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Flowering-stage heat tolerance in pearl millet
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Flowering-stage heat tolerance in pearl millet

  1. 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. 0.000 5.000 10.000 15.000 20.000 25.000 30.000 35.000 40.000 45.000 50.000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 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) 0 10 20 30 40 50 60 70 80 90 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 SeedSet(%) Series1
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