August 2021 - 28

RESEARCH
Considering the benefits of far-red
for photosynthesis, a new term has
been introduced called extended
photosynthetically active radiation
(EPAR; λ = 400 to 750 nm).
In recent years, high-efficacy LED
fixtures have been replacing highpressure
sodium and fluorescent
lamps due to their energy savings.
Many of these lamps are composed
of blue and red diodes, resulting
in a magenta hue. These photons
correspond well to the original
definition of PAR and do well when
used as supplemental lighting
because the ambient sunlight
in the greenhouse will provide a
broad spectrum of light including
far-red. The problem arises when
propagation is separated from
the greenhouse where it relies on
artificial light as its sole source
of photosynthetic radiation. In
this situation, narrow waveband
red-blue lighting may not give
optimum plant photosynthesis or
leaf expansion.
Research conducted by the
USDA-LAMP Project (Lighting
Approaches to Maximize Profits)
at Cornell University has focused
on the neglected photons, like
far-red radiation. The objective of
the research was to investigate
the performance of lettuce and
basil seedlings when growing
in a propagation chamber with
and without far-red radiation. By
encouraging leaf expansion with
far-red, we hypothesized that
once transplanted the seedlings
would capture more light ultimately
leading to a larger harvested size.
EXPERIMENT ONE: LETTUCE
The first experiment was
performed in a growth chamber
with three cultivars of lettuce:
'Rex', 'Salanova Red Oak' and
cv. 'Rex'
'Grand Rapids'. Seedlings were
germinated in rockwool for two
days in perforated 1020 flats
with humidity domes. After
the initial germination, plants
were exposed to white LED light
(delivering a light intensity of
195 µmol·m-2
days (at which point they would only
receive 5 µmol·m-2
·s-1 far-red for
·s-1) supplemented
with far-red radiation (delivering
a light intensity of 5, 10, 20, or
30 µmol·m-2
·s-1) for 20 hours daily
for 10 days (Figure 1). Chamber
temperatures were set to 75º F
during the day and 66º F at night.
At 12 days after seeding, lettuce
plants with 30 µmol·m-2
·s-1
of
supplemental far-red intensity
had fresh weights that were 32%
greater than plants exposed to
only 5 µmol·m-2
·s-1 of far-red
(Figure 2). Leaf area was also
increased by 38% for plants
receiving 30 µmol·m-2
·s-1
. Plants
that were exposed to greater
intensities of supplemental far-red
radiation were larger and growing
faster than those with less in all
cultivars examined.
EXPERIMENT TWO: BASIL
The second experiment evaluated
basil seedling cultivars ('Genovese',
'Prospera' and 'Spicy Bush'). This
experiment was set up similar
to the first with one exception;
a duration component to the
supplemental far-red radiation
was incorporated. Basil seeds
were germinated for two days as
described previously in lettuce.
After germination, all seedlings
were exposed to the same lighting
treatments (white LED delivering a
light intensity of 195 µmol·m-2
+ 5, 10, 20, or 30 µmol·m-2
·s-1
·s-1
far-red radiation for 20 h-1
·d-1).
This time, basil seedlings were
exposed to these lighting treatments
for 10 days or only the first five
cv. 'Red Oak'
another five days). Growth chamber
daytime temperatures were set at
80º F and 75º F at night.
At 12 days after seeding,
basil seedlings were evaluated
for growth parameters. Fresh
weight for seedlings that received
30 µmol·m-2
·s-1 of supplemental
far-red radiation for five days were
25% greater than those that only
received 5 µmol·m-2
·s-1 far-red
(Figure 3). Furthermore, seedlings
that received 30 µmol·m-2
for 10 days had a 54% greater
fresh weight than 5 µmol·m-2
·s-1
far-red. Additionally, leaf area was
increased 19 and 41% for seedlings
exposed to five and 10 days of
30 µmol·m-2
·s-1 far-red, respectively
when compared to basil seedlings
·s-1 far-red
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10.5x7_CPP_MouseEars_.indd 1
cv. 'Grand Rapids'
.
5
10
µmol·m-2
20
·s-1
Figure 2. Seedling lighting treatments (5, 10, 20 or 30 µmol·m-2
28 AUGUST 2021 GPNMAG.COM
30
5
10
µmol·m-2
'Rex', 'Salanova Red Oak' and 'Grand Rapids' seedlings 12 days after seeding.
20
·s-1
30
5
10
µmol·m-2
·s-1
·s-1 supplemental far-red radiation) juxtaposed by treatment and cultivar. Left to right:
20
30

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August 2021

Table of Contents for the Digital Edition of August 2021