Glucosinolate responses of swede, kale, forage and oilseed rape to root damage by turnip root fly (Delia floralis) larvae

Abstract

Two genotypes of kale (Brassica olerucea L). two of rape (one forage and one winter oilseed type, B riapus L) and two of swede ( B rtupus L) grown in a glasshouse were inoculated with turnip root fly (Deliafloralis Fall) eggs at 5 weeks and their roots, stems and leaves sampled after a further 8 weeks of larval feeding. Changes in total and individual glucosinolates were examined in roots, stems and leaves after attack. Damage by Dflorulis larvae to roots caused tissue weight losses in roots ranging from 26 to 48 Yo, relative to controls. The resultant plant stress also caused smaller weight losses in leaf tissue (10-27 Yo) and stems (6-20 YO). On susceptible brassica genotypes, D florulis percent pupal development and mean pupal weights were a factor of x 1.5 greater than on resistant genotypes, resulting in a difference of x 2.4 in total pupal biomass per root. There was no apparent link between D floralis susceptibility and total or individual glucosinolate content of undamaged control roots. Major differences in glucosinolate composition were found between control roots of the six brassicas. Five of the 15 compounds detected had aromatic side chains and were present in all samples. Only three of the 10 aliphatic glucosinolates were common to all six brassicas. The predominant compound in the two kale roots was prop-2-enyl glucosinolate, in the rapes 2hydroxy-but-3-enyl (forage rape cv Hobson) and 2-phenylethyl (oilseed rape cv Ariana) glucosinolates, and in the swedes 2-hydroxy-but-3-enyl glucosinolate. All brassicas showed a similar response in glucosinolate metabolism after root damage. Total glucosinolate content in roots increased due to a two to four fold increase in indole-based compounds. The largest increase for an individual compound after attack was found for I -methoxy-3-indolylmethyl glucosinolate, which increased four to 17 fold. Root damage did not significantly affect stem glucosinolate composition but in leaves caused a 1.2 fold increase in aliphatic glucosinolates with a corresponding decrease in indole-based compounds. The possible ecological and nutritional significance of glucosinolatc responses to root fly darnage is discussed.

Intraspecific Variation in Plant Defense Alters Effects of Root Herbivores on Leaf Chemistry and Aboveground Herbivore Damage

“…Induction of secondary metabolites in roots due to root feeding by insect larvae has been reported for a number of plant and herbivore combinations (Birch et al 1992;Bezemer et al 2003Bezemer et al , 2004Borowicz et al 2003;Van Dam and Raaijmakers 2006) and might be a general plant response similar to aboveground induction due to shoot herbivores (Karban and Baldwin 1997). Irrespective of plant line, wireworms had no significant effect on root biomass, but led to an increase in leaf biomass, pointing to compensatory shoot growth (Wurst and Van der Putten 2007).…”

Mechanisms and ecological implications of plant‐mediated interactions between belowground and aboveground insect herbivores

“…It is generally accepted that plant defenses are attacker-specific (Howe and Jander 2008;Erb et al 2012), and even closely related, congeneric, plant species differ in their defenses against the same herbivore (van Dam and Raaijmakers 2006;Agrawal et al 2014). In addition, individual genotypes of the same species were shown to differ in the allocation of defensive compounds to AG or BG tissues when exposed to herbivory (Birch et al 1992(Birch et al , 1996Hol et al 2004).…”

Defence mechanisms of Brassicaceae: implications for plant-insect interactions and potential for integrated pest management. A review

“…)-parasitoids Birch et al (1992) showed that different Brassica genotypes such as kale, rape and swede after inoculation with turnip root fly (D. floralis) eggs showed a similar response in glucosinolate metabolism. Total glucosinolate content in roots increased due to a two-to fourfold increase in indole-based compounds.…”