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

Shade tolerance is a highly desirable trait when breeding new bermudagrass(Cynodon 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 Rd 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.

Performance and playability of experimental low-input coarsetextured zoysiagrass in multiple climates

A 3-year experiment was conducted to evaluate the performance and playability of 24 coarse-textured zoysiagrass(Zoysia spp.Willd.)experimental genotypes in comparison to five commercially available cultivars maintained as a low-maintenance turf across multiple climates(Indiana,North Carolina,Georgia,Arizona,and California).Following establishment in 2018,plots were maintained under low-maintenance regimes and evaluated for quality,density,uniformity,color,winterkill damage,drought resistance,and golf ball lie in 2019 and 2020.A turf performance index(TPI)was calculated for each treatment at each site,which represented the number of times the treatment occurred in the top statistical group.The unique climate for each site led to differences in TPI scores.For instance,the arid climates of Arizona and California resulted in distinct differences in performance among treatments compared to the other sites.However,consistencies in performance across sites were also observed.For example,the 2018−2019 winter resulted in winterkill differences among entries in both Indiana and North Carolina,which led to some similarities in TPI.Furthermore,the southern humid climates of North Carolina and Georgia produced consistencies in overall TPI.Under the minimal inputs and the hot-humid or arid climates evaluated in this study,all of the check cultivars were some of the poorest performing treatments,which clearly illustrates there is a need for breeding programs to develop zoysiagrass genotypes for these climates.However,experimental lines that exhibited excellent persistence under these conditions were identified indicating the genetic potential for wider adaptation to lower input environments exists within the species.

Seashore paspalum (Paspalum vaginatum Sw.) performance under shade in multi-environment trials

Shade caused by trees or buildings can affect the quality and growth of turfgrasses.Thus,breeding for shade tolerance is an essential component of most turfgrass improvement programs.The objective of this study was to evaluate the performance of seashore paspalum(Paspalum vaginatum Sw.)breeding lines under shade in multi-environment trials.Germplasm sources were 20 lines from the University of Georgia seashore paspalum breeding program and two checks,the cultivars'SeaDwarf'and'SeaStar'.Field trials were conducted from 2016 to 2019 under shade structures designed to reduce ambient sunlight at three locations:Citra(FL),Tifton(GA),and Raleigh(NC).The response variables evaluated were percent living ground cover(%GC),dark green color index(DGCI),canopy height(CH)and turfgrass quality(TQ).Data were analyzed by mixed model approaches using ASReml-R,and the t-statistics were used to group the entries.Significant genetic variances were observed in the single-location-repeated-measures analysis for CH and DGCI at Citra and Tifton,%GC at Citra,and TQ at Raleigh.Spearman correlations of the predicted values for entries between locations ranged from low to moderate,with the exception of between Citra and Tifton(0.76)for CH.There were a few breeding lines with superior performance to the entry average for all traits for which the entry variance was significant.In conclusion,genetic variability was observed for all traits and superior seashore paspalum breeding lines for multiple traits were identified under shade.