Effect of Water Stress & the Interaction between Fertilizer & Inoculum Concentration

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Presentation given by Dennis Ochola, Bioversity International, on the 'Effect of Water Stress & the Interaction between Fertilizer & Inoculum Concentration'. The presentation was given at the International Horticultural Congress 2014.

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Read more about Dennis Ochola here:
http://www.bioversityinternational.org/about-us/who-we-are/staff-bios/single-details-bios/ochola-dennis/

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  • Effect of Water Stress & the Interaction between Fertilizer & Inoculum Concentration

    1. 1. Effect of Water Stress & the Interaction between Fertilizer & Inoculum Concentration Dennis Ochola, Research Associate, Bioversity International International Horticultural Congress 2014 - 19th August
    2. 2. 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
    3. 3. 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 Technoserve Piet van Asten, IITA
    4. 4. Key Constraints of Banana • Xanthomonas wilt • Banana weevil • Black sigatoka • Fusarium wilt • pH • Potassium • Nitrogen • Phosphorous Pests & Diseases Soil Nutrient Depletion • Drought stress • Temperature spikes • Floods Climate Change
    5. 5. 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.
    6. 6. 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 MIGHT DECREASE BY 10-15%
    7. 7. 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.
    8. 8. Effect of Water stress on BXW Development Research Question Does duration & timing of water stress increase susceptibility to Xanthomonas wilt?
    9. 9. 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.
    10. 10. 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)
    11. 11. Stress measurements with a pF Meter 1.9 2.1 Moderate stress 2.3 2.3 2.8 2.8 3 2.5 2 1.5 1 0.5 0 SF 2W 4W SF+3W 2W+3W 4W+3W pF value Water stress treatments Extreme stress Stress free
    12. 12. BXW Parameters: Incubation period 16.7 cd 13.6 b 15.6 c 12 a 15.1 bc 11.7 a 20 15 10 5 0 Incubation period (dpi) Water stress treatments
    13. 13. BXW Parameters: Incidence 2268 a 2147 a 2735 ab2734 ab 2899 b 3162 bc 3500 3000 2500 2000 1500 1000 500 0 AUDiPC Water stress treatments
    14. 14. BXW Parameters: % severity index 2735 ab 2268 a2147 a 3162 c 2734 b2899 bc 1400 1200 1000 800 600 400 200 0 AUPSiPC Water stress treatments
    15. 15. 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.
    16. 16. 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.
    17. 17. Fertilizer & Inoculum Concentration & BXW Development Research Question Does improved plant nutrition contribute to increased Xanthomonas wilt resistance?
    18. 18. 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.
    19. 19. 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)
    20. 20. Fertilizer + Banana Growth Fertilizer Plant 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) ** ** **
    21. 21. Fertilizer + Inoculum on BXW Incidence p<0.01 p>0.05 0npk 125npk 250npk 105 100 95 90 85 80 75 4e 6e 8e 12e Incidence (%) Log10 cfu mL-1 120 100 80 60 40 20 0 4e 6e 8e 12e 0npk 125npk 250npk Fertilizer Treatment
    22. 22. Fertilizer + Inoculum on BXW Severity 80 70 60 50 40 30 20 10 0 p<0.01 p>0.05 0npk 125npk 250npk 4e 6e 8e 12e Wilt Index (%) Log10 cfu mL-1 80 70 60 50 40 30 20 10 0 4e 6e 8e 12e 0npk 125npk 250npk Fertilizer Treatment
    23. 23. Mortality (%) Inoculum (cfu mL-1) Fertilizer Treatment Meanx 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
    24. 24. 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.
    25. 25. 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.
    26. 26. Thank you www.bioversityinternational.org

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