Physiology and Associated Metabolic Expression in Soft Wheat Genotypes Under Terminal Heat Stress.

Stress due to high temperature at grain filling has emerged as a major constraint to achieve global food security to meet the needs of 9.6 billion people expected in 2050. Terminal heat stress has become a common limiting factor for almost all wheat growing regions in the USA.  Almost no information is available regarding genetic variations for heat tolerance in soft wheat germplasms in the USA. We evaluated six soft wheat genotypes: AGS2000, USG3120 (Commercial varieties), LA03200E-2, LA06027E-P7, GA06493-13LE6, and VA12W-72 with a heat tolerant check “Ventnor” for terminal heat stress. The genotypes were subjected to heat stress 10 days after anthesis initiated up to maturity under controlled greenhouse conditions. Temperatures of 35/28^oC and 24/18^oC were induced for heat treated and controlled plants (16 hour day/8 hour night), respectively. The genotypes were characterized for leaf and spike temperatures, chlorophyll content, thylakoid and plasma membrane damage, individual grain weight, grain weight, grain number, heat susceptibility index (HSI), and for global metabolic expression. USG3120 showed the least damage to thylakoid, plasma membrane, and chlorophyll among all of the wheat genotypes.  The damage to individual kernel weight ranged from 36% (USG3120) to 51% (LA03200E-2 and Ventnor).  All soft wheat genotypes showed less or similar kernel weight damage compared to Ventnor. HSI values ranged from 0.57 (LA03200E-2) to 1.41 (USG3120).  The genotypes are now under the investigation for metabolic expression. The genotypes were characterized for a wide variety of primary and secondary metabolites. Our results indicate that genetic variation exists in soft wheat for terminal heat stress.