library(pls)
train <- plsr(Y ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data=mydata, scale=T, validation="none")
tenfold <- plsr(Y ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data=mydata, scale=T, validation="CV")
loo <- plsr(Y ~ X1 + X2 + X3 + X4 + X5 + X6 + X7 + X8, data=mydata, scale=T, validation="LOO")

Comp 1 Comp 2 Comp 3 Comp 4 Comp 5 Comp 6 Comp 7 Comp 8
training     42     12     12     15    7.7    1.7    9.3   0.43
tenfold      42     12     12     15    7.7    1.7    9.3   0.43
loo          42     12     12     15    7.7    1.7    9.3   0.43