Genotypic variation in the regrowth of Lolium perenne following clipping: effects of nutrients and endophytic fungi

1. The objective of this research was to determine the extent to which regrowth rate after clipping and the specific leaf area (SLA) of genotypes of Lolium perenne were influenced by soil nutrients and endophytic fungi. 2. Twelve infected genotypes were cloned into ramets. Half were treated with a systemic fungicide that greatly reduced endophyte levels; half were untreated and retained high endophyte levels. Ramets of each genotype were subjected to low, medium or high levels of nutrients in a glasshouse for 11 weeks. 3. Plants were clipped at soil level at 11 weeks, allowed to regrow for 14 weeks and clipped again. SLA was determined at 11 and 25 weeks. Regrowth rate was calculated based on changes in leaf area and leaf dry mass between 11 and 25 weeks. 4. As a main effect, endophytes had no influence on regrowth rates and mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with regrowth rates. However, after clipping, regrowth responses to soil nutrients and endophytes were genotype-specific. Some genotypes in the high endophyte group showed an enhancement of regrowth, whilst others showed no response or a depressive effect of endophytes. 5. At the time of leaf clipping, SLA was significantly affected by genotype, nutrients and endophytes. At medium nutrients, the SLA of high endophyte plants was significantly lower than that of low endophyte plants. However, the SLA of the regrowth was affected by nutrients but not endophytes. Mean endophyte levels, as measured by hyphal counts within the leaves of five genotypes at high and low nutrients, were not correlated with SLA at 11 or 25 weeks. 6. For both high and low endophyte plants, regrowth rate was negatively correlated with SLA. 7. Perennial ryegrass possesses genotypic variation in the ability to regrow following defoliation and this ability is conditioned by abiotic (nutrients) and biotic (endophyte) factors.