Phosphorus Translocation Between Small, Non-Reproductive Tillers and the Main Plant of Maize

Tiller growth and development are generally limited under high plant populations used in modern maize (Zea mays L.) production. The physiological relationship between the main plant and small, barren tillers has not been clarified. Two experiments were conducted to investigate the existence, direction, and relative magnitude of P translocation during different phenological intervals, and to observe the effect of tiller senescence on P translocation. A foliar application of ³²P was made at each of three growth stages to the tiller or to the most recently expanded leaf on the main stalk of several maize plants grown hydroponically in the greenhouse. Plants were later separated into tiller, main plant, and roots and were assayed for radioactivity. In a field experiment, foliar applications of ³²P were made to tillers of maize grown on a Sharpsburg silty clay loam (Typic Argiudoll, fine, montmorillonitic, mesic) when the main plants were in the 11- to 12- or 15- to 16- leaf stage. Aboveground tissue was removed 32 or 33 days after treatment and assayed for radioactivity. Apparent translocation of ³²P from main plant to tiller was very small or nonexistent in plants grown in the glasshouse, whereas translocation from tillers to the main plant and roots was substantial. More than 24% of the radioactivity found in the whole plants at sampling had been translocated from the tiller, even though tillers accounted for <0.3% of the total dry weight at the 16-leaf stage. In the field study, movement of isotope to developing grain from a tagged tiller depended directly on total grain weight and was greater when the tiller did not senesce before sampling. The presence of active, barren tillers may therefore be an important characteristic for reducing maize yield losses where environmental stress limits nutrient absorption and assimilation during late vegetative and early reproductive growth.