Endophyte persistence and toxin (lolitrem b) production in a Danish seed crop of perennial ryegrass.

摘要

The mutualistic association between perennial ryegrass (Lolium perenne L.) and the endophytic fungus Neotyphodium lolii is of agricultural significance. The fungus can provide the plant with resistance to several pests and enhance the growth of the plant, however, the fungus also triggers production of toxic metabolites with severe effects on livestock. In Denmark, N. lolii-infected perennial ryegrass is grown for seed production. In order to follow the establishment of the perennial ryegrass endophyte, the infection levels of perennial ryegrass, pre-basic, basic and F1 seed, from nine locations and the mycelium density within the infected plants during the growing seasons 1998-2000, were investigated. The endophyte was well established in most plants and the mycelium content within plants showed seasonal variation. Examinations of seed infection rates demonstrated no immediate disadvantages of the endophyte infection under Danish growing conditions. The lolitrem B experiment was based on farm-scale results from endophyte-infected seed crops of perennial ryegrass cv. Delaware. The aim was to monitor the toxin content during the spring to autumn growing season in order to evaluate the fodder quality of secondary products from a seed crop, such as straw and regrowth taken after seed harvest. A clear seasonal variation in the lolitrem B level was observed in top and stubble fractions in 1998-2000. The highest level of lolitrem B occurred in the top fraction during July 1998 at Brorfelde. The mean concentration was 1.46 ppm, a level that is sufficient to induce mild ryegrass stagger..