Changes in the sensitivity of parasitic weed seeds to germination stimulants

Abstract

The effects of preconditioning temperature and preconditioning period on the sensitivity of parasitic weed seeds to the synthetic germination stimulant GR24 were studied under laboratory and field conditions. The temperature during preconditioning of Orobanche cumana and Striga hermonthica seeds strongly affected the responsiveness of the seeds to the applied germination stimulant. Preconditioning at an optimal temperature (21°C for O. cumana and 30°C for S. hermonthica) rapidly released dormancy and increased the sensitivity to GR24 by several orders of magnitude. After reaching maximum sensitivity, prolonged preconditioning rapidly induced secondary dormancy, i.e. decreased sensitivity of O. cumana and S. hermonthica to GR24. The rapid change in sensitivity of preconditioned seeds to germination stimulants during prolonged preconditioning was particularly visible at low concentrations of GR24. GR24 at higher concentrations (0.1 and 1 mg l -1 ) usually induced high germination of both species, regardless of the preconditioning period. The striking similarities between the response of parasitic weed seeds to GR24, described here, and results in the literature on non-parasitic wild plant seeds are discussed. Our results show that parasitic weed seeds are highly sensitive to the germination stimulant for a short period of time only, and then enter into secondary dormancy relatively quickly. The similar germination pattern of S. hermonthica seeds preconditioned for prolonged periods of time under laboratory and field conditions suggests that the mechanism observed is of ecological significance.

Striga seed-germination activity of root exudates and compounds present in stems of Striga host and nonhost (trap crop) plants is reduced due to root colonization by arbuscular mycorrhizal fungi

“…gesnerioides seeds Ten milligrams of Striga seeds (approximately 1,500 seeds) was surface-sterilized according to the method of Matusova et al (2004). The seeds were placed in 2% (v/v) NaOCl to which was added two drops of liquid (hand) soap for 5 min in a beaker.…”

SEED GERMINATION AND PLANT DEVELOPMENT IN Escobedia grandiflora (OROBANCHACEAE): EVIDENCE OF OBLIGATE HEMIPARASITISM?

“…In order to germinate, seeds of obligate parasitic plants require the presence of the host plant whose roots secrete substances that are perceived by the seed of the parasite and thus stimulate its germination (Bouwmeester et al, 2007;Westwood et al, 2010;Cardoso et al, 2011). For example, in species of Orobanche L. (Plakhine et al, 2012), Phelipanche Pomel (Matusova et al, 2004) and Striga Lour. (Matusova et al, 2004), a very low germination rate (<10 %) has been found in the absence of hosts in all cases.…”

“…For example, in species of Orobanche L. (Plakhine et al, 2012), Phelipanche Pomel (Matusova et al, 2004) and Striga Lour. (Matusova et al, 2004), a very low germination rate (<10 %) has been found in the absence of hosts in all cases. The system of chemical recognition assures that germination begins only when the root of the potential host is available in the immediate vicinity (Mohamed et al, 2001;Joel et al, 2011).…”

History of the race structure of Orobanche cumana and the breeding of sunflower for resistance to this parasitic weed: A review

“…Results obtained by Morozov (1947) established that sunflower root cells contain substances which activate germination of broomrape seeds and in that way support the development of a sprout (stimulators). Long after that, Alonso (1998), Wegmann (1998), Matusova et al (2004) and Höniges et al (2008) also pointed out the importance of broomrape germination stimulants (see 'Overview of its biology and genetics' section for more details). Low exudation of germination stimulants by sunflower roots has been described as a pre-attachment resistance mechanism to race E in the sunflower line LR1, derived from H. debilis subsp.…”

“…Orobanche cumana-sunflower co-evolution: A review not stimulated by host roots, seeds enter into secondary dormancy (Matusova et al, 2004). In P. ramosa and O. cumana, it has been demonstrated that seeds need a minimum 4 days conditioning period at 21°C, during which a global DNA demethylation occurs, which is an epigenetic process required for the seed to become responsive to GS (Lechat et al, 2015).…”