Seed Treatment With Jasmonic Acid and Methyl Jasmonate Induces Resistance to Insects but Reduces Plant Growth and Yield in Rice, Oryza sativa.

Santhi Bhavanam,Michael Stout

doi:10.3389/fpls.2021.691768

Santhi Bhavanam, Michael Stout

Open Access

https://doi.org/10.3389/fpls.2021.691768

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Abstract

When applied exogenously to plants, jasmonates [i.e., jasmonic acid (JA) and methyl jasmonate (MeJA)] increase plant resistance against herbivores, and their use in pest management has been suggested. For integration into pest management programs, the benefits of the resistance induced by jasmonates must outweigh the costs of jasmonates on plant growth and yield. A previous field study in rice found that seed treatment with MeJA reduced densities of the rice water weevil, Lissorhoptrus oryzophilus, but also reduced plant growth. Yields from MeJA plots were similar to yields from control plots. Because this study was conducted under field conditions with natural levels of pest populations, it was unclear whether effects on growth and yield were due to direct effects of MeJA treatment on the plant or due to lower reductions in rice water weevil densities. Therefore, the present study was designed to characterize the effects of JA and MeJA seed treatment on rice plant growth and yield in a pest-free environment under greenhouse conditions. Seed treatment with 2.5 mM JA and 2.5 mM MeJA enhanced resistance in rice plants to rice water weevils when plants were exposed to weevils 30 days after planting. Seed treatment with MeJA reduced seedling emergence and plant height at 4 and 14 days after planting, respectively, compared to JA and control treatments. However, numbers of tillers per plant at 45 days after planting and days to heading were unaffected by jasmonate seed treatment. Of four yield components (panicles per plant, filled grains per panicle, percent unfilled grains, and filled grain mass) that were measured, only filled grain mass was reduced by seed treatment. Plants grown from MeJA-treated seeds showed 31% lower grain masses compared to plants grown from control-treated seeds. Thus, the effects of seed treatment with MeJA on plant growth were stronger immediately post-treatment and subsided over time, such that plant growth mostly recovered 6 weeks after treatment. At maturity, MeJA may reduce one but not all components of yield. Despite similar effects on rice water weevil resistance, the negative effects of JA seed treatment on plant growth and yield were smaller compared to MeJA seed treatment.

Highlights

Jasmonic acid (JA), its methylated derivative methyl jasmonate (MeJA) and its conjugate with isoleucine (JA-Ile), collectively referred to as jasmonates, are phytohormones that regulate several physiological and developmental processes in plants (Ali and Baek, 2020)
The numbers of first instar rice water weevils emerging from plants grown from seeds treated with MeJA (z = −2.94, p = 0.009) or jasmonic acid (JA) (z = −3.14, p = 0.005) were lower than the numbers of first instars that emerged from plants grown from untreated seeds (Figure 1), verifying that seed treatment with MeJA- and JA-induced resistance to rice water weevil in rice
Mean numbers of tillers produced per plant at 45 days after planting were not affected by seed treatment with MeJA or JA (F2, 27 = 0.25, p = 0.78; Figure 2C)

Summary

Introduction

Jasmonic acid (JA), its methylated derivative methyl jasmonate (MeJA) and its conjugate with isoleucine (JA-Ile), collectively referred to as jasmonates, are phytohormones that regulate several physiological and developmental processes in plants (Ali and Baek, 2020). Seed treatments with plant elicitors have mostly been investigated in tomato, Solanum lycopersicum L., with a few additional studies on cabbage, Brassica oleracea and rice, Oryza sativa L. These studies provide evidence that seed treatment with JA or MeJA can increase resistance against herbivores in plants (Worrall et al, 2012; Paudel et al, 2014; Strapasson et al, 2014; Haas et al, 2018; Kraus and Stout, 2019). Unlike applications of plant elicitors by foliar spray or soil drench, which are usually made at or near the time of pest infestation, seed treatments are made before seeds are planted, and the duration of induction of defenses by seed treatments is a critical consideration for the efficacy of seed treatments (Worrall et al, 2012; Haas et al, 2018; Kraus and Stout, 2019)

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