Journal
Journal of Applied Horticulture, 14(2):114-117, 2012
Appl
Relationship of nutritional status of field grown Thompson
Seedless grapevines with powdery mildew incidence
Jagdev Sharma*, A.K. Upadhyay, Indu S. Sawant and S.D. Sawant
National Research Centre for Grapes, Pune (MS)-412307, India. *E- mail: jsharmagrape@yahoo.com
Abstract
Relationship between nutritional status of open field grown Thompson Seedless grapevines and powdery mildew incidence was
studied for two years at two growth stages. Amongst different nutrients, potassium showed highest degree of significant and negative
correlation with the powdery mildew disease rating (r= -0.817 and -0.875) at two growth stages. Regression analysis also revealed
the importance of potassium nutrition in powdery mildew incidence. During the first year of the study, N, P, K, Ca, Mg and Na when
regressed together accounted for 82.7 % (R2 = 0.826) variation in disease incidence and potassium alone accounted for 66.8 % variation
in disease incidence (R2 = 0.667). During the second year N, P, K, Ca, Mg and Na when regressed together accounted for 85.7 % (R2
= 0.857) variation in disease incidence and potassium alone accounted for 76.6 % variation in disease incidence (R2 = 0.765).
Key words: Powdery mildew, nutritional status, grapevines, potassium, disease incidence
Materials and methods
Powdery mildew is one of the major diseases of grapevines in
India. The disease is mainly managed by fungicide application.
However, fungicidal efficacy varies from vineyard to vineyard.
It is known that the nutritional status of plants has a substantial
impact on their predisposition to pests and diseases. All essential
mineral elements are reported to influence disease incidence or
severity (Huber, 1978 and 1980; Graham and Webb, 1989) and
potassium is of particular importance. Perrenoud (1990) reviewed
almost 2450 literature references on this subject and concluded
that the use of potassium (K) decreased the incidence of fungal
diseases in 70% of the cases. Potassium alters the compatibility
relationship of the host-parasite environment within the plant
(Marschner, 1995). Sweeny et al. (2000) have found reduced
incidence of diseases as a result of K fertilization in different
crops. Increased incidence of powdery mildew in vines exhibiting
inward leaf curling (symptoms of potassium deficiency) has
been observed (Sharma et al., 2009). Leaf curling interferes in
fungicide coverage thereby promoting the disease development.
Crop loss in field grown vines due to downy mildew was also
higher in potassium deficient grapevines (Sawant et al., 2010).
Petiole samples exhibiting varying degree of inward leaf curling
(potassium deficiency symptom) and powdery mildew incidence
were sampled on 45th and 90th day after foundation pruning
during 2009 and 2010, respectively from field grown vines in
experimental plots of NRC for Grapes, Pune. In order to get
wide range of nutrient contents, vines grown on different stock
scion combinations were sampled and rated for disease severity.
Nutrient composition of petioles was studied as per standard
methods of analysis. All the vines were grown under uniform
package of practices, including the fungicides applied for the
control of powdery mildew. The 5th leaf position was selected
for nutrient analysis on 45th day after pruning. Each sample was
collected from a set of three vines. Severe powdery mildew
incidence was observed on the basal leaves at 90th day after
pruning. The leaves at 3rd to 7th nodes (middle representative)
were selected for analysis from vines having severe disease
incidence as well as those having fewer incidences. The basal 10
leaves on each shoot were rated for disease incidence (visually
active fungal growth) on a scale of 0-4 (Fig.1). The data were
analyzed by correlation and stepwise regression using SAS
software. Data on micronutrients is not presented as they were
not related to the disease incidence and the vines were sprayed
with micronutrients.
The effect of mineral nutrition on diseases has been determined
either through observing the effects of fertilization on disease
severity, comparing the mineral concentration in resistant and
susceptible cultivars or correlating conditions influencing mineral
availability with disease incidence or severity or combination
of these factors. Since very little information is available on the
relation of the nutritional status of the grapevines with powdery
mildew incidence, relationship between nutritional status of the
open field grown Thompson Seedless vines raised in different
stock scion combinations and powdery mildew incidence at two
different growth stages of grapevines was worked out.
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Introduction
Results and discussion
The data on nutrient contents and powdery mildew ratings are
presented in Table 1 and 2 and correlation coefficients in Table
3. The nutrient contents particularly that of N, P and K varied
greatly in different stock scion combinations. Nitrogen has been
implicated in many studies to increase the disease incidence.
Nitrogen exhibited positive but non-significant correlation with
disease rating (r=0.3536) and (r=0.3056). Although there was
strong and positive correlation between N:K ratio and disease
rating during both the years, nitrogen content might not have
played a direct role in increasing the disease rating in the present
Relationship of nutritional status of field grown Thompson Seedless grapevines with powdery mildew incidence
Table 2. Nutrient status of vines and disease incidence 90th day after
foundation pruning during 2010
Plot
number
N
(%)
P
(%)
K
(%)
Ca
(%)
Mg
(%)
Na
(%)
1.
1.06
0.52
2.04
2.04
0.96
0.44
Cl Powdery
(%) mildew
rating
0.35
1.5
2.
1.13
0.33
2.55
2.17
0.86
0.73
0.35
1.2
3.
1.21
0.3
1.85
2.05
0.83
0.63
0.42
1.3
4.
0.85
0.48
2.35
2.15
0.92
1.15
0.7
1.3
5.
1.13
0.45
1.78
2.21
1.12
0.5
0.4
1.5
6.
0.96
0.35
2.65
2.13
0.95
0.8
0.35
1.3
7.
1.1
0.28
1.8
1.85
0.84
0.55
0.35
1.2
8.
1.03
0.52
2.16
2.06
1.02
1.03
0.42
1.2
9.
1.24
0.5
1.85
2.29
0.93
0.46
0.46
1.3
10.
1.13
0.3
1.95
1.95
0.91
0.72
0.32
1.2
Table 1. Nutrient content of vines and powdery mildew ratings on 45th
day after foundation pruning during 2009
Plot
N
number (%)
P
(%)
K
(%)
Ca
(%)
Mg
(%)
Na
(%)
1.
0.78
0.27
0.71
0.63
0.97
0.18
Cl Powdery
(%) mildew
rating
0.11
1.5
2.
0.76
0.22
1.02
0.71
0.75
0.23
0.18
1.2
3.
0.63
0.25
0.73
0.77
0.88
0.23
0.25
1.5
4.
0.62
0.26
1.00
0.69
0.77
0.28
0.21
1.2
5.
0.90
0.26
0.66
0.65
1.00
0.18
0.11
3.0
6.
0.99
0.25
0.66
0.61
1.00
0.15
0.18
7.
0.89
0.25
0.64
0.68
0.96
0.23
8.
0.95
0.35
1.65
0.52
0.91
9.
0.78
0.33
1.53
0.56
0.83
10.
0.50
0.42
1.85
0.57
11.
0.62
0.40
1.63
12.
0.76
0.32
13.
0.74
14.
11.
1.15
0.35
1.69
1.89
0.95
0.56
0.4
1.2
12.
0.95
0.56
2.4
2.32
1.18
1.09
0.75
1.5
13.
1.18
0.23
1.28
1.85
0.80
0.65
0.4
3.2
14.
1.12
0.48
1.06
2.14
0.86
0.42
0.35
3.8
15.
1.12
0.2
1.17
2.05
0.63
0.75
0.35
3.6
16.
1.17
0.6
1.33
2.06
0.92
0.37
0.42
3.2
17.
1.21
0.28
1.02
1.85
1.02
0.65
0.46
3.2
18.
1.03
0.52
1.15
2.21
1.12
0.39
0.32
3.7
19.
1.13
0.22
1.1
2.15
1.13
0.7
0.42
3.2
20.
1.16
0.32
1.02
2.16
0.73
0.68
0.46
3.3
21.
1.24
0.26
1.16
2.06
0.94
0.68
0.32
3.2
Table 3. Correlation coefficient (r) between powdery mildew rating and
petiole nutrient content
Nutrient (%)
45th days after pruning
90th day after pruning
N
0.3536
0.3056
P
-0.4631*
-0.1909
3.0
K
-0.8170*
-0.8750*
0.11
3.2
Ca
0.4125*
-0.03878
0.33
0.50
1.0
Mg
0.4902*
-0.1678
0.33
0.46
1.1
0.96
0.38
0.64
1.0
Na
-0.5999*
-0.3390
0.65
0.85
0.35
0.64
1.1
Cl
-0.5837*
-0.2211
0.78
0.64
1.17
0.16
0.18
2.1
0.30
0.57
0.70
0.95
0.19
0.21
2.1
0.62
0.32
0.60
0.72
0.89
0.20
0.21
2.0
15.
0.62
0.29
0.53
0.67
1.15
0.15
0.14
2.4
16.
0.74
0.34
0.75
0.68
0.95
0.19
0.11
2.3
17.
0.71
0.40
1.55
0.53
0.83
0.24
0.21
1.0
18.
0.66
0.40
1.52
0.55
0.85
0.25
0.21
1.0
19.
0.75
0.32
1.30
0.56
0.90
0.25
0.25
1.2
20.
0.72
0.35
1.60
0.53
0.78
0.20
0.21
1.0
21.
0.66
0.32
0.80
0.64
1.10
0.19
0.21
2.0
22.
0.71
0.34
0.75
0.64
0.96
0.24
0.14
2.2
23.
0.64
0.36
0.62
0.56
1.20
0.18
0.21
2.4
24.
0.64
0.32
0.58
0.62
1.02
0.21
0.18
2.3
25.
0.64
0.31
0.68
0.66
1.09
0.15
0.18
2.1
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situation since its content was not high at 45th day (Table 1) as
per the petiole nutrient standards (Sharma and Shikhamany,
2008). Further, at 90th day during 2010, nitrogen content in
some of the healthy vines was higher than that in affected
vines. Amongst different nutrients, potassium showed highest
degree of significant and negative correlation with the disease
rating (r=-0.8170*) followed by P (r=-0.4631*) at 45th day after
pruning. At 90th day K again exhibited significant and negative
correlation (r=-0.8750*) with disease rating (Table 3). Other
nutrients did not exhibit significant correlation. Since more
than one nutrient exhibited significant correlation at 45th day of
sampling with disease rating stepwise regression analysis was
carried out. Regression analysis also revealed the importance
of potassium nutrition in powdery mildew incidence. N, P, K,
Ca, Mg and Na when regressed together accounted for 82.7 %
variation in disease incidence. Potassium alone accounted for
66.8 % variation in disease incidence (R2 = 0.6678) on 45th day
of sampling. During the second year, N, P, K, Ca, Mg and Na
when regressed together accounted for 85.7 % (R2 = 0.8573)
variation in disease incidence. Potassium alone accounted for
76.6 % variation in disease incidence on 45th day of sampling.
Potassium is one of the essential and major nutrients in viticulture
involved in a variety of functions in grapevines. Its deficiency in
grapes causes inward leaf curling. Inward leaf curling symptoms
are commonly observed during the vegetative growth period in
115
* Significant at P<0.05
vigorously growing vines in a vineyard and more vigorous shoots
in a vine vineyards where the K applications are either inadequate
or not made (Sharma et al., 2009a). Further leaves of vines
having severe powdery mildew incidence also exhibited ‘shiny
spots’ on leaves associated with potassium deficiency (Sharma
et al., 2009b). Leaf curling interferes in fungicide coverage
thereby promoting the disease development. Further shaded
conditions are always favourable for spore germination and
mycelial growth than sunny conditions (Willocquet et al., 1996).
Increased sensitivity to powdery mildew incidence exhibiting
leaf curling (potassium deficiency symptoms) has also been
reported by Mundankar et al. (2008) and Sharma et al. (2009a).
Nutrition alters the compatibility relationship of the host-parasite
environment within the plant. However, K is especially critical
in the production and transport of fungus inhibiting phenolic and
116
Relationship of nutritional status of field grown Thompson Seedless grapevines with powdery mildew incidence
Fig. 2. Severe leaf curling and higher powdery mildew incidence in unfertilized vines (RHS) compared to vines fertilized with potassium (LHS).
flavonoid compounds and a shortage of K reduces the amount of
the plants’ natural antifungal compounds at the site of infection
(Marschner, 1995). Bowen et al. (1992) found no difference in
Uncinula necator infection in water sprayed and K2HPO4 sprayed
leaves of potted grapevines. However, their studies did not
mention K and P content of the leaves. In their studies, the amount
of K2HPO4 used in the spray was not enough to change the P and
K content of the vines. However, in studies carried out by Saleh
et al. (2007), vines fertilized with low NPK concentration were
more susceptible to disease than those fertilized with high levels.
Reuveni et al. (1993) observed that number of grape clusters
infected by U. necator and the severity of infection were greater
on vines fertilized with a low level of NPK (50% infection) than
in plants fertilized with a high level (9.5% infection). During
2010, one set of Thompson Seedless vines (20 vines) was
fertilized with recommended doses of K and also sprayed with
K at fortnightly interval (Fig. 2) during the foundation pruning
and the other set of vines was neither fertilized nor sprayed
with potassium. Disease incidence was recorded on 90th day
when the environmental conditions for powdery mildew were
highly favourable. Unfertilized vines exhibited severe inward
leaf curling symptoms and more incidence of powdery mildew
as compared to fertilized vines (Fig. 2). The average petiole
K content in vines having more disease incidence was lower
(1.21%) than those having less incidence (1.95%).
These results suggest that powdery mildew incidence is related
Complementary Copy
Fig. 1. Disease rating 1/4 (LHS), disease rating 2/4 (middle) and 4/4 (RHS) on 90th day
to nutritional status of the vines. Amongst different nutrients,
potassium was the most important nutrient whose deficiency
increased the sensitivity of grapevines to powdery mildew
disease. Thus maintaining the optimum level of potassium in
grapevines should become a part of the integrated disease
management strategy for Indian vineyards.
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