Biological Control of Root Parasitic Weeds with Plant Pathogens

Abstract

Root parasitic weeds are nutrition specialists. Using special organs, the haustoria, they penetrate into the vessels of roots of host plants in order to supply themselves with water and nutrients. They can be either facultative or obligate, obligate parasitic weeds being considered as one of the most serious constraints to food production in many parts of the world. Obligate parasites are either hemi-parasites with chlorophyll, like species of the genus Striga (Scrophulariaceae), witchweeds, or holo-parasites without chlorophyll such as species of the genus Orobanche (Orobanchaceae), broomrapes. Forty Striga species are reported world-wide: 33 in Africa, 7 in Asia and 4 endemic in Australia. Eleven species are parasites on agricultural crops. The genus Orobanche has more than 100 species but only 7 are considered as economically significant parasitic weeds (Parker and Riches, 1993; Raynal-Roques, 1996).