INFLUENCE OF CONDITIONS AND GENOTYPE ON THE AMOUNT OF STRIGA GERMINATION STIMULANTS EXUDED BY ROOTS OF SEVERAL HOST CROPS

Witchweeds (Striga spp.) are important root parasites of many cereals and legumes. Striga seeds do not germinate unless exposed to specific chemical signals produced by host and nonhost roots. We report a simpl e method for obtaining large quantities of relatively clean root exuda te from several crop plants. A Striga seed germination assay was used to quantify stimulant activity produced and identify potential low sti mulant producing resistant host plants. Stimulant activity produced by sorghum cultivars susceptible to Striga was several orders of magnitu de greater than that of some resistant cultivars. Nonhost plants with capacity to stimulate germination of Striga were also identified. Stim ulant activity produced was much greater for plants grown using a shor t day length. In addition to germination stimulants, root exudates als o contained inhibitor(s) of germination.