Interactive effects of arbuscular mycorrhizal fungi and intercropping with sesame (Sesamum indicum) on the glucosinolate profile in broccoli (Brassica oleracea var. Italica)

This study determined interactive effects of arbuscular mycorrhizal (AM) fungi and sesame (Sesamum indicum) intercropping on glucosinolate concentrations in broccoli (Brassica oleracea var. Italica) plants. An experimental intercropping model of a horizontal three-compartment split-root system was used. It comprised the middle (combi) compartment shared by one part of the root system of the two intercropped plants, and two outer (solo) compartments with the other part of each root system. Broccoli was intercropped either with an AM host plant (sesame) or an AM non-host plant (broccoli). All intercropping combinations were cultivated in soil that was either mycorrhiza free [-M] or inoculated with Rhizophagus irregularies [+M]. Although broccoli roots were not internally colonised by mycorrhiza, AM inoculation of broccoli intercropped with sesame induced a systemic increase of indole glucosinolates in broccoli roots and leaves. This increase differed in the individual indole glucosinolate: in particular, 3-indolylmethyl glucosinolate was enhanced in leaves and its methoxylated derivative 4-methoxy-3-indolylmethyl glucosinolate was raised in roots. These interactive effects suggest that the activity of AM fungi in the (combi) compartment was stimulated by the AM host plant sesame, leading to a persistent invasion of AM fungi of the broccoli root surface. This may lead to a constant defence response in broccoli. The broccoli biomass was not negatively affected by AM fungal inoculation. When intercropped with sesame, the dry matter of broccoli shoots was increased.