Wood Vinegar and Spermidine Enhance Salt Tolerance in Rice

Introduction

Soil salinity is a major challenge for global rice production, particularly in regions where salt-sensitive cultivars are widely grown. Salinity stress can drastically reduce yield, affecting food security. This study investigates the effects of exogenously applied spermidine (Spd), a naturally occurring polyamine involved in plant growth regulation and stress response, and wood vinegar on improving the salt tolerance of two salt-sensitive rice cultivars, 'Khao Dawk Mali 105' (KDML105) and 'RD6'. The research was conducted under both greenhouse and field conditions, evaluating physiological responses, yield, and overall plant resilience to saline environments.

Experimental Design and Application

Greenhouse Experiment

  • Rice plants were grown in sandy loam soil and subjected to salinity stress (30 mM NaCl).
  • Spermidine was applied as a foliar spray in three concentrations: 0.1, 0.5, and 1.0 mM (millimolar, representing millimoles per liter).
  • Treatments were applied daily for seven days before imposing salt stress.
  • Physiological traits, leaf chlorophyll content (SPAD values), and yield components were analyzed.

Field Experiment

  • Conducted in a saline field with two distinct zones: low salinity (EC = 3 dS m⁻1) and high salinity (EC = 10 dS m⁻1).
  • Rice cultivars KDML105 and RD6 were sprayed with either 0.5 mM Spd or wood vinegar at 1:300 and 1:500 dilutions.
  • Foliar treatments were applied daily for seven days at the booting stage.
  • Yield components, seed setting percentage, and grain weight were evaluated.

Key Findings

Greenhouse Results

  • Among the spermidine concentrations tested, 0.5 mM was the most effective in mitigating salt stress.
  • Flag leaf area increased by 59%, chlorophyll content by 15%, and specific leaf area by 8% in treated plants compared to controls.
  • Yield-related parameters showed significant improvements: filled grain weight increased by 33%, and 100-grain weight by 18% in spermidine-treated plants under salt stress.

Field Results

  • Under low salinity, both Spd and wood vinegar enhanced grain yield, with KDML105 showing the highest increase of 66% in filled grains per panicle.
  • At high salinity, wood vinegar at 1:500 dilution provided the most effective yield improvement, increasing grain yield by 49% in KDML105 and 45% in RD6.
  • The number of filled grains per panicle increased by 37% in KDML105 and 25% in RD6 under foliar treatment.
  • RD6, being more sensitive to salinity, exhibited a lower response compared to KDML105 but still benefited from treatment.

Implications

  • Spermidine (0.5 mM) was more effective in moderate saline conditions.
  • Wood vinegar (1:500 dilution) proved to be a viable alternative for highly saline soils due to its lower cost and ease of application.
  • The findings indicate that wood vinegar could serve as an accessible, cost-effective biostimulant to improve rice cultivation in saline-prone areas.

Conclusion

This study provides strong evidence that exogenous application of spermidine and wood vinegar can mitigate the negative effects of salinity on rice production. Further research on optimizing application timing and concentration could enhance their practical use in rice farming.

Article based on: Exogenous Application of Spermidine (Spd) and Wood Vinegar Improves Salt Tolerance in Salt-Sensitive Rice (Oryza sativa L.)