Developmental responses to sowing date in wheat, barley and rapeseed

Two cultivars of each bread wheat (Triticum aestivum L.), malting barley (H ordeum vulgare L.) and spring rapeseed (Brassica napus L.), were grown in a wide range of different sowing dates in Buenos Aires, Argentina. The aims of this study were (i) to analyse how the number of leaf primordia and the rate of leaf emergence interact to modify the duration of different pre-flo wering phases and (ii) to establish how different yield components initiate d during those phases are affected when the duration of these phases are mo dified by wide range of sowing dates. The results showed interactions betwe en photoperiod and temperature for wheat and rapeseed producing different c ombination for the length of the pre-flowering phases. Barley reached flora l initiation earlier than wheat and rapeseed and had a shorter 'intrinsic e arliness'. Plastochron and phyllochron varied among different sowing dates in the thre e species. In most cases the relationship between the cumulative number of leaves on the main shoot of wheat and barley and thermal time was describe by a bilinear model with the earlier leaves emerging faster than the later ones. However, the opposite pattern was observed for rapeseed which showed a slower rate of leaf emergence for the first than for the lasts leaves. The changes observed in the rate of leaf emergence throughout plant ontogen y, might delay or hasten the duration of the later reproductive phase durin g which the spikes grow and some of the initiated floret primordia becoming fertile. Extending the duration of the stem elongation phase in wheat and barley produced more fertile florets per spikelets. (C) 2001 Elsevier Scien ce B.V. All rights reserved.