Methyl jasmonate spray for the protection of broad-leaf trees against oomycete and fungal pathogens

Abstract

Methyl jasmonate (MeJA) is a volatile hormone produced by plants in response to stress. Exogenous application of MeJA enhances resistance to pathogens in conifers, but little is known if resistance is also enhanced in broad-leaf trees. This article reports on five independent experiments carried out to determine the preventive and curative effects of MeJA spray in broad-leaf trees in response to relevant pathogens. In Castanea sativa seedlings, preventive MeJA spray at 1 mM was the most effective dose against Phytophthora cinnamomi , and protection lasted one year. For Quercus ilex and Q. suber seedlings, double spray of MeJA at 0.2 mM, before and after inoculation, and single spray of MeJA at 1 mM before inoculation were the most effective treatments against P. cinnamomi , respectively. MeJA spray had no effect on the mycorrhization of plants. Quercus robur and Fraxinus excelsior plants were sprayed with 0, 0.2, 1, 5 and 10 mM MeJA, before and after Phytophthora plurivora infection, but no protection was observed. Finally, Ulmus minor trees were sprayed at 1 and 10 mM MeJA, and protection against Ophiostoma novo-ulmi was dose- and genotype-dependent. It is concluded that MeJA spray can induce resistance in broad-leaf trees against widespread and highly virulent pathogens, but the effect may vary depending on the tree species and pathogen combination. Protection of broad-leaf trees could be obtained only if the appropriate dose and timing is used.

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