TEMPERATURE RESPONSE OF VERNALIZATION IN WHEAT - MODELING THE EFFECT ON THE FINAL NUMBER OF MAINSTEM LEAVES

This paper outlines a modelling approach which predicts the effect of both continuous and intermittent low temperature regimes on the final number of leaves in winter wheat. The model takes account of the balan ce between the concurrent processes of leaf primordium initiation and rare of saturation of vernalization, and their response to temperature . The inverse of the time to saturation of vernalization, at which sta ge final leaf number is set, is modelled as a linear Function of verna lizing temperature. between 0 and 17 degrees C. The rate of leaf primo rdium initiation is modelled using the established linear relationship between rate and temperature above 0 degrees C. Final leaf number is hence the product of the number of leaf primordia initiated once verna lization is saturated. In the model, genotypes are characterized by (1 ) the slope and intercept of the linear response of the rate of satura tion of vernalization to temperature in the vernalizing range, and (2) by a development rare towards floral transition at on-vernalizing tem peratures (above 17 degrees C). The model is tested against data from experiments where six cultivars of winter wheat plants of different ag es were exposed to a range of low temperature regimes, including conti nuous and intermittent vernalizing temperatures. Overall, the model pr edicted, with r(2) values of 70-90%, the final leaf number across a ra nge of six to 21 leaves. Prediction of final leaf number for some cult ivars was better in continuous than in intermittent vernalizing regime s. This modelling approach can explain the often-conflicting reports o f the effectiveness of different temperatures for vernalization, and t he interaction of plant age and vernalization effectiveness. (C) 1996 Annals of Botany Company.