Pollen‐Based Screening of Soybean Genotypes for High Temperatures

Abstract

Soybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures > 35°C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50°C at 5°C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 μm). Mean cardinal temperatures (Tmin, Topt, and Tmax) were 13.2, 30.2, and 47.2°C for PG and 12.1, 36.1, and 47.0°C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum (Tmax), minimum (Tmin), and optimum (Topt) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat‐tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30°C) compared with heat‐intermediate (PI 471938) and heat‐sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumellae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88‐5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [CO2] did not modify reproductive parameters or CTRI. The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature‐tolerant genotypes and temperature‐dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.

Determination of cardinal temperatures for sugar apple ( Annona squamosa L.)

“…The in vitro germination and pollen tube length data in response to temperature were used to estimate the cardinal temperatures, that is, T min (minimum temperature at which the pollen grain germinates), T opt (optimal temperature at which the pollen grain reaches maximum germination) and T max (maximum temperature above which pollen grain does not germinate), and these were analyzed using linear and nonlinear regression models that are widely used in these studies (Acar and Kakani, 2010;Salem et al, 2007). The adjustments of the regression equations, which describe the response of pollen germination to temperature, were compared by the variance explained by the coefficient of determination (R²) and the standard error.…”

“…Thus, the minimum (T min ), optimum (T opt ) and maximum (T max ) temperatures were estimated as described by Acar and Kakani (2010) and Salem et al (2007) using Equations 2, 3 and 4.…”

Convergence of agricultural intensification and climate change in the Midwestern United States: implications for soil and water conservation

“…Corn plants exposed to temperatures above 308C have shown impacts on cell division, grain kernel development and yield (Commuri and Jones 2001;Jones et al 1984). In soybean, night air temperatures above 238C reduce seed growth, and crop pollination has shown declines above 308C (Baker et al 1989;Salem et al 2007). Increasing temperatures at night affect all plants, affecting fruit quality along with quantity.…”

Soybean Yield Formation: What Controls It and How It Can Be Improved

“…Temperature stress in soybean is manifested through effects on photosynthesis and CGR (Paulsen, 1994), reproductive abnormalities (Salem et al, 2007), and phenological events (Huxley and Summerfield, 1974). Among these factors, the effect on canopy photosynthesis and CGR has the greatest effect on yield.…”

“…Among these factors, the effect on canopy photosynthesis and CGR has the greatest effect on yield. Temperatures above 35 0 C can inhibit pollen germination and pollen tube growth (Salem et al, 2007;Koti et al, 2004). However, since anther dehiscence occurs at 8 to 10 A.M., temperatures in most soybean growing areas would not be above the critical level during these events.…”