To explore the influence of arbuscular mycorrhizal fungus (AMF), P level and auxin on plant lateral root (LR) formation, AMF strain (Rhizophagus irregularis BGC JX04B) was inoculated to Poncirus trifoliata seedlings at two P levels, which was applied with IBA, TIBA and water as control, and the regulative effects of AMF, P level and auxin on LR formation of trifoliate orange were investigated. The results showed that AMF did not significantly affect the plant biomass and LR number, but significantly decreased the 1st order LR length. P level did not significantly affect the plant biomass, LR number and length. TIBA significantly decreased the plant biomass, LR number and length, while IBA did not significantly influence these parameters. AMF and auxin showed significant interaction on the primary root length, and AMF, P level and auxin showed significant interaction on the 2nd and 3rd order LR number. These data suggested that auxin signaling pathway could be involved in the regulation of AMF and P level on LR formation, and the auxin transportation should be the key factor in LR formation of trifoliate orange.
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