Evaluating <i>Rhizobium</i> and <i>Bradyrhizobium</i> species as potential biocontrol agents for root rot fungi in soybean seedlings

Monica D. Nakei; Pavithravani B. Venkataramana; Patrick A. Ndakidemi; Monica D. Nakei; Pavithravani B. Venkataramana; Patrick A. Ndakidemi

doi:10.48130/tia-0024-0007

Figures (4) Tables (6)

Figure 1.
The soybean rot symptoms observed on (a) seedling, (b) flowering and (c) matured plants.
Figure 2.
Various disease symptoms observed and used in scoring disease incidence and symptoms.
Figure 3.
Fungal growth inhibition by cell free culture filtrates of rhizobial strains in agar disc-diffusion assay. No inhibition of (a) F. solani, (e) M. phaseolina, (i) R. solani, and (m) F. phaseolina by B. japonicum TZSR39C, inhibition of (b) F. solani, (f) M. phaseolina, (j) R. solani, and (n) F. oxyporum by Rhizobium sp. TZSR12C, inhibition of (c) F. solani, (g) M. phaseolina, (k) R. solani, and (o) F. oxyporum by Rhizobium sp. TZSR25B, and inhibition of (d) F. solani, (h) M. phaseolina, (l) R. solani, and (p) F. oxyporum by Bradyrhizobium sp. TZSR41A.
Figure 4.
The effect of rhozibia species and Trichoderma harzianum on germination of soybean seeds in the soils having root rot fungi contaminats. In front of each ID numbers, 12C, 25B and 41A there is common ID TZSR. FS = F. solani, MP = M. phaseolina, RS = R. solani and FO = F. oxyporum. The X-axis is biocontrol agents, in front of each ID number, 12C, 25B and 41A there is common ID TZSR. The labels (a)−(e) are biocontrols with (a) combination of two fungi, (b) four fungi, (c) without fungi, (d) one pathogen, and (e) three pathogens.

Treatment	Diameters of inhibition zones (mm)				Colony diameters (mm)
Treatment	FS	MP	RS	FO	FS	MP	RS	FO
Control	0.0	0.0	0.0	0.0	0.0	0.0	0.0	0.0
Rhizobium sp. TZSR12C	5.0	1.3	2.3	***	8.7	6.3	23.7	22.7
Rhizobium sp. TZSR25B	8.3	1.7	***	***	5.3	4.7	24.0	25.0
Bradyrhizobium sp. TZSR41A	5.7	2.3	***	***	7.7	4.0	23.0	23.7
*** Growth inhibited but no zone of inhibition was formed. FS = F. solani, Mp = M. phaseolina, RS = R. solani and FO = F. oxyporum.

Table 1.

In vitro growth inhibition of root-rot fungal pathogens by cell free culture filtrates of rhizobial strains in agar disc-diffusion assay.

Parameter	Mean	Ratings	SD
Soil pH (H₂O)	6.60	N	0.01
Electrical conductivity (dS/m)	0.22	NYR	0.04
Organic carbon (%)	3.20	VH	0.07
Total nitrogen (%)	0.36	M	0.1
Extractable phosphorus (mg·kg⁻¹)	83.95	VH	0.63
Copper (mg·kg⁻¹)	2.28	H	0.05
Zinc (mg·kg⁻¹)	8.09	VH	0.01
Manganese (mg·kg⁻¹)	10.96	VH	0.36
Iron (mg·kg⁻¹)	10.53	VH	0.09
Exchangeable calcium (cmol₍₊₎ kg⁻¹)	14.05	VH	0.01
Exchangeable magnesium (cmol₍₊₎ kg⁻¹)	3.12	VH	0.09
Exchangeable sodium (cmol₍₊₎ kg⁻¹)	0.09	VL	0.01
Exchangeable potassium (cmol₍₊₎ kg⁻¹)	0.40	M	0.03
Cation exchange capacity (cmol₍₊₎ kg⁻¹)	19.12	M	0.56
Exchangeable sodium percentage (%)	0.56	M	0.05
Texture	Sandy Clay Loam
VH = very high, H = high, M = medium, VL = very low, N = neutral and NYR = No yield reduction. S.D. = Standard Deviation^[25].

Table 2.

Physicochemical parameters of an experimental soil.

Treatment	RDI (%)	RDS (%)	FDI (%)	FDS (%)
FO + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + Rhizobum sp. TZSR25B	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + Bradyrhizobium sp. TZSR41A	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + NOB	61.33 ± 5.67^b	20.00 ± 4.04^ab	50.00 ± 9.81^b	10.00 ± 1.73^b
FO + T. harzianum	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + Rhizobum sp. TZSR12C	16.67 ± 9.53^a	5.33 ± 3.93^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + Bradyrhizobium sp. TZSR41A	0.00 ± 0.00^a	0.00 ± 0.00^a	5.67 ± 5.67^a	0.00 ± 0.00^a
FS + NOB	61.33 ± 5.67^b	29.00 ± 5.86^ab	38.67 ± 5.67^b	8.00 ± 1.00^b
FS + T. harzianum	5.67 ± 5.67^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
MP + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
MP + Rhizobum sp. TZSR25B	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
MP + Bradyrhizobium sp. TZSR41A	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
MP + NOB	5.67 ± 0.00^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
MP + T. harzianum	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + Rhizobum sp. TZSR25B	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + Bradyrhizobium sp. TZSR41A	11.00 ± 11.00^a	2.33 ± 2.33^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + NOB	66.67 ± 9.53^b	38.67 ± 22.26^b	39.00 ± 11.00^b	7.67 ± 2.33^b
RS + T. harzianum	16.67 ± 9.53^a	3.33 ± 2.03^a	0.00 ± 0.00^a	0.00 ± 0.00^a
p-Value	<0.001	<0.001	<0.001	<0.001

Table 3.

The effect of rhizobia species and Trichoderma harzianum as biocontrol inoculants on single root rot fungi of soybean plants.

Treatment	RDI (%)	RDS (%)	FDI (%)	FDS (%)
FO + MP + Rhizobum sp. TZSR12C	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + MP + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + MP + Bradyrhizobium sp. TZSR41A	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FO + MP + NOB	72.33 ± 14.68^b	32.33 ± 3.93^b	39 ± 14.74^b	7.67 ± 2.91^a
FO + MP + T. harzianum	22.33 ± 5.33^a	6.33 ± 3.33^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + FO + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + FO + Rhizobum sp. TZSR25B	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + FO + Bradyrhizobium sp. TZSR41A	5.67 ± 5.67^a	1.00 ± 1.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + FO + NOB	83.33 ± 16.67^b	43.33 ± 8.82^b	61 ± 14.74^bc	22.33 ± 7.86^bc
FS + FO + T. harzianum	16.67 ± 9.53^a	3.33 ± 2.03^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + MP + Rhizobum sp. TZSR12C	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + MP + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + MP + Bradyrhizobium sp. TZSR41A	17.00 ± 0.00^a	3.00 ± 0.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + MP + NOB	88.67 ± 5.67^b	30.00 ± 6.81^b	72.33 ± 5.33^c	24.33 ± 5.93^bc
FS + MP + T. harzianum	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + Rhizobum sp. TZSR12C	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + RS + Bradyrhizobium sp. TZSR41A	22.33 ± 5.33^a	6.33 ± 3.33^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + NOB	83.33 ± 9.53^b	33.33 ± 3.76^b	61.33 ± 5.67^bc	33.33 ± 6.67^c
FS + RS + T. harzianum	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + Bradyrhizobium sp. TZSR41A	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + NOB	100 ± 0.00^b	33.33 ± 6.67^b	77.67 ± 5.33^c	25.67 ± 4.67^bc
RS + FO + T. harzianum	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + MP + Rhizobum sp. TZSR12C	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + MP + Rhizobum sp. TZSR25B	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + MP + Bradyrhizobium sp. TZSR41A	11.33 ± 5.67^a	2.00 ± 1.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
RS + MP + NOB	88.67 ± 5.67^b	28.67 ± 4.33^b	67.00 ± 0.00^bc	13.00 ± 0.00^ab
RS + MP + T. harzianum	11.33 ± 5.67^a	2.00 ± 1.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
p-Value	<0.001	<0.001	<0.001	<0.001
FS = F. solani, MP = M. phaseolina, RS = R. solani and FO = F. oxyporum, NOB = no biocontrol and TZSR = Tanzania soybean rhizobia, RDS = root disease severity, FDI = foliar disease incidence, and FDS = foliar disease severity.

Table 4.

The effect of rhizobia species and T. harzianum as biocontrol inoculants on combination of two root rot fungi of soybean plants.

Treatment	RDI (%)	RDS (%)	FDI (%)	FDS (%)
FS + FO + MP + Rhizobum sp. TZSR12C	22.33 ± 5.33^a	4.33 ± 1.33^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + FO + MP + Rhizobum sp. TZSR25B	17.00 ± 0.00^a	3.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + FO + MP + Bradyrhizobium sp. TZSR41A	22.33 ± 5.33^a	4.33 ± 1.33^a	11.33 ± 5.67^a	2.00 ± 1.00^a
FS + FO + MP + NOB	89.00 ± 11.00^b	46.67 ± 6.67^b	44.33 ± 5.67^bc	17.67 ± 2.33^b
FS + FO + MP + T. harzianum	22.33 ± 5.33^a	4.33 ± 1.33^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + RS + FO + Rhizobum sp. TZSR12C	17.00 ± 0.00^a	3.00 ± 0.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + FO + Rhizobum sp. TZSR25B	17.00 ± 0.00^a	3.00 ± 0.00^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + RS + FO + Bradyrhizobium sp. TZSR41A	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + FO + NOB	100.00 ± 0.00^b	40.00 ± 11.55^b	72.33 ± 5.33^cd	29.00 ± 2.00^c
FS + RS + FO + T. harzianum	22.33 ± 14.68^a	7.67 ± 6.23^a	16.67 ± 16.67^ab	3.33 ± 3.33^a
FS + RS + MP + Rhizobum sp. TZSR12C	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + MP + Rhizobum sp. TZSR25B	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + MP + Bradyrhizobium sp. TZSR41A	22.33 ± 5.33^a	6.33 ± 3.33^a	5.67 ± 5.67^a	1.00 ± 1.00^a
FS + RS + MP + NOB	100.00 ± 0.00^b	40 ± 11.55^b	83.00 ± 0.00^d	27.67 ± 5.33^c
FS + RS + MP + T. harzianum	22.33 ± 14.68^a	4.33 ± 2.96^a	5.67 ± 5.67^a	1.00 ± 1.00^a
RS + FO + MP + Rhizobum sp. TZSR12C	5.67 ± 5.67^a	1.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + MP + Rhizobum sp. TZSR25B	11.33 ± 5.67^a	2.00 ± 1.00^a	0.00 ± 0.00^a	0.00 ± 0.00^a
RS + FO + MP + Bradyrhizobium sp. TZSR41A	11.33 ± 5.67^a	2.00 ± 1.00^a	17.00 ± 0.00^ab	3.00 ± 0.00^a
RS + FO + MP + NOB	94.33 ± 5.67^b	43.33 ± 3.33^b	72.33 ± 5.33^cd	29.00 ± 2.00^c
RS + FO + MP + T. harzianum	33.33 ± 16.67^a	10.00 ± 5.77^a	0.00 ± 0.00^a	0.00 ± 0.00^a
p-Value	<0.001	<0.001	<0.001	<0.001
* FS = F. solani, MP = M. phaseolina, RS = R. solani and FO = F. oxyporum, NOB = no biocontrol and TZSR = Tanzania soybean rhizobia, RDS = root disease severity, FDI = foliar disease incidence and FDS = foliar disease severity.

Table 5.

The effect of rhizobia species and T. harzianum as biocontrol inoculants on combination of three root rot fungi of soybean plants.

Treatment	RDI (%)	RDS (%)	FDI (%)	FDS (%)
FS + RS + FO + MP + Rhizobium sp. TZSR12C	27.78 ± 5.56^a	5.56 ± 1.11^a	0.00 ± 0.00^a	0.00 ± 0.00^a
FS + RS + FO + MP + Rhizobium sp. TZSR25B	27.78 ± 5.56^a	7.78 ± 2.94^a	5.56 ± 5.56^a	1.111 ± 1.11^a
FS + RS + FO + MP + Bradyrhizobium sp. TZSR41A	27.78 ± 5.56^a	10.00 ± 3.33^a	11.11 ± 5.56^a	2.222 ± 1.11^a
FS + RS + FO + MP + NOB	77.78 ± 14.7^b	46.67 ± 8.82^b	72.22 ± 11.11^b	40.00 ± 10.00^b
FS + RS + FO + MP + T. harzianum	38.89 ± 5.56^ab	7.78 ± 1.11^a	5.67 ± 5.67^a	1.00 ± 1.00^a
p-Value	0.02	<0.001	<0.001	<0.001
FS = F. solani, MP = M. phaseolina, RS = R. solani and FO = F. oxyporum, NOB = no biocontrol and TZSR = Tanzania soybean rhizobia, RDS = root disease severity, FDI = foliar disease incidence, and FDS = foliar disease severity.

Table 6.

The effect of rhizobia species and Trichoderma harzianum as biocontrol inoculants on combination of four root rot fungi of soybean plants.