Principles of Plant Genetics and Breeding

A
B
C
Males
(a) Conceptual
Paired row
parents used as females. Design II is a factorial mating
scheme similar to Design I (Figure 8.6). It is used to
evaluate inbred lines for combining ability. The design is
most adapted to plants that have multiple flowers so that
each plant can be used repeatedly as both male and
female. Blocking is used in this design to allow all the
mating involving a single group of males to a single
group of females to be kept intact as a unit. The design is
essentially a two-way ANOVA in which the variation
may be partitioned into difference between males (m)
and females (f) and their interaction. The ANOVA is as
follows:
Source df MS EMS
Males n 1 − 1 MS 1 σ 2 w + rσ 2 mf + rnσ2 m
Females n 2 − 1 MS 2 σ 2 w + rσ 2 mf + rn 1 σ2 f
Males × females (n 1 − 1)(n 2 − 1) MS 3 σ 2 w + rσ 2 mf
Within progenies n 1 n 2 (r − 1) MS 4 σ 2 w
σ 2 m = [MS 1 − MS 3 ]/rn 2 = 1 / 4 V A
rσ 2 f = [MS 2 − MS 3 ]/rn 1 = 1 / 4 V A
rσ 2 mf = [MS 3 − MS 4 ]/r = 1 / 4 V D
σ 2 w = MS 4 = 1 / 2 V A + 3 / 4 V D + E
D
E
F
D
E
F
D
E
F
Females
INTRODUCTION TO QUANTITATIVE GENETICS 143
AD
AE
AF
BD
BE
BF
CD
CE
CF
Progeny
× × × × × × × × ×
A D A E A F B A B E B F C D C E C F
(b) Practical
Figure 8.6 North Carolina Design II. (a) This is a factorial design. (b) Paired rows may be used in the nursery for factorial
mating of plants.
The design also allows the breeder to measure not
only GCA but also SCA.
North Carolina Design III
In this design, a random sample of F2 plants is backcrossed
to the two inbred lines from which the F2 was
descended. It is considered the most powerful of all the
three NC designs. However, it was made more powerful
by the modifications made by Kearsey and Jinks that adds
a third tester (not just the two inbreds) (Figure 8.7).
The modification is called the triple testcross and is
capable of testing for non-allelic (epistatic) interactions,
which the other designs cannot, and also capable of
estimating additive and dominance variance.
Diallel cross
A complete diallel mating design is one that allows the
parents to be crossed in all possible combinations,
including selfs and reciprocals. This is the kind of
mating scheme required to achieve Hardy–Weinberg