66
PNL Volume 19 1987 RESEARCH REPORTS
ORANGE COTYLEDONS (Orc) AND ORANGE LEAVES (orl): NEW GENES ON
CHROMOSOME 1
Swiecicki, W. K. Plant Breeding Station, Wiatrowo, Poland
Routine observations of seed samples in the Pea Genebank at
Wiatrowo revealed large differences in hue among accessions with
yellow cotyledons, from white to light-orange. Moreover, in the
accession obtained from China ('Ren-shou-da-bai Wan-dou'=
WT 11145), after removing of the seed coat, the cotyledons have a
clear orange color. This character was first described at the
workshop of pea geneticists and collection curators at Alnarp,
Sweden (4). Orange cotyledons are of particular interest because
they apparently have not been noticed although they've existed for
a long time. For the most part, varieties have been classified as
having either yellow (I) or green (i) cotyledons.
Preliminary results of crosses involving WT 11145 were repor-
ted earlier (1,5). It was stated that the character orange coty-
ledons is controlled by a dominant gene Orc (independent from I).
It is quite possible to suppose that this was a primary feature in
Pisum evolution. It was also stated that recessive allele i is
epistatic to both Orc and orc; genotypes Orc i as well as orc i
have green seeds.
Moreover, plants with orange-yellow Leaf color were observed
in segregating populations, but especially in the pure line
Wt 11145. Therefore the possibility of a modifying effect of ano-
ther color gene was considered. But in the locus/allelism tests
Wt 11145 (Orc) x Wt 10006 (o) and Wt 12134 (py) the F1 plants
had normal leaf color and orange cotyledons.
Simultaneously the carotenoid content of seeds was investi-
gated (3). Seeds of line Wt 11145 contained an additional carote-
noid fraction not found in the standard yellow seeds of Wt 3527.
Wt 11145, the type Line for Orc, was crossed with two tester
lines, WL 1267 and WL 1393 from the Weibullsholm Pea Collection,
to test for linkage. The F1 plants were normal and fully fer-
tile (normal karyotype). F2 generations of both crosses were
grown in the field in 1984.
Most markers showed an undisturbed monohybrid segregation,
including the gene Orc. Unexpectedly, the yellow-orange leaf
color segregated independently as a monogenic recessive
(Table 1A). For this character the name orange leaves (orl) was
proposed. From the F2 population Wt 11145 (Orc orl) x WL 1393
(orc Orl) recombinants Orc Orl and orc orl were selected.
Therefore two genes were found in accession Wt 11145.
An analysis of the dihybrid segregat ion produced another sur-
prise. In the population Wt 11145 x WL 1393 no evidence of lin-
kage was detected between Orc or Orl and the following markers: A
(chr. 1); K,Mifo,0h,S,Wb (chr. 2); B,St (chr. 3); N (chr. 4); and
Te,_U (chr. 5). However, both Orc and Orl showed linkage with D on
chromosome 1 (Table IB, Fig. 1). In the F2 population of
Wt 11145 x WL 1267, linkage between Orc and Orl was also detected
(Cr0=23.3+4.2). It has not been possible to determine the CrO
value with D because both parent lines have the same allele at D.
A second gene-marker is necessary to determine on which side of
the D locus the new genes are localized. In the D-segment Rup,
PNL Volume 19 198 7 RESEARCH REPORTS
67
Table 1. Phenotypic distribution in F2 population segregating for
Orange cotyledons and orange leaves from WT 11145 x WL 1393
A. Monohybrid F? segregation
D
382
d
102
Total
484
Chi-square
(3:1)
3.977
Orc
478
orc
160
638
0.002
Orl
490
orl
124
614
7.559
B. Joint segregation of Orc and Orl with D
Orc D
321
Orc d
40
orc D
61
orc d
62
Total
4 84
Joint
chi-square
84.81
Recomb.
fract.
24.21
S.E.
2.29
Orc Orl
337
Orc orl
122
orc Orl
153
orc orl
2
614
45.25
13.14
3.95
D Orl
274
D orl
90
d Orl
92
d orl
10
466
10.70
34.73
4.01
68 PNL Volume 19 1987 RESEARCH REPORTS
Table 2. Phenotypic distribution in F2 population segregating for
Orange cotyledons from Wt 11145 x Wt 11073.
A. Monohybrid F? - segregation
D
187
d
46
Total
233
Chi-square
(3:1)
3.43
Orc
159
orc
43
202
1.48
Orl
236
orl
62
298
2.79
Idh*
225.
idh
75
300
0.00
I
202
i
52
254
2.78
B. Joint segregation of Orc with D and Idh
D Orc
106
D orc
15
d Orc
17
d orc
16
Total
154
Joint
chi-square
18.9
Recomb.
fract.
26.2
S.E.
4.2
Orc Idh
111
Orc idh
47
orc Idh
40
orc idh
3
201
10.0
27.1
6.4
D Idh
131
D idh
56
d Idh
46
d idh
0
233
18.0
15.5
6.4
* - Because of co-dominant inheritance for 3:1 ratio in calculations
the fast-variant has been added to heterozygotes.
PNL Volume 19 1987 RESEARCH REPORTS
69
Sru, and Pur are mapped but the most useful variant may be the
isozymic locus Idh. Weeden and Marx (6) showed close linkage of
Idh with D and Pur with the suggestion that Idh is located between
these two. So a cross between Wt 11145 (Orc I orl D Idh-slow) x
Wt 11073 (orc i Orl d Idh-fast) was made at Wiatrowo. In F2
(field 1986) an undisturbed monohybrid segregation was found for
all genes (see Table 2A and the footnote). The electrophoretic
separation for Idh was done in the Biochemical Laboratory at
Wiatrowo.
The linkage of Orc with markers of chromosome 1 has been
confirmed, both with D and Idh (Table 2B). The CrO value for the
gene-pair Orc-D is almost identical with that from the previous
cross combination (Table IB). But despite undisturbed monohybrid
segregation there was no evidence of linkages for Orl in this
cross.
If Idh is located between D and Pur (6), then the data from
Tables IB and 2B suggest the following gene order: Pur - Idh - D -
Orc - Orl?
Fig. 1. The map distances in D segment on chromosome 1
Acknowledgement:
I wish to express my sincere gratitude to Mr. B. Wolko, M. Sc.
from Wiatrowo's Biochemical Laboratory, for electrophoretic sepa-
ration of Idh.
1. Blixt, S. and W. K. Swiecicki. 1983. PNL 15:9-10.
2. Ludwicki, J. and W. K. Swiecicki. 1983. PNL 15:41-42.
3. Ludwicki, J. and W. K. Swiecicki. 1985. PNL 17:51-53.
4. Swiecicki, W. K. 1982. Documentation of Genetic Resources:
A Model. S. Blixt, J. T. Williams, eds., NGB/IBPGR, Rome,
pp. 59-64.
5. Swiecicki, W. K. and S. Blixt. 1984. PNL 16:70-72.
6. Weeden, N. F. and G. A. Marx. 1984. J. Heredity 75:365-370.
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x Editor's Note: x
x Recently, while inspecting seed samples of about a dozen x
x USDA Plant Introduction (P.I.) accessions, I noticed that x
x P.I. 143484 (from Iran) has orange cotyledons. x
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