Evidences of inhibited arbuscular mycorrhizal fungal development and colonization in multiple lines of Bt cotton

A “sandwich system” was used to investigate the effect of transgenic Bacillus thuringiensis (Bt) cotton (Gossypium hirsutum L.) on early stages of arbuscular mycorrhizal (AM) fungal life cycle. Spore germination and pre-symbiotic hyphal differentiation of AM fungus Rhizophagus irregularis were decreased in the rhizosphere of transgenic Bt cotton isolines (Jin26, GK12 and Jin44) compared with in that of their corresponding parental non-transgenic isolines (Jin7, Si3 and Ji492); and the appressorium number, colonization intensity and arbuscule abundance were lower in Bt plant roots. More collapsed arbuscules were also observed in Bt roots. The results of statistical analysis demonstrate that Bt-trait significantly contributes to the inhibition of pre-symbiotic development and AM fungal colonization, which might be attributed to either Bt toxin toxicity or interference of signal perception between AM fungi and the hosts. The specific mechanism requires further study.