The Utilization of Degree Days for the Characterization of Developmental Stages of 26 Winter Wheat Cultivare

Abstract

Twenty six winter wheat cultivars representing early maturing (Em), medium early maturing (Mm), and late maturing (Lm) cultivar groups were grown in the field for two growing seasons. The dates at which plants reached the double ridge (DR) and terminal spikelet (TS) stages were determined using anatomical analysis of shoot apices. Thereafter the dates of anthesis (AN) and full maturity (MA) were recorded. The length of the time spans between subsequent developmental stages was then expressed both chronologically (number of days, d) and in terms of thermal time (degree day, °C d) which was calculated with the basal temperature equalling to zero. The results obtained confirmed the suitability of the utilization of degree days for the description of the time course of plant development, because the great differences in the time between subsequent developmental stages recorded between the two growing seasons when expressed in terms of numbers of days markedly diminished when expressed in terms of degree days. For example the period DR-MA expressed in number of days amounted in the year 1986 only to 87 % when related to the number of days recorded in the year 1985, whereas the corresponding value expressed in terms of degree days amounted to 98 %. The utilization of degree days is especially suitable for the AN-MA period (956 and 937 degree days in the years 1985 and 1986, respectively) within which temperature is the main factor determining the rate of plant development. Further analyses of the effects of basal temperatures, vernalization, and daylength appear to be necessary for a better understanding of the length of the period to the DR stage and differences among groups of cultivars and among different cultivars.