Theses and Dissertations

Issuing Body

Mississippi State University


Reddy, K. Raja

Date of Degree


Document Type

Dissertation - Open Access



Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Plant and Soil Sciences


We are now witnessing changing environmental conditions and these changes will likely continue into the coming decades due to projected increases in temperatures on the earth surface. Recent model projections suggest that the global mean surface air temperatures will increase by 1.4 to 5.8 °C by 2100. The consequences of these high temperatures include reductions in crop yields. Soybean is one of the major crops grown in the US, where high temperatures (>35 °C) during reproductive growth decreased yield. Two experiments were conducted to determine the effects of temperature on soybean pollen germination properties and identify responses to temperature among genotypes. Pollen collected from 44 genotypes grown outdoors in large pots was subjected to in vitro temperature treatments that varied from 15 to 50 °C at 5 °C increments in Experiment I. The mean cardinal temperatures (Tbase, Topt, and Tmax), averaged over 44 genotypes, were 13.2, 30.2 and 47.2 °C for pollen germination and 12.1, 36.1 and 47.0 °C for pollen tube growth. The relationship between Tbase and Topt for pollen germination was high indicating that genotypes with high Tbase also had higher Topt. The relationship was weak between Tbase and Tmax. The Topt for pollen tube growth was 5.8 ¢XC higher than the Topt for pollen germination. The study also showed significant genotypic variability for physiological parameters studied, but no significant correlations between the observed physiological parameters with any of the pollen germination or pollen tube growth parameters were studied. This indicated that physiological parameters, measured under ambient conditions may not be useful to identify reproductive tolerance to high temperatures in soybean. Total response index (TSRI), the sum of individual responses of all pollen parameters differentiated genotypes and their tolerance to high temperature. A heat-tolerant genotype (DG 5630RR) identified using TSRI technique, when grown at optimum and high temperature conditions in experiment II, were actually less sensitive to high temperatures compared to heat-sensitive and heat-intermediate sensitive genotypes indicating that pollen can be used as screening tool for heat tolerance. The identified high-temperature tolerant genotypes, based on pollen germination parameters, might be useful in current and future soybean breeding programs.



soybean||Pollen germination||Pollen tube length||temperature||in vitro