Abstract

1. Did Recurrent Selection For Yield Affect Iowa Stiff Stalk Synthetic Maize Population Grain Fill Characteristics? Steve Eichenberger1, Fernando Miguez1, Jode Edwards2 and Allen Knapp1,(1)Agronomy Dept., Iowa State Univ., Ames, IA 50011, (2) USDA-ARS, Ames, IA 50011 Abstract Hybrid maize yield increases, new product development, and increased stress tolerance can be more easily achieved with a better understanding of the physiological and genetic basis for phenotypic changes in response to recurrent selection for yield. The purpose of this study was to identify changes in grain fill characteristics and their interaction with plant density in a closed population and identify a model that accurately models grain fill in this population. A non-linear logistic model was fitted to the data. Final kernel dry weight was influenced by population, plant density, and their interaction. Kernel fill rate and kernel fill duration were affected by population only. • Materials and Methods • Field experiments were conducted at two locations near Ames, IA with three replications per location in 2009. • The experiment was a split plot design with plant density as the main plot treatment and pedigree as the sub-plot treatment. • Plant densities were 53,000 and 77,000 seeds per hectare. • Sixteen plants from each subplot were tagged and the silking date was recorded for each plant. • Two ears from each treatment were harvested at weekly intervals beginning 15 days after silking. • Ten kernels from each ear were removed from spikelet positions 10-15 from the base of the ear. • Kernels were dried at 70° until dry weight remained constant. • Populations • BSSS- Iowa Stiff Stalk Base Population • BSSS(R)C17 Seventeen cycles of reciprocal selection with BSCB1 (Iowa Corn Borer Synthetic Number 1). • BS13(HI)C5- Five cycles of selection with inbred B97 as tester (beginning with BS13(S)C0). • BS13(S)C0- Derived by intermating selected lines from BSSS(HT)C7. • BSSS(HT)C7 – Seven cycles of half-sib selection with double cross hybrid IA13 as tester. • Analysis • A non-linear logistic model was fitted to the data. • The asymptote, x-mid points, and scale parameters of the logistic function were calculated using R statistical software. • Logistic Function • Formula • Kernel Weight= Asymptote/1+Exp(X-x-mid point/scale) • X = GDD after silking • Parameters • Asymptote- End of the linear phase of growth. Represents final kernel weight. Represents kernel fill duration. • X-mid point- The point on the x-axis when kernel fill is 50% complete. • Scale –The amount of time in growing degree days for kernel filling to go form 50 to 75% complete. Represents kernel fill rate. • Results • Final kernel dry weight was influenced by population and plant density at P < .05 (Table 2). • Kernel fill rate and kernel fill duration were influenced by population at P < .05 (Table 2). • Kernel fill rate and kernel fill duration were not influenced by planting density at P < .05. (Table 2). • BS13(HI)C5 and its cross with BSSS had a higher final kernel dry weight and kernel fill duration than BSSS (Table 2). • The base population(BSSS) crossed with any other population had a higher final kernel dry weight than the BSSS population (Table 2). • BS13(HI)C5 was the only population that had a kernel fill rate different from the base population(BSSS) (Table 2). • The F1 progeny of the cross between BSSS and BSSS(R)C17 showed a heterotic affect at P < .05. (Table 1). • BSSS(R)17 had a greater grain fill duration than the base population, but no change in final kernel dry weight(Table 2). • Introduction • The Iowa Stiff Stalk Synthetic Maize Population was created by intermating 16 lines of primarily Reid Yellow Dent background, and has undergone continuous recurrent selection since 1939 (Lamkey, 1992) . The criteria for selection include increased grain yield and reduced moisture content (Hagdorn et al., 2003). The BSSS maize population has made significant contributions to the hybrid maize seed industry. Inbreed lines from BSSS include B14, B37, B73, and B84 (Darrah and Zuber, 1986). These inbreeds made up 19% of all parent material used in hybrid maize seed in 1980 (Lamkey et al., 1991). • Yield increases over the past 70 years have averaged 115 kg ha-1 yr-1 (Duvick 2005). Although yield per unit land area has increased greatly, yield per plant has remained relatively constant. Newer hybrids yield more because of their increased tolerance to high plant density (Duvick 2005). • In maize, final yield is determined by the number of kernels per unit area by the weight of those kernels (Borras et al., 2009). The rate of dry matter accumulation in kernels and the duration of dry weight accumulation have been suggested as significant factors that influence yield potential (Poneleit and Egli, 1979). In commercial maize hybrids there is a great amount of variation in the final weight of kernels. This variation comes from a difference in both kernel fill rate and duration (Borras et al., 2009). It is still unclear of what combination of rate and duration provides the optimum pattern for kernel fill in a given environment (Borras et al., 2009). • Objectives • Identify changes of grain fill characteristics as a result of recurrent selection. • Identify how plant density affects these characteristics. • Identify a model that accurately models grain fill in the Iowa Stiff Stalk Synthetic Population • Conclusions • These conclusions are based on one year of data, and a second year of data is currently under analysis. However at this time we conclude that: • Recurrent selection for yield affected duration of kernel fill but not final kernel dry weight in the BSSS(R)C17 population. • BS(HI)C5 had a greater final kernel dry weight while BSSS(R)C17 did not. • Its possible yield advancement in the BSSS(R)C17 population came from variables other than increased kernel weight. • Heterotic affects may be present in the in the F1 progeny of the BSSS/BSSS(R)C17 cross. • More work is needed to define the relationship between grain fill parameters, source sink characteristics, and yield. Table 1. Contrast of parents vs. progeny to test for heterosis in the final kernel weight. Kernel Dry Wt. (Grams) References Borras L., Zinselmeier C., Lynn M., Westgate M.E., Muszynski M.G. (2009) Characterization of Grain-Filling Patterns in Diverse Maize Germplasm. Crop Science 49:999-1009. DOI: 10.2135/cropsci2008.08.0475. Darrah L.L., Zuber M.S. (1986) 1985 UNITED-STATES FARM MAIZE GERMPLASM BASE AND COMMERCIAL BREEDING STRATEGIES. Crop Science 26:1109-1113. Duvick D.N., Cassman K.G. (1999) Post-green revolution trends in yield potential of temperate maize in the north-central United States. Crop Science 39:1622-1630. Duvick D.N. (2005) GENETIC PROGRESS IN YIELD OF UNITED STATES MAIZE (Zea mays L.). Maydica 50:193-202. Egli D.B. (2004) Seed-fill duration and yield of grain crops, Advances in Agronomy, Vol 83, Elsevier Academic Press Inc, San Diego. pp. 243-279. Hagdorn S., Lamkey K.R., Frisch M., Guimaraes P.E.O., Melchinger A.E. (2003) Molecular genetic diversity among progenitors and derived elite lines of BSSS and BSCB1 maize populations. Crop Science 43:474-482. Lamkey K.R. (1992) 50 YEARS OF RECURRENT SELECTION IN THE IOWA STIFF STALK SYNTHETIC MAIZE POPULATION. Maydica 37:19-28. Lamkey K.R., Peterson P.A., Hallauer A.R. (1991) FREQUENCY OF THE TRANSPOSABLE ELEMENT UQ IN IOWA STIFF STALK SYNTHETIC MAIZE POPULATIONS. Genetical Research 57:1-9. 88=Low Plant Density 128=High Plant Density Table 2. Values for each parameter, with its contrast to BSSS. NS=Non Significant *= Significant at P-value equal to or less than .05 **=Significant at P-value equal or less than .01