Occurrence of arbuscular mycorrhiza in Castanospermum australe A. Cunn. & C. Fraser and effects on growth and production of castanospermine

Abstract

 Castanospermum australe A. Cunn. & C. Fraser is the only species of the genus Castanospermum (the Moreton Bay chestnut or black bean) native to NE Australia. One constituent of the plant, castanospermine, can inhibit the AIDS virus. The present study investigated possible symbioses between its roots and arbuscular mycorrhizal (AM) fungi. The effects of mycorrhizal fungi on the growth of the plant and yield of alkaloid castanospermine were also studied. The mycorrhizosphere soil and roots of C. australe collected from various sites in and around Sydney, Australia showed AM symbiotic associations with roots, with arbuscules and vesicles in the root cortices. Wet sieving and decanting yielded AM fungal spores, mainly Glomus spp. A positive correlation was found between AM fungal infection and the castanospermine content of seeds of field-grown trees. Field study results were confirmed by growing seedlings under greenhouse conditions and inoculating them with Glomus intraradices Schenck and Smith (INVAM isolate KS906) and Gigaspora margarita Becker & Hall (INVAM isolate BR444–2). The AM fungi increased the growth and P contents of plants and the yield of castanospermine in the leaves, irrespective of the P treatment. No correlation was found between the alkaloid contents of leaves from mycorrhizal seedlings and from non-mycorrhizal plants which received P. No significant difference in the production of castanospermine was found between P treatments when G. margarita was used as inoculum.