Effect of drought on the growth of Lolium perenne genotypes with and without fungal endophytes

1. Grass leaves are often inhabited by fungal endophytes that can enhance host growth. In some forage species, endophytes improve host resistance to, and recovery from, drought. 2. Our objective was to determine if the growth of genotypes of Lolium perenne L. was improved by endophytes during recovery from drought. 3. Thirteen infected genotypes were cloned into ramets. Half were treated with a systemic fungicide to eliminate the endophyte (E-); half were untreated and retained high endophyte levels (E+). In a glasshouse, half of all E- and E+ ramets were watered regularly, whilst half were exposed to a 2 week drought on two occasions, each followed by a 3 week recovery period. 4. After the first drought and recovery period, endophytes significantly reduced tiller production in the drought-stressed group. 5. After the second drought and recovery period, effects of drought on live leaf area and dry mass were highly dependent on host genotype, but not endophytes. The mean tiller mass of E+ ramets after drought was significantly less than that of watered E+ ramets, but this was not true in E- ramets. For six genotypes there was greater mass allocation to storage in the tiller bases of E- ramets after drought. 6. This perennial ryegrass population showed marked genotypic variation in the ability to recover from drought stress, but endophytes played little or no role in this ability. For some host genotypes there may be a metabolic cost of harbouring endophytes during environmentally stressful conditions.