Does fungal infection increase the palatability of oilseed rape to insects?

Abstract

BACKGROUNDMultiple and simultaneous attacks by pathogens and insect pests frequently occur in nature. Plants respond to biotic stresses by activating distinct defense mechanisms, but little is known about how plants cope with multiple stresses. The focus of this study was the combined interaction of fungal infection caused by Leptosphaeria maculans (synonym Plenodomus lingam) and arthropod infestation by the diamondback moth (Plutella xylostella) in oilseed rape (Brassica napus). We hypothesized that infection by the fungal pathogen L. maculans could alter oilseed rape palatability to P. xylostella‐chewing caterpillars. Feeding preference tests were complemented with analyses of defense gene transcription, and levels of glucosinolates (GLSs) and volatile organic compounds (VOCs) in L. maculans‐inoculated and non‐inoculated (control) leaves to determine possible causes of larval choice.RESULTSCaterpillars preferred true leaves to cotyledons, hence true leaves were used for further experiments. True leaves inoculated with L. maculans were more palatable to caterpillars over control leaves during the early stage of infection at 3 days post inoculation (dpi), but this preference disappeared in the later stages of infection at 7 dpi. In parallel, genes involved in the salicylic acid and ethylene pathways were up‐regulated in L. maculans‐inoculated leaves at 3 and 7 dpi; L. maculans increased the level of total aliphatic GLSs, specifically glucobrassicanapin, and decreased the level of glucoiberin at 3 dpi and altered the content of specific VOCs. A group of 55 VOCs with the highest variability between treatments was identified.CONCLUSIONWe suggest that the P. xylostella preference for L. maculans‐inoculated leaves in the early stage of disease development could be caused by the underlying mechanisms leading to changes in metabolic composition. Further research should pinpoint the compounds responsible for driving larval preference and evaluate whether the behavior of the adult moths, i.e. the stage that makes the first choice regarding host plant selection in field conditions, correlates with our results on larval host acceptance. © 2024 Society of Chemical Industry.

Integrated pest control in oilseed crops—new advances from the rapeseed research community

“…27 The bad news is that fungal infection may increase palatability of oilseed rape to insects. 28 The re-disposition of Phoma-like anamorphs in Pleosporales done 10 years ago led to further change in fungus taxonomy; L. maculans has been re-named Plenodomus lingam, whereas L. biglobosa has been termed P. biglobosus. However, the community of OSR plant pathologists still use L. maculans and L. biglobosa, due to the connection of these names to the resistance genes (Rlm), avirulence genes (AvrLm) and proteins (Lema), produced by these fungi.…”