Once-over Harvest Yield of Cucumber Hybrids Made with a Determinate Parent

Cucurbit Genetics Cooperative Report 19:17-20 (article 6) 1996

Todd C. Wehner
Department of Horticultural Sciences, North Carolina State University, Raleigh, NC 27695-7609

Richard L. Lower
Department of Horticulture, University of Wisconsin, Madison, WI 53706

Cucumber (Cucumis sativus L.) plant architecture offers new ways of improving cultivar performance in once-over harvest. Besides the indeterminate (normal) type, two plant types that have ben used successfully in cucumber breeding are the determinate (dede genotype) and the small leaf, multiple branched type originating from LJ90430, an accession from India belonging to C. sativus var. hardwickii (R.) Alef. Although C. s. var. hardwickii has small, bitter fruits with little known horticultural value, the multiple branching, multiple fruiting habit is interesting to plant breeders (Horst and Lower, 1978). In previous plant breeding work, our experience has been that a determinate male parent can improve the yield of the hybrid significantly. Since the determinate trait is recessive, the positive effect on the hybrid may be due to other genes that just happened to be in the determinate inbreds being used, or to additive effects in the de allele (the Dede heterozygote having some of the useful traits of the dede homozygote). The research of Lower and Den Nijs (1979) on lines isogenic for determinate (DeDe) and dede) and compact (CpCp and cpcp) offers some insight to the heterotic effects of determinate type in hybrids in heterozygous at the de locus.

The determinate trait is controlled by a single, recessive gene named de (Denna, 1971; George; 1970; Hutchins; 1940; Odland and Groff, 1963; Robinson et al., 1976). there are modifier genes involved with the determinate type, and early flowering causes greater expression of the dwarf, determinate character than late flowering. Plant homozygous recessive for de have short vines because the apical meristem changes into floral buds (Hutchins, 1940), Originally, breeders used the determinate plant type hoping that the smaller vines would improve yield by providing a higher optimum planting density than for the normal type. However, in a two year, multiple harvest trial with 3 planting densities (24, 36, and 72 thousand plants/ha (TPH)), both determinate ‘Spacemaster’ and indeterminate ‘Pacer’ had an optimum density above 72 TPH for yield (Munger et al., 1982). Optimum density of pickling cucumbers tested at 4 planting densities (65, 129, 258, and 516) for yield ($/ha) in multiple harvest trials was around 129 TPH for the two determinate cultivars (Wehner and Miller, 1987). Therefore, the optimum density for the determinate plant type was not higher than for the indeterminate plant type.

A major advantage of C. s. var. hardwickii has been its high combining ability for fruit number in crosses with indeterminate C. sativus inbreds (Kupper and Staub, 1988). Unfortunately, determinate inbreds crossed to LK 90430 produce an unexpected F2 progeny, with the determinate, multiple-branched combination missing or deficient in number (Delaney and Lower, 1984, 1985). Thus, it may be difficult to develop inbreds with both the determinate and the multiple-branched habit.

The objective of this study was to compare cucumber hybrids involving a determinate male parent crossed with indeterminate, determinate, or C.s. var. hardwickii female parents for yield in once-over harvest. Additionally, we were interested in measuring the effect of planting density, and whether the hybrids had different optimum densities for maxi um yield.

Methods. The experiment was conducted at the Agricultural Research Station near Hancock, Wisconsin. Recommended cultural practices were used, including raised beds and overhead irrigation. The experiment was a randomized complete block design with 3 replications. Treatments were 3 hybrids (indeterminate, determinate, and C.s. var. hardwickii – all crossed with a common determinate) and 4 densities (26, 52, 108, and 215 TPH).

Plots were 3 rows wide and 3.1 m long, with 1.5 m alleys separating their ends. Rows were 0.77 m apart center to center. The center row was harvested once-over when ‘Calypso’ check plots had 10% oversized (50 mm diameter) fruits. There were adequate staminate flowers and bees available for pollination. No pollination problems (excessive crooked or nubbin fruits were observed.

Plots were seeded on 12 June 1986 with 2 seeds per hill. Plots were thinned to the correct stand two weeks later, and all plots (center row only) harvested on 5 August. Data were collected on number of plants, total fruits, cull fruits, and oversized fruits per plot. From those data, we calculated total yield (total fruits per hectare), number of fruits per plant (total fruits per plot / total plants per plot), marketable yield (total minus cull fruits/ha), early yield (oversized fruits/ha), and percentage culls (culls out of total).

Analysis of variance was performed on plot data and regression was used to determine optimum density for maximum yield.

Results. We were most interested in marketable yield, although the conclusions would have been the same for total yield, since % culls was not a significant effect over density or plant type. Total and marketable yield were highly correlated, and were maximized at the highest density tested (215 TPH) for the hybrids made with the determinate or C.s. var. hardwickii female parent (Table 1). For the hybrid made with the indeterminate female parent, total and marketable yield were maximized at 108 TPH.

Early yield was maximized at 108 TPH for the hybrids made with indeterminate and determinate female parents, and at 52 TPH for the hybrid made with the C.s. var. hardwickii female parent. The hybrid made with C.s. var. hardwickii was later than the other two hybrids reflecting the late flowering habit of the C.s. var. hardwickii female parent. Growers willing to wait one or two weeks longer for harvest may be able to obtain significantly higher yields, especially with C.s. var. hardwickii plant types.

As expected, fruits per plant decreased as plant density increased (Table 1). However, the drop in number of fruits per plant (2.4 to 3.4 at 26 TPH to 0.9 to 1.2 at 215 TPH) was more than compensated by the increase in plants per hectare.

The determinate x determinate hybrid has a high total and marketable yield, but the C.s. var. hardwickii x determinate hybrid was slightly higher. Although the differences among plant types were not significant, this test does demonstrate the value of determinate and C. s. var. hardwickii inbreds for producing elite hybrids for use by the processing industry in once-over harvest.

Conclusions. Marketable yield was maximized at about 215 TPH for the determinate x determinate and C.s. var. hardwickii hybrids, and at 108 TPH for the determinate x indeterminate hybrid. Maximum yield occurred at the highest or second highest plant density despite the fact that the number of fruits per plant dropped to their lowest values. The C.s. var. hardwickii plant type had significantly lower early yield than the other two plant types, but total yield was the highest of the three types. Since C. s. var. hardwickii does require more time to reach maturity, growers must be willing to wait for the fruits to reach proper size.

The experiment involved only one hybrid of each plant type tested at a single location and year, so caution must be used in interpreting these results. However, determinate and C.s. var, hardwickii plant types appear to offer promise over the indeterminate type as parents for hybrid production using high yielding determinate male parents.

Table 1. Fruit production (total yield, total fruits per plant, marketable yield, early yield, and percentage culls) from hybrids made with an indeterminate, determinate or C.s. var. hardwickii female, parent crossed with a determinate male parent^z .

Female parent Plant type	Plant density	Total yield	Fruits/plant	Mark yield	Early yield	% culls
Indeterminate	26	87.5	3.4	84.6	7.2	3.3
Indeterminate	52	149.2	2.9	134.9	11.5	10.2
Indeterminate	108	202.3	1.9	180.8	12.9	11.1
Indeterminate	215	193.7	0.9	173.6	11.5	11.3
Determinate	26	83.2	3.2	78.9	4.3	4.6
Determinate	52	116.2	2.3	110.5	11.5	4.3
Determinate	108	202.3	1.9	183.6	15.8	9.4
Determinate	215	246.7	1.1	225.2	7.2	9.1
Hardwickii	26	61.7	2.4	58.8	0.0	5.3
Hardwickii	52	91.8	1.8	86.1	5.7	6.5
Hardwickii	108	203.7	1.9	189.4	1.4	6.9
Hardwickii	215	262.5	1.2	249.6	0.0	4.7
Mean		158.4	2.1	146.3	7.4	7.2
CV (%)		27	26	28	78	70
F ratio: Type		NS	NS	NS	**	NS
F ratio: Density		**	**	**	NS	NS
F. ratio: TxD		NS	NS	NS	NS	NS
Correlation (total vs. fruits/plant) r = -0.41
Correlation (total vs. marketable) r = 0.99**
Correlation (total vs. early) r = 0.15NS
Correlation (total vs. % culls) r = 0.1NS

^zData are means of 3 replications of once-over harvest from the center row of a 3-row plot.
Density, total, marketable, and early yield are in thousands per hectare.
*,**,NS Indicates significant at the 5% or 1% level, or not significant, respectively.

Literature Cited

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2. Delaney, D.E. and R. L. Lower. 1985. Segregation of the determinate (de) allele in crosses between Cucumis sativus L.. and C. sativus var. hardwickii R. (Alef.) Cucurbit Genet. Coop. Rpt. 8:2-3.
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12. Wehner, T.C. and C.H. Miller. 1987. Optimum plant density for multiple-harvest yield of determinate and indeterminate cucumbers. Cucurbit. Genet. Coop. Rpt. 10:29-30.