No abstract

rate around the time of silking (Edmeades and Daynard, 1979;Tollenaar et al., 1992;Andrade et al., 1993; Accurate prediction of kernel number per plant is critical for yield and

The objective of this study was to develop a simple, rapid and accurate technique to quantify maize (Zea mays L.) pollen shed under field conditions, capitalizing on the capacity of pollen to fluoresce and recent improvements in microscopic methods for acquiring, processing, and analyzing fluorescence signals from biological systems. Pollen shed naturally by the tassels was captured daily on passive pollen traps placed at apical ear level. Fluorescence microscopy was used to generate digital images of the trapped pollen, and pollen density per unit area was counted using commercial imaging software. Visual confirmation of fluorescing pollen grains indicated high measurement accuracy (r2 = 0.99) for the entire range of pollen shed densities typically encountered in the field. Pollen was randomly distributed across the surface of the pollen trap, and six to eight images per trap provided greater than 95% confidence for the mean trap value. The entire process of sample preparation, image capture, and image counting required less than 6 min per trap. The accuracy and ease of use of this technique make it ideal for characterizing the pattern of maize pollen production and dispersal under field conditions.

In maize (Zea mays L.) hybrid seed production, achieving the optimum seed yield per unit land area often is based on limited information about the quantity of pollen shed by the male and practical experience synchronizing pollen shed by the male inbred with silk emergence by the female inbred. We recently reported that kernel production per hectare could be simulated fairly accurately under pollen‐limited conditions from simple measures of pollen shed and silking dynamics. The objective of this study was to determine whether a simple mechanistic description of the flowering dynamics of male and female inbreds could be used to simulate and optimize kernel production in seed production fields. We estimated kernel production on the basis of flowering dynamics in six commercial seed fields located near Washington, IA, in 2002, which differed in the quantity of pollen production and silk emergence. In all cases, the fields were managed and harvested by standard seed industry methods. Harvested kernel number varied from 8.4 to 23.1 million kernels per female hectare. Simulated kernel number was closely correlated with these measured values (r2 = 0.98). This result indicates that relative differences in kernel production can be assessed directly from inbred flowering dynamics. Examples are provided to show how inbred management can be modeled to optimize harvested kernel number for a given inbred pair. Model simulations, however, overestimated harvested kernel number by 11%, on average, which implies that other plant factors, such as pollen viability, prolificacy, pollen capture by the canopy, or kernel abortion in response to leaf removal during detasseling might have limited kernel production across the six seed fields. Information about these variables can be incorporated readily into the kernel set model to improve its accuracy. This study indicates that kernel production in a hybrid seed field can be simulated from simple measures of inbred flowering dynamics. The model is a useful tool for optimizing harvested kernels for an established inbred pair or for defining initial management protocols for new combinations of inbreds.

Adequate pollen production is an essential prerequisite for achieving high yields in commercial corn (Zea mays L.) production and for insuring high levels of genetic purity in the production of hybrid seed. Documenting the timing and intensity of pollen shed are fundamental to these goals, but methods to describe patterns of pollen release from maize tassels are limited and laborious. Our objective was to explore characteristics of tassel morphology that could be used as simple and indirect measures of pollen production per plant under field conditions. The progress of tassel development was documented using a nine‐stage scale based on easily‐quantified morphological characteristics. Genetic variation among hybrids and inbreds as well as environmental variation across planting densities and years was correlated with levels of pollen production. This analysis revealed that a change in tassel dry weight during pollen shed was not an accurate measure of pollen production per tassel. Likewise, no single morphological characterization captured all the genetic and environmental variation in pollen production per tassel. But a combination of morphological traits incorporated into a Tassel Area Index (TAI) accounted for up to 89% of the variation in pollen production among hybrids in response to population density, and 64% of the variation in pollen production among inbred heterotic groups. Because data collection is simple, quick, and non‐destructive, the Tassel Area Index approach is well‐suited for distinguishing genetic variation in pollen production and relative responses to treatments under field conditions. The accuracy of the technique could be increased, if necessary, by incorporating additional information about flower density or pollen production per anther. But this would entail a much greater investment of time and resources.