Page 168 - Breeding and regulatory opportunities, Renaud

Chapter 5

Variance components were reported as coeicients of variation, i.e.,
̅

CV=100 V ⁄ ,
x

with V the variance corresponding to specfic ffects and̅ the trait mean

. Repeatability was calculated from the variance components in its most genera

l form a

s
H2 =V /(V +V /nL+V /nS+V /nM+V /(nL.nS)+V /(nL.nM
) G G GL GS GM GLS GL
M
+M /(nS.nM) +M /(nL.nS.nM) +e /(nL.nS.nM.nR))
VGS VGLS V

,
where the variance components correspond to the terms in the mixed mode

l above. The terms nL, nS, nM and nR stand for the number of locations (2: Main

e and Oregon), number of ‘seasons’ (4: Fall 2006, Spring 2007, Fall 2007, Sprin

g 2008), management (2; organic and conventional), and replicates (2 or 3)

.
Genotypic means were calculated by taking genotypic maineffect fixed instea

d of random in the mixed models above. Pairwise comparisons between genotypi

c means were performed using GenStat procedure VMCOMPARISON. Correlation

s on the basis of genotypic means were referred to as genetic correlations

. Genotypic stabilities under organic and conventional conditions were calculate
x
d as the variance for individual genotypes across all trials in the system

.
To assess the feasibility of selection for organic conditions (the target environ

- ment) under conventional conditions, we calculated the ratio of correlate

d response (for organic conditions using conventional conditions), CR, to direc

t response (for organic conditions in organic conditions), DR, as the product o

f the genetic correlation between organic and conventional systems rG) and th
(
e ratio of the roots of conventional and organic repeatabilities (and respectively)

:
CR/DRrC HO
=GH⁄

.
A ratio smaller than 1 indicates that selection is better done directly unde

r organic conditions when the aim is indeed to improve the performance i

n organic conditions

.
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