Cuphea Production and Management - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 297

well under the mild temperate summer climate and relatively fertile soils of the US
Corn Belt region. In west central Minnesota, C. wrightii , C. lutea , C. calophylla ,
C. carthagenensis , C. koehneana , C. palustris , C. procumbens , C. tolucana , and
C. llavea have been grown, and they all have flowered and produced seed. Forcella
et al. [ 25 ] studied the growth, seed yield, and oil characteristics of PSR23 cuphea
grown from southwestern Iowa to northwestern Minnesota along a latitudinal
transect of 41-49 N. In the absence of drought, vegetative growth of plants did
well all along this transect. However, seed yields, oil content, and capric acid
content, the major fatty acid of PSR23 oil, were all greater in Minnesota than in
Iowa and tended to increase with latitude up to 45 N. Increases in seed yield and oil
content were best associated with decreased air temperature, particularly during
midsummer to late summer when plants were flowering and setting seed. Similar
results were reported by Kim et al. [ 70 ] who studied PSR23 and another related
cultivar HC-10 at field sites in Iowa, Illinois, Minnesota, and North Dakota. In this
study, growth and biomass yield and seed yield and oil content were distinctly
greater in Minnesota and North Dakota than Iowa and Illinois for both cultivars.
Soil environment was also studied, but the results were generally better associated
with climate than soil environment. Three wild species ( C. viscosissima , C. lutea ,
and C. wrightii ) that show good potential for domestication were also included in
the study and were found to perform equally well across all four locations.
Because field studies indicated that growth of cuphea under high temperatures
might be detrimental to its development, Gesch and Forcella [ 65 ] studied cuphea's
response to temperature under controlled environment conditions. Plants were
subjected to day/night temperature regimes of 18/12, 24/18, and 30/24 C with a
16 h photoperiod. The study confirmed that vegetative growth adapts well to a wide
range of temperature. In part, this was due to cuphea's ability to acclimate its
photosynthetic machinery to compensate for different growth temperatures.
Cuphea's vegetative growth was greatest under the 24/18 C treatment, and the
optimum temperature for leaf photosynthesis was predicted to be 23 C based on its
quadratic response to temperature. Conversely, reproductive growth (i.e., flowering
and seed set) was greatest at 18/12 C and declined linearly with increased growth
temperature [ 65 ]. The growth rate of reproductive tissues was 18 % less under
24/18 C than at 18/12 C, and reduced reproductive growth was mainly due to
reduced number of flowers and fertilized seeds per capsule [ 65 ]. By comparison, the
optimum temperature for cuphea's (PSR23) reproductive growth is much lower
than rice ( Oryza sativa L . ) and corn ( Zea mays L.) and slightly higher than that of
spring wheat ( Triticum aestivum L.) which is 20-25 C during the day [ 71 ]. Other
germplasm lines developed from the cross of C. viscosissima and C. lanceolata are
likely to respond to temperature similarly to PSR23, although further research is
needed to verify this.
Although PSR23 cuphea has indeterminate growth, about 110-120 days of
growth, from the time plants emerge to harvest, are typically required to reach
optimum yield maturity in the northern Corn Belt region. When planted in early to
mid-May, flowering generally begins in mid-July to late July and peaks in
mid-August. After this, cuphea will continue to flower at a minimal rate until killed
by a hard frost. Early field studies with PSR23 cuphea indicated that approximately