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

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 e mergence from natural shore days (SD, 12.6 h d(-1)) to artificially ex tended long days (LD, 15.0 h d(-1)), and vice versa, under both ambien t (19 degrees C) and warmer (26 degrees C) temperatures created beneat h polythene enclosures. All plants at 19 degrees C flowered within 106 -160 d after emergence whereas only those transferred from LD to SD fl owered at 26 degrees C during the investigation (202 d). A well-define d photoperiod-insensitive pre-inductive phase (a(1)) was detected afte r emergence; it lasted for 26 d at 19 degrees C but increased to 49 d at 26 degrees C. Thereafter, SD hastened and LD delayed progress to fl owering until a third phase, the photoperiod-insensitive post-inductiv e phase (a(3)) of pre-flowering development. At 19 degrees C, a(3) was 66 d while the duration of the inductive phase in SD (I-S) was 25 d a nd in LD (I-L) it was 72 d. Plants were also moved from ambient to war mer temperatures and vice versa within either SD or LD at different du rations after emergence. In SD all plants flowered during the investig ation (250 d) whereas in LD only the plants transferred from the warme r to the ambient temperature regime flowered. During the initial stage s of development plants were less sensitive to supraoptimal temperatur es so that developmental progress from emergence to first flowering wa s 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 t o 77 d from emergence flowered at similar times to those kept at ambie nt temperature from emergence. Since a(1) = 26 d and a(1) + I-S = 51 d , we suggest that these results imply that exposure to supra-optimal t emperature in SD during the latter 60% of the photoperiod-sensitive in ductive phase (I-S) of pre-flowering development delayed progress to f lowering. In contrast, exposing plants to supra-optimal temperature du ring either the photoperiod-insensitive pre-inductive phase (a(1)) or part of the photoperiod-insensitive post-inductive phase (a(3)) or dur ing.the first 40% of the photoperiod-sensitive inductive phase did not delay progress to flowering.