Broomrape (Orobanche cernua) control before attachment to host through chemically or biologically manipulating seed germination

Abstract

Seven series of laboratory and glasshouse experiments were conducted to investigate different methods of testing and studying the effect of several chemicals, root exudates of germinating crop seeds, and their interactions on Orobanche cernua. Compared to experiments in an incubator, better results were obtained when seed germination was tested in the presence of seedlings of host plants under glasshouse conditions. GR24 at 0.1 and 1.0 mg kg-1 was the most effective in stimulating the germination of O. cernua seeds, followed by gibberellic acid at 10 and 20 mg kg-1. Without the addition of chemicals, trap crops strongly increased germination, with green gram (Vigna radiata) and sunn hemp (Crotalaria juncea) being particularly effective. There was an interaction between the effects of chemicals and trap crops. A positive effect of trap crops was observed even when there was already strong stimulation by GR24 at 1.0 mg kg-1, but under these conditions, trap crops were less effective at 0.1 mg kg-1 GR24. No differences between cultivars in their effect on O. cernua germination could be detected within one host plant species.

Revisiting strategies for reducing the seedbank of Orobanche and Phelipanche spp.

“…The application of nitrogen fertilisers limited practical importance as a control measure for O. crenata (Dhanapal & Struik, 1996). However, the cost of this technique in pasture could be offset by increased yield.…”

“…for P. aegyptiaca , Egyptian clover ( Trifolium alexandrinum L.) for O. crenata , sunhemp ( Crotalaria juncea L.) and mung bean [ Vigna radiata (L.) Wilczek] for O. cernua Loefl. (Dhanapal & Struik, 1996). Fenugreek stimulates P. ramosa seed germination, but not the seeds of O. foetida Poir.…”

Potency of some synthetic stimulants and root exudates on the germination of Phelipanche spp.

“…According to Aly (2007), Elzein & Kroschel (2003) reported that the application of germination stimulants to induce suicidal seed germination of parasitic weeds appears attractive for biosafety reasons; there is rapid soil decomposition and high biological activity at very low application rates. Compounds structurally related to strigolactone are potent synthetic germination stimulants for many Striga and Orobanche/Phelipanche species (Zwanenburg & Wigchert 1998;Wigchert et al 1999) but their usage in the field has not been practical up to now due to the high cost involved in their synthesis and also their instability in soils with high pH (Dhanapal & Struik 1996;Kroschel 2001;Lopez-Raez et al 2008). Therefore, detailed studies are needed to solve the issues about the cost and the formulation of the substances, which are affecting the efficiency and stability of them in the field conditions.…”

“…Once broomrape seeds have ger minated, they must establish contact with the host roots rapidly in order to derive nu trients and water for further growth and development. This germination phase is a critical period in the life cycle of the parasite (Musselman & Press 1995;Dhanapal et al 1996). If broomrape seeds are stimulated to germinate in the absence of host plants, the parasite seedlings die because of lack of nutrition.…”

“…They could be used to induce suicidal germination by treating the soil before the crop is sown (Lopez at al 2008). Because the isolation and purification of strigol in large amounts from root exudates appears impractical; an artificial synthesis of strigol is necessary to obtain enough compounds for commercial use (Dhanapal & Struik 1996). The application of germination stimulants to induce suicidal seed germination of parasitic weeds appears attractive for biosafety reasons, rapid soil decomposition, and high biological activity at very low application rates (Elzein & Kroschel 2004).…”