Enormous rhizobial diversity resident in Ethiopian soils: A potential hotspot to realize the benefits of BNF
Tulu Degefu (PhD)Hawassa University, College of Natural and
Computational Sciences, Department of Biology Hawassa, Ethiopia
THE GLOBAL NITROGEN CYCLE
NO2-
N2 NH4+
NO3-
Nitrogen fixation Biomass
NH4+ + NO2
- → N2 + 2H2OANAMMOX
NO2- Nitrification
Denitrification
NO
N2OAssimilatory
NO3- reduction
orDNRA
The first step in Nitrogen cycle
Rhizobial niches
Symbiotic MutualistsInside the noduleEndophytes of legumes
Saprophytic
Endophytes of non-legumes
Root cortex
Nitrogen fixation 255 ×106 t N is fixed annually through
Three ways ★ Atmospheric Nitrogen fixation ★ Industrial Nitrogen fixation ★ Biological Nitrogen fixation (BNF)
BNF contributes 139 to 170 ×106 t N / yr
Comparatively: Less than the total N reserves (105,
000 ×106 t N), but
2 to 3 times greater than inputs of N from fertilizers (65 ×106 t N/yr).
50% of the biologically fixed N is fixed through Legume-rhizobial association
In areas of arable agriculture, legumes contribute >80%25-30% protein intake world-wide
Pulses:-
Eragrositis teff
Pre-requisites for BNFmax Symbiotic N fixation is fully realized
only if legumes are nodulated with effective rhizobia
Genotype Environment Management
[(L R) E M]
Our own earlier research in Ethiopia, HwU
As many as 16 different agroclimatic zones
Among the eight important primary gene centers of the world (Vavilov, 1951)
Centre of origin for many leguminous crop plants
Despite this, investigations of rhizobia in Ethiopian soils are scarce
• 19 sites ● 21 Legume
spp.● Alt. 1190 –
2800m a.s.l. ● Tº 9 - 32 ºC
(min – max)● RF 450 –
1350 (mm) ● pH 4.8 – 9.6
Strains isolated form Ethiopian soils
Addis Ababa
Awassa
Abergele
Alemaya
Arba- minch Borena-negele
3N48E
6N
9N
12N
15N
33E 36E 40E 44E Moyal
e
Nazret
Ziway
Yavelo
Sampling Route
The beauty of d
iversit
y study is
when yo
u have
large number of sa
mples from diffe
rent
Legumes & Agroecology
Techniques
Collecting nodules Trapping
Authentication of rhizobial isolates on homologous host
0.1
Devosia neptuniae
Beijerinckia indica ●
S. morelense
Blastobacter dinitrificans
AC26e
AC104c1 AC104a
AC62a AC82d
M. tianshanense
AC64c
R. hainanense
B. japonicum
AC86c1
B. liaoningense
M. plurifarium
S. kummerowiae
AC29c
AC39d
AC91e
AC22d
AC79a
S. xinjiangensis
AC86a
AC70c
S. arboris
S. kostiense
S. fredii
AC97a
R. loessense
R. etli
S. terangae
AC27e
AC21a2
AC92d
B. yuanmingense
AC51e
AC107e
AC87k1
AC93e
AC87k3
S. americanus
AC101b
AC21c2
39c1
AC65c
M. mediterraneum
B. elkanii
A. albertimagni
R. galegae
A. undicola
AC88a
AC4d
AC100b
A. rhizogenes
AC90e1
AC90b
AC52c
S. adhaerens
AC72a
AC10d
AC100a AC82b
R. tropici R. leguminosarum
Rhizobium sp. (SDW024)AC56b
R. indigoferaeR. sullae
R. yanglingenseR. gallicum
R. mongolenseRhizobium sp. (X59)
R. giardiniiRhizobium sp. (SDW058)
AC73d R. huautlense
A. vitis AC97c1
AC77b AC11a A. larrymooreiA. rubi
A. tumefaciensAC42c A. radiobacterAC79c1
AC47d AC47a
AC18a AC20b
AC38b2 AC10a1 AC1b S. saheli
S. medicae AC28a
AC50e S meliloti
M. chacoenseAC88c
M. loti M. ciceri
M. huakuii M. amorphae
AC99d AC39a
100e AC98a
Xanthobacter autotrophicus ●Azorhizobium caulinodans
Met. organophylum ●Met. nodulans
AC94a AC87b1
AC64a AC64b
AC87L AC87n
AC86b2 AC92c 100
99
93
9994
83
100
82
9880
89
71
94
86
83
60
71
98
77
89
100
95
92
85
56
58
93
94
74
97
91
96
100
96
90
93
6172
70 Rhizobium
I (2)II
III (2)IV
V (2)VI
VIII VII
IX (2)
Agrobacterium
I
II
III IV
Ensifer
I(2)
II
III (3)
IV
V
Mesorhizobium
I (7)
II
Bradyrhizobium
I (2)
II
III (3) IV V VI
VII (2)
VIII
Methylobacterium
Neighbour-joining Phylogeny estimated from partial 16S rRNA (203 unnamed test strains)
Steadily growing number o
f rhizo
bia in our biobank
more than 500 str
ains
13 strainsTotal nitrogen accumulation in pigeon pea varieties inoculated with bradyrhizobia isolates
Results from similar investigations greenhouse- Haricot bean (P. vulgaris)- Soybean (G. max)- Chickpea (Cicer arietinum)- Lentil (Lens culinaris)- Cowpea
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 Shoot dry wt. Plant-1 SUNAINAShoot dry wt. Plant-1 MH-97-6Shoot dry wt. Plant-1 SML32Shoot dry wt. Plant-1 SML134
Rhizobial strains
Shoo
t dry
wt.
plan
t-1(g
)
Mung bean varieties vs R.strains
23 strains
Symbiotic effectiveness of indigenous rhizobia and P fertilizer … Haricot bean (Phaseolus vulgaris L.) at Boricha, S. Ethiopia
(Tarekegn 2010)
Nodule Nodule Leaf Treatment number dry wt. area
plant-1 (g) (cm2)Inoc.HB 99 40.78de 0.54c 2.29cd
HB113 52.00bc 0.69b 2.62cb
HB 67 37.44ef 0.50c 2.19d
HB110 59.22b 0.69b 2.78b
HB 429 66.78a 0.78a 3.28a
HB 92b 62.00ab 0.72ab 2.51bc
HB 48 44.22de 0.67b 2.35cd
23 kg N ha-1 57.78bc 0.60b 2.77b
- Inoc. & -N 33.00f 0.47c 1.78e
P (Kgha-1)0 43.96c 0.54b 31.42c
23 48.52b 0.67a 34.79b
46 55.26a 0.70a 38.03a
Table: Effect of rhizobium inoculation and P fertilizer on nodulation and growth of haricot bean at 50% flowering stage, field trial at Boricha (Tarekegn, 2010)
Same letter(s) in a column are not significant, p< 0.05
HB 429
HB 92b
HB110
HB113
HB 48
HB 67
HB 99
N+ (23Kg)
N- & R-
01020304050607080
Noulde number as affected by inoculation
Rhizobium Strains
Nod
ule
Num
ber/
plan
t
ab
cd
f
bc
debccd
ab
Number Number Hundred Grain Straw HarvestTreatment of pods of seed seed yield yield index
plant-1 pod-1 weight (g) (ton ha-1) (ton ha-1) (%)Inoc.HB 99 8.56c 2.91b 35.22cd 1.34de 2.75bc 35.0bc
HB113 9.03bc 3.36a 40.30b 2.03ab 3.26ab 39.2ab
HB 67 8.44c 2.78b 35.60cd 1.54cd 2.68c 37.8ab
HB110 10.50ab 3.38a 41.00ab 1.81bc 2.80bc 40.2ab
HB 429 11.25a 3.42a 44.42a 2.36a 3.38a 41.6a
HB 92b 9.20bc 3.02ab 41.00ab 1.92b 3.14ab 38.3ab
HB 48 8.73bc 2.85b 36.50c 1.74bc 2.76bc 39.6ab
23 kg N/ha 10.50ab 3.03ab 41.80ab 1.92b 2.88bc 40.5ab
No Inoc. & -N 7.47c 2.36c 32.60d 1.17e 2.76bc 31.2c
P (Kgha-1) 0 7.72c 2.78b 36.48c 1.13b 2.53b 32.8b
23 9.60b 3.05a 38.60b 2.01a 3.11a 40.5a
46 10.58a 3.21a 41.01a 2.13a 3.16a 41.2a
Table: Effect of rhizobium inoculation and P fertilizer on grain yield, yield components and harvest index on haricot bean (P. vulgaris) (Tarekegn, 2010)
Same letter(s) in a column are not significant, p< 0.05
HB 429
HB113 HB 92b
HB110 HB 48 HB 67 HB 99 N+ N- & I-0
0.5
1
1.5
2
2.5
Grain yield (t/ha) as affected by inoculation
rhizobiumStrains
Grai
n yi
eld
(t/h
a)
a
bbc
e
bccd
b
de
ab
Table: Plant and soil residual N contents as influenced by Inoculation and P fertilization on P. vulgaris, Boricha, S. Ethiopia (Tarekegn, 2010)
Nitrogen Nitrogen ResidualTreatment content in content in nitrogen
straw (%) grain (%) (%)Inoc.HB 99 0.69 2.65c 0.14bc
HB 113 0.73 3.01abc 0.15ab
HB 67 0.69 2.87bc 0.13bcd
HB 110 0.73 2.92bc 0.14bc
HB 429 0.78 3.33a 0.17a
HB 92b 0.73 3.05ab 0.15ab
HB 48 0.70 2.91bc 0.14bc
23 kg N ha-1 0.71 2.94bc 0.11cd
No Inoc. & -N 0.67 2.10d 0.11cd
P (Kgha-1)0 0.69 2.61b 0.12b
23 0.70 2.96a 0.14ab
46 0.78 3.02a 0.15a
HB 429
HB 92b
HB 113
HB 110
HB 48
HB 67
HB 99
N+ N- & R-
00.5
11.5
22.5
33.5
Grain N content (%) as affected by inoculation
Rhizobium Strains
Grai
n N
cont
ent (
%)
aabc bc
d
bc bc b cab
Our lab HwU A technician working on
pure rhizobial strains in the laminar flow chamber in the soil microbiology laboratory at HwU
Investigating purity and Gram staining under microscope
In general From genetic and symbiotic characterization,
Ethiopia represent a hotspot
Cross-inoculation experiments (few + target hosts (Haricot bean, soyabean, chickpea, cowpea, lentils etc.) demonstrated variations in performance
Thus, great potential for selecting elite strains for prompting sustainable agriculture and to benefit small holder farmers
But!!! Handling, preparation and
application of these strains as legume seed inoculants
Improve crop yield Soil fertility and Nutritional quality (protein content) of
the legume crops
Thank you