Trunk injection delivery of dsRNA for RNAi-based pest control in apple trees

Abstract

Background: RNA interference (RNAi) is a promising new approach for controlling insect pests without the use of synthetic pesticides. Trunk injection is a delivery system for woody plants that harnesses the vascular system of the tree to transport materials to the tree canopy. Full size apple trees were injected with double-stranded RNA (dsRNA), and season-long leaf samples were taken to measure the vascular mobility and temporal persistence of dsRNA, using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

Results: The qRT-PCR results revealed that the quantities of dsRNA in the apple leaves of treated trees were significantly greater than those in the leaves of untreated trees for both 2019 and 2020 studies. The peak dsRNA concentration in 2019 was 242 pg/30 mg of leaf tissue, and in 2020 was 16.4 pg/30 mg. The persistence of dsRNA in the apple tree canopy in 2019 was at least 84 days, and in 2020 was at least 141 days.

Conclusions: The highest mean measurement of dsRNA on a single date in 2019 was 242 pg, which is approximately equivalent to 8 ng/1 g leaf tissue. The projection using the highest replicate concentration from the same date is approximately equivalent to 27 ng/1 g leaf tissue, which may be sufficient to be considered biologically active. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Keywords: RNA interference; integrated pest management; vascular delivery.

Fig. 1

Trunk injection of dsRNA into a 20 year‐old semi‐dwarf apple tree using the TREE I.V. system for delivering dsRNA treatment solutions, with injection ports placed under main scaffold branches of each tree.

Fig. 2

Schematic of the primer and probe locations on the 500 bp dsRNA sequence. *Dual labeled probe (5′ Modification: FAM; 3′ Modification: MGB‐NFQ).

Fig. 3

Mean amount of dsRNA (femtogram) ± SE in the apple leaves for the 2019 (A) and 2020 (B) trials. 2019 days after treatment (DAT): 3 (23 May), 14 (3 June), 35 (24 June), 56 (15 July) and 84 (12 August). 2020 DAT: 56 (3 June), 84 (1 July), 112 (29 July) and 141 (27 August) days after treatment (DAT). Asterisk indicates significant difference between treated and untreated control (t test, p < 0.05) on the same day after treatment (DAT).