conditions
B. Arun a, B.D. Singh b, S. Sharma a, R. Paliwal a, A.K. Joshi a,*
a
Department of Genetics and Plant Breeding, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi 221005, India
b
School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi 221005, India
Received 16 April 2007; accepted 29 April 2007
Abstract
In a substantial rice–wheat cropping system area of South Asia, wheat sowing often gets too delayed and exposed to terminal heat stress.
Therefore, farmers prefer varieties that are able to perform well under a short growing period. Tissue culturally regenerated plants of wheat variety
cv. HUW 234, the most widely cultivated variety of North Eastern Plain Zone (NEPZ) of India were screened using immature embryo as explant.
Days to heading and maturity, yield and other yield components and resistance to leaf rust and spot blotch were evaluated. A few somaclones in R3
and R4 generations displayed significant earliness for days to heading and maturity, improved yield traits and resistance to leaf rust and spot blotch
diseases. The superior performance of two of the variants was confirmed in the R5 generation in 3 years of testing under two dates of conventional
and zero-till sowing. Stability analysis also suggested superiority of the two somaclones across 12 environments. This appeared to confirm the
possibility of obtaining useful somaclonal variants of wheat for very late sown as well as zero-till managed agriculture. The superior performing
somaclones can be used as parents in the ongoing breeding programmes targeting late sown wheat in South Asia exposed to terminal heat stress.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Tissue culture; Somaclonal variation; Triticum aestivum; Somatic embryogenesis; Zero till; Late sowing; Terminal heat stress
1. Introduction
Potential application of somaclonal variation in crops has
been proposed as a supplementary tool to well established
breeding approaches (Ahloowalia, 1982; Cheng et al., 1992;
Ivanov et al., 1998). Plants regenerated from the embryogenic
calli of wheat have revealed variants for various agronomic and
quality characters such as plant height, stem thickness, leaf size,
spike shape pollen fertility, gliadin storage protein, presence or
absence of awns, maturity, plant type, etc. (Ahloowalia, 1982;
Maddock et al., 1985; Carver and Johnson, 1989; Cheng et al.,
1992). Somaclones have also been reported for various traits
such as higher 1000 grain weight, protein concentration,
sedimentation values, harder kernels (Hanson et al., 1994);
plant height, spike length, main tiller diameter (Symillides
et al., 1995; Ivanov et al., 1998); kernels per spike and kernel
weight (Ryan et al., 1987; Mohmand and Nabors, 1990);
* Corresponding author. Tel.: +91 542 2367948; fax: +91 542 2368174.
E-mail address: [email protected] (A.K. Joshi).
0378-4290/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.fcr.2007.04.011
resistance to brown rust (Tuchin et al., 1996; Rana et al., 1996);
early maturity, high yield and superior quality (Liang et al.,
1996); frost tolerance (Dorffling and Melz, 1997); resistance to
scab caused by Fusarium spp. (Yang et al., 1998) and, higher
yield, earliness and resistance to spot blotch (Arun et al., 2003).
Apparently, there have been many reports on the isolation of
somaclones for various traits in wheat. However, reports
displaying agronomically useful variations of wheat suiting to
late sown conditions and Resource Conservation Technologies
(RCTs) such as zero till that are spreading fast in rice–wheat
cropping areas of South Asia (Joshi et al., 2007a), are scanty.
The optimum time of wheat sowing in the eastern parts of
Indo-Gangetic plains of Indian subcontinent is 15–25
November. However, in a substantially large area, especially
that falling under 11–12 mha rice–wheat cropping system of
South Asia (Hobbs and Morris, 1996; Pandey et al., 2005; Joshi
et al., 2007a), wheat sowing often gets delayed primarily due to
late harvesting of paddy (Joshi et al., 1997). This delayed
sowing, which in around 4–5 million hectares goes even
beyond third week of December, causes substantial loss to
wheat yield due to terminal heat stress and lack of sufficient
B. Arun et al. / Field Crops Research 103 (2007) 62–69
period for crop growth and development (Joshi et al., 2007b).
Therefore, the farmers demand wheat varieties that are able to
perform well under late sown conditions of rice–wheat
cropping system. The other major problems of this zone are
terminal heat stress and spot blotch and leaf rust diseases (Joshi
et al., 2002; Pandey et al., 2005; Duveiller et al., 2005). Spot
blotch disease caused by Bipolaris sorokiniana (sacc.) shoem
syn. Drechslera sorokiniana (Sacc.) Subrm and Jain (syn.
Helminthosporium sativum, teleomorph Cochliobolus sativus)
is considered as no. 1 pathogen of wheat in eastern parts of
South Asia encompassing India, Nepal and Bangladesh (Saari,
1998; Joshi et al., 2004a,b, 2007c,d). Superior performance of
wheat varieties under zero-till sowings is being seen as an
additional advantage since RCTs are expected to dominate
rice–wheat cropping system areas of India in the coming future
(Joshi et al., 2007a).
The present study reports the isolation of significantly
superior variants of wheat variety cv. HUW 234 (the most
popular cultivar of eastern Gangetic plains of South Asia under
late sown conditions) for earliness, disease resistance and yield
components under conventional as well as zero-till sowings.
These variants can be used as donor for terminal heat tolerance
that is gaining importance in view of the increasing threat of
global warming.
2. Materials and methods
All the experiments were conducted at the research station
of Banaras Hindu University, Varanasi, India (North Eastern
Plains Zone, 25.28N and 83.08E). This centre falls under North
Eastern Indo-Gangetic plains of India and has loam alluvial
soil having neutral pH (7.2). In all the years of experiments,
same agronomic practices recommended for normal fertility
(120 kg N:60 kg P2O5:40 kg K2O ha1) were followed. Full
doses of K2O and P2O5 were applied at the time of sowing.
Nitrogen was supplied in split applications, 60 kg N ha1 at
sowing, 30 kg N ha1 at the first irrigation (21 days after
sowing) and 30 kg N ha1 at the second irrigation (45 days
after sowing). The previous crop in each year was paddy and
the variety used was MTU 7029.
2.1. Tissue culture and plant regeneration
One of the most popular cultivars of eastern Gangetic plains
of South Asia, cv. HUW 234 (HUW 12/CPAN 1666//HUW 12)
was used as explant source. Selfed seeds from the nucleus seed
plots were used as seed source. Immature embryos were
cultured and plants were regenerated following the protocol
described in our earlier study (Arun et al., 2003). The
regenerated plantlets were referred to as R0 (Hanson et al.,
1994). In total, 389 R0 spikes were harvested at maturity as
single spike, to raise ear to row R1 progeny.
2.2. Field evaluation of R1 generation
The 389 R0 spikes were screened in two sets of experiments.
In the first experiment, single spikeline (R1) of 2 m lengths were
63
evaluated for yield traits and resistance to spot blotch along
with parent as check. In the second experiment, single row of
1 m was sown separately for each R1 to evaluate their resistance
to leaf rust.
In the first set, the R1 population was artificially inoculated
with spot blotch pathogen B. sorokiniana, using most
aggressive isolate (No. ICMP-13584; Auckland, New Zealand)
identified at Varanasi, India (Joshi and Chand, 2002; Joshi et al.,
2007c). Spot blotch was measured at growth stage 77 (Zadoks
et al., 1974) using disease severities (%) as reported earlier
(Joshi et al., 2004a,b). Area under disease progress curve
(AUDPC) estimate was based on the plot disease severities at
different growth stages (Van der Plank, 1963). Spot blotch
severities (%) were assessed three times; at growth stage 65
(anthesis half complete to complete), 73 (early to medium milk)
and 77 (early dough) (Zadoks et al., 1974). Area under disease
progress curve (AUDPC) which is reported to be a pragmatic
approach to measure resistance (Jeger, 2004) was calculated
using following formula (Roelfs et al., 1992):
AUDPC ¼
a X
Y i þ Y ðiþ1Þ
i¼1
2
ðtðiþ1Þ ti Þ
where Yi is the disease level at time ti and t(i + 1) ti is the
time(days) between two disease scores.
In the second set that was planted for leaf rust evaluation,
spreader rows of susceptible cultivar Agra Local were sown in
the alleys and borders, 3 weeks before the sowing of
experiment. For this disease, an artificial epiphytotic was
created using race 77-5 which is the most virulent and
frequently identified races from the Indian subcontinent (Nayar
et al., 1994). The infector rows and the somaclonal variants
were sprayed with 1 g of leaf rust uredospores suspended in 10 l
of water with 2–3 drops of Tween 20 as dispersant solution. The
field inoculations were done in the evening every third day till
rust symptoms became visible on the susceptible spreaders.
Field assessment of leaf rust severity at adult plant stage was
based on a modified Cobb scale (Peterson et al., 1948).
On the basis of resistance to leaf rust and spot blotch, higher
1000 grain weight, earliness and yield components, 47 putative
variants were selected for further evaluation in R2 generation
under very late sown condition, i.e., second week of January
1999.
2.3. Field evaluation of R2 generation
Variants (R2) were evaluated in a three sets of unreplicated
trial along with the parent. First set was kept as protected by
using fungicide Tilt at GS 54 and GS 69 (Zadoks et al., 1974) to
prevent the attack of two common fungal diseases (leaf rust and
spot blotch) and enable proper evaluation of yield traits. The
other two experiments were conducted separately under
artificial epiphytotic conditions for leaf rust and spot blotch
diseases, respectively. Plot size for protected experiment was
two rows of 2.5 m length, while for the other two experiments
the plot size was kept single row of 2.5 m length. All the three
sets were sown under very late sown (11 January 1999)
64
B. Arun et al. / Field Crops Research 103 (2007) 62–69
conditions. In the two sets used for evaluation of leaf rust and
spot blotch disease, the experiment was done as described for
R1 generation.
2.4. Field evaluation of R3 generation
Thirteen somaclones (R3) found superior in previous
generation were tested in a replicated trial under very late
(11 January 2000) sown conditions. The plot size for each
somaclones and check variety HUW 234 was six rows of 3 m
length with row spacing of 20 cm. Spreader rows of susceptible
cultivars Sonalika and Agra Local were planted in borders to
promote disease development. Observations were recorded for
days to heading and maturity, yield per plot, yield per day and
resistance to leaf rust and spot blotch diseases. Two separate
sets of R3 somaclones were grown for the evaluation of leaf rust
and spot blotch resistance keeping single row of 2.5 m for each
line as described for R2 somaclones.
2.5. Field evaluation of R4 generation
Twelve somaclones that were significantly superior in R3
generation were further evaluated in a replicated trial in R4.
This trial was planted on 11 January 2001 in a randomized
block design with three replications. The plot size for each
somaclone was kept as six rows of 3 m length having row to row
spacing of 20 cm. The seed rate was 120 kg/ha. Spreader rows
of susceptible cultivars Sonalika and Agra Local were planted
in borders to promote disease development. The checks used in
this trial were cv. HUW 234 (parent) and three other cultivars
recommended for late sown conditions viz., cv. Halna, cv.
Sonalika and cv. NW 1014. Observations were recorded for
days to heading, yield, yield traits, leaf rust and spot blotch
severities.
2.6. Evaluation of R5 somaclones in conventional and zerotill sowings
Eight R5 somaclones were further evaluated for two dates of
sowing in three crop seasons 2001–2002, 2002–2003 and 2003–
2004 under conventional and zero-till sowings following
Randomized Complete Block Design (RCBD) with three
replications. Four somaclones (HUW 234-4-277, HUW 234-4284, HUW 234-4-304 and HUW 234-4-344) that displayed
high levels of leaf rust infection in the R4 generation were not
included in the trial. The two (late and very late) dates of
sowings in three years of testing were 15–20 December and
14–16 January, respectively. The plot size for each somaclone
was nine rows of 6 m. The seed rate was 150 kg/ha in all
sowings. Parent cultivar HUW 234 as well as three other
prominent cultivars (Halna, NW 1014 and Sonalika) of eastern
Gangetic plains of South Asia, were used as checks. In each
year, spot blotch and leaf rust were evaluated by growing
separate small nurseries as done in R3 and R4 generations. Leaf
rust severities were recorded on four dates starting from the date
when the most susceptible check (Halna) started displaying rust
infection around 60%. AUDPC for leaf rust was estimated as
described for spot blotch.
For zero-till planting, a nine tine zero-till machine (M/S
National Agro, Ludhiana, India) was used. In order to ensure
proper seed distribution, the furrows were opened with machine
and seeds were hand sown maintaining equal quantities for each
furrow. Fertilizer was placed using machine. Other crop
management practices were kept same as followed in
conventional sown experiment.
Observations were recorded for yield/plot, days to maturity,
1000 grain weight and disease severities for spot blotch and leaf
rust diseases. AUDPC was calculated for spot blotch disease
using the disease scores of different observations as described
previously. Border effect was avoided by harvesting only seven
rows of 5 m (leaving two border rows and 0.5 m on the lengths
of each row of the plot). Data were analyzed using SAS
computer programme (SAS Institute, 1997). Duncan’s multiple
range test was applied to compare means of somaclones.
Stability analysis for 6 traits of somaclones in 12 environments
was also done using Site Regresion Model (Crossa et al., 2002)
in SAS software.
3. Results
3.1. Performance of somaclones in R1 and R2 generation
Out of 389 lines evaluated in R1 (data not shown), 47 were
found promising on the basis of earliness, 1000 grain weight
and leaf rust and spot blotch resistance.
3.2. Evaluation of somaclones in R3 generation
Analysis of variance (Table 1) showed significant differences for different traits. The variants displayed significantly
early maturity and resistance to leaf rust and spot blotch
diseases (Table 2) and 10 appeared significantly higher yielding
as compared to the parent.
Table 1
Analysis of variance for various traits of somaclonal variants of HUW 234 in R3 generation under delayed sowing condition
Source of variation
d.f.
Replicate
Treatment
Error
2
13
26
Mean sum of squares
Days to heading
Days to maturity
Yield/plot
Yield/day
Leaf rust
Spot blotch AUDPC
0.09
1869.91**
0.45
0.09
4567.20**
0.55
0.001
0.037**
0.001
0.16*
72.03**
0.06
9.52
777.79**
5.67
2200.02*
204457464.01**
837.58
*Significant at P = 0.05, **significant at P = 0.01.
B. Arun et al. / Field Crops Research 103 (2007) 62–69
65
Table 2
Mean performance of variants of HUW 234 in R3 generation under delayed sowing
Variants/parent
Days of heading
Days to maturity
Yield/plot (kg)
Yield/day (g)
Leaf rust score
Spot blotch AUDPC
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
HUW
63.67
66.00
66.33
64.67
63.67
64.67
64.33
65.00
66.33
67.67
66.33
67.33
66.33
67.67
100.33
103.33
100.67
97.33
98.67
103.33
103.67
99.00
102.67
104.00
102.33
101.00
103.33
106.00
1.31
1.26
1.43
1.35
1.43
1.55
1.43
1.47
1.46
1.36
1.47
1.56
1.39
1.35
13.06
12.19
14.20
13.87
14.49
15.00
13.79
14.85
14.22
13.08
14.37
15.45
13.45
12.74
40.00
30.00
40.67
30.00
30.67
50.00
20.00
25.33
25.00
40.33
30.00
15.00
30.67
70.00
950.00
1130.00
955.00
1007.50
1142.50
985.00
1130.00
1130.83
1007.60
1102.50
1003.33
940.00
1080.00
1687.77
1.13
1.25
0.04
0.42
12.26
48.58
234-3-277
234-3-301
234-3-304
234-3-325
234-3-341
234-3-344
234-3-44
234-3-173
234-3-282
234-3-284
234-3-345
234-3-346
234-3-13
234 (parent)
L.S.D. (5%)
Table 3
Analysis of variance for various traits and disease scores of somaclonal variants of HUW 234 in R4 generation under delayed sowing condition
Source of
variation
d.f.
Replicate
Treatment
Error
2
15
30
Mean sum of square
Plant
height
(cm)
Days to
heading
Spike
length
(cm)
Grain/
spike
Spikelets/
spike
Grain
weight/
spike (g)
1000 grain
weight (g)
Grain
yield/
plot (kg)
Hecto.
weight (g)
Biomass/
plot (kg)
Harvest
index
Leaf
rust
Spot
blotch
AUDPC
19.62
141.11*
10.60
0.54
12.77*
0.46
0.36
1.52*
0.27
21.42
88.42*
13.72
0.44
1.63*
0.60
0.01
0.10*
0.02
0.61
11.38*
1.09
0.01
2.72*
0.01
1.05
15.45*
1.34
0.115
0.278*
0.072
7.95
3066.24*
6.59
0.39
310.60*
1.22
5.35*
920.86*
1.71
*Significant at P = 0.05.
3.3. Evaluation of somaclones in R4 generation
Analysis of variance (Table 3) showed significant difference
for the traits under observation. Although 11 variants were
significantly early in maturity than the parent (Table 4), only 2
(HUW 234-4-44 and HUW 234-4-346) displayed significantly
more grain yield than the parental cultivar cv. HUW 234 and the
other check cv. NW-1014. However, in comparison to two other
checks cv. Halna and cv. Sonalika, all the variants except HUW
234-4-341 had significantly more grain yield. In general, the
Table 4
Mean performance of the variants of HUW 234 for yield traits and disease scores under delayed sowing condition in R4 generation
Variant/checks
Height
(cm)
Days to
heading
Spike
length
(cm)
Grains/
spike
Spikelet/
spike
Grain
weight/
spike (g)
1000 grain
weight (g)
Hecto.
weight (g)
Yield/
plot (kg)
Biomass/
plot (kg)
Harvest
index
Leaf
rust
score
Spot
blotch
AUDPC
HUW 234-4-277
HUW 234-4-301
HUW 234-4-304
HUW 234-4-325
HUW 234-4-341
HUW 234-4-344
HUW 234-4-44
HUW 234-4-173
HUW 234-4-282
HUW 234-4-284
HUW 234-4-345
HUW 234-4-346
HUW 234
Halna
NW-1014
Sonalika
83.2
81.9
84.1
86.3
82.4
83.7
85.2
84.4
85.4
84.0
81.9
79.9
89.9
68.5
98.7
84.6
60.3
59.3
58.3
58.5
58.3
57.8
59.8
57.5
59.0
61.3
60.5
57.8
62.0
55.0
61.3
57.8
8.1
8.7
9.2
8.9
9.2
8.7
8.8
8.9
9.2
8.8
8.7
8.7
9.3
7.3
9.4
10.2
38.0
52.8
55.3
42.3
54.0
45.3
50.3
48.3
47.5
48.8
48.0
47.3
50.3
46.5
39.8
47.0
15.8
16.0
15.8
14.3
15.3
14.8
15.3
15.0
15.5
15.8
14.8
15.0
16.0
13.8
15.8
15.0
1.5
1.7
2.1
1.6
1.9
1.7
2.0
1.8
1.8
1.7
1.7
1.9
1.8
1.7
1.5
1.8
32.2
37.3
36.3
35.8
36.0
37.4
36.7
37.2
38.1
35.6
35.9
37.6
33.5
35.0
38.8
38.3
80.6
82.3
80.6
80.8
81.2
85.5
84.2
82.0
83.5
79.8
81.4
84.1
79.9
83.2
84.1
76.2
3.5
3.7
3.6
3.5
3.4
3.7
4.1
3.6
3.6
3.5
3.5
4.0
3.5
3.4
3.1
3.2
6.6
6.7
6.8
6.4
6.2
6.6
7.2
6.4
6.4
6.3
6.7
7.0
6.3
6.5
5.9
6.3
53.0
55.2
52.9
54.7
54.8
56.1
56.9
56.3
56.2
55.6
52.2
57.1
55.6
52.3
52.5
50.8
50.0
30.0
40.0
30.0
30.0
50.0
10.0
30.0
20.0
50.0
30.0
20.0
70.0
90.0
40.0
90.0
1473.8
1526.3
1024.5
1494.0
1011.0
946.5
996.8
1569.8
1059.0
1633.5
953.3
1009.5
1668.8
2211.0
1666.5
2220.0
4.6
1.0
0.7
5.3
1.1
0.21
1.5
1.6
0.2
0.4
4.3
15.6
58.7
L.S.D. (5%)
66
B. Arun et al. / Field Crops Research 103 (2007) 62–69
Table 5
Mean squares for performance of somaclones of wheat in late (15 December) and very late (10 January) sowings in two methods of sowings (conventional and zero
till) in 3 years (2002, 2003 and 2004) of testing
Factors
d.f.
Grain yield
Days to heading
1000 grain weight
Spot blotch AUDPC
Leaf rust AUDPC
Year (yr)
Tillage (tl)
Sowing date (sd)
yr*tl
yr*sd
yr*tl*sd
yr*tl*sd
Rep (yr*tl*sd)
Genotype (geno)
yr*geno
tl*geno
sd*geno
yr*tl*geno
yr*sd*geno
tl*sd*geno
yr*tl*sd*geno
Error
2
1
1
2
2
2
2
24
11
22
11
11
22
22
11
22
264
0.102
0.050
1.496**
0.100
0.091
0.225
0.225**
0.108**
1.513**
0.008*
0.002
0.023*
0.005
0.006
0.004
0.006
0.005
0.050
51.958
280.043**
0.189
0.089
0.066
0.066
13.643**
120.827**
0.008
0.098
8.176**
0.008
0.008
0.098
0.008
0.072
11.28
9.86
2035.68**
0.60
5.05
1.36
1.36*
8.26**
32.91**
0.46
0.46
2.98**
0.31
0.51
0.65*
0.40
0.364
7559.05
14820.65
481823.06**
9252.05
5499.93
6267.67
6267.67**
34857.99**
5144327.08**
3083.69**
1278.52
9975.05**
1265.78
873.06
799.77
593.64
890.78
2315.90
7190.76
61.13
13588.32*
4787.69
7604.53
5957.39
2387.51
2865324.70**
4672.67
3071.44
2106.58
5012.33
5013.78
4091.27
5397.50
4822.41
**Significant at P < 0.01, *significant at P < 0.05.
Fig. 1. Stability analysis for four traits using Site Regresion Model (Crossa et al., 2002) involving eight somaclone variants (R5) and four check varieties (HUW 234,
Sonalika, NW 1014 and Halna) tested for two dates of 3 years in two ways (conventional and zero till) of sowings.Note: For somaclonal variants of HUW 234
abbreviated names have been used such that HUW5173 = HUW 234-5-173; HUW5282 = HUW 234-5-282; HUW5301 = HUW 234-5-301; HUW5325 = HUW 2345-325; HUW5341 = HUW234-5-341; HUW5345 = HUW 234-5-345; HUW5346 = HUW 234-5-346; HUW544 = HUW 234-5-44.
550.0
560.4
541.3
505.2
473.2
415.2
227.4
144.7
701.3
1055.5
277.7
1029.1
fg
g
fg
ef
e
d
b
a
h
i
c
i
f
f
f
e
e
d
b
a
g
h
c
h
67
variants displayed significantly lower score of leaf rust and spot
blotch AUDPC in comparison to the parental variety.
3.4. Evaluation of R5 somaclones in conventional and zerotill sowing
538.8
566.6
541.6
497.2
463.8
419.4
230.5
140.2
697.2
1066.6
284.7
1038.8
Mean
The analysis of variance for yield, yield traits and AUDPC of
spot blotch and leaf rust diseases of the somaclones evaluated in
two planting dates for 3 years in two ways of sowings indicated
that there were significant differences among genotypes tested
(Table 5). For grain yield, significant differences were noted for
date of sowing but not for year and tillage.
Duncan’s multiple range test suggested that two somaclones
(HUW 234-5-44 and HUW 234-5-346) were clearly superior to
the parent HUW 234 as well as other check cultivars under both
dates of sowings across 3 years (Table 6). No interaction was
noted for tillage methods and the two variants were superior in
both ways of sowings. These two somaclones also possessed
significantly lower spot blotch and leaf rust AUDPC values and
maintained acceptable 1000 grain weight. The stability analysis
over 12 environments (Fig. 1) also demonstrated the superiority
of these two variants for different traits.
1482.1
1485.9
1352.9
1412.1
1399.7
1446.4
1344.2
1350.7
1630.2
2276.7
1549.8
2492.2
1511.27 d
1509.21 d
1377.48 a
1438.48 b
1423.77 b
1480.1 c
1362.89 a
1366.28 a
1704.11 f
2331.88 g
1591.12 e
2527.39 h
1453.08
1462.63
1385.73
1375.78
1412.68
1328.33
1325.54
1335.15
1556.41
2221.53
1508.48
2457.03
35.69
35.24
35.53
34.63
35.42
34.98
36.43
37.12
35.50
34.62
36.34
37.69
Means with the same letter are not significantly different based on Duncan’s new multiple range test at P = 0.5.
4. Discussion
a
33.66
33.32
33.36
32.05
33.21
33.06
34.22
35.54
33.07
32.55
33.95
33.66
39.35
37.90
37.79
38.32
37.81
38.30
38.04
38.66
37.88
36.68
39.67
40.21
61.22
63.05
62.37
59.97
61.72
61.97
60.30
60.37
62.72
56.72
63.47
60.35
60.44 f
62.04 i
60.24 e
59.2 b
61.24 h
61.14 g
59.84 c
60.04 d
62.24 j
56.04 a
62.84 k
59.24 b
62.00
64.05
60.70
62.20
62.80
64.50
60.75
60.70
63.20
57.40
64.10
61.45
d
d
d
bc
b
bc
a
a
b
f
cd
e
2.48
2.49
2.48
2.54
2.55
2.54
2.68
2.70
2.57
1.95
2.52
2.21
2.41
2.43
2.37
2.47
2.48
2.47
2.64
2.65
2.41
1.94
2.33
2.15
HUW 234-5-173
HUW 234-5-282
HUW 234-5-301
HUW 234-5-325
HUW 234-5-341
HUW 234-5-345
HUW 234-5-346
HUW 234-5-44
HUW 234
Halna
NW-1014
Sonalika
2.55
2.54
2.58
2.61
2.63
2.61
2.72
2.75
2.62
1.96
2.61
2.25
cd
d
bcd
bc
b
b
a
a
bc
f
bc
e
DII
de
cd
e
bc
b
bc
a
a
de
h
a
a
Mean
d
g
b
d
e
h
b
b
f
a
g
c
DII
DI
DI
Mean
g
b
d
i
f
e
h
h
c
j
a
h
DI
c
f
f
e
f
e
ef
d
f
g
b
a
DII
de
f
ef
h
f
f
c
a
f
g
cd
de
d
ef
de
g
de
f
c
b
ed
g
c
a
DI
Mean
d
d
b
b
c
a
a
a
f
g
e
h
DII
Mean
d
d
a
b
b
c
a
a
f
g
e
h
561.1
554.1
540.9
513.1
482.6
411.1
224.3
149.3
705.5
270.8
1044.4
1019.4
e
e
e
de
d
c
b
a
f
b
g
g
DII
DI
Leaf rust score (%)
Spot blotch AUDPC
1000 grain weight
Days to heading
Grain yield/plot
Mean of traits in two dates of sowings a
Genotypes
Table 6
Mean performance of the R5 variants of variants of HUW 234 for yield traits and resistance to spot blotch and leaf rust tested for three years (2003, 2004 and 2005) under late (25 December) and very late (10 January)
sowing following conventional and zero-till methods
B. Arun et al. / Field Crops Research 103 (2007) 62–69
Available reports on the use of somaclonal variants of wheat
indicate that the variants have been obtained for normal sown
condition in which plants get sufficient time for their growth
and development (Ahloowalia, 1982; Kranz and Lörz, 1993). In
our previous study (Arun et al., 2003) we had identified
somaclones, of which some were stably expressing superiority
for yield and spot blotch resistance under timely sown
condition. In this study, two somaclones displayed significant
superiority for yield and shorter maturity durations and were
substantially stable across 12 environments exposed to terminal
heat stress (Table 6 and Fig. 1). It was interesting to note that the
variants also displayed significantly lower AUDPC values for
leaf rust and spot blotch (Table 6), two of the most important
diseases of South Asian nations India, Nepal and Bangladesh
(Saari, 1998; Joshi et al., 2007c). The significant improvement
in days to heading is a desirable agronomic trait for rice–wheat
cropping areas of South Asia where late sowing of wheat is
quite frequent (Joshi et al., 2007a). The superior yield
performance combined with significantly lower disease
reaction and earliness for heading could be considered to be
of major agronomic importance for a vast wheat area under the
threat of increasing temperature due to global warming (Joshi
et al., 2007b). This is especially more encouraging with respect
to spot blotch disease caused by B. sorokiniana which is
considered the most important wheat pathogen in eastern South
Asia (Saari, 1998; Duveiller et al., 2005; Joshi et al., 2007c).
Further, impressive performance of somaclones in zero-till
sowing proves their usefulness under reduced tillage which is
gaining popularity in rice–wheat cropping areas in South Asia
(Hobbs, 2001; Joshi et al., 2007a), which at 14 million hectares
cover around one-third of the total rice area and two-fifths of the
total wheat area in India, Pakistan, Nepal, and Bangladesh, and
68
B. Arun et al. / Field Crops Research 103 (2007) 62–69
account for some 30% of those nations’ rice and wheat outputs
(Hobbs and Morris, 1996) and over half of the 24 million
hectares of rice–wheat systems in the Asian subtropics (Ladha
et al., 2000; Joshi et al., 2007a). Such shorter duration wheat
lines are also desired in warmer areas where temperature rises
very early and wheat gets not more than 120 days to complete
its life cycle.
According to Carver and Johnson (1989) development of
somaclonal variants with enhanced yield potential compared to
parent control has proven especially difficult. However, despite
the absence of a tissue culture-derived increase in average grain
yield of any population, significant increases were noted for
spike density, biomass, heading date and grain protein content
(higher percentage) (Carver and Johnson, 1989). Cheng et al.
(1992), while studying the frequency, occurrence and
inheritance of somaclonal variation in winter wheat observed
that a majority of variations were agronomically inferior, but
variants with improved maturity and plant stature as well as
disease resistance were also selected. Results of Symillides
et al. (1995) showed that significant variation can be generated
for several characters through in vitro culture. Ivanov et al.
(1998) evaluated somaclones in R3 and R4 generations for
variation in agronomic and morphological characters and
observed both negative and positive statistically significant
change. They however found this tool helpful in improving the
plant height and spike length because both the traits were
statistically stable in two successive generations (R3 and R4).
Quershi et al. (1992) could also found many tissue culture
derived families that were superior for kernels/spike and high
grain yield/spike; however a majority of their families were
significantly longer in maturity, an undesirable agronomic
character for their region. Enhancement of resistance to spot
blotch disease of wheat has also been observed in the
somaclones (Arun et al., 2003). Although, Wenzel and
Foroughi (1990) had reported that it was not possible to
improve the rather high level of Helminthosporium resistance
of variety Pictic, the absolute numbers indicated that the lower
level of resistance of the other variety Atys might have been
increased.
In the present study, although many somaclones appeared to
display superiority in different generations, two somaclones
(HUW 234-5-44 and HUW 234-5-346) were significantly
superior throughout different generations as compared to the
parent (HUW 234) and other check varieties. The 3 year trial in
two sowing dates and tillage approaches appear to confirm the
superiority of these two somaclones (Table 6 and Fig. 1). The
superior performance of these somaclones in successive
generations establishes their stability and also suggests that
it is possible to isolate significantly superior somaclonal
variants of agronomic importance for late sown and zero-till
management exposed to terminal heat stress conditions. The
cultivar HUW 234 is the most popular cultivar of eastern
Gangetic plains of South Asia under late sown conditions and
still occupies more than 2 million hectares mostly under rice–
wheat cropping system (Joshi et al., 2007a). For many years,
almost all breeding programmes working for eastern Gangetic
plains of South Asia especially that of India have been focusing
on developing a cultivar that can replace this variety in farmers
fields. In this context the superior performance of somaclones
assumes significance. The two somaclones may not necessarily
be directly used as varieties but can be used as a donor parent in
the ongoing breeding programmes targeting shorter cultivars
having good yield and resistance in warmer and humid areas of
India, Nepal and Bangladesh where terminal heat stress and
spot blotch are the cause of increasing concern.
Acknowledgements
Authors gratefully acknowledge Dr. G. Ortiz Ferrara,
Principal Scientist and Regional Coordinator CIMMYT South
Asia, Nepal, for his valuable advice during the course of this
study. Help given by Dr. Jose Crossa and Dr. R.C. Sharma
(Visiting Scientist), CIMMYT, Meixco in the analysis of data is
also duly acknowledged.
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