giles.wheat {agridat} | R Documentation

## Straw length and ear emergence for wheat genotypes.

### Description

Straw length and ear emergence for wheat genotypes. Data are unbalanced with respect to experiment year and genotype.

### Usage

    data("giles.wheat")

### Format

A data frame with 247 observations on the following 4 variables.

`gen`

  genotype. Note, this is numeric!

`env`

  environment

`straw`

  straw length

`emergence`

  ear emergence, Julian date

### Details

Highly unbalanced data of straw length and ear emergence date for wheat genotypes.

The 'genotype' column is called 'Accession number' in original data. The genotypes were chosen to represent the range of variation in the trait.

The Julian date was found to be preferable to other methods (such as days from sowing).

Piepho (2003) fit a bilinear model to the straw emergence data. This is similar to Finlay-Wilkinson regression.

### Source

R. Giles (1990). Utilization of unreplicated observations of agronomic characters in a wheat germplasm collection. In: Wheat Genetic Resources. Meeting Diverse Needs. Wiley, Chichester, U.K., pp.113-130.

### References

Piepho, HP (2003). Model-based mean adjustment in quantitative germplasm evaluation data. Genetic Resources and Crop Evolution, 50, 281-290. http://doi.org/10.1023/A:1023503900759

### Examples

    library(agridat)
    data(giles.wheat)
    dat <- giles.wheat
    dat <- transform(dat, gen=factor(gen))
    dat <- transform(dat, env=factor(env))
    dat1 <- subset(dat, !is.na(straw))
    dat2 <- subset(dat, !is.na(emergence))

    # Traits are not related
    # with(dat, plot(straw~emergence))

    # Show unbalancedness of data
    if(require(lattice) & require(reshape2)){
      redblue <- colorRampPalette(c("firebrick", "lightgray", "#375997"))
      levelplot(acast(dat, gen ~ env, value.var='emergence'),
                col.regions=redblue,
                xlab="genotype", ylab="year",
                main="giles.wheat - straw length")
    }

    ## Not run:

    # Analysis of straw length

    require(emmeans)
    require(gnm)

    # Mean across years. Matches Piepho Table 7 'Simple'
    m1 = lm(straw ~ gen, data=dat1)
    emmeans(m1, 'gen')

    # Simple two-way model.  NOT the bi-additive model of Piepho.
    m2 = lm(straw ~ gen + env, data=dat1)
    emmeans(m2, 'gen')

    # Bi-additive model. Matches Piepho Table 6, rows (c)
    library(gnm)
    m3 <- gnm(straw ~ env + Mult(gen,env), data=dat1)
    cbind(adjusted=round(fitted(m3),0), dat1)

    # Analysis of Ear emergence

    require(emmeans)

    # Simple two-way model.
    m4 = lm(emergence ~ 1 + gen + env, data=dat2)
    emmeans(m4, c('gen','env')) # Matches Piepho Table 9. rpws (c)
    emmeans(m4, 'gen') # Match Piepho table 10, Least Squares column

    ## End(Not run)

[Package agridat version 1.16 Index]