Characterization of bermudagrass (Cynodon dactylon L.) germplasm for nitrogen use efficiency

Bermudagrass is the most important warm-season pasture in the Southern USA with exceptional forage production potential and abiotic stress tolerance. However, it requires high nitrogen (N) supply to reach its full biomass and quality potential. Our objectives were to: (1) develop a nitrogen use efficiency (NUE) screening protocol for bermudagrass in controlled or semi-controlled conditions, (2) identify contrasting genotypes for NUE from natural variants and, (3) develop a knowledge base of NUE in bermudagrass. A collection consisting 290 Cynodon sp. genotypes was first pre-screened in the greenhouse. Thirty-nine genotypes with high NUE, five with low NUE were selected for further evaluations along with 5 checks in greenhouse and hoop-house under four N rates. Biomass, crude protein and N content were evaluated. N uptake efficiency (NUpE), N utilization efficiency (NUtE) and NUE were calculated based on biomass production. Genotypes showed significant influences (P < 0.0001) in all of the response variables. The genotype × N rate interaction was not significant for NUE in both environments. NUE had strong correlation with biomass production and NUpE, which got stronger as N rates increased. In N limiting conditions, bermudagrass showed a trade-off between biomass maintenance and crude protein content. Lower N applications increased biomass production over crude protein. However, when N is abundant the crop has the ability to improve crude protein. Several genotypes presented high NUE due their high NUtE and NUpE. Genotypes with contrasting NUE were selected and subjected to further field evaluation. Superior genotypes for NUE will be used in the breeding program to enhance NUE in bermudagrass.