International conference on
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN
REGION UNDER CHANGING CLIMATE
Nondestructive evaluation of leaf chlorophyll content by multiple
regression analysis of RGB image components: a case study of
Quinoa and Amaranth grown under different irrigation strategies
Riccardi M., Mele G., Pulvento C., Lavini A., d’Andria R., Jacobsen S.E.
By: Dr. Giacomo Mele
CNR- Institute for Agricultural and Forest Mediterranean Systems (ISAFoM)
10–15 March, 2013
Agadir, Morocco
Introduction
•
Leaf chlorophyll content (Chl) is a key indicator of the
physiological status of a plant;
•
Chl content is linked directly to photosynthetic potential and
primary production;
•
Chl gives an indirect estimation of the nutrient status as
considerable leaf N is incorporated in that pigment;
•
Drought stress is one of the environmental factors affecting
photosynthesis and Chl content. Chl destruction, as often
observed under water stress, is deleterious causing chlorosis,
reduction in both growth and yield.
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Aim
•
In agriculture, digital image analysis has been used to
characterize color in apples, distinguish weeds from crops,
identify storage associated color change in chickory and apple,
to evaluate senescence rates in spring wheat and durum wheat
and to evaluate Chl a content in algae.
•
The aim of the present work was to evaluate the possibility to
use the information contained in RGB digital images as an
alternative choice for a fast, inexpensive and nondestructive
prediction of leaf Chl content in Quinoa and Amaranth leaves.
•
The performance of the proposed method, to estimate leaf Chl
content, was compared to the most used field method (SPAD).
Both methods calibrated with the measurements of Chl content
as determined with a standard method.
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Chl determination
Leaf Chl concentration is traditionally
determined by using .wet chemical methods
(destructive, expensive, laborious and time
consuming).
The Minolta SPAD-502 leaf Chl meter is one
of the most used hand-held Chl meter
suggested for the rapid and nondestructive
assessment of Chl content.
SPAD measures the absorbance of a leaf at 650 and 940 nm and
calculates a SPAD value
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
RGB digital images method
RGB
Components
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
RGB components
A color in the RGB color model is described by indicating how
much of each of the red, green, and blue is included. The color is
expressed as an RGB triplet (r,g,b), each component of which can
vary from zero to 255 in 24bit images (3x8bit channels) providing a
spectrum of 2563=224=16777216 colors.
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Plant material
Quinoa
Amaranthus
Genotypes
Chlorophyll ( µ g cm -2 )
Min
Max
A7
1.5
24.0
A12
1.0
20.0
A14
2.0
25.1
Titicaca
1.2
40.4
Blanquita
0.6
30.1
Jancha grano
1.9
55.6
Jujui Rosada
3.1
31.2
Kurmi
1.2
42.0
Puno
0.7
37.2
Real
1.2
40.4
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Methodology
C
A
L
I
B
R
A
T
I
O
N
60 leaves of each Quinoa and Amaranth genotype
Chl content determination
SPAD readings
Chl estraction
(standard method)
Relationship SPAD number vs.
laboratory determined Chl
determination of
RGB components
Relationship (single and all)
RGB components vs. laboratory
determined Chl
20 leaves of each Quinoa and Amaranth genotype
VALIDATION
NE
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Models calibration
Amaranth (180 leaves)
Quinoa (420 leaves)
0.82
0.85
SPAD
0.91
0.91
1 RGB
component
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Models calibration
Amaranth (180 leaves)
R2=0.93
Quinoa (420 leaves)
R2=0.93
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Model Calibration
Amaranth
Quinoa
Chl = aSPAD2 + bSPAD +c
Amaranth
Quinoa
Chl = exp-aG
Chl = exp-aR
Ln(Chl) = aR + bG + cB + d
NO DIFFERENCES IN PARAMETERS BETWEEN
DIFFERENT GENOTYPES IN EACH SPECIE
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Validation - RMSE (predicted vs, measured)
2.52
5.07
1.97
2.87
1.22
2.08
A
m
a
r
a
n
t
h
60
L
e
a
v
e
s
Q
u
i
n
o
a
140
L
e
a
v
e
s
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Noise equivalent (NE)
1) NESPAD ΔChl = RMSE(SPAD vs.Chl)/[d(SPAD)/d(Chl)]
2) NER or G ΔChl = RMSE(R or G vs.Chl)/[d(R or G)/d(Chl)]
3) NERGBΔChl = RMSE(RGB vs.Chl)/[d(RGB)/d(Chl)]
Amaranth
Quinoa
G
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Case study
Amaranth (A12)
Beginning of
Flowering
Chlorophyll content (µg cm-2)
30
a
25
a
Flowering
50%
b
b
20
c
c
Panicle
formation
15
Milky grain
a
b
10
5
Quinoa (cv. Titicaca)
c
a
Drought
grain
100
50
b
c Maturity
6 leaves
25
0
29
•
•
48
64
77
DAS
82
92
102
In Amaranth plants Chl decreased with the decrease of water
applied from DAS 64 after the first irrigation
In Quinoa plants Chl decreased with the decrease of water
applied only for 25 treatment (DAS 64) but after a period of
adaptation Chl of 25 treatment was higher than 100 and 50
(DAS 82)
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE
Conclusions
•
RGB digital image method was able to estimate Chl content
more accurately than SPAD (higher R2 and lower RMSEP
values)
•
The multi regression model of all RGB components more
accurately predicted total chlorophyll content respect to single
regression
•
SPAD meter showed a reduced accuracy when Chl content was
above 10 and 23 µg/cm2 for Amaranth and Quinoa respectively
•
The proposed leaf image analysis method provides a quick,
nondestructive and reliable quantitative measure of the
chlorophyll content in the whole range of chl contents, offering
good results for Quinoa and Amaranth
SUSTAINABLE WATER USE FOR SECURING FOOD PRODUCTION IN THE MEDITERRANEAN REGION UNDER CHANGING CLIMATE