Download Genetic Control of Albinism in Pickerelweed

Journal of Heredity 2007:98(4):356–359
doi:10.1093/jhered/esm046
Advance Access publication June 29, 2007
ª The American Genetic Association. 2007. All rights reserved.
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Genetic Control of Albinism in
Pickerelweed (Pontederia cordata L.)
LYN A. GETTYS
AND
DAVID S. WOFFORD
Department of Agronomy Plant Genetics and Breeding, University of Florida IFAS, 304 Newell Hall,
Box 110500, Gainesville, FL 32611-0500.
Address correspondence to L. Gettys at UF/CAIP, 7922 NW 71 Street, Gainesville FL 32653, or e-mail: [email protected].
Pickerelweed (Pontederia cordata L.) is a diploid (2n 5 2x 5
16) perennial aquaphyte. Preliminary studies revealed that
a group of nonalbino pickerelweed plants maintained for
breeding and inheritance studies regularly produced albino
seedlings. The objective of this experiment was to determine
the number of loci, number of alleles, and gene action controlling albinism in pickerelweed. Five nonalbino parental lines
were used in this experiment to create S1 and F1 populations.
F2 populations were produced through self-pollination of F1
plants. Evaluation of S1, F1, and F2 generations allowed us
to identify a single diallelic locus controlling albinism in these
populations of pickerelweed, with albinism completely recessive to normal green leaf production. We propose that this
locus be named albino with alleles A and a.
Pickerelweed (Pontederia cordata L.) is a diploid (2n 5 2x 5 16)
perennial aquaphyte found in marshes, swamps, streams,
ditches, and shallow water along the margins of lakes and
ponds (Godfrey and Wooten 1979; Bell and Taylor 1982;
Tobe et al. 1998). The species is widely used as an ornamental
in water gardens and as a native plant in wetland mitigation
and restoration projects. Preliminary studies of pickerelweed
revealed that albino seedlings were regularly produced by
a group of normal (nonalbino) plants maintained for breeding and inheritance studies.
Albino plants lack chlorophyll and are nonphotosynthetic; as a result, these plants are unable to generate the energy
required to sustain life. Chlorophyll deficiencies may develop
as a result of point mutations (Svab and Maglia 1986) or deletions (Day and Ellis 1984), but the impact on plant survival is
the same—albinism is lethal in pickerelweed and other nonparasitic plant species. The phenomenon of albinism has intrigued researchers for years, and genetic control of the trait
has been described in a number of species (see Börner and
Sears 1986; Klekowski and Godfrey 1989). Albinism may be
controlled by a single locus or by multiple loci, but this lethal
trait is necessarily recessive to normal green leaf production.
Single gene control of albinism has been described in a number of species, including maize (Shull 1915; Neuffer et al.
1997), soybean (Barwale and Widholm 1987), and Western
356
white pine (Bingham et al. 1972), whereas two or more loci
control the trait in plantain–banana hybrids (Ortiz and
Vuylsteke 1994), Solanum chacoense (Birhman et al. 1994),
and groundnut (Coffelt and Hammons 1971, 1973; Dwivedi
et al. 1984).
There is no published information describing the genetic
control of albinism in pickerelweed. The objective of this experiment was to determine the number of loci, number of
alleles, and gene action controlling albinism in an experimental population of pickerelweed.
Materials and Methods
The plants used in this experiment were part of a population
maintained for genetic and breeding studies at the University
of Florida in Gainesville. All plants were grown in 1-l nursery
containers filled with a commercially available potting mix
amended with 10 g of controlled-release fertilizer per container. Plants were subirrigated and kept in a pollinator-free
glasshouse with air temperature maintained at 27 C (day)
and 16 C (night). Most plants produced more flowers when
grown under long days; therefore, supplemental lighting was
employed to artificially extend daylength to 16 h in this study.
Five parent plants (coded WS, WM, BS, BM, and BL)
were utilized in this experiment; all were nonalbino with normal green leaves. Parent WS was purchased from a commercial source, while the remaining parents were collected from
natural populations throughout southern Florida. Each collected parent was selected from a different geographically isolated location so it is unlikely they share a common ancestor.
Each parent was self-pollinated to create the S1 families WS
5, WM 5, BS 5, BM 5, and BL 5. Cross- and reciprocal
pollinations were performed between parents to create the F1
families WS BM, WS BL, WM BS, WM BL, BS BM, BS BL, and BM BL. Representative nonalbino samples were selected from each F1 family and self-pollinated to
generate F2 families. Cross- and reciprocal pollinations to
create F1 families were performed between December 2001
and April 2002, while self-pollinations of parents and F1
plants (to produce S1 and F2 families, respectively) were conducted between January and June 2003.
Brief Communications
All flowers in each inflorescence were pollinated using the
same pollen source. Anthers borne superior to stigmas were
removed to facilitate access to the stigmatic surface and to
prevent self-pollination when appropriate. Daily pollination
data were recorded on jewelry tags placed on each inflorescence. Each completed inflorescence was enclosed in a small
mesh bag and secured with a plastic-covered twist tie until
fruits were ripe (usually 23–30 days after completion of pollinations). Fruits were air-dried for ;7 days and then dried
floral tissue was removed from the enclosed seeds with a
rubber-covered rub board. Seeds were germinated under
;5 cm of water in glass half-pint (250 ml) bottles, with additional water added as needed to maintain a constant depth.
Germinated seeds were scored for leaf color (green or albino)
several times each week, and germination conditions were
maintained for a minimum of 8 weeks. Identification of seedlings expressing albinism was possible 2 or 3 days after radicle
emergence, as leaves of albino seedlings were pure white with
no traces of green (Figure 1). Affected seedlings were monitored for an additional 7–10 days after germination to ensure
that the classification of albinism was accurate. Selected nonalbino F1 seedlings were transplanted into 612 cell packs
filled with a commercially available potting mix and irrigated
with an automatic mist system for 3–4 weeks until the seedlings were ;30 cm tall. These F1 seedlings were transplanted
into 1-l nursery containers, sub-irrigated, and kept in a
pollinator-free glasshouse under the conditions described
above. Plants were grown to reproductive maturity and then
self-pollinated to produce F2 seeds. No maternal effects were
noted; therefore, data for each family were pooled within
each cross/reciprocal set. Data from S1 and F1 families were
used to develop a working model of genetic control of albinism in pickerelweed. Development of this model allowed
the assignment of genotypes to parents; the model was then
verified by analyses of F2 families. All data were analyzed
using goodness-of-fit (chi-square or v2) tests with Yates’ correction for continuity (Steel et al. 1997). A test for heterogeneity of the data for F2 families from different crosses was
performed to determine whether it was appropriate to pool
data for all F2 progeny.
Results and Discussion
All S1 progeny in the families BS 5 and BM 5 had normal
green leaves. The S1 family WS 5 produced 44 green and 22
albino seedlings, while WM 5 was composed of 50 green and
21 albino seedlings. The family BL 5 also segregated for albinism and had 77 green and 27 albino seedlings. The segregation patterns of the S1 families WS 5, WM 5, and BL 5
were not statistically different from a 3 green:1 albino ratio (P 5
0.1179, P 5 0.3730, and P 5 0.8208 for WS 5, WM 5, and
BL 5, respectively). All F1 progeny in 5 of the families had normal green leaves, while progeny in the F1 families WS BL and
WM BL segregated for albinism in patterns that were not statistically different from a 3 green:1 albino ratio (Table 1).
The simplest model that would produce the seedling types
recovered in these S1 and F1 families is a model with 2 alleles at
Figure 1. Albino seedling of pickerelweed.
one locus and green leaves completely dominant to albino
leaves. Genotypes were assigned to all 5 parents using the proposed model and segregation of S1 and F1 progeny. The parents
BS and BM were homozygous dominant (AA), while the
parents WS, WM, and BL were heterozygous (Aa).
Multiple nonalbino plants were randomly selected from
each of the 7 F1 families and self-pollinated to create segregating and nonsegregating F2 populations. Six of the 7 F2
population ratios conformed to those expected under the
proposed model, but populations from the family WS BL differed from the expected ratio (Table 2). The deviation
in this single family is small (P 5 0.04) and is most likely due
to sampling error, given the small number of F1 plants that
were self-pollinated and the strong support for the model
provided by the other families in this experiment.
Chi-square analysis of segregating populations revealed
that progeny in each population segregated in a manner that
did not differ from the expected 3 green:1 albino ratio. Tests
for heterogeneity among populations within each family were
not significant, so intrafamily data were pooled. These pooled
intrafamily F2 progeny segregated in a 3 green:1 albino ratio
as expected (Table 1). Heterogeneity chi-square analysis performed on all segregating F2 populations was not significant
(P 5 0.21), so all data for segregating F2 progeny were
pooled. These pooled progeny segregated in a manner that
was not significantly different from the expected 3 green:1
albino ratio (Table 1).
Conclusions
The results of this experiment suggest that albinism in these
populations of pickerelweed is controlled by 2 alleles at one
locus; gene action is completely dominant, with albinism recessive to production of normal green leaves. Our research
with these populations of pickerelweed revealed that selfpollination of homozygous plants (genotype AA) produced
only green-leaved offspring, whereas self-pollination of
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Journal of Heredity 2007:98(4)
Table 1. Classification of plants of pickerelweed in the F1 and F2 generations for green or albino leaf color. Cross- and reciprocal
pollinations are pooled within each parental set and are listed by the cross (e.g., observations attributed to WS BM include data from
WS BM and from BM WS). Chi-square values for segregating populations are based on a Mendelian 3:1 ratio
No. of plants
observed
Expected ratio
No. of plants
expected
Green
Albino
Green
Albino
v2
P
Parents
Generation
Genotype
Green
Albino
WS BM
WS BM
WS BM
WS BL
WS BL
WS BL
WM BS
WM BS
WM BS
WM BL
WM BL
WM BL
BS BM
BS BM
BS BL
BS BL
BS BL
BM BL
BM BL
BM BL
All seg.
F2, families.
F1
F2
F2
F1
F2
F2
F1
F2
F2
F1
F2
F2
F1
F2
F1
F2
F2
F1
F2
F2
Aa AA
AA 5
Aa 5
Aa Aa
AA 5
Aa 5
Aa AA
AA 5
Aa 5
Aa Aa
AA 5
Aa 5
AA AA
AA 5
AA Aa
AA 5
Aa 5
AA Aa
AA 5
Aa 5
149
609
317
70
191
1165
125
795
533
65
445
1043
141
1152
84
917
542
109
598
598
0
0
128
22
0
399
0
0
159
28
0
368
0
0
0
0
167
0
0
217
—
—
3
3
—
3
—
—
3
3
—
3
—
—
—
—
3
—
—
3
—
—
1
1
—
1
—
—
1
1
—
11058.25
—
—
—
—
1
—
—
1
—
—
333.75
69
—
1173
—
—
519
69.75
—
352.75
—
—
—
—
531.75
—
—
611.25
—
—
111.25
23
—
391
—
—
173
23.25
—
0.88
—
—
—
—
177.25
—
—
203.75
—
—
3.36
0.06
—
0.22
—
—
1.51
1.29
—
0.37
—
—
—
—
0.79
—
—
1.15
—
—
0.08
0.91
—
0.66
—
—
0.24
0.31
—
—
—
—
—
—
0.40
—
—
0.28
F2
Aa 5
4198
1438
3
1
4227
1409
0.80
0.37
heterozygous plants (genotype Aa) resulted in green and albino progeny in a Mendelian 3:1 ratio. We propose that this
locus controlling albinism in pickerelweed be named albino
with alleles A and a.
Single-gene control of albinism is not uncommon in the
plant kingdom. Shull (1915) described similar genetic systems
that control 2 types of albinism in maize—one producing
pure white seedlings and the other resulting in yellowish
white (chlorina) seedlings; both types of albinism are recessive, simply inherited, and controlled by a single diallelic locus. Neuffer et al. (1997) listed a multitude of other systems
(e.g., the white, luteus, and chlorophyll loci) that condition albinism in maize in the same manner. Barwale and Widholm
(1987) identified a chlorophyll deficiency in soybean that
is controlled by a single recessive gene, while Bingham et al.
(1972) reported that albinism in Western white pine is conditioned by a single recessive gene as well. Recessive lethal
alleles are routinely maintained in heterozygous individuals
within populations and typically have no deleterious effect
on the fitness of heterozygous plants; however, it is unclear
whether lethal recessive alleles provide any hidden benefit to
populations.
Table 2. Classification of segregating (S; F1 parent 5 Aa) and nonsegregating (NS; F1 parent 5 AA) F2 populations of pickerelweed
derived from self-pollination of F1 plants. Cross- and reciprocal pollinations are pooled within each parental set and are listed by the cross
(e.g., observations attributed to WS BM include data from WS BM and from BM WS)
No. of F2
population
No. of F2
population
Observed
Expected ratio
Expected
Parents
Genotype
S
NS
S
NS
S
NS
v2
P
WS BM
WS BL
WM BS
WM BL
BS BM
BS BL
BM BL
Aa AA
Aa Aa
Aa AA
Aa Aa
AA AA
AA Aa
AA Aa
10
22
9
17
0
5
11
10
3
6
7
12
7
9
1
2
1
2
—
1
1
1
1
1
1
—
1
1
10
16.67
7.5
16
—
6
10
10
8.33
7.5
8
—
6
10
0.00
4.20
0.27
0.05
—
0.08
0.05
0.99
0.04
0.61
0.83
—
0.77
0.82
358
Brief Communications
Acknowledgments
This research is presented by the senior author as partial fulfillment for the
Doctor of Philosophy degree and was supported by the Florida Agricultural
Experiment Station. Mention of a trademark or a proprietary product does
not constitute a guarantee or warranty of the product by the Florida Agricultural Experiment Station and does not imply its approval to the exclusion
of other products that may be suitable. We would like to thank David Sutton,
Paul Pfahler, and Eric Ostmark for their contributions to this experiment.
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Press.
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340:389–391.
Neuffer MG, Coe EH, Wessler SR. 1997. Mutants of maize. Plainville (NY):
Cold Spring Harbor Laboratory Press.
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Received July 26, 2006
Accepted May 14, 2007
Corresponding Editor: Susan Gabay-Laughnan
359