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.

www.bioversityinternational.org

Thank you