Keynote Presentation 07 by Tom Sinclair at the International Conference on Pulses in Marrakesh, Morocco, 18-20 April 2016

1. Pulse Nitrogen Fixation: A Key to
Improve Global Crop Production

2. Nitrogen Accumulation Required for
Crop Growth
• Every new cell requires nitrogen
• Maximum metabolic activity
requires nitrogen
• Redistribution of nitrogen required
to maximize seed growth

3. Perspective on N2
Fixation Research
Energy crisis of 1970’s spurred
major new efforts in N2 fixation
Assumed that bacteria partner was key to
increasing N2 fixation
Now, clear that host plant is the dominate
partner in regulating N2 fixation
Failure in perspective still resonates today

4. Host Plant Control of N2 Fixation
Foster effective fixers
(nodule sanctioning)
Unique features of nodules regulate fixation rate
Closed water system
Oxygen flux to nodule interior
Sensitivity to N feedback
Fixation highly integrated into plant circulation
Water
Nitrogen
(rarely, carbon critical)

5. Nodule
Sanctioning
R.F. Denison
The American Naturalist
2000, 156:567-576

6. O2
5-555
5 – 60
µmol m-3

7. Interior O2 concentration: 5 – 60 µmol m-3
Infected cell O2 Km: 30 – 50 µmol m-3
Usual mitochondria O2 Km: 100 – 130 µmol m-3
(Millar et al., 1996, Plant, Cell, Env. 18:715-726)

8. Hence, at O2 = 40 µmol m-3
Infected cell activity = 0.44 – 0.57 Vmax
Mitochondria activity = 0.24 – 0.28 Vmax
Therefore, ineffective bacteria may have
respiration about half of effective bacteroids
That is, sanctioning

9. Feedback Regulation

10. Biswas and Gresshoff (2014) Int J Mol Sci 15:7380-7397

12. N-compounds
Sucrose
Water
Circulatory System
N-compounds
Water

13. Drought Limitation

14. Soil Drying →

16. Identification of N2 Tolerant Germplasm
~ 3,500 Plant Introductions
Field Screen Low petiole ureide
~ 250 PI Selections
Field Screen N accum. under drought
24 PI Selections
Glasshouse Test ARA with drying soil
11 Tolerant PIs

18. Soil Drying →
Soil Drying →

19. Hutcheson x PI 471938
(drought sensitive) (drought tolerant)
Heterozygous Inbred Families (HIF)
Thirteen HIFs tested
Is N2 fixation tolerance trait
readily transferred to progeny?

21. N2 Fixation Drought
Tolerance
Limited
Transpiration
Maturity
Group
Parental
Pedigree1
Antecedents2 Rank Antecedent
With Trait
Rank Antecedent
With Trait
R02-1325 V 93705-35-1 x
PI 227557
93705-35-1 = Jackson x KS 4895 1 50% PI 227557
25% Jackson
8 No known source
N05-7432 VIII N7002 x
N98-7265
N7002 = N7001 x Cook
N98-7265 = Hutcheson x PPI
471938
2 25% PI 471938 3 12.5% PI 416937
R05-5559 V UA4805 x
PI 471938
UA4805 = Hartz 5545 x KS 4895 3 50% PI 471938 linear No known source
N04-9646 VII Boggs x
NTCPR94-
5157
Boggs = G81-152 x Coker 6738
NTCPR94-5157 = Davis x N73-1102
N73-1102 = Tracy x Ransom
4 No known source 4 No known source
N06-7194 VIII N98-7265 x
N93-110-6
N98-7265 = Hutcheson x PI 471938
N93-110-6 = Young x PI 416937
5 25% PI 471938 5 25% PI 416937
R09-1069 V R01-52F x
Ozark
R01-52F = R93-5455 x Minsoy
R93-5455 = Jackson-derived line x
PI 416937
Ozark = Holladay x DP 415
6 6.25% Jackson 1T 12.5% PI 416937
N06-7543 VII NC-Roy x
N8001
NC-Roy = Holladay x Brim
N8001 = N7001 x Cook
7 No known source 7 12.5% PI 416937
R07-5235 V R01-52F x
R02-6268F
R01-52F = R93-5455 x Minsoy
R93-5455 = Jackson-derived line x
PI 416937
R02-6268F = KS 4895 x Jackson
8 31.25% Jackson 9 12.5% PI 416937
R09-1121 V R01-888F x
R05-5559
R01-888F = Jackson x KS 4895
R05-5559 = UA 4805 x PI 471938
9 25% Jackson
25% PI 471938
1T No known source
R07-7044 V Lonoke x
NTCPR94-
5157
Lonoke = Manokin x Asgrow 6297
NTCPR94-5157 = Davis x N73-1102
N73-1102 = Tracy x Ransom
10 No known source 6 No known source
Progress in Developing Elite Breeding Lines (AR & NC)

22. Simulated Yield Response to
N2 Fixation Drought Tolerance
75 %
(wet)
Median
25 %
(dry)
Use Africa
Results
instead

23. Conclusions
 Host sanctioning in suppressing retarding
expansion of ineffective bacteria
 Host regulates circulation of water and N
compounds controlling N2 fixation rates
 Host regulates N2 fixation rate during water-
deficit conditions

28. Mating of Jackson with several
high-yielding lines (1993)
Jackson x KS 4895

29. 100 200 300 400
-60
-30
0
30
60
90
Consistent
Yield Gain
Check Yield (g m-2
)
YieldDiffer.(gm-2
)
[R01-581F-Check]

30. 75
85
95
105
115
125
135
0
10
20
30
40
R01-416F
R01-581F
Jackson:75
KS4895: 91
N accumulation (mg plant-1
)
Frequency(%)

32. Initial screen for N2 Fixation Drought
Tolerance
Cultivar R5 to R7 N Accum
Decrease Drought/WW
Jackson 1 0.86
CNS 2 0.72
Coker 368 1 0.72
Roanoke 3 0.67
SCE 82-222 3 0.55
Coker 156 7 0.53
Asgrow 7372 6 0.46
SCE 82-303 7 0.19
Sall and Sinclair. 1991. Plant Soil. 133:31-37.