Control of the Germination Responses of<i>Amaranthus retroflexus</i>L. Seeds by their Parental Photothermal Environment

Abstract

Germination responses of the seeds of Amaranthus retroflexus L. were affected by the photo period, temperature, and level of solar radiation experienced by their parent plants. Seeds from parents grown continuously in short days (SD, 8 h) lost post-harvest dormancy more rapidly and had a higher dark germination, as well as a greater responsiveness (at 30 °C) to pretreatments at low temperature (5 or 10 °C) and to short illuminations, than seeds from parents grown continuously in long days (LD, 16 h). Dark germination and responsiveness of the seeds to promotive treatments were both higher when their parents were transferred at flowering from LD to SD than when grown continuously in LD. These responses were lower when their parents were similarly transferred from SD to LD than when grown continuously in SD. The promotive effects of parental post-flowering SD on dark germination (at 30 °C) were enhanced by reduction of parental temperature (from 27/22 °C to 22/17 °C), but the respon siveness of the seeds to low temperature pretreatment was reduced. Inflorescences developing in LD produced seed with higher germinability when flowering was notinduced(LD throughout) than when it was induced (either by SD till flowering, or by three SD cycles when 4-5 leaves appeared). Reduced levels of solar radiation had opposite effects in the different parental photoperiods : dark germination and the responsiveness to low temperature pretreatments were reduced in LD, but were increased in SD. Differences in the germination responses resulting from differences in the parental environ ment could not be correlated with differences in seed coat thickness or seed dry weight.