Branch roots of young maize seedlings, their production, growth, and phloem supply from the primary root

Branch root development on the primary root of maize (Zea mays L.) seedlings was followed for 9 d after planting. This period includes the shift from seedling heterotrophy to autotrophy. Linear density of branches in the basal region ranged from similar to 38 cm(-1) at the base to similar to 10 cm(-1) beyond 10 cm. Branch roots in the first similar to 8 cm were produced before assimilate was available. Branch length decreased from similar to 26 mm at 1 cm along the primary root to similar to 8 mm at 10 cm from the base. Without the cotyledon, branch root density in the basal region was similar to 10 cm(-1) and roots were short (similar to 5 mm). Beyond 8 - 10 cm both measurements matched those of intact seedlings. Dark-grown seedlings had basal branch root densities higher than those without cotyledons but none beyond 10 cm. There were more and smaller diameter sieve tubes in the basal region of the primary root. These decreased distally in number but had larger diameters where branches formed after assimilate was available. Proliferation of basal branch roots in very young seedlings can have major advantages for successful seedling establishment in the field and could be screened for without difficulty.