Effects of Thiourea and Allylthiourea on the Germination of the Seed of Striga lutea

Abstract

Striga lutea is a parasite belonging to the Scrophul-ariaceæ which attacks the roots of a number of crop plants. As with some other closely allied species, the seeds will germinate normally only after exposure to a stimulant produced by a host root¹. Observations, however, on the effects on germination of a series of substances known to have biological activity in other connexions indicate that the host stimulant may be replaced, to a limited extent, by certain comparatively simple compounds. The experiments in which these observations were made involved incubating parasite seeds at 22° C. for twenty-one days on moist filter paper, transferring them to another culture vessel provided with filter paper moistened with a solution of the experimental substanee, incubating for a further period of some days at 22° C, and finally exposing the culture to 34° C. for 24–48 hours. Thus the experimental process embodied three separate phases, each necessitated by a particular condition; the first by the fact that the parasite seed reacts vigorously to the host stimulant only after exposure to moisture for some days; the second by the effect of immediate exposure to the higher temperature with the substitute stimulant, which is that of inhibiting germination; and the third by the fact that neither with the normal nor with the substitute stimulant does extensive germination occur at the lower temperature, however prolonged is the period of incubation.