Comparative levels of dimethyltryptamine- and tyramine-related alkaloid toxins in Australian cultivars and some wild populations of Phalaris aquatica

Abstract

Phalaris (Phalaris aquatica L.) is a temperate perennial grass which occasionally causes toxicity in livestock. Immunoassays (ELISAs) were used to measure the level of the dimethyltryptamine and related alkaloid group (TRYP) and the tyramine-related group of alkaloids (TYR) in cultivars, breeding populations and wild accessions of phalaris. Herbage was sampled from grazed swards or spaced plants at several sites and times. Component alkaloids in 4 cultivars were also determined by thin-layer chromatography (TLC). Levels of TYR were higher than TRYP at all times of sampling. Alkaloid levels varied widely with site and sampling time, green herbage sampled in autumn being much higher than herbage sampled from July onwards. Plants sampled in autumn usually appeared moisture stressed and this may have been 1 factor causing high alkaloid levels in autumn. Comparative levels of TRYP in older cultivars agreed with published information. Two semi-winter dormant cultivars, Australian and the new and closely-related Australian II, were both higher than other cultivars in TRYP (maximum levels 18–20 mg/100 g fresh weight) but similar to most in TYR. Among winter-active cultivars, Holdfast and Sirolan were very low in TRYP (maximum levels <0.5 mg/100 g fresh weight) but Holdfast was the highest of all cultivars in TYR. While we argue on the basis of the TLC analyses and from previous work that the bulk of TYR in phalaris cultivars is N-methyltyramine, Holdfast was an exception in having one-third of its TYR as the less toxic hordenine in TLC analyses. Other new cultivars, Landmaster and Atlas PG, and breeding populations being developed as potential cultivars for acid soils or with improved grazing tolerance were generally higher than Holdfast and Sirolan, and similar to Sirosa, in TRYP (maximum levels 1–5 mg/100 g fresh weight). All were less than Holdfast in TYR. Two sets of wild accessions, 1 of which is being used in the development of a cultivar for the North-West Slopes of NSW, were relatively high in TYR alkaloids.