Do alternate wetting and drying irrigation technologies and nitrogen rates affect rice sheath blight?

Water and nitrogen management play vital roles in rice production. However, the mismanagement of either may trigger plant disease epidemics such as sheath blight of rice, caused by Rhizoctonia solani, which is favoured by wet conditions, high relative humidity, and high nitrogen fertiliser levels.

In order to understand how different combinations of water and nitrogen management affect sheath blight epidemics, we conducted two separate split-plot experiments with two irrigation regimes in the dry seasons of 2015 and 2016. The main plot irrigation treatments in both experiments were: flooded, maintaining 10cm standing water through the season and alternate wetting and drying (AWD), a water saving technology developed by the International Rice Research Institute (IRRI) and partners as adaptation strategy for water-scarce environments. In 2015 the split plots were nitrogen (N) applications applied as 0 kg ha-1, 120 kg ha–1, and 150 kg ha–1 total N. In 2016 changes were made to address issues discovered in 2015. In 2016 split plots were N applications at 60 kg ha-1 and 180 kg ha-1 total N. Nitrogen was applied in splits in both seasons.

Disease scoring was the same in both experiments using a sheath blight assessment scale for field evaluation developed at IRRI to assess the severity on infected sheaths and leaves while sheath blight incidence on tillers were counted per hill. Five and four disease assessments were made in 2015 and 2016, respectively. Data were analysed using the area under the disease progress stairs (AUDPS) and multivariate generalised linear mixed models. We were unable to detect any differences in disease in either experiment due to irrigation methods, N rates or the interaction of the two treatments in either season. Our findings indicate that farmers can safely adopt the AWD technology without risk of increasing sheath blight disease.

A/Prof Adam H Sparks leads the summer crop pathology research at USQ in the Centre for Crop Health, previously he worked with the International Rice Research Institute (IRRI) as a plant disease management specialist. Dr Nancy P Castilla works at the International Rice Research Institute (IRRI) as a researcher studying methods to control rice disease and offers training and support for capacity building for national partners. Dr Bjorn Ole Sander works at IRRI as a scientist in IRRI’s climate change research group with a focus on greenhouse gas (GHG) mitigation technologies, which include alternate wetting and drying.

Transcript

1. Do alternate wetting and drying irrigation technologies and nitrogen rates affect rice sheath blight? Adam H Sparks (Centre for Crop Health, USQ, Toowoomba) Nancy P Castilla (IRRI, Los Baños, Philippines) B Ole Sander (IRRI, Los Baños, Philippines)
2. Sheath blight causes yield losses • Up to 50% losses in US • IRRI found ~6%/year in tropical Asia • Host plant resistance is elusive Photo credit: N P Castilla
3. • Causal agent: Rhizoctonia solani • Disease is favoured by • Warm temperatures, 28-32˚C • High relative humidity, 85-100% • High nitrogen rates Photo credit: N P Castilla
4. Illustration: NP Castilla
5. Safe AWD has two major benefits • Reduced water usage • Reduced greenhouse gas emissions • Reduces sheath blight? Photo credit: IRRI
6. What is Safe AWD? 1. Flood after transplanting 2. Water depth drops to 15 cm below the surface 3. Re-flood the field to a depth of 5 cm above the surface 4. Repeat until 1 week before flowering 5. Keep flooded from 1 week before to 1 week after flowering 6. After flowering water level can drop to 15 cm below the surface before re-flooding Photo credit: IRRI
7. Does AWD affect sheath blight? Photo credit: N P Castilla
8. Nitrogen and water management affects sheath blight disease? Photo credit: A H Sparks
9. Two separate studies 2015 and 2016 Dry Seasons IRRI Experiment Station Photo credit: A H Sparks
10. Split plot design • Four Replications • Main plot: Water management • Control - Flooded • Alternate Wetting and Drying (AWD) Photo credit: N P Castilla
11. Same data were captured • 2 sample areas/plot (1m x 1m) • For 9 hills/sample area • Number of tillers/hill • Number of tillers with sheath blight • Sheath blight severity rating • Tillers (4/hill) • Leaves (6 leaves/tiller)
12. Same rating scale Rating Scale - Severity • 0 - 0 • 1 - 1% • 2 - 5% • 3 - 15% • 4 - 50% • 5 - >50%
13. Different N rates • Sub-plot : Nitrogen management (split application) • 2015 • Control – 0 kg/ha • 100 kg/ha (3) • 120 kg/ha (3) • 2016 • Control 60 kg/ha (2) • 180 kg/ha (3) Photo credit: A H Sparks
14. • Plot Sizes • 2015 • Experiment size: 1,152 sq m • 2016 • Experiment size: 3,472 sq m Different sizes Photo credit: IRRI
15. Different inoculation methods • 2015 • 20 days after transplanting • 20 bottles • 1 bottle = 151g/plot (4m x 11m) • 2016 • 41 days after transplanting • 10 bottles/one sampling area/plot • 1 bottle = 151g • Sampling area = 1m x 1m Photo credit: N P Castilla
16. Data Analysis • Most of the data did not meet assumptions of normality • MCMCglmm, a Bayesian approach implemented in R • Analysed Area Under Disease Progress Stairs (AUDPS)
17. Were the changes successful?
19. Does AWD affect sheath blight? Photo credit: N P Castilla
20. No
21. Yes
22. No Yes
23. Does nitrogen affect sheath blight? Photo credit: N P Castilla
24. Yes No
25. Conclusion • 2016 methods appear more effective • Safe to adopt AWD • Does it reduce sheath blight?
27. Reproducible Research https://phytopathology.github.io/rice_awd_pests/