Pre-flowering Growth and Development of the Inflorescences of Maize: I. PRIMORDIA PRODUCTION AND APICAL DOME VOLUME

The growth and development of the main stem and the two uppermostaxillary apices of maize were studied during the period fromemergence until flowering. Plants were grown in the field undervarying levels of applied nitrogen fertilizer at two times ofsowing. The effects of daylength were isolated from those oftemperature by making comparisons of growth and developmenton a thermal time basis. The growth and development of the terminal (male) apex and thetwo uppermost axillary (female) apices followed the same patterns,with apex volumes increasing curvilinearly with increase innumber of leaf or husk primordia. The RGR(relative growth rateof volume) of the terminal apex was, however, only approximatelyone-tenth of the axillary apices. There was no difference ingrowth and development between the first and second axillaryapices before flowering: other factors, such as accumulationof dry weight, rather than primordia production, must be responsiblefor an axillary apex's potential to bear grain. Applied N, andto a lesser extent short days, increased the rates of growthand development of all the apices. For example, applied N increasedthe RGR (volume) of the apical domes, and the rate of productionof spikelet primordia, by about 25%. All axillary apices and treatments showed a single relationshipbetween number of spikelets and surface area of the ear: a favourableenvironment (e.g. high N) simply accelerated the progressionof spikelet production and area expansion along this singlepath. We conclude that this path is probably determined geneticallyand that N and time of sowing influence potential yield of maizethrough effects on the surface area of the ear but not on thedensity of spikelets formed. Key words: Maize, inflorescence, N application, daylength, temperature, apex volume