I. Goldringer et al., ADJUSTMENT FOR COMPETITION BETWEEN GENOTYPES IN SINGLE-ROW-PLOT TRIALS OF WINTER-WHEAT (TRITICUM-AESTIVUM), Plant breeding, 112(4), 1994, pp. 294-300
Several statistical methods were investigated for improving yield esti
mation for 72 genotypes of winter wheat tested in a single-row-plot (S
RP) trial. The different analytical models were compared using several
criteria: the residual mean square fit; the standard error of differe
nces of genotype means; the correlations of genotype means with means
from six-row-plot (6RP) reference trial; the expected genetic gains re
lative to 6RP trial from selecting the 10 top yielding genotypes. Ther
e was no significant correlation between the unadjusted genotype means
for SRP and 6RP. Genotype yields were positively correlated with heig
ht in SRP, but this correlation was reversed in 6RP. Using the mean he
ight difference of a plot with its two neighbours as a covariate to ad
just for competition in SRP reduced the standard error of difference o
f genotype means and substantially increased their correlation with th
e 6RP means. The predicted selection efficiency in SRP trial increased
from zero, before adjustment, to 83% of 6RP trial. Including the diff
erence in heading date and the effect of guards at borders as covariat
es in the SRP analysis improved the residual mean square fit but had n
o effect on correlation with 6RP means or selection efficiency. A prod
ucer-competitor model in which individual competitor effects were esti
mated for each genotype gave a substantial improvement in fit over the
covariate models but a much lower correlation with 6RP means and sele
ction efficiency. Yield selection in early generation wheat trials bas
ed on single-row plots could be considerably strengthened by use of a
plot covariate derived from height difference between neighbours.