Unraveling Mechanisms Inducing Heat Stress Resilience in Sorghum during Flowering.

Experiment 1 -Twenty-four geographically and genetically diverse sorghum NAM (Nested Association Mapping) founder lines flowering pattern was followed at half an hour interval starting from 6 AM till 12 PM over multiple flowering days in greenhouse. Experiment 2 - flower opening pattern of 3 popular hybrids (Pioneer, Dekalb and Maturity Check) were observed in the field. Experiment 3 -two relatively heat stress resilient accessions (Macia and P898012) based on our previous experiments, one elite US cultivar (RTx 430) and 1 hybrid (Dekalb) were tested for flowering pattern and heat stress resilience. All four cultivars were exposed to control (32°C/22°C day/night temperature), high temperature treatment during early morning (40°C/22°C; 6 to 11AM) and high temperature during day (40°C/22°C; 9AM to 4PM) lasting 12 flowering days using the growth chamber facility. In Experiments 1 and 2, flowering peak was completed within two hours of dawn, triggering the hypothesis that sorghum primarily follows heat escape mechanism to avoid heat stress during flowering. Although flower opening pattern was consistent across all three experiments, very high level of heat stress (40°C; Experiment 3) resulted in complete absence of grain formation preventing us from testing the hypothesis that embryo development/abortion are most vulnerable than pollen viability. Hence, a fourth experiment with same 4 genotypes were exposed to two more intermediate heat stress treatments (OT 32/22°C, HT 35/22°C, 38/22°C and 40/22°C day/night temperature; 9AM to 4PM). In vitro pollen germination, in vivo pollen germination, and ovary enlargement from the spikelets collected after 1, 2, 4, 6, 8, 12 and 24 hours after anthesis are currently investigated. We aim to unravel the role of early fertilization events, embryo development/abortion on seed-set and grain development processes and findings will be discussed in the context of breeding strategy to tackle heat stress impact during flowering in sorghum.