No abstract

M aize (Zea mays L.) is monoecious with staminate (male) fl owers borne on an apical infl orescence (commonly referred to as a tassel) and pistillate (female) fl owers produced on lateral branches that develop grain bearing rachises (commonly referred to as ears). For an individual plant, anthesis for the male fl owers is defi ned when at least one fl ower exserts anthers that dehisce and shed pollen. Female fl owers are considered open when the fi rst pollen receptive stigmas emerge from the ear (hereafter called silking). These processes are defi ned diff erently at the population level, but still refl ect functional maturity relative to pollination. Anthesis and silking are achieved when a predetermined proportion of plants reach the stage (typically 50%). Environmental conditions that alter plant growth around fl owering aff ect the temporal separation ABSTRACT The capacity to predict time to silking relative to anthesis in maize (Zea mays L.) has important implications for breeding and seed production. We developed a theoretical quantitative framework for simulating the anthesis to silking interval (ASI) based on plant growth and biomass partitioning to the ear. We tested this framework to simulate the progress of silking relative to anthesis in nine inbreds and four hybrids whose plant growth rate (PGR) during fl owering was altered by stand density, thinning, or defoliating treatments. Time to 50% anthesis varied with genotype but was not affected by canopy modifi cations (P < 0.01). The ASI, however, varied with genotype and canopy modifi cations (P < 0.01). The proportion of plants reaching silking ranged from 12 to 100% across treatments. There were signifi cant (P < 0.001) genotype × treatment interactions for PGR around anthesis and plantto-plant variability in growth rate. Genotypes differed in biomass partitioning to the ear, the pattern of ear biomass (EB) accumulation, and the EB required to achieve silking. Despite these effects, the plant biomass framework accurately simulated silking dynamics relative to anthesis for the 36 treatment combinations (R 2 = 0.86, RMSE = 16.7%). These results show that coupling the expansion growth process of silking with plant growth around fl owering is a useful and robust approach for modeling ASI at the population level.

Controlling pollination of the female inbred is critical to achieve maximum kernel set and high levels of genetic purity in maize (Zea mays L.) hybrid seed production. Although kernel set associated with inbred fl owering dynamics is fairly predictable, it has not been possible to predict the level of outcrossing resulting from adventitious pollen entering the seed fi eld. Our objective was to combine our kernel set model with a new Lagrangian pollen dispersal model to determine whether outcrossing could be simulated from fl owering dynamics and estimates of pollen drift . Th is study was conducted in a commercial seed production fi eld in which male and female planting dates were varied to provide a range of fl owering synchronies and risk for outcrossing. Kernel production varied from 13.4 × 10 6 to 24.5 × 10 6 kernels ha −1 . Outcrossing at fi eld locations 100 to 170 m from an adventitious pollen source varied from 1.4 to 18% as determined by allelic variation at 13 loci. Th e kernel set model accurately simulated variation in kernel production (R 2 = 0.83; RMSE = 0.3 × 10 6 ) when silk receptivity was limited to 4 d. Percentage outcrossing due to adventitious pollen also was accurately simulated (R 2 = 0.78; RMSE = 0.8) for wind conditions and plant development patterns typically encountered in maize hybrid seed production. Th e combined kernel set and pollen dispersal models provide a novel and robust approach for defi ning management strategies to optimize kernel production and genetic purity.

Coupling Time to Silking With Plant Growth Rate in Maize 108 I would like to recognize and gratefully thank many people who helped me achieve this project. Primary and principal, to my family, Pilar and friends, who provided essential emotional support and encouragement. Additionally, I would like to extend personal thanks to Mark Westgate for his patience, guidance and support during this project. The committee members have also provided important input and assistance, my appreciation to Susana Goggi, Raymond Arritt and Lance Gibson. Thanks to Horan BioProduction Inc. and Syngenta Seeds Inc., for providing me the opportunity of working on their fields.