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Pearl millet has recently emerged as a significant irrigated summer season cereal crop in north-western India. But its flowering coincides with air temperatures of ≥40 °C, leading to reduced seed set and poor grain yield in most of the available hybrids, although a few hybrids with good seed set and high yield potential are widely cultivated. Under a recent initiative to diversify the genetic base of heat tolerant hybrids, field screening of 221 hybrid parental lines (both B- and R-lines), 53 germplasm accessions and 4 improved populations over four-year period revealed large genetic variability in seed set at daily maximum air-temperature of ≥42 °C during flowering. Two locations data on 46 medium maturing genotypes screened during summer 2009 showed that seed set in pearl millet started declining when maximum air temperatures reached 42 °C and decreased in curvilinear fashion to 20 percent at 46 °C. Similar relationship of seed set with minimum and mean temperature was observed with threshold values of 26.4 °C and 34.2 °C, respectively. Similarly, the relationship of percent seed set with vapor pressure deficit (VPD) showed threshold value of 6.2 kPa for maximum VPD, 1.2 kPa for minimum VPD and 3.7 kPa for mean VPD. Seed set on 2 each of heat tolerant and susceptible genotypes fitted well on the seed set-temperature response curve for the maximum, minimum and mean air temperatures. Based on 3 to 4 year field screening (2009–2012), five hybrid seed parents (ICMB 92777, ICMB 05666, ICMB 00333, ICMB 02333 and ICMB 03555) and a germplasm accession IP 19877 with 61 to 69% seed set as compared to 71% seed set in a heat tolerant commercial hybrid 9444 (used as a control) was identified. Intra-population variability for heat tolerance was observed in four populations, and highly heat tolerant progenies from two of them were identified. Evaluation of six hybrid parents under controlled environment (maximum temperature of 43 °C and minimum temperature of 22 °C) revealed boot-leaf stage of pearl millet plant to be more heat sensitive than panicle-emergence stage, and investigations on 6 A-/B-pairs under controlled environment (max. temperature of 44 °C and min. temperature of 22 °C) revealed female reproductive system of pearl millet to be more heat sensitive than pollen. Comparison of 23 hybrids and their parents for seed set at high air temperature (>42 °C) showed heat tolerance as a dominant trait, implying heat tolerance in one parent would be adequate to produce heat tolerant hybrids in pearl millet. Heat tolerant composite developed using identified lines showed high mean seed set under high air temperatures during flowering. |
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