Conditioning duration and agents involved in broomrape seeds responding to germination stimulants

Weedy broomrape species, such as sunflower broomrape (Orobanche cumana Wallr.) and Egyptian broomrape [Phelipanche aegyptiaca Pers. (syn. O. aegyptiaca)], require a period of pre-conditioning before they can respond to germination stimulants. Thus, the sensitivity of weedy broomrape seeds to germination stimulants could be an important factor for broomrape control. In this study, the influence of conditioning agents, conditioning period (0-21 days) and germination stimulants on the germination of sunflower broomrape and Egyptian broomrape seeds was analyzed. Without conditioning, the sunflower and Egyptian broomrape seeds exhibited negligible germination responses to the stimulants. The germination rate of the broomrape seeds increased rapidly with conditioning period and reached a maximum under a conditioning period of 4-10 days; further prolonged conditioning resulted in a decrease in the germination rate. Gibberellic acid (GA(3)) could not only break the dormancy of the sunflower and Egyptian broomrape seeds but also maintained the high sensitivity of these seeds even after 21 days of conditioning. Furthermore, 100 A mu M of GA(3) induced the germination of the Egyptian broomrape seeds. The stimulants that induced Egyptian broomrape germination were ranked in decreasing order as GR24 (76.8 %), strigol (76.1 %), tobacco root exudates (49.5 %), dehydrocostus lactones (DCL, 39.2 %), and maize root exudates (18 %). In contrast, GA(3) did not directly induce sunflower broomrape seed germination, which responded to strigol (62.8 %) > maize root exudates (58.2 %) > GR24 (57.9 %) > tobacco root exudates (41.6 %) > DCL (41.3 %). These results indicate specialized recognition of germination stimulants by sunflower and Egyptian broomrape. This study may contribute to a better understanding of parasitic weed germination and may lead to improved control strategies.