The ryegrass endophyte in a cool-moist environment

Abstract

The endophytic fungus (Acremonium lolii) of perennial ryegrass (Lolium perenne) was studied in a field grazing experiment in a cool-moist environment, supplemented by more detailed glasshouse experiments on its interaction with white clover (Trifolium repens), biotic factors such as nematodes and its impact on the morphology and physiology of the host.

Parturition of sheep was found to be delayed, wool growth reduced and faecal soiling increased on endophyte-infected compared to endophyte-free pastures. Lamb growth rates were not affected by the endophyte in cool-moist years, but were lower on endophyte-infected pastures under drought conditions.

The delay in lambing date is hypothesised to be the result of delayed mating, as lamb birth weights were not affected and no delay in lambing date was observed when ewe cycling was synchronised.

Wool growth was only measured in cool-moist years which precluded insights into the importance of environmental factors.

Differences in faecal soiling between endophyte-free and endophyte-infected pastures were greater under drought conditions.

The endophyte had no effect on pasture composition and production in cool-moist years. The clover ratio of endophyte-infected pastures was depressed under drought conditions.

The presence of an endophyte provided plants with some advantage against biotic factors such as nematodes and the Argentine stem weevil (Listronotus bonariensis) even under cool-moist conditions.

The population dynamics of the Argentine stem weevil showed that it progresses through only one generation per year in the cool-moist environment of Southland.

In glasshouse experiments it was shown that the endophyte should be regarded as a parasite of the ryegrass plant in the absence of major biotic or abiotic stresses. Shoot production was significantly (up to 50 %) lower for endophyte-infected compared to endophyte-free plants in two of the glasshouse experiments. When placed under severe moisture stress, endophyte-infected plants had a higher level of osmotic adjustment (OA) than endophyte-free plants. This higher OA may improve the survival chances of the plants when stressed.

Fewer plant parasitic nematodes were observed in pots in which endophyte-infected, especially wildtype infected, plants grew compared to pots in which endophyte-free plants grew.

A genotype by endophyte interaction was observed for plant characteristics such as shoot and root yields, tiller numbers and number of plant parasitic nematodes in pots. The presence of an endophyte had a positive effect on companion white clover growth under ideal growing conditions (access to adequate water and average temperatures of 18.5 °C).

It is concluded that in the absence of abiotic and biotic stresses there is no requirement for ryegrass plants to be infected with the endophyte as no beneficial but a number of detrimental effects from its presence were observed.

It is concluded that there is no need for pastures in cool-moist environments to contain an endophyte and that the severity of problems associated with the endophyte increase with the level of stress applied to the plants.