Genetic control of heading date and spikelet number in common wheat (T. aestivum L.) line 'Noa'.

The phenology and build-up of spikelet number under 10 h day-length were studied in five wheat lines: the multispikelet line 'Noa', the regular line 'Mara', the F1 hybrid between them and monosomics 2D of 'Mara' and of this hybrid (lacking the 2D chromosome of 'Mara'). 'Noa' had a longer spike development phase, a higher initial number of spikelet primordia and a slower rate of spikelet production than 'Mara'. The F1 hybrid was similar to 'Noa' in its high initial number of spikelets and to 'Mara' in its high rate of spikelet production. This hybrid had a shorter spikelet phase than both parents. Deletion of one dose of the 'Mara' 2D chromosome from either 'Mara' or the F1 hybrid caused a reduction in the rate of spikelet production and an increase in the duration of the spikelet phase. These effects were due to the reduced dosage of the 2D chromosome. However, in the F1 hybrid this deletion also caused an increase in the spike development phase - an indication that 'Noa' carries on its 2D chromosome a recessive gene for late heading date which acts on the spike development phase. This gene of 'Noa' is independent of the day-length sensitive gene ppd, and is different from 'Noa's dominant gene for large initial number of spikelets.