Flowering-stage Heat tolerance in Pearl millet
SK Gupta* and KN Rai
International Crops Research Institute for the Semi-Arid Tropics, Patancheru 502 324, Andhra Pradesh, India.
*Corresponding author: Senior Scientist (Pearl millet breeding), s.gupta@cgiar.org
Screening under controlled environment
• Pearl millet entries were grown in pots in the open.
• Pots in the open were shifted to growth chambers at flowering stage.
• Growth chambers were simulated for a normal day with maximum temperature of 43°C.
• Plants remained in growth chamber for 12-15 days.
• Plants were taken out of chamber after seed set, and seed set percentage was recorded.
Pearl millet panicles with reduced seed set
due to high temperatures at flowering time.
Diagram depicting the reciprocal crossing strategy to determine the reproductive growth stages responsible for
temperature stress sensitivity.
Field screening for heat tolerance
• A nursery comprising 100-200 pearl millet genotypes (advanced lines, germplasm accessions
and populations) was annually screened at 5-6 test locations in the target region (Gujarat,
Rajasthan and Uttar Pradesh) during February-March to May-June of 2009, 2010 and 2011.
• The nursery was staggered planted at 10-day interval.
• Seed-set data on plants exposed to temperatures of more than 42°C were used to identify heat
tolerant lines.
Based on the mean performance over three years (Table 1),
• Entries identified with good seed set at temperatures of >42°C were:
❖❖ Designated seed parental lines: ICMB 05666 (68%), and ICMB 92777(62%)
❖❖ Germplasm line: IP 19877 (68%)
❖❖ Populations: MC 94 (15-90%), ICTP 8202 (38-82%), ICMV 82132 (75-90%)
❖❖ 9444, the commercial heat tolerant hybrid used as check had 60 to 70% seed set in different years
Nov 2012
Introduction
• Pearl millet (Pennisetum glaucum [L.] R. Br.) is an important coarse grain cereal cultivated for
grain and fodder on about 30 million hectares worldwide. India is the largest producer of this crop
(9.5 m ha).
• Primarily cultivated as a rainfed crop in the rainy season, average grain yield of 800-1000 kg/ha.
Why pursue heat tolerance
in pearl millet?
Pearl millet as summer crop
• Recently pearl millet has emerged as a
summer season crop (>500,000 ha) in
parts of Rajasthan, Gujarat and Uttar
Pradesh states of India.
• Hybrids of 80-85 days duration,
cultivated under well-irrigated and well-
managed conditions, produce 4-5 tons
of grain and 8-10 tons of dry fodder per
hectare.
• However, only a few hybrids can
tolerate high air temperatures (often
>42°C) during the flowering, that
affects seed set.
Bumper crop of Hybrid 9444 during summer in
Gujarat.
Table 1: Summary of breeding lines found heat-tolerant
in summer 2009, 2010 and 2011 screening
Year Entries Seed set (%)
2009, 2010, 2011
B-lines ICMB 05666 68
ICMB 92777 62
Germplasm line IP 19877 68
Check 9444 71
2010, 2011
B-lines ICMB 03555 59
ICMB 00333 57
ICMB 02333 55
Check 9444 65
2011
B-lines ICMB 04999 51
ICMB 05888 56
ICMB 06111 50
ICMB 06555 65
ICMB 07222 56
ICMB 09111 59
ICMB 09222 59
R-lines 8-progenies from
MC-94 55-60
9-progenies from
ICTP-8202 61-65
Checks 86M86 57
Nandi 52 61
9444 59
Seed set of pearl millet lines.
• Results indicated that flowering period heat tolerance in pearl millet is a dominant trait (Table 2).
Table 2: Reaction of different types of crosses to high temperature at flowering time at three locations,
summer season 2011
Type of Cross Number of hybrids Reaction to heat stress (T*/S*)
S x T/T x S 14 All T
T x T 9 8T, 1S
S x S 3 2S, 1T
*:T-Heat Tolerant; S-Heat susceptible
Growth chamber studies with 6 hybrid
parents showed that:
• Boot leaf stage was more sensitive to high
temperature exposure (12% seed set)
compared to panicle emergence stage (35%
seed set). Under normal conditions (control)
seed set was 94% (Table 3).
• When stigma was exposed to high
temperatures, the seed set was 7-10%,
depending upon pollen was exposed to high
temperature or not (Table 4).
• However, when stigma was not exposed
to high temperature, the seed set was
63% when pollen was exposed to high
temperature. Under normal conditions
(control), seed set was 81% (Table 4).
Temperatures and Relative Humidity in growth chamber
(24 hr schedule).
Screening of plants in growth chamber simulated for a
day with maximum air-temperature of 43°C.
Table 3: Seed set in hybrid parents at two different reproductive growth stages in controlled
environmental conditions and control at ICRISAT, Patancheru
6 hybrid parents
Seed set (%)
Growth stage of plant for heat treatment
Control Boot leaf stage Head emergence stage
Overall mean 93.9 12.4a*
35.0a, b
*: shows significance of t-test at p=.05 (a: between control and treatment; b: between the treatments)
Table 4: Mean seed set in crosses to study the effect of heat stress on male and female reproductive
organs under controlled environment conditions
6 A-B- pairs
Seed set (%)
A heat x B heat
(stigma) x (pollen)
(Treatment 1)
A heat x B control
(stigma) x (pollen)
(Treatment 2)
A normal x B heat
(stigma) x (pollen)
(Treatment 3)
A normal x B normal
(stigma) x (pollen)
(Treatment 4)
Overall mean 6.7a2a3*
10.4b1b2*
62.9c1*
80.9
*: shows significance of t-test at p=.05 (a1: between treatments 1 and 2; a2: 1 and 3; a3: 1 and 3; b1: 2 and 3; b2: 2 and 4; c1: 3 and 4)
Conclusions
• Multi-location and multi-year field screening of pearl millet breeding material revealed large
genetic variability for seed set under high air temperature at flowering time.
• Heat tolerant sources were identified for future use.
• Boot leaf stage was found more sensitive to high temperature exposure compared to panicle
emergence stage; stigma found more sensitive to high temperatures than pollen grains.
• The dominant nature of heat tolerance in pearl millet implies that one heat tolerant parent is
sufficient to produce a heat tolerant hybrid.
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TEMP
HUM
Female Plant (A-line) (A Control)Male Plant (B-Line) (B Control)
Control
Temperature stress
Male Plant (B-Line) (B heat) Female Plant (A-line) (A heat)
Fig: Seed set of pearl millet lines at 42 C at flowering time in summer
2009 ( mean of Aligarh and Bhabhar)
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SeedSet(%)
Series1