Wednesday, November 7, 2007
261-15
Variation for Minimum Leaf Epidermal Conductance in Ontario-Adapted Soybean.
Hugh J. Earl, Alison E. Walden, and Istvan Rajcan. Plant Agriculture, University of Guelph, Crop Science Building, Guelph, ON N1G 2W1, Canada
Several previous studies have identified substantial variation for leaf minimum epidermal conductance (MEC, total conductance to water vapour of dark adapted leaves) among soybean lines. More recently MEC was shown to be strongly negatively correlated to whole plant water use efficiency, an important determinant of yield potential where soil water is limiting. However, there are no published data on the extent of variation for MEC among commercial varieties adapted to the northern Corn Belt. In the present work, our objectives were i) to assess the variation in MEC among commercial varieties adapted to the soybean growing regions of Ontario (2450 to 3150 crop heat unit zones), ii) to compare the range in MEC among these commercial varieties to that known to exist among other soybean germplasm, and iii) to identify parents of existing mapping populations that differed for MEC, so that QTL controlling the trait might be identified. We developed a novel closed (re-circulating) gas exchange system and used it to measure MEC of 17 conventional and 13 glyphosate-tolerant Ontario soybean varieties, 24 parents of soybean mapping populations and 10 soybean lines from other regions chosen for their extreme MEC values (both high and low). Plants were grown in a greenhouse in a randomized complete block design with seven replications. We found extensive variation among commercial varieties adapted to Ontario (7.7 to 17.0 mmol m-2 s-1); this range was similar to that found among the 10 lines specifically chosen for their extreme MEC values (6.6 to 14.0). The mapping population parents had MEC values ranging from 7.7 to 39.5. The broad range of MEC values among commercial lines suggests that contemporary Ontario soybean varieties may differ substantially for water use efficiency. The results also indicate that existing mapping populations could be used to identify genomic regions controlling the MEC trait.