Isolation of prostrate turfgrass mutants via screening of dwarf phenotype and characterization of a perennial ryegrass prostrate mutant

Prostrate turf varieties are desirable because of their increased low mowing tolerance,heat resistance,traffic resistance and ground coverage compared with upright varieties.Mutation breeding may provide a powerful tool to create prostrate varieties,but there are no simple,straightforward methods to screen for such mutants.Elucidation of the molecular basis of the major‘green revolution’traits,dwarfism and semi-dwarfism,guided us to design a simple strategy for isolating dwarf mutants of perennial ryegrass(Lolium perenne L.).We have shown that gamma-ray-mediated dominant dwarf mutants can be easily screened for at the three-leaf stage.About 10%of dwarf mutant lines also displayed a prostrate phenotype at mature stages(>10 tillers).One prostrate line,Lowboy I,has been characterized in detail.Lowboy I had significantly shorter canopy,leaf blade and internode lengths compared with wild type.Lowboy I also exhibited greater tolerance to low mowing stress than wild type.Exogenous gibberellic acid(GA)restored Lowboy I to a wild-type phenotype,indicating that the dwarf and prostrate phenotypes were both due to GA deficiency.We further showed that phenotypes of Lowboy I were dominant and stably inherited through sexual reproduction.Prostrate turfgrass mutants are difficult to screen for because the phenotype is not observed at young seedling stages,therefore our method represents a simple strategy for easily isolating prostrate mutants.Furthermore,Lowboy I may provide an outstanding germplasm for breeding novel prostrate perennial ryegrass cultivars.