FLOWERING IN PIGEONPEA IN KENYA: SENSITIVITY TO PHOTOPERIOD AND TEMPERATURE DURING PRE-FLOWERING DEVELOPMENT

Abstract

Plants of the photoperiod-sensitive, late-maturing pigeonpea (Cajanus cajan) cv. KAT777 were grown in pots in modified field environments at Katumani, Kenya. They were transferred at different durations after emergence from natural short days (SD, 12.6 h d⁻¹) to artificially-extended long days (LD, 15.0 h d⁻¹), and vice versa, under both ambient (19 °C) and warmer (26 °C) temperatures created beneath p olythene enclosures. All plants at 19 °C flowered within 106–160 d after emergence whereas only those transferred from LD to SD flowered at 26 °C during the investigation (202 d). A well-defined photoperiod-insens itive pre-inductive phase (a₁) was detected after emergence; it lasted for 26 d at 19 °C but increased to 49 d at 26 °C. Thereafter, SD hastened and LD delayed progress to flowering until a third pha se, the photoperiod-insensitive post-inductive phase (a₃) of pre-flowering development. At 19 °C, a₃ was 66 d while the duration of the inductive phase in SD (I_S) was 25  d and in LD (I_L) it was 72 d. Plants were also moved from ambient to warmer temperatures and vice versa within either SD or LD at different durations after emergence. In SD all plants flowered during the investigation ( 250 d) whereas in LD only the plants transferred from the warmer to the ambient temperature regime flowered. During the initial stages of development plants were less sensitive to supra-optimal temperatures so that developmental progress from emerg ence to first flowering was the same whether plants were held at warmer or ambient temperatures during the first 35 d from emergence. Furthermore, plants transferred from the ambient to the warmer temperature in SD at any time from 49 to 77  d from emergence flowered at similar times to those kept at ambient temperature from emergence. Since a₁ = 26 d and a₁ + I_S = 51 d, we sugg est that these results imply that exposure to supra-optimal temperature in SD during the latter 60% of the photoperiod-sensitive inductive phase (I_S) of pre-flowering development delayed progress to flowering. In contrast, expos ing plants to supra-optimal temperature during either the photoperiod-insensitive pre-inductive phase (a₁) or part of the photoperiod-insensitive post-inductive phase (a₃) or during the first 40% of the photo period-sensitive inductive phase did not delay progress to flowering.