ESTIMATING APICAL DEVELOPMENT USING THE EXTERNAL GROWTH-CHARACTERISTICS OF WHEAT

Certain apical developmental stages have been shown to be of value in guiding management practices or indicating sensitivity to stresses. Because the determination of apex development, however, requires a high degree ot skill, the use of external macromorphological growth parameters of spring wheat (Triticum aestivum L.) to predict apex developmental stage was examined in this study. The growing degree days (GDD), growth period on days (DAY), number of leaves, number of surviving tillers, height of uppermost node, height of uppermost stipule and the length of ear primordium were used as growth parameters. Field trials were carried out as plot trials and on-farm trials in 1989-91. The growth parameters of three spring wheat cultivars and their ear developmental stages were determined at 2-3 day intervals after emergence to pollination in the plot trials. The relationship between the development of the ear and the growth parameters of each cultivar was studied using polynomial regression up to 3rd degree and stepwise regression analysis. The accuracy of the mathematical functions were tested against independent data determined from the farm trials. To get a reliable estimate of the apex developmental stage, DAY and GDD were found to be the most useful parameters. Furthermore, the growing time (maturation class) of a cultivar should be taken into a consideration.