Impact of Heat Stress on Pollen Germination and Post Flowering Response in Diverse Sorghum Genotypes Under Field Condition.

Heat stress is one of the major abiotic stress factor that adversely affects growth and development of sorghum. Climate and crop models indicate an increase in daily mean temperature that can negatively impact yield of grain crops including sorghum.  Earlier studies conducted in controlled environmental conditions reveal flowering and post-flowering stages to be vulnerable to heat stress exposure, while field evaluation of heat stress impact is limited. Hence, this study was conducted to quantify heat stress response in twenty-four diverse sorghum genotypes using field based heat tent facility. In addition, pollen germination potential of the same 24 genotypes was tested for heat stress tolerance, from plants grown under greenhouse conditions. Using the field based tents, heat stress was imposed from booting stage to maturity. At flowering, in vitro pollen germination, gas exchange and chlorophyll fluorescence were measured and grain yield was recorded at complete maturity. Heat stress decreased in vitro pollen germination (2 to 95%), photosynthesis (0.5 to 50 %), photochemical efficiency of PS II (Fv/Fm; 1 to 8%) and grain yield (16 to73%) and increased thylakoid membrane damage (Fo/Fm; 2 to 27%). Although, seed weight was increased in most of the sorghum genotypes it did not compensate for grain yield loss recorded due to heat stress exposure. Pollen grains from genotype SC155 recorded highest tolerance to heat stress as it had least reduction in in vitro pollen germination under severe heat stress compared with control.  On the other hand, Macia and P898012 recorded higher grain yield and in vitro pollen germination. Hence they can be considered as ideal donors for mapping genomic regions responsible for heat stress tolerance by utilizing currently available bi-parental mapping populations in a common female parent (RTx430) background.

Key words – Sorghum, heat stress, flowering, pollen germination, yield