Endosperm Modified by Cross‐Pollinating Maize to Induce Changes in Dry Matter and Nitrogen Accumulation

The question of whether the vegetative source or kernel sink represents the major constraint for grain yield of maize ( Zea mays L.) has not been satisfactorily answered. In a field experiment, the sink of two hybrids, Pioneer brand 3732 (P3732) and B73 ✕ Mol7 was modified through cross‐pollination to study effects of sink alteration on dry matter and N accumulation. The two hybrids were grown with 268 kg N ha −1 spring‐applied in a randomized split‐plot design with four replications. Sib‐pollination and reciprocal crosses were made by controlling the pollen source. Dry weight and N content in plant parts as well as black layer development in kernels were analyzed at various stages during kernel maturation. Modification of the P3732 endosperm genotype by cross‐pollination with B73 X Mol7 pollen significantly increased kernel weight, kernel protein content and protein concentration, and grain yield. These increases were the result of increased assimilate production in vegetative tissues rather than improved partitioning efficiency. The P3732 crossed kernels delayed black layer development for about 10 d. Increases in protein concentration were primarily in the form of zein. In contrast, modification of the B73 ✕ Mo 17 endosperm by crosspollination with P3732 pollen had no effect on these traits. The effects of sink alteration on total plant dry matter and N accumulation were also different between P3732 and B73 ✕ Mol7 in that sink alteration of P3732 increased the accumulation of these two traits in vegetative tissues during the period of grain‐fill. These observations confirm that sink determination of grain yield is hybridspecific.