Towards estimating shade response of bermudagrass (<i>Cynodon</i> spp.) using field-based photosynthetic properties

Abstract

Shade tolerance is a highly desirable trait when breeding new bermudagrass (<italic>Cynodon</italic> spp.) lines, but current screening methods can take many years to complete. There is a clear need for large-scale turfgrass breeding programs to reliably, accurately, and quickly predict shade tolerance in their germplasm. The objectives of this research were to: (i) build custom chambers to reproducibly estimate photosynthetic characteristics from turfgrass canopies at different light intensities and (ii) determine which photosynthetic characteristics are indicative of past shade performance. A custom-built chamber was constructed to determine average photosynthetic characteristics for the whole plant by studying the turfgrass canopy at natural leaf angles for light interception. Shade tolerant (11-T-56) and shade sensitive (Tifway) bermudagrass cultivars were used to examine the effectiveness of the chamber within an array of photosynthetic characteristics when the grasses were grown in full-sun and 73% shade environments. Light compensation point, chlorophyll content, quantum yield, dark respiration rate, and maximum quantum yield of photosystem II were evaluated in this trial. Based on the results of this study, the authors recommend that light compensation point or maximum quantum yield be further evaluated as an accurate indicator of shade tolerance when performed in the field on spring days with grasses grown in full sun or 73% shade environments. Lower R_d rates and ambient temperatures on spring days appear to minimize unexplained variance in the data, which would allow researchers to better detect genotypic differences during this season.