Induction of Secondary Dormancy in Chenopodium bonus-henricus L. Seeds by Osmotic and High Temperature Treatments and Its Prevention by Light and Growth Regulators

Abstract

Factors controlling the establishment and removal of secondary dormancy in Chenopodiwm bonus-henricus L. seeds were investigated. Unchilled seeds required light for germination. A moist-chilling treatment at 4 C for 28 to 30 days removed this primary dormancy. Chilled seeds now germinated in the dark. When chilled seeds were held in the dark in -8.6 bars polyethylene glycol 6000 solution at 15 C or in water at 29 C a secondary dormancy was induced which increased progressively with time as determined by subsequent germination. These seeds now failed to germinate under the condition (darkness) which previously allowed their germination. Continuous Ught or daily brief red Ught irradiations during prolonged imbibition in polyethylene glycol solution at 15 C or in water at 29 C prevented the establishment of the secondary dormancy and caused an advancement of subsequent germination. Far red irradiations inmediately following red irradiation reestabUshed the secondary dormancy indicating phytochrome participation in "pregerminative" processes. The growth regulator combination, kinetin + ethephon + gibberellin A4+A7 (GA4+7), and to a relatively lesser extent GA4+7, was effective in preventing the establishment of the secondary dormancy and in advancing the germination or emergence time. Following the estabUshment of the secondary dormancy by osmotic or high temperature treatments the regulator combination was relatively more active than lght or GA4+7 in removing the dormancy. Prolonged dark treatment at 29 C seemed to induce changes that were partially independent of light or GA4+7 control. The data presented here indicate that changes during germination preventing dark treatment determine whether the seed will germinate, show an advancement effect, or will become secondarily dormant. These changes appear to be modulated by Ught and hormones.It is well known that seeds of many plant species indigenous to the temperate regions become dormant or inactive in the soil and do not germinate until exposed to light (31, 36). Many weed seeds that are previously non-light-requiring become light-requiring during burial in the soil (9, 36) and show profound seasonal changes in germination pattem and light requirement (31). In a preliminary study, Karssen found (Fig. I) at harvest time in the fall, lose such requirement by burial in the soil during winter months, and reestablish a light requirement (secondary dormancy) during spring.Dormancy or germinability of a seed is governed by the nature of pre-and postmaturation changes in the seed itself and the adjoining tissues of the mother plant, as well as changes following harvest. The term, primary dormancy, could be used to designate dormancies induced by preharvest changes and secondary dormancy used to describe dormancies induced following harvest by natural or artificial means. The same or different agents may be required to prevent or break both the primary and the secondary dormancy. A true test that a seed has become secondarily dormant is that it fails to germinate ...

Anesthetic Effects on Secondary Dormancy and Phytochrome Responses in Setaria faberi Seeds

“…Causes of secondary dormancy are poorly understood. Suggested mechanisms are based somewhat on factors for which sensitivity is lost such as phytochrome, hormones, and temperature (2,8,(10)(11)(12). Earlier studies with secondary dormancy in Rumex crispus L. seeds suggested changes in membrane properties influenced the temperature-induced loss in response to phytochrome (20).…”

Implication of Ethylene in the Release of Secondary Dormancy in Amaranthus caudatus L. Seeds by Gibberellins or Cytokinin

“…Moreover, GA 3 with the cytokinin, and ethylene are effective in breaking secondary dormancy (skotodormancy) in Lactuca serriola seeds (Small and Gutterman 1992). Also combination of kinetin, ethephon, and GA 4+7 removed secondary dormancy in Chenopodium bonus-henricus L. (Khan and Karssen 1980).…”

Dormência em sementes de plantas daninhas como mecanismo de sobrevivência: breve revisão

“…Estudos com sementes de Chenopodium bonus-henricus resultaram na indução à dormência, utilizando-se de solução com PEG, em potencial de -0,86 MPa, quando mantidas no escuro à 15 ºC (Khan & Karssen, 1980). Para as sementes de Rumex crispus, Saminy & Khan (1983) verificaram que a indução ocorreu em potencial bem menor (-1,57 MPa), porém mantidas iluminadas a 15 ºC.…”

“…No entanto, essa regra não é válida para todas as espécies. Para Sisymbrium officinale, o elevado Ø w induz à dormência, por permitir a expansão da mucilagem que cobre a semente, impedindo a entrada do oxigênio para o embrião; induz também a dormência secundária dessa espécie (Karssen, 1980(Karssen, -1981. Porém, já para Datura stramonium, planta daninha comum no Brasil, a água inibe a germinação devido à formação de uma barreira física à entrada do oxigênio para o embrião, embora o excesso de água não pareça induzir à dormência, representando apenas o atraso na germinação, até que algum outro fator ambiental induza à dormência (Reisman-Berman et al, 1989).…”