Fig. 7

Polyamines inhibit the growth and development of M. oryzae and increase disease resistance. a, b Polyamines (SPD and SPM) inhibit the mycelium growth of M. oryzae. 1 mM and 5 mM of PUT, SPD, and SPM were added to the culture medium, respectively. Fresh mycelium was cultured in the medium for 7-d and mycelium growth diameter was measured. Values are mean ± SE. ** indicate the significant difference from control at P < 0.01 by student’s t-test. c Polyamines suppressed the appressorium formation. The conidial (1 × 10⁵/mL) suspension with 0.1, 1, and 5 mM of putrescine, spermidine, and spermine, respectively, were placed on the glass slide. The spores were incubated in a box containing moisture at room temperature, and images were taken at 12 hpi. Scale bars = 5 µm. d–f Estimation of spore development by applying PUT, SPD, and SPM. The conidial suspension supplied with 0.1, 1, and 10 mM of putrescine, spermidine, and spermine was placed on a glass slide separately, and incubated at room temperature for 12 h. Values are mean ± SE. g, h Disease symptoms and relative fungal biomass of the polyamine (SPD and SPM) pretreated WT and OsSAMDC transgenic plants after M. oryzae infection. Two-week-old rice seedlings were sprayed with 1 mM of SPD and SPM for 24 h. Then the conidial suspensions (1 × 10⁵ conidia/mL in 0.02% Tween-20) were sprayed onto the SPD and SPM pretreated rice seedlings. Images were taken at 6 dpi. The fungal biomass was determined by qPCR of M. oryzae Pot2 gene against the rice OsACTIN gene. Values are means ± SD (n = 3). Different letters indicate the significant differences based on 1-way ANOVA with Tukey’s HSD test