THE DEPENDENCE OF GERMINATION ON PHOTOPERIOD, LIGHT QUALITY, AND TEMPERATURE, IN CHENOPODIUM SPP.

Abstract

In Chenopodium botrys, darkness was suboptimal for germination at all temperatures. At low to intermediate temperatures (10 to 20 °C) short photoperiods were optimal while longer ones were supraoptimal. At high temperatures (25° to 35 °C) extremely long photoperiods were optimal and all shorter ones were suboptimal. There was less germination in light of low than high red to far-red (R/FR) spectral energy ratios, particularly in long photoperiods. Decreasing the R/FR ratio for the terminal 30 minutes of daily photoperiods restricted germination considerably in short but not in extreme long photoperiods (18 and 20 hours). It is postulated that sub- and supra-optimal amounts of phytochrome-P_fr were produced, respectively, in the sub- and supra-optimal photoperiods, which resulted in less germination; further, that the temperature-induced responses may be due to a lower optimum requirement for P_fr at low than at higher temperatures and, or, a faster rate of dark reversion of P_fr to P_r may occur with increase in temperature. This provides a correlative scheme similar to that postulated for floral initiation of C. rubrum, whether optimum response is in short or long photoperiods.Ambiphotoperiodism, resembling the response previously shown in C. rubrum floral initiation, occurred in C. botrys germination. This may be indicative of endogenously controlled rhythms interacting with the phytochrome system.Several Chenopodium spp. germinated more in darkness than in long photoperiods of low R/FR ratio. Indirect evidence suggests that there may be formation of phytochrome-P_fr in darkness, sufficient to promote germination.On the basis of laboratory tests with Chenopodium spp. two ecologically significant phenomena are postulated. Firstly, there may be restriction of germination in areas shaded by green plants. There was more germination in light with R/FR ratios similar to that of sunlight (1.3) than sunlight transmitted through green vegetation (0.70 to 0.12). Secondly, stages of incomplete germination of seeds, in which there is rupture of the testa and loss of previous light requirements, may be of adaptive value, particularly under arid conditions. Seeds with incomplete germination remained viable for prolonged periods, whether kept moist or dried, but germinated very rapidly when transferred to optimum conditions.