Evaluating the fungal endophyte Neotyphodium occultans for resistance to the rice leaf bug, Trigonotylus caelestialium, in Italian ryegrass, Lolium multiflorum

Abstract

Fungal endophytes of the genus Neotyphodium (Ascomycota: Clavicipitaceae) form symbiotic associations with many grass species of the subfamily Pooideae, including some important forage and turf grasses from the genus Lolium. Some Neotyphodium-infected grasses have enhanced resistance to the rice leaf bug, Trigonotylus caelestialium (Kirkaldy) (Heteroptera: Miridae), one of the major pests in rice production in Japan. The insects can grow on Lolium grasses and thus cause a conflict of interest between production of forage and rice. Endophyte-mediated resistance to T. caelestialium is likely to be conferred by N-formylloline, one of the major loline alkaloids (saturated 1-aminopyrrolizidines) observed in some grass–Neotyphodium associations. We checked the feasibility of using Neotyphodium occultans, the native endophyte of Italian ryegrass (Lolium multiflorum Lam.), to reduce T. caelestialium, as this endophyte produces N-formylloline, but no known mammalian toxins. To this end, we conducted choice and no-choice feeding assays using T. caelestialium first instars and 35 N. occultans-infected Italian ryegrass plants with different in planta N-formylloline concentration. Some N. occultans-infected ryegrass showed significant resistance to T. caelestialium. The preference and the survival of this insect were considerably lower on infected plants, and the higher the in planta N-formylloline concentration, the greater the adverse effects on the insect. The incremental risk of death of the insect was assumed to be due to intake of the chemical, and in addition, to the decreased amount of feeding caused by its insect-deterrent effect. These results indicated that the use of the N. occultans–grass associations has potential to reduce T. caelestialium propagation in ryegrass crops. The breeding of N. occultans-infected Italian ryegrass cultivars with high N-formylloline concentrations should be an effective way to develop pasture grasses with a greater protective effect against T. caelestialium.