Alkaloid Levels in Phalaris aquatica L. as Affected by Environment

Phalaris aquatica L. (also referred to as P. tuberosa L.), a species widely grown in Australia, may have forage potential in the southeastern U.S. and, therefore, has been made the subject of an Auburn University breeding program. In Australia, however, livestock toxicities have been reported from alkaloids in the forage. Field, greenhouse, and environmental chamber experiments were conducted to determine the effect of N fertilization, radiation density, and drought stress on alkaloid concentration of Phalaris aquatica lines. Nitrogen applications up to 336 kg/ha had no effect on alkaloid concentrations in the field on a Cahaba fine sandy loam (Typic hapldult, fine-loamy, siliceous, thermic) soil, and 224 kg/ha had only a slight effect in an environmental chamber study. Shading to 30 or 55% of full sun caused slight alkaloid increases in the field, but decreased radiation had no effect in an environmental chamber. The order of alkaloid concentration in aerial portions of individual plants of two genotypes was: upper one-half of leavesã leaf sheathsãstems. Drought stress caused greater alkaloid increases both in field and environmental chamber studies than did any other factor. In Australia, toxicity frequently occurs after severe drought, while in the southeastern U.S. drought is less frequent and severe. Also, pasture composition in the southeastern USA is more diverse, a factor known to lessen toxicity potential probably by dilution. In addition, cattle (which areless susceptible to toxicity than sheep) predominate on pastures in this region, and the chronic form of toxicity occurs only in Co deficient areas, a condition not prevalent here. It is concluded from comparisons to conditions in Australia that the probability of toxicity to grazing animals due to high alkaloid concentrations in P. aquafica in the southeastern U.S. is low, and that selection for low alkaloid types is presently unnecessary.