Interactions between host plant genotype and Neotyphodium fungal endophytes affects insects

Abstract

Neotyphodium endophytes usually confer resistance on their host grasses to insect attack, but can also occasionally increase host plant susceptibility to particular insects. In either case host plant genotype interaction with the endophyte appears to play a role in determining the strength of the interactions between the insect and its host. An example of this is the relationship between the root aphid, Aploneura lentisci and perennial ryegrass infected with different strains of endophyte. Aphid numbers on individual ryegrass plants infected with the Wild-type endophyte are generally similar to, or less than, those on endophyte-free (Nil) ryegrass whereas populations on plants infected with the AR1 endophyte are significantly higher. By analysing for differences between individual plants using data from five different samplings, significant differences in both the total number of root aphid per plant and aphid loading (number/g of root) were found among 20 plants infected with either the Wild-type or AR1 (P<0.01). Host plant genotype of Nil plants also significantly affected aphid numbers (P<0.05) but not aphid loading. Population growth of aphids subsequently showed a strong effect of plant genotype for AR1-infected plants but not for Nil plants. In a further trial using cloned plants from half-sibling families of both AR1 and Wild-type, there were significant family effects on aphid numbers/plant, suggesting heritable variation for host control and that selections could be made for AR1 plants that supported low numbers of this insect. There was no comparable variation amongst families infected with Wild-type endophyte in the same experiment