Todd C. Wehner - Journal Articles
A Recessive Gene for Revolute Cotyledons in Cucumber
T. C. Wehner, J. E. Staub, and J. S. Liu
Journal of Heredity 89: 86-87 (1998)
An experiment was conducted to determine the genetics of the
revolute cotyledons trait in the cucumber inbred NCG-093 (short
petiole mutant). NCG-093 was crossed with inbred WI2757 to produce
F1, F2, and BC1 generations for evaluation. The F1 progeny had
normal cotyledons, and the segregation of the F2 progeny fit a
ratio of 3 normal : 1 revolute cotyledons. The BC1A (F1 x WI 2757)
progeny had normal cotyledons, and the segregation of the BC1B
(F1 x NCG-093) fit a ratio of 1 normal : 1 revolute cotyledons.
We concluded that revolute cotyledons in NCG-093 was conferred
by a single recessive gene, revolute cotyledons-2, for which we
propose the symbol rc-2. A mutant from 'Burpless Hybrid'
was previously described as having revolute cotyledons, controlled
by the rc gene. However, that mutant was apparently lost,
making it impossible to test allelism with the gene in NCG-093.
Cotyledon mutants are useful for linkage studies in cucumber
(Cucumis sativus L.), because they can be identified in
early stages of plant growth (Pierce and Wehner, 1990). Three
single-gene mutations of cotyledon shape have been reported previously:
rc, revolute cotyledons (Whelan et al., 1975) where the
cotyledons are cupped downwards and are shorter and narrower than
normal; sc, stunted cotyledons (Shanmugasundarum et al.,
1971) where the cotyledons are small and concavely curved; and
wy, wavy rimed cotyledons (Iida and Amano, 1990), where
the cotyledons have wavy rims and white centers. The revolute
cotyledons mutant apparently has been lost, but the other two
are available in germplasm collections.
We recently discovered a revolute cotyledons mutant in the self-pollinated
progeny of line NCG-093, which was derived from an unknown line
obtained from Russia. The mutant can be observed reliably as soon
as the cotyledons are fully expanded, and it has cotyledons whose
edges are curved partly downwards (revolute), especially when
the plants are young (Fig. 1). The size
and green color of the mutant cotyledons are the same as the normal
cotyledons of WI 2757 (Peterson et al., 1982). The true leaves
of the seedlings are also normal, and the cotyledons become difficult
to distinguish from normal cotyledons when the plants reach the
four-true-leaf stage.
Figure 1. Cucumber seedlings from the
F2 progeny of WI 2757 x NCG-093, six days after seeding in a greenhouse
flat, showing revolute cotyledons (rc-2) (top) and normal
cotyledons (bottom).
In order to study the inheritance of the revolute cotyledons
mutant, NCG-093 and WI 2757 were increased by self-pollination
and checked for uniformity of cotyledon type to develop parental
inbred lines. The two inbreds were crossed using hand pollination
in a greenhouse. The F1 progeny were self-pollinated to produce
the F2 generation, and also backcrossed to each parent to produce
the BC1A (F1 x WI 2757) and BC1B (F1 x NCG-093).
Seedlings were grown in flats of vermiculite on benches in the
greenhouse (temperature 20°C-35°C, with a 13-14 h photoperiod).
Six days after seeding, plants were evaluated for cotyledon phenotype
and classified as revolute or normal.
The cross of normal cotyledons WI 2757 with revolute cotyledons
NCG-093 produced all normal F1 progeny (Table 1). Segregation
in the F2 progeny fit the 3:1 expected ratio (P > .96), assuming
the trait was controlled by a single, recessive gene. Progeny
segregation in the BC1A and BC1B generations verified the inheritance
pattern for a single, recessive gene observed in the F2 progeny.
The BC1A (to NCG-093) segregated in a 1:1 ratio, with an adequate
fit to expected values (P > .05). No revolute cotyledons seedlings
were observed in BC1B (to WI 2757).
We concluded that there was a single recessive gene for revolute
cotyledons-2 in NCG-093 for which we propose the symbol, rc-2.
The mutant of Burpless Hybrid having revolute cotyledons described
by Whelan et al. (1975) was lost, so it was impossible to compare
the mutants for similarity, or to cross them to test for allelism.
Seeds of NCG-093 can be obtained from TCW.
References
Iida S and Amano E, 1990. Pollen irradiation to obtain mutants
in monoecious cucumber. Gamma Field Symp. 29:95-111.
Peterson CE, Williams PH, Palmer M and Louward P, 1982. Wisconsin
2757 cucumber. HortScience 17: 268.
Pierce LK and Wehner TC, 1990. Review of genes and linkage groups
in cucumber. HortScience 25: 605-615.
Shanmugasundarum S, Williams PH and Peterson CE, 1971. A recessive
cotyledon marker gene in cucumber with pleiotropic effects. HortScience
7:555-556.
Whelan EDP, Williams PH and Abul-Hayja A, 1975. The inheritance
of two induced cotyledon mutants of cucumber. HortScience 10:267-269.
From the Department of Horticultural Science, North Carolina State
University, Raleigh, NC 27695-7609 (Wehner); USDA/ARS, Department
of Horticulture, University of Wisconsin, Madison, WI 53706 (Staub);
and Department of Horticulture, Nanjing Agricultural University,
Nanjing, 210014, China (Liu). The use of trade names in this publication
does not imply endorsement by the NCARS or USDA of the products
named, nor criticism of similar ones not mentioned.
Received October 3, 1996
Accepted May 5, 1997
Corresponding Editor: Gary E. Hart
Table 1. Inheritance of revolute cotyledons (rc-2) in the cucumber
cross WI 2757 x NCG-093.
No. No. Expect-
ob- expect- ed
served ed ratio
Generation (N:R)a (N:R) (N:R) X2 P value
WI 2757 (PA) 44:0 44:0 1:0 - -
NCG-093 (PB) 0:16 0:16 0:1 - -
F1 54:0 54:0 1:0 - -
F2 122:41 122:41 3:1 0.002 0.96
BC1A 79:0 79:0 1:0 - -
BC1B 47:33 40:40 1:1 2.45 0.11
a R = revolute and N = normal cotyledons.
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