Cucurbit Genetics Cooperative Report 12:9-10 (article 4) 1989
Cucumber Yield Improvement Through Breeding in the Southeast
U.S.A.
Todd C. Wehner
Department of Horticultural Science,
North Carolina State University, Raleigh, NC 27695-7609
It is of interest to cucumber breeders in the U.S.A. to
determine how much progress they have made in the improvement
of yield. yield is a complex trait, and is affected by sex
expression, disease resistance, and cultural practices,
as well as other factors. All of those have been improved
over the past decades by researchers in public and private
institutes.
In a survey of cucumber breeders made in 1987, the primary
objectives for trait improvement listed were yield, disease
resistance, fruit quality, and earliness/sex expression
(2). With emphasis on many traits, progress on any one will
be slow because selection for many traits simultaneously
reduces the selection intensity on each trait. In my recurrent
selection program, 14 populations are subjected to a 5%
selection intensity (20 families kept out of 400 tested)
for yield, earliness, quality, and disease resistance (mostly anthracnose, downy mildew and gummy stem blight).
Actual selection intensity is approximately 40% for yield
and 50% each for earliness, quality and disease resistance
(.05=.40 x .50 x .50 x .50). Thus, one would not expect
much progress to be made where many traits are being selected
simultaneously.
Nevertheless, progress has been made for yield, even after
accounting for the contributions of improvement in cultural
practices, sex expression and disease resistance. For example,
the cultivars released form the public breeding programs
run sequentially by Carroll Barnes, Richard Lower, and me
in the Carolinas have lead to continuously improved yield
even though many releases study was to estimate the improvement
made for yield in pickling cucumbers grown in the southeast
U.S.A.
Methods. Five cultivars which are most similar
in type (gynoecious hybrid pickling cucumbers with resistance
to the southern foliar disease) developed in the Carolinas
over the last 2 decades were grown in trials in Clinton,
NC under standard cultural practices (1). The trials were
run in the spring when there was no foliar disease load,
and in the summer when anthracnose, downy mildew and gummy
stem blight were moderate to severe. The trials were run
in 1981 through 1985 using 3 replications and 6 harvests.
No summer trials were run in 1982 and 1983.
Irrigation was used to supplement rainfall. Weeds, diseases
and insects were controlled as needed using labeled pesticides.
Weight of all fruits produced, regardless of size (most
being grade 2 and 3 with a diameter of 27 to 50 mm), were
summed over harvests to get total yield. Yield was regressed
on release date to determine the progress made per year.
Release date is not completely accurate in determining when
the material was developed. 'Raleigh', for example could
have been released in 1985 if it had been given top priority
in the program.
Results. It is interesting to note that the cultivars
do not keep the same rank for any one trial as the overall
mean (Table 1). In general, yield increased with each subsequent
release, with an average of 0.4 t/ha each year of breeding.
That yield progress was made even though other traits (such as fruit color, fruit shape, and length: diameter ratio)
were being improved.
Since the 5 cultivars were tested under the same cultural
practices, and had similar sex expression and disease resistance,
progress in yield must have been due to direct improvement
of the trait. Thus, I conclude that we have not hit a yield
plateau in cucumber breeding, but have been working on so
many traits that progress on each one of them is slow.
Table 1. Yield (t/ha) of disease resistant, gynoecious pickling cucumber hybrids grown in field trials (spring and summer) in Clinton, NC.z
|
|
1981 |
1982 |
1983 |
1984 |
1985 |
|
Release date |
Cultivar name |
Spr |
Sum |
Spr |
Spr |
Spr |
Sum |
Spr |
Sum |
Mean |
1969 |
Explorer |
19 |
20 |
29 |
34 |
31 |
22 |
38 |
37 |
28.8 |
1973 |
Carolina |
20 |
10 |
28 |
33 |
41 |
21 |
45 |
38 |
29.6 |
1975 |
Calypso |
21 |
21 |
32 |
34 |
42 |
30 |
41 |
41 |
32.7 |
1979 |
Regal |
24 |
18 |
40 |
38 |
41 |
27 |
48 |
41 |
34.6 |
1987 |
Raleigh |
26 |
26 |
37 |
34 |
33 |
27 |
52 |
48 |
35.5 |
z Data are means of 3 replications and 6 harvests.
Literature Cited
- Hughes, G.R., C.W. Averre and K.A. Sorensen. 1983. Growing
pickling cucumbers in North Carolina. N.C. Agric. Ext.
Serv. AG-315.
- Wehner, T.C. 1988. Survey of cucumber breeding methods
in the U.S.A. Cucurbit Genet. Coop. Rpt. 11: 9-12.
