Cucurbit Genetics Cooperative Report 10:27-28 (article 17) 1987
Value of 12 Season-Location Combinations for Cucumber
Yield Trials in North Carolina
Department of Horticultural Science, North Carolina State University, Raleigh,
New experimental breeding lines of pickling and fresh-market cucumbers
are tested in many North Carolina environments before release as cultivars
for use in the state. The early stages of testing are most efficiently done
using 2 to 3 replications per entry harvested once-over when the check cultivar
has 10% oversized fruits (3, 4). The optimum plot size for such trials is
approximately 1.5 x 1.5m (2).
The most efficient component of environment to use as the factor for
repetition is years, followed by seasons, locations, and, finally, replications
(5). However, additional years of testing add greatly to the time required
to complete a cycle of selection and pollination. Therefore, it may be best
to use season-location combinations as the method of sampling the environment
before releasing an experimental. line as a new cultivar. A number of methods
have been proposed for choosing the ideal environment (1). The best environments
for testing new lines for use in a region are representative of the region,
and provide maximum separation of the lines involved. In other words, a
good environment should be correlated with the mean of all environments,
and have a large standard deviation among line means.
The objective of this study was to determine which season-location combinations
make the best testing environments for use in initial testing of experimental
lines in North Carolina.
Methods. A random set of hybrids, inbreds, cultivars and experimentals
was tested in North Carolina for yield and quality. The 44 lines were chosen
to represent new and old, tall and dwarf, resistant and susceptible (to
southern foliar diseases), and pickling and fresh-market types (22 lines
Plots were 25-plant rows 1.5 m long and 1.5 m apart seeded on raised
beds. The environments consisted of 2 years (1984, 1985), 3 seasons (spring,
summer, fall), 4 locations (Clayton, Clinton, Castle Hayne and a stress
field in Clinton), and 2 replications. The stress environment consisted
of heavier soil and only half the irrigation, fertilization and pesticide
applications given the main Clinton location. Yield was measured as fruit
number in a single-harvest trial. Harvest was made when 10% of the fruits
were oversized in the check plots ('Calypso' for pickling and 'Poinsett
76' for fresh-market genotypes).
Results. The correlations for line performance at each of the
12 seasonlocation environments with line performance over all environments
were all significant at the 1% level (data not shown). However, coefficients
of determination (r2) and standard deviations for line means
([sigma]L) were highest at the Clinton and Stress locations for
all seasons tested (Table 1). No other season-location combinations had
both high r2 and high [sigma]L.
Therefore, a test involving 2 plots per line could be run efficiently
using a spring season at the Clinton and Stress locations (in May and June),
leaving enough time to intercross or self-pollinate the best lines before
the end of the growing season (in July through September).
Table 1. Coefficients of determination (r2) and standard deviations
of line means ( [sigma]L) for 16 location-season combinations
evaluated for usefulness as yield trial environments in North Carolina.
z Data are from 1984 and 1985 tests of 22 pickling and 22 fresh-market
y Stress location was at Clinton, with low inputs of fertilizer, pesticides
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