Kernel Set and Flower Synchrony within the Ear of Maize : II. Plant Population Effects

Kernel number (KN) per plant declines with increasing plant population (PP) in maize ( Zea mays L.) and controversy exists about the critical period for spikelet abortion. In this work, the effect of PP (5 and 9 plants m −2 ) on floral differentiation and kernel set was analyzed for two genotypes of contrasting prolificacy at Grignon, France, (48°51′N). Kernel set variability was tested at Balcarce (37°45′S), Argentina, with three PP (2, 8, and 16 plants m −2 ) and athinning treatment (from 16 to 2 plants m −2 ) at silking. Plants were grown with no water or nutrient restrictions. At 9 plants m −2 , floral differentiation was delayed in apical ears but almost all spikelets started silk elongation. In subapical ears, 17% of the spikelets of the nonprolific hybrid and 19% of the prolific hybrid had not completed development at silking. At 5 plants m −2 these proportions were reduced to 6%. Significant (P < 0.01) differences were detected in apical ear length after the onset of rapid ear growth (silking −20 d), resulting in reduced ear biomass at silking at high PP. Barrenness occurred at 16 plants m −2 (0.5 ears plant −1 ), but spikelet abortion took place in all apical ears after silking, except at 2 plants m −2 (control). Kernel number per plant was not related to the degree of floral differentiation reached at silking, but to the amount of intercepted photosynthetically active radiation (KN = 149.5 + 204.6 MJ plant −1 d −1 , r 2 = 0.92) when the silking −15‐d period was included in the calculations. Presilking limitations to ear growth appear to reduce ear sink strength.