Independent Segregation Among 11 Gene Loci in Cucumber

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Cucurbit Genetics Cooperative Report 20:1-2 (article 1) 1997

Todd C. Wehner and J. S. Liu
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609

Research on morphological gene mutants of cucumber (Cucumis sativus L.) has resulted in 146 loci being identified in six linkage groups (3). Although many studies have reported linked genes, information about genes that are not linked also is useful in helping geneticists avoid making crosses to study traits that will not provide significant linkage data.

The objective of this study was to analyze segregation data for a series of traits that were found to be unlinked as part of previous linkage studies.

Four families were used to study linkage in six inbred lines: NCG-091 x WI 2757, NCG-093 x NCG-101, NCG-091 x Wis. SMR 18, and NCG-042 x WI 2757. Eleven genes were segregating in the four families (Table 1). The inbred lines used as parents were self-pollinated and grown in the greenhouse to verify and fix uniform trait expression. Seeds of the two parents, F1, F2, and BC1 to each parent were produced. There were 45 plants evacuated of each parent, 54 of the F1, 50 to 136 of the F2, and 28 to 72 of the BC1 per family. Seeds were planted in the greenhouse in flats of vermiculite to facilitate evaluation of the seedling traits. After seedling data were collected, plants were transplanted to the field for later evaluation of vegetative, flowering, and fruiting traits.

Data were collected on seedling traits before transplanting, on vegetative traits 30 to 40 days after transplanting, and on flowering and fruit traits 45 to 70 days after transplanting. Plants were evaluated for each trait using the published descriptions (2, 3), and the parental lines for comparison. Bitterfree (bi) was evaluated by tasting the cotyledons of single plants, rinsing the mouth with water after each plant, and eating a soda cracker after sampling bitter plants. Crinkled leaf (cr), glabrous-2 (gl-2), long hypocotyls (lh), and yellow cotyledon (yc-1) were evaluated at the seedling stage in flats. Plants were evaluated for femaleness (F), black spines (B), numerous spines (ns), orange fruit color (R), tuberculate fruit (Tu), and white fruit color (w) at the flowering and fruiting stages in the field.

Data were analyzed using the SASGENE, a SAS computer program for analysis of gene segregation and linkage relationships (1).

All of the 11 loci studies segregated properly as single genes. The 19 pairs of genes that could be tested all segregated independently (Table 2). Therefore, those gene loci should be located on separate chromosomes, or be at least 50 cM apart. Geneticists and plant breeders interested in those gene combinations can work without concern for having to break linkages.

Table 1. Gene designation and phenotypic description of cucumber cultivars and inbred lines tested in the gene linkage experiment.z

Trait (symbol)

Dominant

Recessive

SMR 18

WI 2757

NCG101

NCG091

NCG042

NCG093
Bitterfree (bi) Bitter Bitterfree + – + – + +
Black spines (B) Black White + – – – – +
Crinkled leaf (cr) Smooth Crinkled + + + + – +
Female (F) Gynoeccious Monoecious – + – – – +
Glabrous-2 (gl-2) Pubescent Glabrous + + + + – +
Long hypocotyls (lh) Short Long + + + + – +
Numerous spines (ns) Few Numerous + – + + + +
Orange fruit color (R) Orange Cream + – – – – +
Short petiole (sp) Long Short + + + + + –
Tuberculate fruit (Tu) Warty Smooth + – + + + +
White fruit color (w) Green White + + – + + +
Yellow cotyledon (yc-1) Green Yellow + + + + – +

z Genotype is listed as dominant (+) or recessive (-).

Table 2. Linkage relationships among 11 gene loci in cucumber as determined from F2 and BC1 segregation data.z

Gene pair

Generation

Phase

A_B_

A_bb

aaB_

aabb

Chi-square

df

Prob.

RF
bi–B F2 R 73 27 27 9 0.4 3 0.94 I
bi–lh BC1 C 14 14 21 19 2.2 3 0.52 I
Bi–ns F2 C 43 17 13 2 1.7 3 0.63 I
bi–R F2 C 31 17 17 7 5.4 3 0.14 I
Bi–w F2 R 69 31 31 5 4.5 3 0.20 I
cr–F F2 C 48 26 22 10 6.1 3 0.10 I
cr–ns F2 R 55 27 28 12 7.1 3 0.06 I
F–gl-2 F2 C 25 11 16 3 4.4 3 0.22 I
lh–ns F2 R 45 15 9 4 2.2 3 0.53 I
lh–R F2 C 38 21 10 3 5.7 3 0.12 I
lh–Tu F2 R 39 20 10 3 4.6 3 0.20 I
ns–gl-2 F2 R 26 11 9 4 0.7 3 0.87 I
sp–B F2 R 78 24 22 12 2.0 3 0.56 I
sp–w F2 R 71 31 29 5 3.5 3 0.32 I
w–B BC1 C 21 15 14 22 2.8 3 0.42 I
w–B F2 C 75 25 25 11 0.8 3 0.85 I
yc-1–cr BC1 C 16 19 18 19 0.3 3 0.95 I
yc-1–F BC1 C 14 11 16 13 1.0 3 0.81 I
yc-1–gl-2 BC1 C 9 7 9 3 3.4 3 0.33 I
yc-1–gl-2 F2 C 27 16 14 1 6.2 3 0.10 I
yc-1–ns F2 R 58 26 25 13 6.1 3 0.10 I

z Phase is coupling (C) or repulsion (R); all gene pairs segregated independently (I).

Literature Cited

  1. Liu, J. S., T. C. Wehner, and S. B. Donaghy. 1997. SASGENE: A SAS computer program for genetic analysis of gene segregation and linkage. J. Hered. 88: 253-254.
  2. Pierce, L.K. and T.C. Wehner. 1990. Review of genes and linkage groups in cucumber. HortScience 25:605-615.
  3. Wehner, T.C. 1993. Gene list update for cucumber. Cucurbit Genetics Coop. Rpt. 16:92-97.