Effect of Unequal Competition from Bordering Rows on Pickling Cucumber Yield Trial Results

Cucurbit Genetics Cooperative Report 6:38-39 (article 18) 1983

Todd C. Wehner and Conrad H. Miller
Department of Horticultural Science, North Carolina State University, Raleigh, NC 27650

Plant breeders usually test new experimental lines for several years in replicated, multiple-harvest trials to determine whether the line should be released for production in a particular growing area. However, because of limitations on the amount of land available for trials, or on the amount of seed available for each experimental line, trials are often planted with unbordered plots. Thus, border rows are used only around the outside of the trial so that the lines are not being tested in monoculture, but rather in mixed plantings with different genotypes in adjacent plots.

Competition between different genotypes has been recognized as an important factor causing bias in yield trials of some crops, such as soybean (2). Unbordered plots of soybeans are acceptable for the northern U.S.A., but not for the southern U.S.A. where more foliage growth occurs (1). The objective of this experiment was to determine whether unequal competition occurs in pickling cucumber yield trials planted with unbordered plots.

Methods. Two hybrids (‘Calypso’ and ‘Southern Belle’) and an inbred (‘M 21’), all developed at North Carolina State University, were chosen as pickling cucumbers adapted to the area that had different growth habits. ‘Calypso’ is a tall, indeterminate cultivar, ‘M 21’ is a dwarf, determinate line, and ‘Southern Belle’ is a medium-size, indeterminate cultivar. The 3 lines were planted May 17, 1982 in 3-row plots 4.6 m wide and 6 m long in a randomized complete block design with 6 replications. The 3 lines were planted in 9 combinations of border and center rows. Thus, each of the 3 lines were planted in center rows with either ‘Calypso’, ‘Southern Belle’ or ‘M 21’ in the border rows to simulate bordered or unbordered plots. The center row of each plot was harvested 6 times (twice weekly) from June 24 through July 12. Fruit were graded into 4 sizes by diameter (No. 1 was <26mm, No. 2 was 27–38 mm, No. 3 was 39–50 mm, No. 4 was >51 mm), counted and weighed. Fruit value ($/ha) was calculated using $0.31, $0.14, $0.09, and $0.00 dollars/kg for grades 1, 2, 3 and 4 respectively ($14.00, 6.50, 4.00 and 0.00 dollars/cwt, respectively).

Results. Yield of the dwarf line, ‘M 21’, was significantly reduced when it was grown adjacent to rows of the tall cultivars, ‘Calypso’ and ‘Southern Belle’ (Table 1), Yield of ‘M 21’ was reduced 13% from that of bordered plots (‘M 21’ in the border rows) when the medium-size cultivar, ‘Southern Belle’, was grown in the border rows, and 20% when the large cultivar, ‘Calypso’, was grown in the border rows.

Table 1. Yield of 3 pickling cucumber lines in bordered (same line in border rows) and unbordered (different line in border rows) plots.z
Line planted in the 3-row plot		Total yield		Yield ($/ha) in harvest
Center	Borders	$/ha	q/ha	1	1–2	1–3	1–4	1–5
M 21	M 21	2511b	435b	277b	672b	1281b	1918b	2091b
	S. Belle	2192*	392ns	290ns	657ns	1119+	1649*	1814*
	Calypso	1999**	353*	271ns	555ns	980**	1505**	1647**
S. Belle	M 21	2161ns	495ns	623ns	1080ns	1498ns	1876ns	1973ns
	S. Belle	2054b	463b	584b	1052b	1442b	1788b	1870b
	Calypso	2118ns	506ns	557ns	1073ns	1444ns	1803ns	1929ns
Calypso	M 21	2014ns	492ns	503ns	1124+	1470ns	1782ns	1862ns
	S. Belle	1935ns	481ns	515ns	975ns	1315ns	1651ns	1762ns
	Calypso	1954b	475b	473b	990b	1356b	1661b	1771b
LSD (5%)		278	71	80	148	180	224	226
Mean (all treatments)		2104	454	455	909	1323	1737	1858
CV (%)		11	13	15	14	12	11	10
zVine lengths at first harvest for ‘M 21’, ‘Southern Belle’ (S. Belle) and ‘Calypso’ were 37, 47 and 67 cm, respectively. Data are means over 6 replications and 6 harvests.
ns,+,*,**Yield not significantly different from bordered plot (b), and significantly different at the 10, 5 and 1% levels, respectively.

Cumulative yield of unbordered plots of ‘M 21’ was reduced both in fruit value and in fruit weight, but only after the second harvest (of 6). That indicated that problems occurred only after the cultivars in the border rows grow large enough to compete with the dwarf plants in the center row of the plot.

Yields of ‘Calypso’ and ‘Southern Belle’ were not significantly affected by the presence of either tall or dwarf lines in adjacent rows. Thus, it appears that yield trials can be conducted with unbordered plots, provided that dwarf, determinate lines are tested in separate trials from tall, indeterminate lines.

Literature Cited

1. Hanson, W. D., C. A. Brim and K. Hinson. 1961. Design and analysis of competition studies with an application to field plot competition in the soybean. Crop Sci. 1:255–258.
2. Schutz, W. M. and C. A. Brim, 1967. Inter-genotypic competition in soybeans. I. Evaluation of effects and proposed field plot design. Crop Sci. 7:371–376.