Inoculation with the native Rhizobium gallicum 8a3 improves osmotic stress tolerance in common bean drought-sensitive cultivar

Figures & data

Table I. Effect of osmotic stress on growth parameters: PDW (plant dry weight, g. plant⁻¹); Leaf area (cm² plant⁻¹); Leaf number (Leaf plant⁻¹); R/S (root to shoot ratio); NAR (Net assimilation rate, g DW cm⁻² day⁻¹) and SLA (Specific leaf area, cm² g LDW⁻¹) in a drought-sensitive common bean ‘cv. Coco blanc’ inoculated with CIAT (reference strain) or 8a3 (native strain) and submitted to low (25 mM) and high (75 mM) mannitol-induced osmotic stress during 15 days. Values represent mean±SE (n = 6). Numbers followed by a different letter within a column are significantly different at p ≤ 0.05 according to LSD analysis.

Symbiosis	Coco-CIAT			Coco-8a3
Mannitol (mM)	0	25	75	0	25	75
PDW	2.8±0.2 a	2.1±0.1 b	0.9±0.2 d	3.3± 0.2 a	2.8±0.2 b	1.9±0.1 c
Inhibition rate (%)	–	25	68	–	15	42
Leaf area	622±22 a	506±17 b	310±9 c	655±242 a	623±21 a	487± 12 b
Inhibition rate (%)	–	19	50	–	12	26
Leaf number	10±2 a	7±1 b	4±1 c	10±2 a	8±2 a	6±1 b
Inhibition rate (%)	–	30	60	–	30	50
R/S	0.2±0.1 c	0.3± 0.1 b	0.4±0.1 a	0.2±0.1 c	0.3±0.1 b	0.5±0.1 a
Inhibition rate (%)	–	1.5	2	–	1.5	2.5
NAR	0.14±0.1 a	0.11± 0.1 b	0.04±0.1 c	0.17±0.1 a	0.15±0.1 a	0.08±0.1 b
Inhibition rate (%)	–	21	71	–	12	53
SLA	650±25 a	534±21 b	231±8 d	679±22 a	600±21 a	344±11 c
Inhibition rate (%)	–	18	64	–	12	49

Table II. Effect of osmotic stress on nodule performance: NDW (Nodule dry weight, mg plant⁻¹); nodule number (nodule plant⁻¹); ANW (average nodule weight, mg nod⁻¹); N/R (Nodule to root ratio); ARA (Acetylene reduction activity, µmol C₂H₄ h⁻¹ plant⁻¹); Fixed N (mmol Plant⁻¹); Lb (Leghaemoglobin, mg gFW⁻¹) and EURS (efficiency of utilization of the rhizobial symbiosis) in a drought-sensitive common bean ‘cv. Coco blanc’ inoculated with CIAT (reference strain) or 8a3 (native strain) and submitted to low (25 mM) and high (75 mM) mannitol-induced osmotic stress during 15 days. Values represent mean±SE (n = 6) only for ARA determination (n = 3). Numbers followed by a different letter within a column are significantly different at p ≤ 0.05 according to LSD analysis.

Symbiosis	Coco-CIAT			Coco-8a3
Mannitol (mM)	0	25	75	0	25	75
NDW	200±18 a	165±12 b	98±9 d	210±15 a	188±11 a	131±08 c
Inhibition rate (%)	–	18	51		10	38
Nod. number	225±24 a	109±13 b	85±6 c	218±19 a	101±9 b	66±5 d
Inhibition rate (%)	–	52	62	–	54	70
ANW	0.9±0.01 b	1.5±0.05 a	1.2±0.05 b	1.0±0.03 b	1.9±0.07 a	2.0±0.08a
Inhibition rate (%)	–	–70	–30	–	–93	−106
N/R	0.25±0.1 a	0.22±0.1 a	0.12±0.1 b	0.23±0.1 a	0.20±0.1 a	0.12±0.1 b
Inhibition rate (%)	–	12	52	–	13	48
ARA	19±2 a	15±2 a	5±1 c	19±1 a	17±2 a	8±1 b
Inhibition rate (%)	–	17	72	–	11	58
Fixed N	8±2 a	5±1 b	2±2 c	8±3 a	6±2 a	4±1 b
Inhibition rate (%)	–	29	71	–	14	43
Lb	25±5a	21±5 a	10±2 b	28±4 a	25±4 a	16±3 b
Inhibition rate (%)	–	16	60	–	11	43
EURS	1.4±0.3 a	1.3±0.4 a	0.9±0.1 b	1.6±0.4 a	1.5±0.3 a	1.5±0.1 a
Inhibition rate (%)	–	9	34	–	5	5

Table III. Effect of osmotic stress on water relations: LRWC (leaf relative water content,%); NRWC (nodule relative water content,%); WUE (water use efficiency, g DW ml⁻¹) in a drought-sensitive common bean ‘cv. Coco blanc’ inoculated with CIAT (reference strain) or 8a3 (native strain) and submitted to low (25 mM) and high (75 mM) mannitol-induced osmotic stress during 15 days. L denotes leaves, N denotes nodules, S denotes shoots and IR denotes inhibition rate (%). Values represent mean±SE (n = 6). Numbers followed by a different letter within a column are significantly different at p≤0.05 according to LSD analysis.

Symbiosis	Coco-CIAT			Coco-8a3
Mannitol (mM)	0	25	75	0	25	75
LRWC	70±13 a	67±11 b	34±5 c	68±14 a	61±10 a	31±4 c
Inhibition rate (%)	–	4	51	–	10	54
NRWC	80±15 a	54±10 b	22±7 d	81±16 a	59±9 b	35±5 c
Inhibition rate (%)	–	33	73	–	27	57
PWUE	0.14±0.01 a	0.06±0.01c	0.04±0.01 d	0.17±0.01 a	0.1± 0.02 b	0.06±0.01 c
Inhibition rate (%)	–	57	71	–	41	65
SWUE	0.34±0.02 a	0.21±0.03 b	0.17±0.01 c	0.27±0.02 a	0.21±0.02 b	0.15±0.01 c
Inhibition rate (%)	–	38	50	–	22	44
NWUE	0.022±0.004 a	0.008±0.002 b	0.002±0.001 c	0.022±0.005 a	0.008±0.001 b	0.008±0.001 b
Inhibition rate (%)	–	64	91	–	64	64

Table IV. Effect of osmotic stress on osmotic adjustment: LTSS (Leaf total soluble sugar, mmol g^-1 DW); NTSS (Nodule total soluble sugar, mmol g DW ^-1); L. Proline (Leaf proline content, mmol FW g^-1); N. Proline (Nodule proline content, mmol FW g^-1); in a drought-sensitive common bean ‘cv. Coco blanc’ inoculated with CIAT (reference strain) or 8a3 (native strain) and submitted to low (25 mM) and high (75 mM) mannitol induced osmotic stress during 15 days. TRC denoted treated/control ratio. Values represent mean±SE (n = 3). Numbers followed by a different letter within a column are significantly different at p ≤ 0.05 according to LSD analysis.

Symbiosis	Coco-CIAT			Coco-8a3
Mannitol (mM)	0	25	75	0	25	75
LTSS	112±15 c	324±22 b	534±27 a	152±11 c	376±13 b	554±26 a
TCR	–	3	5	–	2	4
NTSS	274±17 c	312±22 b	422±32 a	277±13 c	300±25 b	352±21 b
TCR	–	1.1	1.5	–	1.1	1.3
L Proline	0.5±0.01 a	0.3±0.01 b	0.1±0.01 c	0.5±0.01 a	0.3±0.01 b	0.1±0.01 c
IR (%)	–	40	80	–	40	80
N Proline	1.4±0.1 c	2.8±0.3 b	5.2±0.5 a	1.7±0.1 c	2.7±0.1 b	5.9±0.4 a
TCR	–	2.0	3.7	–	1.6	3.5