Abstract
Three Orobanche species, O. crenata, O. ramosa and O. aegyptiaca, failed to infect flax roots (Linum usitatissimum) at 30, 45 and 60 days from sowing, but heavy infection was observed with O. crenata on faba bean roots (Vicia faba) at 45 and 60 days from sowing. Flax seed exudates markedly induced the germination of O. crenata and O. ramosa in vitro; germination in O. crenata was much higher (75%) than in O. ramosa (16.6%). No germination response was obtained with O. aegyptiaca, and some germination activity (13.7%) was obtained with Striga hennonthica. The active material exists in the flax crop (non-host) only in the first eight days after sowing, contrary to faba bean (host) in which active material exists at the later growth stages (30-60 days from sowing). Partial purification of extracts of flax roots at 30-60 days from sowing were ineffective in stimulating the germination of Orobanche spp. in vitro. Differences in the time course of promotive activity in the faba bean host and flax crop non-host during their growth, coupled with the secretion of active material in a very short period in flax, suggest that the use of flax as a trap crop for eliminating Orobanche infection in a field producing faba beans has limited success.
