Is Sorghum Truly Tolerant or an Efficient Escaper of Heat Stress during Flowering?.

Is sorghum truly tolerant or an efficient escaper of heat stress during flowering?

Anuj Chiluwal, Vinutha Kanaganahalli KS, John Sunoj VS, Aiqing Sun, Impa Somayanda, Vara Prasad PV and Krishna Jagadish SV

Department of Agronomy, Kansas State University, Manhattan, KS, USA

Plants develop resilience to abiotic stresses including heat stress either by employing escape, avoidance, tolerance mechanisms or by their combination. Sorghum is widely grown in the arid and semi-arid regions of the world and is considered to be highly resilient to heat stress during the reproductive stages. Till date, there have been no efforts towards systematic observation of the flowering behavior in sorghum, which forms the basis for addressing the objective highlighted in the title. Twenty-four geographically and genetically diverse sorghum genotypes flowering pattern was followed every half an hour over multiple flowering days in a greenhouse.  All the tested genotypes completed their flowering peak within two hours after dawn, triggering the hypothesis that sorghum primarily follows heat stress escape mechanism. In addition to the flower opening pattern, all genotypes were tested for flowering and post flowering heat stress response using the heat tents under field conditions. Based on the findings from heat tents, two relatively heat stress resilient genotypes (Macia and P898012), one common US cultivar (RTx 430) and 1 hybrid (Dekalb) were selected for detailed physiological characterization using the growth chamber facility. Plants in heat stress study were exposed to three different treatments each having three replications: control (32°C/22°C day/night temperature), high temperature treatment during early morning (40°C/22°C day/night temperature; 6 to 11 AM), coinciding with their peak flowering and high temperature during day (40°C/22°C day/night temperature; 9 AM to 4 PM) for 12 flowering days. Flower opening pattern, in vitropollen germination and embryo abortion, seed-set and yield per plant is currently being recorded. Simultaneously, the timing of flower opening is currently being investigated in popular commercial hybrids. Our findings will be discussed in the context of a breeding strategy to tackle heat stress impact during flowering in sorghum. 

Key words – sorghum, flower opening time, heat stress, pollen germination, seed-set, stress resilience