Associations between drought resistance, regrowth and quality in a perennial C4 grass

Abstract

Climate change has brought a sharp and renewed focus on plant breeding programs to develop cultivars with improved performance in dry environments. The pleiotropic effects of selection for drought resistance are not well understood in perennial C4 grasses. The objective of this study was to determine the commercial production characteristics including sod strength and post-harvest regrowth of bermudagrass ecotypes selected for drought resistance. These attributes were studied in a set of bermudagrasses (Cynodon dactylon), a species used extensively around the world for forage and turfgrass. Three field experiments using 12 genotypes contrasting for drought resistance were evaluated, on bermudagrass turf production facilities, for quality and regrowth after the canopy (sod) was mechanically removed. Among the genotypes tested, there was large genotypic variation for rhizome dry matter (RhDM) (0.01–0.81kgm−2), aboveground dry matter (ADM) (0.59–0.17kgm−2) and root dry matter (RDM) (0.04–0.12kgm−2). Regrowth of the canopy was positively correlated to RhDM (r=0.79∼0.80) and negatively correlated to ADM (r=−0.69∼−0.74) but there was no association with RDM. Biomass partitioning determined at the time of the second harvest revealed that genotypes with more rapid regrowth had larger proportional DM distributed to rhizome (63.5% vs 7.1%) than to aboveground (27.2% vs 86.5%) and root (8.5% vs 8.1%). Our previous research with these genotypes showed a strong correlation between drought resistance and RhDM prior to the drought period. Consequently, an analysis of the relationship between drought resistance measured previously and post-harvest regrowth in the experiments described here revealed a strong positive correlation (r>0.64). Genotypic variation for sod strength, an important turf quality attribute, was large ranging from 1281kgm−2 to 5671kgm−2. However, sod strength was neither correlated to drought resistance, nor the traits measured from harvested sod such as stolon diameter, internode length, number of branches and single stolon strength, nor to dry matter distribution. These results may reflect the existence of a range of different mechanisms for sod strength present in the material tested. Nevertheless, there were genotypes e.g., MED1 that combined the favorable traits of drought resistance, faster regrowth rate and higher sod strength and could be used as an important genetic resource for future breeding. MED1 was one of several highly rhizomatous genotypes in the study that originated from the Mediterranean climatic zone of Australia.