Stomatal Resistance, Leaf Temperature, and Chlorophyll Content of Sorghum Hybrids Varying In Maturity.

Although agronomic characteristics of hybrids varying in maturity have been widely studied, little information exists concerning their physiological differences.  Therefore, the objective of our study was to determine if stomatal resistance, leaf temperature, and leaf chlorophyll content differed between two DEKALB grain sorghum [Sorghum bicolor (L.) Moench] hybrids.  They were DKS 36-16 and DKS 44-20, of medium-early and medium maturity, respectively, when grown under field conditions in Kansas.  Seeds were planted in a greenhouse in pots (23 cm diam.; 21.5 cm tall) of soil (33% sand; 51% silt; 16% clay).  Stomatal resistance and leaf temperature were measured 55 days after planting with a Decagon Devices (Pullman, WA) diffusion porometer, and chlorophyll content was measured 119 days after planting with a Konica Minolta (Osaka, Japan) SPAD chlorophyll meter.  Height was measured 46 and 60 days after planting.  Dry weight was determined at harvest, 152 days after planting.  Average stomatal resistances (and standard error; n = 24) of DKS 36-16 and DKS 44-20 were 929+118 and 936+127 s/m, respectively.  Average leaf temperatures of DKS 36-16 and DKS 44-20 were 24.8+0.3 and 25.0+0.2 ^oC.  Average SPAD units of DKS 36-16 and DKS 44-20 were 42.6+1.5 and 43.0+2.2.  Average plant height 46 days after planting for DKS 36-16 and DKS 44-20 was 28.7+0.7 and 29.4+0.7 cm.  Average height 60 days after planting for DKS 36-16 and DKS 44-20 was 47.0+1.9 and 46.0+2.1 cm.  At harvest, dry weight per plant of DKS 36-16 and DKS 44-20 was 18.1+0.6 and 18.5+0.8 g. The two hybrids did not differ in stomatal resistance, leaf temperature, chlorophyll content, height, and dry weight.  Their difference in maturity was not evident under the greenhouse conditions.  Future work needs to show if hybrids of widely different maturities vary in physiological characteristics.