Inheritance of Fruit Firmness in Genetically Parthenocarpic Pickling Cucumbers

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Cucurbit Genetics Cooperative Report 17:35-37 (article 10) 1994

Kevin L. Cook and James R. Baggett, August C. Gabert
Department of Horticulture, Oregon State University, Corvallis, OR 97331, Sunseeds, Research Station, Brooks, OR 97305

Fruit firmness in genetically nonparthenocarpic cucumber has been reported as a highly heritable (h = 0.42-0.80) quantitative trait with additive gene effects accounting for 99% of the total genetic variation (Peterson et al., 1978; Smith et al., 1978). The number of genes involved is unknown and maternal effective not been important (Peterson et al., 1978). Studies on the inheritance of fruit firmness in cucumber have varied in experimental design, germplasm, and methods for firmness evaluation (Peterson et al., 1978; Smith et al., 1978). Reports on the inheritance of fruit firmness in parthenocarpic germplasm are not available. The objective of this research was to investigate the inheritance of fruit firmness in genetically parthenocarpic pickling cucumber.

Methods. A complete M x N mating pattern (Simmonds, 1979) between five nonparthenocarpic monoecious and four parthenocarpic gynoecious inbred lines was used to estimate general combining abilities (GCA) for fruit firmness in 1992. Parent lines with extreme differences in fruit firmness were chosen. Nonparthenocarpic lines were used as males and parthenocarpic lines were used as females to produce 20 F1 hybrids for evaluation. The male and female parents with the highest and lowest GCA, respectively, were chosen for population development and included the male parents ‘Clinton’ and ‘Armstrong Early Cluster’ (AEC) and female parents W744 and W11983.

Five families were created by crossing each parthenocarpic female with the nonparthenocarpic male parents and by crossing the two pale parents together. Reciprocal F1 , F2, and backcross generations were produced and, with the original parents and F1’s, were evaluated for fruit firmness in 1993 at Brooks, Oregon, using a complete randomized block design. Firmness measurements were made on No. 2 fruit (2.7 – 3.8 cm in diameter), one fruit per plant. Whole fruit and mesocarp firmness was measured with a W.C. Firmness Tester (FPT) with a 7.9 mm round tip and 2.0 mm flat tip plunger, respectively. Whole fruit measurements were taken in the center of the fruit with one side of the fruit flush with the pressure tester and the skin intact. A 2.0 cm wide slice of each fruit was used for measuring mesocarp firmness. Slices were uniformly taken from the stem end of the fruit adjacent to the FPT puncture. Mesocarp measurements were made by puncturing the fruit wall equidistant from the pericarp and endocarp.

Results. Whole fruit firmness was inherited in a quantitative fashion (Table 1). Inheritance appears additive, though some dominance for firmness may be present as F1’s consistently exceeded midparent values (Table 1). Material effects may be present in the ‘Clinton’ x AEC (P2 x P1) and W744 x ‘Clinton’ (P3 x P2) families as firmness was higher in F1 ‘s with ‘Clinton’ as the female (Table 1). Mesocarp firmness was also inherited quantitatively and appears completely additive with no material effects (Table 1).

Discussion. Three principal tissues contribute toward overall texture and firmness of cucumbers” exocarp (skin), mesocarp (carpel wall), and endocarp (seed cavity). Each tissue contains an inherent firmness which contributes directly to overall fruit firmness. A tissue may also contribute indirectly to fruit firmness through size, as thickness in the exocarp and mesocarp or diameter as in the endocarp. Fruit size and harvest date may also affect firmness. Samples were uniform for fruit size, but time of harvest varied by plot. Therefore, whole fruit firmness evaluations include all the tissue and harvest date components. The mesocarp firmness component does not appear responsible for the suspected maternal effects in whole fruit firmness. Future analysis may reveal that reciprocal cross differences for whole fruit firmness are not significant, 9or that other component which was or was not included in this study is responsible for the apparent differences. Dominance as a variance component in whole fruit firmness or parthenocarpic pickling cucumber will also be of interest.

Table 1. Whole fruit and mesocarp firmness of two genetically nonparthenocarpic pickling cucumber inbreds (P1, P2), two genetically parthenocarpic (P3, P4 ) inbreds, and five families developed from the respective inbreds.

Firmness (N)
Fruit
Mesocarp

Population

N
Mean
SD
Mean
SD
Armstrong Early Cluster (P1) 5 53.8 1.3 6.9 0.53
Clinton (P2) 17 80.1 7.6 8.7 0.97
W744 (P3 ) 17 66.7 6.7 7.0 0.67
WI1983 (P4 ) 19 75.6 7.6 8.2 0.56
P2x P1 23 82.3 8.0 8.3 0.97
P1 x P2 23 74.3 7.6 8.0 0.68
(P2x P1) x P1 56 67.6 8.9 7.6 1.17
(P2x P1) x P2 51 81.8 8.5 8.5 1.18
F2 123 72.9 9.3 7.9 1.33
P3 x P1 23 64.9 8.0 6.7 0.73
P1 x P3 19 64.5 8.5 7.1 1.00
(P3x P1) x P1 49 60.1 8.9 6.6 1.00
(P3x P1) x P3 56 70.3 8.5 8.0 0.92
F2 166 69.8 9.8 7.0 1.20
P4x P1 25 71.2 8.0 7.0 0.75
P1x P4 31 73.4 4.9 7.8 0.94
(P4 x P1) x P1 46 67.2 11.1 6.9 1.30
(P4x P1) x P4 – – – – –
F2 147 71.2 8.9 7.2 0.93
P3x P2 14 75.2 7.6 8.6 0.84
P2 x P3 20 83.6 7.1 7.9 0.97
(P3 x P2 ) x P2 51 79.6 8.5 8.6 0.93
(P3 x P2 ) x P3 52 72.1 8.5 7.7 0.78
F2 118 77.0 8.5 8.4 0.95
P4 x P2 23 81.4 7.6 8.4 0.81
P2 x P4 39 82.7 8.0 8.4 0.82
(P4 x P2 ) x P2 47 85.0 7.1 9.0 0.71
(P4 X P2) x P4 59 76.1 6.7 8.2 0.86
F2 131 77.4 8.5 8.5 1.10

Literature Cited

  1. Peterson, R.K., D.W. Davis, R.E. Stucker and W.M. Breene. 1978. Inheritance of firmness in raw cucumber (Cucumis sativus L.) fruit. Euphytica 27:233-240.
  2. Simmonds, N.W. 1979. Genetic aspects: populations and selection-combining ability. p. 110-116. In: Principles of Crop Improvement. John Wiley & Sons, Inc. New York.
  3. Smith, O.S., R.L. Lower, and R.H. Moll. 1978. Estimates of heritabilities and variance components in pickling cucumber. J. Amer. Soc. Hort. Sci. 103:222-22