Minisymposium 9: Global change

Abs # 22004: Temperature sensitivity of pollen viability, seed-set and seed yield of grain-sorghum (Sorghum bicolor L.) is adversely affected by growth at elevated carbon dioxide

Presenter:	Prasad, P.V. Vara , vpaga@mail.ifas.ufl.edu
Authors	Prasad, P.V. Vara  (A)   Boote, Kenneth J (A)   Allen, Jr, L. Hartwell  (B)
Affiliations:	(A): Agronomy Department, University of Florida, Gainesville FL 32611 (B): USDA - ARS, Gainesville FL 32611

One of the important components of global climate change is increase in temperature due to rising concentrations of atmospheric carbon dioxide (CO₂) and other greenhouse gases. Reproductive processes such as pollen germination, seed-set and seed growth are important factors governing yields which are highly sensitive to temperature. Objectives of our research were to (a) quantify the impact of elevated temperature on pollen viability, seed-set, seed growth and seed yield of grain-sorghum at ambient and double ambient CO₂; and (b) determine if the temperature response of pollen viability, seed-set and seed yield is influenced by elevated CO₂. Plants of cv. DK28E were grown in sunlit controlled-environment chambers at daytime maximum/nighttime minimum temperatures of 32/22, 36/26, 40/30, and 44/34 C at ambient (350 μmol mol^-1) and elevated (700 μmol mol^-1) CO₂ from emergence to maturity. Panicles were tagged at emergence and pollen viability was determined at anthesis. The total numbers of filled and unfilled florets from tagged panicles were counted to estimate seed-set. At anthesis, pollen from different treatments were collected and percent germination on artificial medium at temperatures ranging from 10 to 45 C was determined. Only few panicles (<10%) emerged at 40/30 C very late in the season (20 d later than 32/22 C) and no panicle emergence occurred at 44/34 C either at ambient or elevated CO₂. Elevated CO₂ delayed panicle emergence, flowering and start of seed filling at 36/26. Growth at 36/26 C decreased pollen viability and seed-set (proportion of total florets setting seeds) compared to 32/22 C. The percentage decrease in pollen viability and seed-set at 36/26 C was greater at elevated CO₂ compared to ambient CO₂. Seed-set at elevated CO₂ was significantly lower at both 32/22 and 36/26 C due to higher number of florets and lower pollen viability. There was no effect of elevated CO₂ on the cardinal temperatures (Tmin, Topt and Tmax) for pollen germination, which were 19, 30 and 39 C, respectively. The rate and duration of grain-filling was drastically reduced at 40/30 C resulting in smaller seed-size. Elevated CO₂ increased seed yield at 32/22 C but decreased it at 36/26 C. Harvest index at both 32/22 and 36/26 C was lower at elevated CO₂. Foliage and seed temperatures at elevated CO₂ were 1 to 2 C higher than ambient CO₂ across all temperatures. The greater sensitivity of pollen viability, seed-set and seed yield at elevated CO₂ could be attributed to higher tissue temperatures. Future research should be aimed at developing strategies to minimize impact of climate change on crop yields.