Evaluation of Bacillus Strains for Plant Growth Promotion and Predictability of Efficacy by In Vitro Physiological Traits

Table 4

Growth promotion effects of five Bacillus strains on soybean plants in 4 greenhouse pot experiments, with the two strains having the highest measurements for each parameter indicated with shading.

Strain	Shoot fresh weight (g) (% increase)^t				Root fresh weight (g) (% increase)^t				GSF (%)^u	FIT2 (%)^v
	Trial 1	Trial 2	Trial 3	Trial 4	Trial 1	Trial 2	Trial 3	Trial 4
Bacillus megaterium R181	1.3bc^w (18)	1.3ab (18)	3.7ab (16)	3.8ab (3)	0.42b (−9)	0.64b (60)	1.7b (89)	2.1a (31)	50	50
B. safensis R173	1.5ab (36)	1.5a (36)	4.2a (31)	4.2a (14)	0.62ab (35)	0.97a (142)	2.2a (144)	2.1a (31)	88	100
B. simplex R180	—	—	3.9a (22)	3.1b (−16)	—	—	2.2a (144)	1.3c (−19)	50	50
Paenibacillus cineris R177	1.1c (0)	1.1c (0)	—	—	0.38b (−17)	0.35c (−13)	—	—	0	0
P. graminis R200	1.6a (46)	1.2bc (9)	3.5ab (9)	3.6ab (−3)	0.88a (91)	0.41c (3)	1.5b (67)	1.8ab (13)	38	25
Control	1.1c	1.1bc	3.2ab	3.7b	0.46b	0.40c	0.9c	1.6bc	NA^x	NA
ANOVA P	0.001	0.004	0.054	0.059	0.003	<0.001	<0.001	0.004	NA	NA

^tPercentage increase of a growth variable by bacterial treatment compared to the control. ^uGSF = growth stimulation frequency; frequency at which a strain increased growth (at 95% confidence level) in all measurements across trials. ^vFIT2  = Frequency in top 2 strains category. ^wNumbers followed by the same letter in each column are not significantly different at α = 0.05 according to LSD test. ^xNA = not applicable. Significant difference between treatment and control () according to Dunnett’s test. — = no data or strain was not tested.