V. rupestris
is considered more drought resistant than
V. ripar-
ia
(Padgett-Johnson
et al
., 2003). Drought-tolerant plants are
able to keep higher photosynthetic rates for extended period
at lowered cell volume and water potential (Proctor, 2000).
This is also supported by other studies that show drought-
tolerant plant species can maintain normal metabolism while
tolerating elevated ionic concentrations in the cytoplasm and
external environment (Schroeter
et al
., 1999). The
PRI
derived
from simulated EO-1 Hyperion data was consistent with leaf
level measurements even though we only considered the
spectral resolution of Hyperion sensor while radiometric
and spatial resolution, sensor geometry and signal-to-noise
ratio were not accounted for. This further confirmed that
PRI
is a useful indicator of plant physiological status at multiple
scales.
In general, other than previously mentioned leaf biochemi-
cal and biophysical parameters, the identified spectral regions
used to discriminate species and their genotypes are related to
foliar chemistries such as lignin, starch, protein, and cellulose
concentrations (Curran, 1989).
It is worth noting that the organisms used in the study
V.
riparia
and
V. rupestris
are closely related species that are
widely used in commercial vineyards as rootstocks. The
results showed that the species when used as rootstocks, but
not as genotypes within the same species, can be spectrally
discriminated from one another at canopy and satellite scales
indicating that satellite remote sensing can be used to monitor
crop health. Results also showed that remote detection of
V.
riparia
and
V. rupestris
species in its wild habitat are possible;
this is critical for finding native germplasm that can be used
in stress-tolerant plant breeding.
Conclusions
Spectral reflectance factor data acquired in the field together
with foliar properties were used to discriminate two impor-
tant rootstock grapevine species (e.g.,
V. riparia
and
V. rupes-
tris
) and their genotypes within the species. The main results
of this study can be summarized as follows:
1. Our results suggest that the spectral reflectance fac-
tor data of grapevine specie at leaf and canopy level
provided useful information to identify a set of optimal
bands significant for discrimination of two grapevine
species and among genotypes within species. The
wavelength regions include 350-1400 nm, 1480-1870
nm, and 2100-2400 nm at leaf level and 350-427 nm,
527-580 nm, 701-1023 nm, 1326-1884 nm, and 1979-
2419 nm at canopy level. The set of optimal bands
within
NIR
and
SWIR
regions were consistent at both
leaf and canopy levels with respect to its capability to
discriminate species. Although there were no spec-
trally separable bands among the V. riparia geno-
types at canopy level, we identified the 730-1450 nm
wavelength region has the potential to discriminate
genotype pairs of B 50 and Okoboji and GVIT 775 and
Okoboji at leaf level. Within
V. rupestris
, 1390-1585
nm and 1740-2470 nm wavelength regions were identi-
fied for B 38 and R-67-2 genotype groups and 990-2500
nm was identified for R-66-3 and R-67-2 genotype
groups as specific wavelength regions at leaf level. In
addition, at canopy level, 500-633 nm and 696-742 nm
was identified for B 38 and R-67-2 and 517-612 nm and
696-731 nm was identified for R-66-3 and R-67-2 as
optimal wavelengths regions.
2. The 1
st
- and 2
nd
-ds were vital for spectrally discrimi-
nating the grapevine genotypes especially in the
VIS
spectral region. This was mainly due to the pigment
concentration differences between species and among
genotypes. At leaf level, within
V. riparia
species
710-750 nm and 705-755 nm regions were found to be
important for discriminating the B 50 and Okoboji and
GVIT 775 and Okoboji groups , respectively. Similarly,
within
V. rupestris
species, the R-66-3 and R-67-2 group
was spectrally separable in 550-600 nm and 710-750
nm regions, and the R-66-9 and R-67-2 group was spec-
trally separable in the 510-612 nm region. At canopy
level, the 1
st
-d identified a new genotype group (e.g.,
R-65-44 and R-66-9) that was not detected at leaf level
and original raw spectra within
V. rupestris
.
3. Some of the foliar properties such as fresh and dry leaf
weight enabled us to differentiate two grapevine spe-
cies, while
PRI
not only showed great potential to dis-
criminate species but also identified spectrally separable
genotypes group pairs within the
V. rupestris
species.
4. This study is considered as a preparatory step towards
building a spectral library of the important wild grape-
vine species for Missouri’s thriving viticulture economy
using field collected reflectance factor data. Therefore,
these spectral data can be used as endmembers to iden-
tify natural populations of
V. riparia
and
V. rupestris
in
hyperspectral images for the purposes of locating wild
germplasm that could be used in breeding.
Acknowledgments
This research was supported by a grant from The Center for
Sustainability at Saint Louis University - “Sustainable Agri-
culture in a Changing Climate: A Multidisciplinary Approach
to Preservation and Comparative Genomics of Grapevines.”
The authors thank Jason Londo at the
USDA
Grape Germplasm
Research Unit in Geneva, New York for supplying the canes
that established the research vineyard. The authors are grate-
ful to Derek Lyle, June Hutson, Chis Hereford, and Andrew
Wyatt at the Missouri Botanical Garden who helped estab-
lish and maintain the research vineyard. Authors thank the
anonymous reviewers for their constructive comments.
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