SSI: Simultaneous Selection Indices for Yield and Stability

Description Usage Arguments Details Value References See Also Examples

View source: R/SSI.R

Description

SSI computes the Simultaneous Selection Index for Yield and Stability (SSI) according to the methods specified in the argument method.

Usage

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SSI(y, sp, gen, method = c("farshadfar", "rao"), a = 1)

Arguments

y

A numeric vector of the mean yield/performance of genotypes.

sp

A numeric vector of the stability parameter/index of the genotypes.

gen

A character vector of the names of the genotypes.

method

The method for the computation of simultaneous selection index. Either "farshadfar" or "rao" (See Details).

a

The ratio of the weights given to the stability components for computation of SSI when method = "rao" (See Details).

Details

The SSI according to Rao and Prabhakaran (2005) (Ii) is computed as follows:

Ii = [Yi Y..] + α [(1/SPi) ((1/T) Ti=1 (1/SPi))]

Where SPi is the stability measure of the ith genotype under AMMI procedure; Yi is mean performance of ith genotype; Y.. is the overall mean; T is the number of genotypes under test and α is the ratio of the weights given to the stability components (w2) and yield (w1) with a restriction that w1 + w2 = 1. The weights can be specified as required.

α w1 w2
1.00 0.5 0.5
0.67 0.6 0.4
0.43 0.7 0.3
0.25 0.8 0.2

The SSI proposed by Farshadfar (2008) is called the Genotype stability index (GSI) or Yield stability index (YSI) (Farshadfar et al., 2011) and is computed by summation of the ranks of the stability index/parameter and the ranks of the mean yields.

GSI = YSI = RSP + RY

Where, RSP is the stability parameter/index rank of the genotype and RY is the mean yield rank of the genotype.

Value

A data frame with the following columns:

SP

The stability parameter values.

SSI

The computed values of simultaneous selection index for yield and stability.

rSP

The ranks of the stability parameter.

rY

The ranks of the mean yield of genotypes.

means

The mean yield of the genotypes.

The names of the genotypes are indicated as the row names of the data frame.

References

\insertRef

rao_use_2005ammistability

\insertRef

farshadfar_incorporation_2008ammistability

\insertRef

farshadfar_ammi_2011ammistability

See Also

AMGE.AMMI, ASI.AMMI, ASTAB.AMMI, AVAMGE.AMMI, DA.AMMI, DZ.AMMI, EV.AMMI, FA.AMMI, MASV.AMMI, SIPC.AMMI, ZA.AMMI

Examples

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library(agricolae)
data(plrv)
model <- with(plrv, AMMI(Locality, Genotype, Rep, Yield, console=FALSE))

yield <- aggregate(model$means$Yield, by= list(model$means$GEN),
               FUN=mean, na.rm=TRUE)[,2]
stab <- DZ.AMMI(model)$DZ
genotypes <- rownames(DZ.AMMI(model))

# With default ssi.method (farshadfar)
SSI(y = yield, sp = stab, gen = genotypes)

# With  ssi.method = "rao"
SSI(y = yield, sp = stab, gen = genotypes, method = "rao")

# Changing the ratio of weights for Rao's SSI
SSI(y = yield, sp = stab, gen = genotypes, method = "rao", a = 0.43)

ajaygpb/AMMIStbp documentation built on Jan. 27, 2020, 8:53 a.m.