Exogenous Putrescine, not Spermine or Spermidine, Enhances Root Mycorrhizal Development and Plant Growth of Trifoliate Orange (Poncirus trifoliata) Seedlings

In a pot experiment, with an arbuscular mycorrhizal fungus (AMF) Glomus versiforme inoculation, we investigated effects of three polyamines (PAs) putrescine (Put), spermidine (Spd) and spermine (Spm) on root development, plant growth and biomass production of 4-months-old trifoliate orange (Poncirus trifoliata). Compared to the sole AMF inoculation, addition of Put increased mycorrhizal colonization and numbers of entry points, arbuscules and vesicles significantly. Addition of Spm significantly increased mycorrhizal colonization and arbuscules, whilst addition of Spd had no effect on mycorrhizal development. Mycorrhizal plants had significantly higher root total length, projected area, surface area and volume than non-mycorrhizal plants. Compared to the sole AMF treatment, total root length, projected area, surface area and root volume were significantly increased by the Put treatment. Only total root surface area and root volume were significantly increased by the addition of Spm, while no obvious improvement on root development was observed by the Spd supply. Compared to the sole AMF treatment, all the growth parameters and biomass production of both shoots and roots were significantly enhanced by Put treatment, but not by Spd treatment. Our results demonstrated that citrus plant performance and root morphology could be enhanced by dual application of G. versiforme and exogenous Put. (C) 2010 Friends Science Publishers