Effects of bacteria-free filtrate from Bacillus megaterium strain L2 on the mycelium growth and spore germination of Alternaria alternata

Figures & data

Figure 1. The inhibitory effects of culture filtrate on A. alternata mycelial growth after seven days. (A) Control; (B) 1.5%; (C) 3.0%; (D) 6.0%; (E) 10.0%; (F) 15.0%; (G) 20.0%.

Table 1. The inhibitory effects of bacteria-free filtrate on A. alternata mycelial growth.

	3 d post-treatment (b1)		5 d post-treatment (b2)		7 d post-treatment (b3)
Concentration	Colony diameter (mm)	Inhibition rate (%)	Colony diameter (mm)	Inhibition rate (%)	Colony diameter (mm)	Inhibition rate (%)
Control (a1)	23.4 ± 0.2	–	49.5 ± 0.3	–	72.5 ± 0.5	–
1.5% (a2)	16.4 ± 0.4	30.2	36.3 ± 0.4	26.7	53.5 ± 0.2	23.6
3.0% (a3)	15.6 ± 0.2	33.6	35.6 ± 0.1	28.1	47.2 ± 0.2	34.9
6.0% (a4)	13.7 ± 0.7	41.7	32.2 ± 0.2	34.9	43.6 ± 0.5	39.9
10.0% (a5)	8.7 ± 0.4	63.0	26.4 ± 0.4	46.7	35.8 ± 0.2	50.6
15.0% (a6)	7.4 ± 0.2	68.5	21.5 ± 0.4	56.6	31.4 ± 0.1	56.7
20.0% (a7)	5.3 ± 0.2	77.4	14.5 ± 0.3	70.7	17.4 ± 0.6	76.0

Note: The reported values are the average of three replications.

R² = 0.934 > 0.7. It indicates that the model variable 1 and variable 2 fit well.

P = 0.0002 for concentration (a); P < 0.001 for days (b); the data showed to be statistically significant through comparing the two groups as calculated by the method of significant difference.

Figure 2. Morphology of L2-inhibited A. alternata mycelium under a microscope. Microscopic magnification (10×) of (A) the inhibited pathogenic mycelium; (B) expansion of the pathogenic mycelium; (C) abnormal growth of the pathogenic mycelium; (D) protoplast aggregation; (E) influence of bacteria-free filtrate (1.5%) on young mycelial morphology; and (F) control.

Figure 3. The effect of bacteria-free filtrate on A. alternata spore germination (640×). (A) Germ tube vacuolization; (B) abnormal germination of germ tubes; (C) germ tube vacuolization with high-concentration treatment; (D) control.

Table 2. The effect of culture filtrate on A. alternata spore germination.

	Incubation time
	6 h		12 h		24 h
Conc. of bacteria-free filtrate (%, V/V)	Germination rate (%)	Inhibition rate (%)	Germination rate (%)	Inhibition rate (%)	Germination rate (%)	Inhibition rate (%)
Control	43.2	–	72.3	–	91.7	–
10	32.8	18.5	69.8	8.7	87.6	11.5
30	9.8	77.6	14.9	83.6	31.4	65.6
50	4.9	91.1	7.5	90.8	9.3	89.9

Note: 150–200 conidia checked for each treatment.

Table 3. A. alternata spore number reduction and sporulation inhibition rate.

	Incubation time
	7 d		14 d
Dilution factor of the bacteria-free filtrates	Spore number (10^4/mL)	Inhibition rate (%)	Spore number (10^5/mL)	Inhibition rate (%)
Control (a1)	1.21 ± 0.01	–	1.46 ± 0.01	–
80 (a2)	1.01 ± 0.03	16.5	1.22 ± 0.04	16.4
40 (a3)	0.82 ± 0.03	32.2	0.75 ± 0.02	48.6
20 (a4)	0.42 ± 0.02	65.3	0.44 ± 0.04	68.9
10 (a5)	0.35 ± 0.04	71.1	0.39 ± 0.04	73.3
1 (a6)	0.23 ± 0.03	81.0	0.3 ± 0.02	79.5

Note: The reported values are the average of three replications.

R² = 0.941 >0.7. It indicates that the model variable 1 and variable 2 fit well.

P = 0.0047 < 0.005 for concentration (a), the data showed to be statistically significant and indicated as calculated by the method of significant difference.

Figure 4. (A) Conidiophores and (B) conidia chains treated with bacteria-free filtrate.