Nitrogen nutrition and the net accumulation of medicarpin in infection-droplets on excised leaflets of white clover

Abstract Nutritional treatments in pot culture established a range of levels in nitrogen content of white clover corresponding to severe deficiency through to adequacy. Analysis for medicarpin and for leaflet area in relation to nitrogen indicated an inverse relationship in the former and a direct relationship in the latter. However, the two effects did not appear to be causally related to each other. The inverse relationship between medicarpin concentration and the well-known effect of nitrogen in increasing disease severity in many plant species is consistent with the concept that plant nutrition can potentially play a role in disease resistance through its effect on phytoalexin formation.