Development of annual ryegrass toxicity

Abstract

Ryegrass pasture, containing seed galls induced by Anguina agrostis and colonized by Corynebacterium rathayi, was harvested from experimental plots near Katanning in Western Australia. Plant growth stage, numbers of emerged inflorescences and numbers of galls present were estimated for 10 harvests collected at weekly intervals, commencing 22 September when the first inflorescences had emerged. The concentration of toxin (corynetoxins) at each harvest was estimated using a bacterial inhibition bioassay. Levels of toxin were up to 459 ¦g per m2 pasture prior to and during anthesis, but the concentration increased rapidly during the final four harvests (corresponding to ripening) and reached a maximum level of 6292 ¦g m-2. A possible relationship between toxicity and the presence of ultramicroscopic particles observed in the galls was investigated. Galls from each harvest were sectioned and examined under the electron microscope. Particles were not found in galls sampled prior to anthesis, but were found in galls from the last four harvests. From these results, the production of toxin appears to be related to physiological aging of the plant and may also be related to the accumulation of particles.