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Effect of Water Stress & the Interaction between Fertilizer & Inoculum Concentration Dennis Ochola, Research Associate, Bioversity International International Horticultural Congress 2014 - 19th August
Content
Relevance of banana
Key constraints of banana
Banana Xanthomonas wilt (BXW)
Soil nutrient depletion
Drought induced stress
Results 1: Water stress x BXW Development
Results 2: Fertilizer x Inoculum concentration x BXW
Conclusion
Relevance of bananas• Banana is a versatile food and
income crop for millions of smallholders in EC Africa.
• Uganda #2 producer of approx. 10 million tonnes. Annual per capita consumption exceeds 300 kg.
• Continuous & reliable production = Food security (no drought-induced famine). Erosion control.
Piet van Asten, IITA
Technoserve
Key Constraints of Banana
• pH• Potassium• Nitrogen • Phosphorous
• Xanthomonas wilt• Banana weevil• Black sigatoka• Fusarium wilt
Pests & Diseases
Soil Nutrient Depletion
• Drought stress• Temperature spikes• Floods
Climate Change
Banana Xanthomonas Wilt (BXW)• Bacteria - Xanthomonas
campestris pv. muscearum (1.8 – 2.0 µ x 0.7-0.9µ)
• Devastating disease in EC Africa; US$ 50 Million losses.
• 1967 first noted on Enset in the Ethiopian highlands.
• Spread: Insects + contaminated farm tools + diseased suckers.
• No resistance in cultivated ABB, AAA & AAB.
Drought induced stress• Banana water req. >25 mm per
week = 1300 mm per year (very sensitive to water stress).
• Most growing regions experience suboptimal rainfall.
• CSIRO 2050: 100 mm rainfall decline + 2 oC temperature rise.
• Drought = Δ Pathogen suitability + Δ Crop vulnerability.
YIELDS MIGHTDECREASE BY
10-15%
Soil nutrient depletion
• Banana grown on Ferralsols + Acrisols of low inherent fertility.
• Crop is a heavy feeder i.e. 200-400 kg N ha-1 N and 240-480 kg K ha-1.
• Fertilizers not widely used = high prices + limited and poor access.
• Low fertility = reduced vigor + high susceptibility to diseases.
Effect of Water stress on BXW Development
Research Question Does duration & timing of water stress increase
susceptibility to Xanthomonas wilt?
Materials & Methods
• EAHB cv. Mbwazirume (persistent bracts + neuter flowers).• 3.5 mm water per day until robust root system + leaves
• Water stress treatments – withholding water• SF, 2W, 4W, SF+3W, 2W+3W and 2W+4W.• Stress determined with a conventional water filled tensiometer DIK-
8333 pF meter.
• Inoculum and inoculation• Xcm isolated + grown on Cellobiose Cephalexin Agar (CCA) (Mwebaze
et al. 2006)• Bacterial colonies suspended in distilled water + OD adjusted to 0.5
approx. 1 x 108 colony forming units (cfu)mL-1) (Ocimati et al. 2013)• 1 mL of Xcm injected in the petiole with the insulin syringe Micro-Fine+
0.33 x 12.7 mm.
Materials & Methods
• Disease development and wilt index• Six-point scale (0-5) modified from Winstead & Kelman (1952)
0 = no wilt; 1 = 1 wilted leaf; 2 = 2-3 wilted leaves; 3 = 4 wilted leaves; 4 = All leaves wilted; 5 = Dead or collapsed
• Percentage wilt index = [(0a + 1b + 2c + 3d + 4e + 5f/5n) x 100] (Ssekiwoko et al. 2006)
• Incidence = proportion of plants expressing symptoms.• Area under disease progress curve (Jeger & Viljanen-Rollinson, 2001)
AUDiPC + AUPSiPC
• Statistical analysis• GENSTAT 11 Edition (VSNI, UK)• ANOVA• Mean separation LSD (P < 0.05)
Stress measurements with a pF Meter
SF 2W 4W SF+3W 2W+3W 4W+3W0
0.5
1
1.5
2
2.5
3
1.92.1
2.3 2.3
2.8 2.8
Water stress treatments
pF v
alue
Moderate stress
Extreme stress
Stress free
BXW Parameters: Incubation period
SF 2W 4W SF+3W 2W+3W 4W+3W02468
1012141618 16.7 cd
13.6 b
15.6 c
12 a
15.1 bc
11.7 a
Water stress treatments
Incu
batio
n pe
riod
(dpi
)
BXW Parameters: Incidence
SF 2W 4W SF+3W 2W+3W 4W+3W0
500
1000
1500
2000
2500
3000
3500
2268 a 2147 a
2735 ab 2734 ab 2899 b3162 bc
Water stress treatments
AU
DiP
C
BXW Parameters: % severity index
SF 2W 4W SF+3W 2W+3W 4W+3W0
200
400
600
800
1000
1200
1400
2268 a 2147 a
2735 ab2734 b 2899 bc
3162 c
Water stress treatments
AU
PSiP
C
Discussion & Conclusion
• Water stressed plants are physiologically weak = more vulnerable to BXW. Hence BXW to be hastened by both duration + timing of water stress.
• Increased incidence due to prolonged water stress durations = shorter period Xcm to colonize the parenchymatous tissue.
• Scenario in which BXW may be exacerbated by changing climate, with effects large enough affect smallholder production esp. in South-western Uganda.
• Temperature + rainfall data in 25 years show large departures from normal.
Discussion & Conclusion
• Climate change-mediated impacts on plant diseases and efficacy their management + productivity + sustainability of agricultural systems (Chakraborty et al. 2000)
• Shifts in rainfall may alter host-pathogen interaction + temperature spikes lead to breakdown of resistance.
• *Difficult to discriminate stress-induced from Xcm-inducing wilting of banana.
• Xcm-induced wilting is due to reduced water + uptake uptake due to embolism of the xylem from copious EPS production.
Fertilizer & Inoculum Concentration & BXW Development
Research QuestionDoes improved plant nutrition contribute to increased
Xanthomonas wilt resistance?
Materials & Methods
• EAHB cv. Mbwazirume (persistent bracts + neuter flowers).• 3.5 mm water per day until robust root system + leaves
• 3 Fertilizer treatments – 0, 125 & 250 kg/ha
• 4 Inoculum treatments – 1 x 104, 1 x 106, 1 x 108 & 1 x 1012 cfu/mL
• Inoculum and inoculation• Xcm isolated + grown on Cellobiose Cephalexin Agar (CCA) (Mwebaze
et al. 2006)• Bacterial colonies suspended in distilled water + OD adjusted to 0.5
approx. 1 x 108 colony forming units (cfu)mL-1) (Ocimati et al. 2013)• 1 mL of Xcm injected in the petiole with the insulin syringe Micro-Fine+
0.33 x 12.7 mm.
Materials & Methods
• Disease development and wilt index• Six-point scale (0-5) modified from Winstead & Kelman (1952)
0 = no wilt; 1 = 1 wilted leaf; 2 = 2-3 wilted leaves; 3 = 4 wilted leaves; 4 = All leaves wilted; 5 = Dead or collapsed
• Percentage wilt index = [(0a + 1b + 2c + 3d + 4e + 5f/5n) x 100] (Ssekiwoko et al. 2006)
• Incidence = proportion of plants expressing symptoms.• Area under disease progress curve (Jeger & Viljanen-Rollinson, 2001)
AUDiPC + AUPSiPC
• Statistical analysis• GENSTAT 11 Edition (VSNI, UK)• ANOVA• Mean separation LSD (P < 0.05)
Fertilizer + Banana Growth
FertilizerPlant
height (cm)
Pseudostem Girth
(cm)Leaf Area
(cm2)
0 kg npk 89.9 13.4 953
125 kg npk 122.2 15.9 1589
250 kg npk 137.3 17.4 1722
Mean 116.5 15.5 1421
LSD (p<0.05) ** ** **
Fertilizer + Inoculum on BXW Incidence
4e 6e 8e 12e75
80
85
90
95
100
0npk 125npk 250npk
Log10 cfu mL-1
Inci
denc
e (%
)
0npk 125npk 250npk75
80
85
90
95
100
4e 6e 8e 12e
Fertilizer Treatment
p>0.05p<0.01
Fertilizer + Inoculum on BXW Severity
4e 6e 8e 12e0
10
20
30
40
50
60
70 0npk 125npk 250npk
Log10 cfu mL-1
Wilt
Inde
x (%
)
0npk 125npk 250npk0
10
20
30
40
50
60
70 4e 6e 8e 12e
Fertilizer Treatment
p>0.05p<0.01
Mortality (%)
Inoculum(cfu mL-1)
Fertilizer TreatmentMeanx
0 125 250
104 15 ab 7.5 a 5.1 a 9.2 a
106 82.4 de 60.3 cd 72.7 d 71.8 d
108 65.4 d 80.8 de 79.5 de 75.2 de
1012 85.5 e 59.3 cd 67.9 d 70.9 d
Meany 62.1 d 52 c 56.3 cd
Discussion & Conclusion
• Fertilizers boost physiology of plants hence have potential of augmenting disease resistance.
• Majority of cultivated East African highland bananas have no resistance to Xcm infection.
• Xcm concentration has an overriding effect on the effectiveness of fertilizers for BXW management.• Type 3 effector proteins like YopJ-like C55 cysteine protease suppress
innate defenses in banana by enhancing nutrient uptake by Xcm.
• Findings contradict Atim et al. (2013) whereby application of exogenous N, K+ & Ca2+ reduced BXW susceptibility.
Discussion• Studies reveal that fertilizers modulate predisposition to
facultative pathogens like Xanthomonas, Alternaria & Fusarium.
• Slow disease build up in 104 cfu/mL inoculated plants is reminiscent of latent infections.• Xcm survives latently in underground parts of banana mat
(corm) for 1-2 years (Ocimati et al. 2013)• Prolonged duration of Xcm latency is associated with recent
resurgence of disease in fields wherein it had been contained.
• Muted effect of fertilizer suggests a weak interaction with Xcm concentration.
• Exercise caution prior to endorsements against fertilizer use in BXW management.
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