Seasonal changes in germination response of buried seeds of Orobanche crenata Forsk.

Abstract

Summary: Résumé: Zusammenfassung Orobanche crenata seeds, collected in Syria, Egypt and Spain, were buried in the field in Syria (all three seed lots) and Spain (only Spanish seeds) and at regular intervals exhumed and tested for germination, to investigate whether the seeds exhibit an annual dormancy/non‐dor‐ mancy cycle. When exposed directly to the synthetic germination stimulant GR24 for 7 days at 20°C, seeds only germinated in autumn after the first rains and to a limited extent in winter. When the seeds were conditioned for 11 days at 20°C prior to exposure to GR24, germination occurred during summer and autumn, but seeds were dormant in winter and early spring. The observed seasonal pattern in germinability, in relation to rainfall and soil temperature, was largely consistent with the results of an in vitro experiment by Van Hezewijk et al. (1993), investigating the effect of conditioning temperature and conditioning period on germination capacity and the development of secondary dormancy. Moisture and temperature can therefore be considered the major factors regulating induction and alleviation of dormancy in buried O. crenata seeds. There were no basic differences in response owing to site of collection of O. crenata seeds, nor to the location where they were buried. Variations saisonnières des exigences de germination de graines enfouies d'Orobanche crenata Forsk. Des graines d'Orobanche crenata récoltées en Syrie, en Égypte et en Espagne ont été enfouies au champ en Syrie (les 3 lots) et en Espagne (seules les graines d'Espagne) puis ont été exhumées a intervalles régulier pour que leur aptitude à la germination soil évaluée. Le but était de déterminer si les graines possédaient un cycle annuel dormance/non dormance. Quand elles étaient directement exposées au stimulant de germination synthétique GR24 pendant 7 jours à 20°C, les graines ne germaient qu'à l'automne après les premières pluies et peu en hiver. Quand les graines restaient pendant 11 jours à 20°C avant leur exposition au GR24, la germination seproduisait en été et à l'automne mais les graines restaient dormantes en hiver et au début du prin‐temps. Les variations saisonnières d'aptitude à la germination, liées aux précipitations et à la temperature du sol, étaient en accord avec les résultats d'une expérience in vitro de Van Hezewijk et al. (1993) concernant l'effet de la température et de la durée pendant laquelle elle est appliquée, sur l'aptitude à la germination et le développement de la dormance secondaire. L'humidité du sol et sa température peuvent ainsi être considérées comme les principaux facteurs qui induisent et lèvent la dormance de graines de O. crenata enfouies. On n'observait pas de différences importantes dues au lieu de récolte ou à l'endroit oü elles étaient enfouies. Jahreszeitliche Änderungen der Keimung von vergrabenen Samen von Orobanche crenata Forsk. Proben von in Syrien, Ägypten und Spanien gesammelten Orobanche‐crenata‐Samen wurden in Syrien und Proben nur spanischer Herkunft in Spanien im Freiland im Boden ausg...

Changes in the sensitivity of parasitic weed seeds to germination stimulants

“…Although we do not know whether the same processes that we observed under laboratory conditions also occur in the field, the similar germination pattern of S. hermonthica seeds preconditioned for a prolonged period of time under laboratory (sterile) and field (sterile and non-sterile) conditions suggest that they do. This assumption is supported by the work of van Hezewijk et al (1994) and López-Granados and Garcia-Torres (1999), who studied seasonal changes in the germination response of buried seeds of O. crenata. The results from field experiments were highly consistent with the results of in vitro experiments by van Hezewijk et al (1993) on development of secondary dormancy during prolonged preconditioning of O. crenata at different temperatures.…”

Influence of shrub cover on germination, dormancy and viability of buried and unburied seeds of Piptochaetium napostaense (Speg.) Hackel

“…Bags were used to prevent predation, mixing with other seeds and losses when recovering the seeds at the end of the experiment. This technique is widely accepted and has been extensively used in similar experiments (Crist and Friese, 1993;Van Hezewijk et al, 1994;Baskin and Baskin, 1998).…”

Germination Ecophysiology

“…In modelling the life cycle of O. crenata, Grenz and Sauerborn (2007) specified a soil moisture threshold of 22.5 % below which both primary and secondary dormancy can be relieved although the soil type and water potential are not known. These processes can clearly occur for seeds in secondary dormancy during warm, dry Mediterranean summers (van Hezewijk et al 1994b), and equally O. crenata could not succeed as a weed where warm, dry conditions never occur (Grenz and Sauerborn 2007).…”

“…Annual cycles in which physiologically based dormancy is relieved and induced during the course of a year occurred in buried seeds of O. crenata in Syria, Egypt and Spain (Van Hezewijk et al 1994b; López-Granados and García-Torres 1999) as they do in many non-parasitic annuals with persistent soil seed banks in both temperate and tropical soil environments Baskin 1985, 1998;Benech-Arnold and Sanchez 1995;Murdoch and Ellis 2000). O. crenata seeds, which after-ripened in the soil in summer, would then be exposed to some moisture, lose their primary dormancy and become able to germinate in response to germination stimulant in the autumn or winter (Van Hezewijk et al 1994b).…”

“…O. crenata seeds, which after-ripened in the soil in summer, would then be exposed to some moisture, lose their primary dormancy and become able to germinate in response to germination stimulant in the autumn or winter (Van Hezewijk et al 1994b). Secondary dormancy was then induced at low winter temperatures (compare Sect.…”