Exogenous polyamines affect mycorrhizal development of Glomus mosseae-colonized citrus (Citrus tangerine) seedlings

To increase mycorrhizal colonization of citrus, exogenous polyamines (PAs) including putrescine (Put), spermidine (Spd), and spermine (Spm) were applied to three-month-old Glomus mosseae-colonized Citrus tangerine seedlings. Three months after the application of PAs, all the seedlings increased mycorrhizal colonization and entry points, Put and Spm treatments significantly increased the number of arbuscules, and Spd and Put treatments notably increased the number of vesicles. Applications of exogenous Put and Spd, but not Spm, markedly increased shoot and root dry weights of the mycorrhizal seedlings. PAs significantly increased leaf glucose content of mycorrhizal seedlings, and Put and Spd treatments markedly increased leaf sucrose content of mycorrhizal seedlings. Spm treatment significantly reduced root sucrose content of mycorrhizal seedlings, and only Put treatment significantly increased root glucose content of mycorrhizal seedlings. Compared to the sole mycorrhizal inoculation, exogenous PAs significantly reduced allocation of sucrose to root, and additional Spd significantly decreased allocation of glucose to root. The results demonstrated that exogenous PAs applications could improve mycorrhizal development of citrus seedlings, possibly due to changes of leaf and root sugar content.