VERNALIZATION IN WHEAT .2. GENETIC-VARIABILITY FOR THE INTERCHANGEABILITY OF PLANT-AGE AND VERNALIZATION DURATION

Differences in response to vemalization in wheat (Triticum aestivum L. ) were quantified through controlled environment experiments with 26 l ines with diverse geographical origins. Vernalization treatments of 0 to 56 d were applied to plants at their first leaf stage, All plants h eaded irrespective of duration of vernalization treatment. Vemalizatio n response was assessed through the change of final leaf number (FLN) on the main stem at heading. Five lines did not respond to vernalizati on. FLN for vernalization-sensitive lines generally decreased to a min imum as days of vemalization treatment increased. Plants at and after the stage where additional vernalization did not reduce FLN were vemal ization insensitive. The quantitative features of this vernalization r esponse, up to the point of insensitivity, were characterized with a l inear regression: (F-i-6) = alpha-beta T-v, where F-i is FLN observed for a particular vernalization treatment, T-v is the time in days of t hat vernalization treatment, and alpha and beta are the Y-intercept an d the slope of the regression, respectively. This model fitted the exp erimental results well, The parameters alpha and beta varied among lin es, and are useful for quantifying vernalization response in wheat. Th e implication of each parameter can be interpreted biologically: alpha is the ''changeable number of leaves'', i.e., how many leaves can be potentially decreased by vemalization treatment, and beta represents t he ''exchange rate'' between leaf numbers and vemalization days, i,e., how many leaves can be reduced by one day of vemalization treatment.