Growth responses and endogenous IAA and iPAs changes of litchi (Litchi chinensis Sonn.) seedlings induced by arbuscular mycorrhizal fungal inoculation

Seedlings of litchi (Litchi chinensis Sonn.) were inoculated with two arbuscular mycorrhizal (AM) fungal species, Glomus intraradices and Gigaspora margarita. Plant growth response and morphological changes induced by AM inoculation were investigated. Plant endogenous indoleacetic acid (IAA) and isopentenyl adenosines (iPAs) concentrations were determined. With mycorrhizal infection rate of 9.0-18.8%, plant biomasses increased by 13.5-30.1%. Leaf number, leaflet number, total leaf area and first order lateral root number were significantly increased by AM inoculation. Although G. margarita significantly increased plant P content and uptake, no significant difference in N nutrition was observed between mycorrhizal and non-mycorrhizal plants. Enzyme-linked immunosorbent assay (ELISA) indicated the changes in IAA and iPAs induced by AM inoculation. IAA concentrations in shoots and in roots were 5-7 times and 2-5 times higher in mycorrhizal than in non-mycorrhizal plants, respectively. The iPAs concentrations increased by 1.7 times in shoots and by 1.9-2.5 times in roots, due to mycorrhizal inoculation. We suggest that the changes in endogenous phytohormone level may be responsible for morphological alteration induced by AM inoculation.