Ronald L. Phillips
983
fertility of that plant, and the stability of a maize chromosome
appeared to be primarily dependent on the particular maize
chromosome interacting with the oat background. Furthermore,
the ability to recover a particular maize chromosome in F
1
hybrids was not correlated with the ability to produce a fertile
addition line for that chromosome. For instance, 20 F
1
hybrids
with maize chromosome 5 were produced, making the chromo-
some 5 the most frequently recovered chromosome, either as a
single chromosome addition or in combination with other maize
chromosomes; chromosome 2 addition plants were the next most
frequent with 15 F
1
plants produced. Yet, only one of the
chromosome 5 plants was fertile and transmitted the chromo-
some 5 to offspring resulting in the fertile disomic addition
OMAd5.59 in Sun II oat background. This finding can be
contrasted with chromosome 4, which has been recovered as an
addition line nine times, with three of these addition plants being
fertile and transmitting the chromosome 4 to offspring. With
respect to transmission of maize chromosomes, fertile disomic
addition lines fall into different categories. Addition lines car-
rying chromosomes 2, 3, 4, 6, and 9 exhibited little or no
problems with transmission (nearly 100% maternal and paternal
transmission rate). Lines carrying chromosomes 1 and 7 initially
had poor transmission of the maize chromosome, but after
several generations they show good transmission of the maize
chromosome (
Ͼ80% transmission rate), possibly due to selective
breeding for stable diploid offspring. Chromosomes 1, 5, and 8
additions have fertility problems even after several generations
of selection, and chromosome 10 additions have transmitted only
short-arm derivatives to offspring. Eleven disomic additions for
different maize chromosomes, including 2, 4, 5, 6, 7, 8, and 9 in
different oat backgrounds, have been added to the previously
reported set (15), making a total of 50 fertile addition lines
(Table 1).
Irregular Maize Chromosome 5 Transmission in Oat.
Disomic maize
chromosome 5 additions recovered earlier in two different oat
backgrounds (OMAd5.09 in Starter and OMAd5.17 in MN-
hybrid) show significantly diminished paternal transmission,
whereas maternal transmission of the maize chromosome 5 is
only moderately reduced. Crossing a OMAd5.09 plant as male
back to Starter produced four monosomic maize additions
among 58 BC
1
offspring, giving a paternal transmission rate of
6.9% (4 of 58). In 30 F
4
offspring of a disomic addition from the
line OMAd5.09, only 2 plants were disomic additions, which
corresponds to a minimal paternal transmission of 6.7% (2 of
30). Twenty-one plants were monosomic additions, which indi-
cates a probable maternal transmission of 76.7% (23 of 30),
although one or two of the monosomic additions could be from
paternal transmission. In a further experiment analyzing 25 F
4
offspring of a disomic addition from the line OMAd5.17, only
two plants were disomic additions, indicating a paternal trans-
mission of 8% (2 of 25). Seventeen plants were monosomic
additions, which indicates a probable maternal transmission of
76% (19 of 25). Taking data for both oat backgrounds together,
the irregular low paternal transmission of the maize chromosome
5 (6.7–8%) clearly accounts for the low frequency of disomic
addition offspring from disomic chromosome 5 addition plants.
Maize Chromosome 10 Transmission.
Chromosome 10 is the small-
est chromosome, with 190 Mbp in the Seneca 60 complement.
Yet, it was the most frequently eliminated chromosome in (oat
ϫ
maize)F
1
hybrids, indicating a low tolerance for its presence in
oat (4, 10). The first recovered monosomic addition of chromo-
some 10 occurred in a haploid of GAF-Park oat background
(10). Since that time, the plant has been vegetatively propagated
by tiller cloning under short-day conditions. Periodically, tiller
clones have been moved to a long-day regime to induce flowering
for self-pollination or backcrossing with GAF-Park pollen. After
screening thousands of spikelets over a period of
Ϸ3 years, we
recently recovered one seed. This one seed, however, did not
possess maize chromatin; thus, a maize chromosome addition
offspring has not been produced by this plant.
In this new series of oat
ϫ maize crosses, we recovered 11
plantlets that retained maize chromosome 10 as single or mul-
tiple chromosome additions, 9 plantlets in Starter oat back-
ground, and 2 plantlets in Sun II background. One chromosome
10-positive F
1
plant (F
1
-0289-1, Seneca 60
ϫ Sun II) set 189 F
2
seeds in its first four panicles (Table 2). The PCR assay with
Grande 1 showed that 28 F
2
plants originating from three
panicles were maize-positive, and 2 F
2
plants were maize-
negative. GISH analyses revealed 16 disomic and 12 monosomic
addition plants. All 10 F
2
plants originating from the fourth
panicle were maize-negative. In all 28 maize-positive plants, only
Table 1. Fertile oat–maize chromosome addition lines
Added maize
chromosome
Oat host
Maize donor
Addition
No. of
lines
1
Starter
Seneca 60
Disomic
1
2
Starter
Seneca 60
Disomic
9
2
Starter
bz1-mum9
Disomic
1
2
Sun II
Seneca 60
Disomic
2
3
Sun II
Seneca 60
Disomic
1
3
Preakness
Seneca 60
Disomic
1
4
Starter
Seneca 60
Disomic
6
4
Starter
A188
Disomic
2
4
Starter
B73
Disomic
1
5
Starter
Seneca 60
Disomic
1
5
MN-hybrid
Seneca 60
Disomic
1
5
Sun II
Seneca 60
Disomic
1
6
Starter
Seneca 60
Disomic
1
6
MN-hybrid
Seneca 60
Disomic
1
6
Sun II
Seneca 60
Disomic
1
7
Starter
Seneca 60
Disomic
4
7
GAF-Park
Seneca 60
Disomic
1
8
Starter
Seneca 60
Disomic
1
8
Starter
bz1-mum9
Disomic
1
8
GAF-Park
Seneca 60
Monosomic
1
9
Starter
Seneca 60
Disomic
7
9
GAF-Park
Seneca 60
Disomic
1
9
Sun II
Seneca 60
Disomic
1
10S
Sun II
Seneca 60
Ditelosomic
1
1
ϩ 9
Starter
Seneca 60
Double disomic
1
4
ϩ 6
Starter
Seneca 60
Double disomic
1
This table lists all available addition lines and is an update of an earlier list
that involved fewer lines (15).
Table 2. Seed set from fertile oat–maize chromosome
10S additions
F
1
-plant panicle
No. of F
2
seeds
Total Tested Maize-positive Disomic Monosomic
F
1
-0289-1
͞a
51
10
9
3
6
F
1
-0289-1
͞b
59
10
9
5
4
F
1
-0289-1
͞c
48
10
0
0
0
F
1
-0289-1
͞d
31
10
10
8
2
F
1
-5133-1
͞a
6
6
6
3
3
F
1
-5133-1
͞b
0
—
—
—
—
F
1
-5133-1
͞c
1
1
1
0
1*
F
1
-5133-1
͞d
2
2
2
1
†
1*
*Monosomic for maize chromosome 4 and monosomic for maize chromosome
10S derivative.
†
Disomic for maize chromosome 4.
Kynast
et al.
PNAS
͉
June 29, 2004 ͉ vol. 101 ͉ no. 26 ͉
9923
PLANT
BIOLOGY
38_2006-7 Phillips.p65
06-Mar-09, 7:49 PM
983