Fruit Firmness and Quality of Parthenocarpic Versus Nonparthenocarpic Pickling Cucumber Cultivars.

Cucurbit Genetics Cooperative Report 17:30-34 (article 9) 1994

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

Parthenocarpic pickling cucumbers may be advantageous to conventional non-parthenocarpic cultivars due to their higher fruiting capacity and ability to produce fruit under poor pollination conditions (Baker et al., 1973; Pike and Peterson, 1969; Zwinkels, 1986). Texture or firmness of pickling cucumbers is used as a criterion of quality. Parthenocarpic pickling cucumbers have rated lower in texture than nonparthenocarpic types (Longan 1971; Pike and Peterson, 1969). In Europe, parthenocarpic pickling cucumber cultivars tend to soften and become hollow when preserved (Fritz and Weichmann, 1987). The objective of this research was to investigate the effect of genetic and non-genetic parthenocarpy on firmness and fruit quality of pickling cucumber.

Methods. Six genetically parthenocarpic and six nonparthenocarpic pickling cucumber cultivars were chosen for study. Seed was supplied by European (Nunheims, Bejo Zaden) and American (Sunseeds) seed companies and included firm and soft cultivars. Cultivars were gynoecious and either smooth (European type characterized by many small warts and spines) or spined (American type characterized by few large warts and spines). A split-plot design was used with cultivar as the main plot factor and presence or absence of row cover as the subplot factor. Main plot were arranged in a complete random block design with three blocks and bordered with a determinate pickling cucumber hybrid. The subplot factor was randomly assigned. Row covers were applied after flowering began and open and old flowers were removed. Drip irrigation was used. Three weekly harvests were taken. Harvests were initiated when the first oversize fruit (5.1 cm in diameter) was present. Fruit were hand harvested and graded by diameter size as recognized by the Pickling Cucumber Improvement Committee. Ten No. 2 fruit (2.7 – 3.8 cm in diameter) were randomly selected for evaluation. Data from the three harvests were pooled for a total of 30 fruit measured per plot. Whole fruit and mesocarp firmness was measured with a U.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 two cm wide slice of each fruit was used for measuring mesocamp 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, Brinestock samples were went to Steinfeld’s in Portland, Oregon, for preservation.

Results. Parthenocarpic cultivars were significantly softer than nonparthenocarpic cultivars (Tables 1 and 2). Cultivars within the parthenocarpic and nonparthenocarpic types were significantly different from one another (Tables 1 and 2). Fruit produced in the presence of row covers were significantly firmer than those which were produced in the absence of row covers (Tables 1 and 2). Cultivars which were firmer under the row cover tended to be firmer in the absence of row cover (Table 2). Fruit carpel separation and placental hollows occurred most frequently in genetically nonparthenocarpic cultivars grown under row covers (Table 3). Brinestock firmness complemented greenstock firmness for both cultivar and row cover treatments (Table 2).

Discussion. The effect genetic parthenocarpy had on firmness in this study, though significant in the analysis of variance, remains inconclusive due to the inherent nonrandom sampling of the twelve cultivars. Pollination appears to affect fruit firmness regardless of whether or not the cultivar is genetically parthenocarpic. Pollination had a greater softening effect on nonparthenocarpic cultivars than on genetically parthenocarpic cultivars. The effect of the row cover treatment on firmness, if any, could not be separated from the nonpollination effect. Fruit produced in the absence of row cover may be parthenocarpic or pollinated. The firmest fruits, in addition to possessing the highest frequency of fruit

defects. were genetically nonparthenocarpic and produced under the row cover. This interaction between row cover and cultivar type is difficult to explain since the row cover and nonpollination effect are confounded. However, one could hypothesize that pollination had a larger influence on fruit quality in genetically nonparthenocarpic types than genetically parthenocarpic types. A study to further investigate the effect of pollination on firmness of parthenocarpic and non-parthenocarpic cultivars was conducted in 1993 and included four treatments; row cover, no row cover, screen cage, and screen cage with honeybees.

Table 1. Analysis of variance for whole fruit and mesocarp greenstock firmness of six genetically parthenocarpic and six genetically nonparthenocarpic pickling cucumber cultivars grown in the presence or absence of floating row covers at Brooks, Oregon, 1992.

		Firmness (N)
		Fruit		Mesocarp
Variable	df	MS	F	MS	F
Block (Bl)	2	5.54	0.52NS	4.19	0.26NS
Parthenocarpy (P)	1	94.57	8.85**	976.56	59.45****
Cultivar (C) / P	10	124.05	11.61****	116.82	7.11***
Error (a)	22	10.68		16.43
Row cover (R)	1	104.27	12.26**	924.71	58.58****
P x R	1	2.18	0.26NS	109.47	6.95*
C/P x R	10	8.71	1.02NS	7.84	0.50NS
Error (b)	24	8.51		15.79
Total	71

*, **, ***, **** NS Significant at 0.05, 0.01, 0.001, 0.0001, or nonsignificant, respectively, by F tests.

Table 2. Mean whole fruit and mesocarp firmness before and after processing of six genetically parthenocarpic and six genetically nonparthenocarpic pickling cucumber cultivars grown in the presence or absence of floating row covers at Brooks, Oregon, 1992.

	Firmness (N)
	Greenstock				Brinestock
	Row Cover		No Cover		Row Cover		No Cover
Cultivar	Fruit	Meso.z	Fruit	Meso.	Fruit	Meso.	Fruit	Meso.
Genetically parthenocarpic
Nun 0136	87.6	7.27	82.7	6.95	77.0	8.57	73.8	8.14
Alstar	81.8	6.99	77.4	6.17	67.2	8.81	61.8	7.70
Anka	77.4	6.73	75.2	6.42	57.8	8.08	56.0	7.36
Parmel	76.5	6.87	76.5	6.44	63.2	7.29	57.8	6.89
Arena	74.3	6.49	74.7	6.23	59.2	7.71	60.0	7.06
Adonis	72.9	6.58	71.2	5.90	63.2	6.93	54.7	6.67
Mean	78.4	6.82	76.3	6.36	64.6	7.90	60.7	7.30
Genetically nonparthenocarpic
Furax	87.6	8.20	81.2	6.87	–	–	70.3	8.53
Calypso	85.8	8.40	81.8	7.65	–	–	75.6	8.75
Parker	79.6	8.31	81.4	7.26	–	–	68.5	8.50
Stimora	79.6	7.46	78.3	6.54	70.7	9.28	63.6	8.09
Ilonca	78.7	7.24	76.1	6.31	63.6	7.86	55.2	7.27
Alert	74.3	7.15	70.7	6.42	57.4	7.47	63.2	7.45
Mean	80.9	7.79	78.3	6.84	–	–	66.1	8.10

^z Meso. – mesocarp.

Table 3. Placental hollowsz (PH) and carpel separationy (CS) as a percent of the total number of fruit of six genetically parthenocarpic and six genetically nonparthenocarpic pickling cucumber cultivars grown in the presence or absence of floating row covers at Brooks. Oregon, 1992.

	Row Cover		No Cover
Cultivar	% PH	% CS	% PH	% CS
Genetically parthenocarpic
Nun 0136	8	0	10	0
Alstar	4	0	10	2
Anka	12	3	12	2
Parmel	21	6	29	6
Arena	32	5	20	0
Adonis	19	5	14	4
Mean	16	3	16	2
Genetically nonparthenocarpic
Furax	20	9	20	2
Calypso	38	0	17	1
Parker	66	26	22	2
Stimora	31	5	19	2
Ilonca	44	6	21	2
Alert	58	18	26	3
Mean	43	11	21	2

^z Placental hollows (PH) = one or more holes present in the mesocarp.

^y Carpel separation (CS) = separation of fused carpels forming a hollow through part or the entire length of the fruit.

Literature Cited

1. Baker, L.R., J.W. Scott and J.E. Wilson. 1973. Seedless pickles – a new concept. Michigan State University Res. Rpt. 227.
2. Fritz, D. and J. Weichmann. 1987. Nitrogen fertilization and texture of parthenocarpic pickling cucumbers. Acta Horticulturae 194:133-140.
3. Longan, B.J. 1971. The effect of firming agents on quality of parthenocarpic and normal fresh-pack pickles. Masters thesis. Texas A&M University. P. 76.
4. Pike, L.M. and C.E. Peterson. 1969. Inheritance of parthenocarpy in the cucumber (Cucumis sativus L.). Euphytica 18:101-105.
5. Zwinkels, L.A.M. 1986. The present situation and future development in breeding of parthenocarpic pickling cucumber. Acta Horticulturae 220:129-133.