SSI | R Documentation |
SSI
computes the Simultaneous Selection Index for Yield and Stability
(SSI) according to the methods specified in the argument method
.
\loadmathjax
SSI(y, sp, gen, method = c("farshadfar", "rao"), a = 1)
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 |
a |
The ratio of the weights given to the stability components for
computation of SSI when |
The SSI according to \insertCiterao_use_2005;textualammistability (\mjseqnI_i) is computed as follows:
\mjsdeqnI_i = \frac\overlineY_i\overlineY_.. + \alpha \frac\frac1SP_i\frac1T\sum_i=1^T\frac1SP_i
Where \mjseqnSP_i is the stability measure of the \mjseqnith genotype under AMMI procedure; \mjseqn\overlineY_i is mean performance of \mjseqnith genotype; \mjseqn\overlineY_.. is the overall mean; \mjseqnT is the number of genotypes under test and \mjseqn\alpha is the ratio of the weights given to the stability components (\mjseqnw_2) and yield (\mjseqnw_1) with a restriction that \mjseqnw_1 + w_2 = 1. The weights can be specified as required.
\mjseqn\alpha | \mjseqnw_1 | \mjseqnw_2 |
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 \insertCitefarshadfar_incorporation_2008;textualammistability is called the Genotype stability index (\mjseqnGSI) or Yield stability index (\mjseqnYSI) \insertCitefarshadfar_ammi_2011ammistability and is computed by summation of the ranks of the stability index/parameter and the ranks of the mean yields.
\mjsdeqnGSI = YSI = R_SP + R_Y
Where, \mjseqnR_SP is the stability parameter/index rank of the genotype and \mjseqnR_Y is the mean yield rank of the genotype.
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.
AMGE.AMMI
,
ASI.AMMI
,
ASTAB.AMMI
,
AVAMGE.AMMI
,
DA.AMMI
, DZ.AMMI
,
EV.AMMI
, FA.AMMI
,
MASV.AMMI
,
SIPC.AMMI
,
ZA.AMMI
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)
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