Abstract
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.
Highlights
Perennial ryegrass (Lolium perenne L.) is an important turfgrass species, widely used for lawns and athletic fields because of its rapid establishment and attractive, leafy appearance.[1,2] Because of its fast growth rate, perennial ryegrass requires frequent watering, fertilization and mowing, resulting in high establishment and maintenance costs.[3,4] One strategy to reduce upkeep costs would be to use a dwarf variety of perennial ryegrass,[5,6,7] none exists as of yet
The prostrate phenotype observed in Lowboy I was completely abolished following GA3 treatment (Figures 2a and b). These results demonstrate that GA3 treatment is sufficient to restore Lowboy I to a wild-type phenotype, indicating that the mutation found in Lowboy I results in gibberellic acid (GA) deficiency
The prostrate and dwarf phenotypes of Lowboy I were completely eliminated with exogenous GA3 application, demonstrating that both traits are most likely the result of GA deficiency
Summary
Perennial ryegrass (Lolium perenne L.) is an important turfgrass species, widely used for lawns and athletic fields because of its rapid establishment and attractive, leafy appearance.[1,2] Because of its fast growth rate, perennial ryegrass requires frequent watering, fertilization and mowing, resulting in high establishment and maintenance costs.[3,4] One strategy to reduce upkeep costs would be to use a dwarf variety of perennial ryegrass,[5,6,7] none exists as of yet. Dwarf mutants can have lower upkeep costs due to their reduced vegetative growth, which necessitates less frequent mowing and fewer nutrients, and makes them less vulnerable to evaporation. Another strategy would be to create a prostrate variety of perennial ryegrass. Prostrate turf has been shown to improve low mowing tolerance in bluegrass (Poa spp.).[8] The horizontal growth of prostrate turf can protect leaf blades and sheaths, aiding in recovery from mowing stress. Turf that grows in a prostrate manner appears to have greater ground coverage than upright turf because the flat-lying leaves can cover areas with lower turf density
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