Use of ethylene-producing bacteria for stimulation of Striga spp. seed germination

Striga spp. are obligate root-parasitic flowering plants that threaten cere al and legume production, and consequently human well-being, in Africa. Suc cessful control depends on eliminating the seed reserves of Striga spp. in soil and preventing parasitism. A proven method of eliminating these seed r eserves is soil-injection of ethylene gas. This method was used successfull y in the United States to control Striga asiatica, but injection of ethylen e gas is potentially dangerous, very costly, and generally unsuitable in Af rica. The bacterium Pseudomonas syringae pathovar glycinea synthesizes rela tively large amounts of ethylene. In this study a laboratory procedure was developed for testing strains of P. syringae pv. glycinea for efficacy in s timulating germination of seeds of Striga spp. The procedure allows compari sons among bacteria, volatile compounds, root exudates, and synthetic stimu lants for germination of Striga spp. seeds. Seeds of three Striga spp. were tested over a 10-month period. No seed germination was ever observed with sterile water. When compared across Striga spp. the bacterial strains were consistently better stimulators of germination of seeds of the parasites th an ethylene gas or root pieces of a Vigna unguiculata cultivar known to sti mulate germination of parasite seeds. The strains were as effective in germ inating S. aspera and S. gesnerioides seeds as a synthetic germination stim ulant. Our results showing that ethylene-producing bacteria are highly effe ctive in promoting seed germination in Striga spp. suggest that these bacte ria may provide a practical means of biological control of Striga spp. in A frica and other locations. (C) 1999 Academic Press.