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.

Grass, L. and Burris, J. S. 1995. Effect of heat stress during seed development and maturation on wheat (Trititum durum) seed quality. I. Seed germination and seedling vigor. Can. J. Plant Sci. 75: 821-829. Two wheat cultivars, Marzak and Oumrabia, were subjected to three temperature regimes (20115,28121,36129 "C) beginning 10 d after anthesis to maturity. As expected, high temperature resulted in low values of both seed yield and physical traits of seed quality. The effect of temperature on seed germination was not consistent among the two cultivars. High temperature during seed development and maturity had no effect on seed germination of Oum-rabia, whereas it decreased seed germination of Marzak. ln contrast to seed germination, seed vigor was adversely affected by heat sffess. This decline in seed vigor was reflected in reduced shoot and root dry weight, increased shoot/root ratio, reduced root length, low root number per seedling, and high seed conductivity. Excised embryo culture showed mmked differences in the embryo growth potential. Although embryos from all treafinents had germinated, a delay of 24-48 h was observed in the germination of embryos excised from seeds grown under high temperature conditions. Also, their shoot and radicle development over time lagged behind that of embryos isolated from seeds grown under cool temperature conditions. Exposing seeds to high temperature during development and maturity also resulted in low embryo oxygen uptake. Results presented in this study show that the growing conditions, in this instance temperature, of the parent plant affect the quality of its seed.

Grass, L. and Burris, J. S. 1995. Effect of heat stress during seed development and maturation on wheat (Triticum durum) seed quality: II. Mitochondrial respiration and nucleotide pools during early germination. Can. J. Plant Sci. 75: 831-839' Marzak and Oum-rabia wheat seeds were produced under three temperature regimes (20.15 , 28:.21 , 36:29" C) starting l0 d after anthesis through harvest. Nucleotide levels and respiratory activity of mitochondria isolated from imbibing embryos were determined. Mitochondrial structure from the radicle meristem region of imbibed embryos was examined under electron microscopy. Embryos from low-temperature treatments showed rapid accumulation of adenosine triphosphate (ATP) and higher energy levels and rates of oxygen uptake than embryos from high-temperature treatments. Embryos from medium-temperature treatments (Atkinson 1968). Similar to ATP content, this ratio is low in dry seed (< 0.5), but rapidly increases as the seed is wetted (> 0.8) (Moreland et al. 1974;Bewley and Black 1985).zAuthor to whom correspondence should be sent. For personal use only.

Stewart, for their support and ideas which enabled me to complete this study. My extended thanks and appreciations go to Dr. J.S.Burris who was always there to give his insight and steer me in the proper direction. Dr. Burris, I appreciate the opportunity you gave me, accepting me as one of your students to expand my knowledge in seed physiology. To my fellow graduate students, the seed science staff, and all my friends, I would like to thank you for all your help and for the fxui times we had together. I am truly going to miss you all. My deepest thanks go to my family (Mom, Dad, Brothers, Sisters, and Relatives) for their continual support and patience. I am mostly deeply indebted to my wife, Mina for her encouragement, support, tolerance, understanding and love. Your patience and faith made this all possible, I love you. Finally, I dedicate this dissertation to my daughter, Wissal, who came to lighten my life and from whom I received enjoyments and love during the completion of my graduate studies, I love you.