Role of quality of light in the photoperiodic flowering response in four latitudinal ecotypes of Chenopodium rubrum L

The effect of the quality of light on the photoperiodic flowering response in four latitudinal ecotypes of Chenopodium rubrum was examined. Two southern ecotypes, Sel-184 (50°10′ N) and Sel-194 (34°20′ N), displayed an obligate short-day plant under white (W), red (R) and blue (B) light. Sel-372 (62°46′N), the most northern ecotype, was day-neutral in B and W light and had an ambiphotoperiodic response in R light. Sel-374 (60°47′ N) was an ambiphotoperiodic in B light and had a short-day response in W and R light. In the B light regimens, the flowering of Sel-374 was modified from a typical ambiphotoperiodic to day-neutral response by changing the temperature from 20°C to 12°C. The photopriodic flowering response in the 8–16 hr photoperiod was suppressed severely by the reducing light intensity from 3,000 to 1,500 ergs.cm−2.sec−1, but that in continuous illumination was lowered only slightly by decreasing the light intensity. The ambiphotoperiodic flowering response differed in its reaction to light; flowering in the 8-18 hr photoperiod required a high intensity light independent of the quality of light, and flowering in the 24 hr photoperiod was promoted by B light. We considered the ambiphotoperiodic flowering response to be a combination of the obligate short-day flowering response and the flowering response for an extreme long-day condition, which is favored by B light. Therefore, this photoperiodic response probably is an intermediate step in the short-day and day-neutral responses in day-neutralization.