Beyond tillering:
yield slipping down the sink
Tanguy Lafarge
leaf 1 leaf 2 leaf 3 leaf 4 leaf 1 leaf 2 leaf 3 leaf 4 leaf 5 leaf 6 leaf 7 main tiller tiller 1 tiller 2 tiller 3
Outline
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Early tillering
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Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
There is room for improvement at early stage by growing seedlings with higher SLA (better weed competitiveness)
Specific leaf area, cm g-1
300 350 400 450 500 550 600 650 Leaf ar ea, cm 2 20 40 60 80 100 120 H (8) I (7)
The range of variation in SLA is not the cause of higher seedling
vigor of hybrids
Higher SLA triggers higher leaf area and seedling vigor
Days after sowing
10 15 20 25 30 35 S p ec ifi c l eaf a rea , cm g -1 100 200 300 400 500 600 H I
Transplanting, 8 hybrids, 7 inbreds
3 days after transplanting SLA = leaf area
leaf dry weight Calculation of specific leaf area
High plasticity of SLA quantified right after transplanting:
a transient drop in SLA buffered the chock of transplanting
leaf vigor decreases
leaf vigor decreases
transplanted 7 days after sowing transplanted 21 days after sowing transplanted 14 days after sowing IR72 in the main field,
shots taken 34 days after sowing for all 3 situations
Transplanting, hill spacing 20 x 20 cm
Tillering and biomass were favored when transplanting young seedlings
Farmers’ practice:
- 20 to 30 days-old seedlings at transplanting
- 3000 to 10 000 seeds m-2 inside the nursery
Days after sowing 0 20 40 60 80 100 120 140 Numbe r of produ c ti v e t ill e rs pe r p lan t 0 4 8 12 16 20 500 seeds m-2 3000 seeds m-2 10 000 seeds m-2 40 000 seeds m-2
Days after sowing
0 20 40 60 80 100 120 N umb e r o f p ro du c tive tille rs per p lant 0 4 8 12 16 20 24 7 days-old seedlings 21 days-old seedlings 35 days-old seedlings
Seed density (number m-2)
500 3000 10000 40000 Grain y ie ld (kg ha -1 ) 0 1 2 3 4 5 transplanting at 35 DAS
High seed density and extended stay in the nursery induced a delay in tiller emergence and a reduction in grain yield
4 tillers
main field nursery
Seedling age at transplanting (days)
7 21 35 Grai n y iel d (k g ha -1 ) 0 1 2 3 4 5
10000 seeds m-2 in the nursery
- Tiller emergence was delayed if extended
growth duration or high density in the nursery
Grain yield was gradually reduced with respect to the increase in the age at transplanting or in the seed rate
Early tillering: seedling age at transplanting and grain yield
- Tiller emergence resumed right after transplanting whatever the density and age
Days after sowing 0 20 40 60 80 100 120 140 N um be r of prod uc ti v e t ill ers pe r plan t 0 4 8 12 16 500 seeds m-2 3000 seeds m-2 10 000 seeds m-2 40 000 seeds m-2 Sp ec ific le af ar ea (c m 2 g -1 ) 100 200 300 400 500 500 seeds m-2 3000 seeds m-2 10 000 seeds m-2 40 000 seeds m-2 Spe c if ic le af a rea (c m 2 g -1 ) 100 150 200 250 300 350 400 450 7 days-old seedlings 21 days-old seedlings 35 days-old seedlings
Days after sowing
0 20 40 60 80 100 120 Num b e r of prod uc ti v e t ill e rs pe r plan t 0 4 8 12 16 20 7 days-old seedlings 21 days-old seedlings 35 days-old seedlings
Early tillering: plasticity in SLA as a support of tillering
Transplanting 35-days old seedlings Growing 10 000 seedlings m-2 in the nursery
SLA increased with the density in the nursery SLA was maintained at a high value in case of an extended stay in the nursery
- SLA is highly responsive to plant competition at early stage which favored tiller production in the nursery and in the main field
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
Days after sowing 0 20 40 60 80 100 Pr oductive tiller no per plant 0 5 10 15 20 25 30 Inbred Hybrid NPT
Days after sowing
0 20 40 60 80 100 120
P
roductive tiller no per plant
0 5 10 15 20 25 30 35 IR64 LT2 LT3 Hybrid
Days after sowing
0 20 40 60 80 100 120
Pro
ducrive tiller no per plant
0 5 10 15 20 25 30 35 7 days 14 days 21 days
Lower tiller emergence rate
Synchrony in maximum tillering Delayed maximum tillering
Early and rapid tillering is already a characteristic of hybrids and inbreds
Early tillering and leaf area closure are crucial for high biomass
accumulation and high yield
8.71 t ha-1 7.59 t ha-1 7.27 t ha-1 7.75 t ha-1 6.97 t ha-1 6.30 t ha-1 2007 DS -0.5 0 0.5 1 0 20 40 60 80 DAS Co rr e la ti o n co ef fi c ie n t
Correlation of grain yield with leaf area index at early stage when comparing a range of hybrids and inbreds
NPT and LTG: low biomass accumulation because of reduced tillering capacity and more vigorous organs at early stage
Lower tiller emergence rate
- SLA increased rapidly as a response to shading during the vegetative phase
- SLA was back to the control value as soon as the shading was removed at early stage - Tiller production was maintained
for a short period before being affected
Rapid tillering: plasticity of SLA as a buffer to trigger tillering Shading event (70%) were established for
short periods of 9 days in Rad1 and Rad2
The high plasticity of SLA can sustain tiller production for a while at early stage. The plasticity of SLA is reduced at later stage
Specif ic leaf ar ea (cm 2 g -1 ) 150 200 250 300 350 400 TT13 vs SLAR0 TT14 vs SLAR1 TT15 vs SLAR2
Thermal time from transplanting (°C days)
0 300 600 900 1200
Gr
een tiller num
ber per plant 0 10 20 30 Control Rad1 Rad2
Lower plasticity of SLA if a stress
occurs around panicle initiation probably because of the competition between sinks
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
Blade PC 0.0 0.2 0.4 0.6 mean-H mean-I
Days after sowing 11-31 31-45 45-52 Cu lm PC 0.00 0.04 0.08 0.12 0.16
Early cessation of tillering: better sink regulation at early stage
Days after sowing
0 20 40 60 80 100 Product ive tille r no pe r pla n t 0 5 10 15 20 25 30 Inbred Hybrid NPT vegetative phase
Calculation of blade partitioning coefficient: Blade PC = Δdwblade 2→1 / Δtime2→1
Δdwshoot 2→1 / Δtime2→1
Hybrid:
earlier cessation in tiller emergence is associated with earlier partitioning in favor to culm
Comparing partitioning coefficients of 3 hybrids and 3 inbreds of the same phenology
culm
Earlier cessation in tiller emergence may generate an increase in reserves stored in the culm and remobilized during grain filling
High correlation between stem vigor and reserves accumulation
Max imum tiller num ber, m -2 200 300 400 500 600 700 CF AWD
H5 H14 I2 I4 I9 I15 I23 I24 I25
C u lm d ry matter , g plt -1 0.4 0.8 1.2 56 DAS 46 DAS
Days after sowing (days)
0 40 80 120
Productive tiller number per plant 0
10 20 30 40 3 cm water level 8 cm water level
Early cessation of tillering: better sink regulation at early stage
Tiller emergence is affected by water depth: an increase in water depth at mid-tillering until booting stage triggers an earlier
cessation of tiller emergence
period with higher water depth
In contrast, tiller emergence is
extended under AWD management
and culm growth is delayed
Extended tiller emergence under AWD is associated with delayed culm growth and possibly less reserves storage
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
S pecif ic leaf area (c m 2 g -1 ) 150 200 250 300 350 400
Thermal time from transplanting (°C days)
0 300 600 900 1200 Green t iller num ber per plant 0 10 20 30 Control Rad3 S p e c if ic le a f a re a ( c m 2 g -1 ) 100 200 300 400 500 500 seeds m-2, 7 days-old 40 000 seeds m-2, 35 days-old
Days after sowing
0 20 40 60 80 100 120 140 N u mber o f pr od uctive til ler s p er plan t 0 4 8 12 16 500 seeds m-2, 7 days-old 40 000 sds m-2, 35 days-old
Tillering plasticity at later stage: associated with SLA plasticity… …in response to high seedling density
Comparing dynamics of 7-days old and 35-days old seedlings
…in response to extended shading
Production of tillers is favored to the detriment of organ vigor under limited access to radiation in the field
hybrid Pr od uctive tiller n u mbe r pe r plan t 0 6 12 18 24 30 CF AWD inbred
Days after sowing
0 20 40 60 80 100 120 0 4 8 12 16 20 irrigation irrigation
…in response to water drainage Tillering plasticity at later stage: emergence of extra tillers…
Tiller origin T3 T4 T5 T6 T7 T8 T9 Number of primary t illers 0.0 0.3 0.6 0.9 Num ber of tillers per primary t illers 0 1 2 3 4 Control Tiller removal
…in response to early tiller loss
Removal of primary tillers 3 and 4 at their emergence
Higher production of secondary and tertiary tillers attached to primary tillers 5 and 6
Successive water drainage periods before and after flowering
Successive tiller loss in aerobic conditions and tiller emergence in flooded conditions
…in response to heat
…in response to pest injury Tillering plasticity at later stage: emergence of extra tillers…
Initial panicle totally sterile at maturity because of heat
Panicles newly formed after flowering
Newly formed tillers attached to upper nodes of the mother tiller
Rubia et al, 1996
Newly formed tillers to overcome the loss of damaged tillers by stem borers
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
Tiller origin T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 M a x im u m t iller num b er in each colony 0 2 4 6 8 10 Primary tillers Sec+ tert tillers
leaf 1
leaf 2 leaf 3
leaf 4
Specific leaf area, cm g-1
300 350 400 450 500 550 600 650 Lea f area, cm 2 20 40 60 80 100 120 H (8) I (7)
Transplanting, 8 hybrids, 7 inbreds
Thermal time from transplanting (°C days)
0 300 600 900 1200 Spe c if ic lea f area (cm 2 g -1 ) 150 200 250 300 350 400 Rad0 Rad1
Can we breed for plants with primary tillers 2 ?
The higher SLA, the higher leaf area
There is still room to increase SLA
Shading in the field at early stage
The distribution of tillers per plant highlights that there is no production of tillers from the bud 2 of the main tiller
Can higher plant SLA trigger production of tillers from leaf 2?
from top
Days after sowing
20 30 40 50 60 70 80 90 Clump dia m ete r ac ross 3 0 cm spac in g 0 5 10 15 20 25 30 Inbred Hybrid NPT
Days after sowing
20 30 40 50 60 70 80 90 Clump dia m ete r ac ross 1 0 cm spac in g 0 5 10 15 20 25 30 across 30 cm spacing across 10 cm spacing 10 cm 30 cm
• Same and weak sensitivity of hybrids and inbreds
among 16 contrasted genotypes to intra-plant competition:
• No adaptation of IRRI hybrids/inbreds to direct-seeding
– All high-yielding genotypes were bred under transplanting
– Minimal Genotypes x Establishment interaction Is the plant able to adapt its tiller orientation according to access for light in the rice canopy?
Can we breed for plants with plastic tiller orientation?
LAI at max tillering 0 1 2 3 DA S at max til ler in g 0 10 20 30 40 50 60 70
LAI at max tillering
0 1 2 3 4
IR75217H IR72
Can an earlier cessation in tillering increase in grain yield? Days with PI as the reference
-16 -12 -8 -4 DAS at max tillering 0 10 20 30 40 50 60 70
Days with PI as the reference
-16 -12 -8 -4 0
IR75217H IR72
Days with start in internode elongation as the reference
-10 -8 -6 -4 -2
DAS at max tillering
0 10 20 30 40 50 60 70
Days with start in internode elongation as the reference
-10 -8 -6 -4 -2 0
IR75217H IR72
Gathering data from the wet and dry seasons, seedling age at transplanting of 7, 14 and 21 days,
from contrasted water depth (3 to 10 cm) and plant densities (25 to 100 pl m-2)
Days after sowing
0 20 40 60 80 100 120
number of tillers per
plant 0 10 20 30 40 total prim. sec.+tert.
Predicting cessation of tillering with a mechanistic crop model?
No correlation between cessation of tillering and…
…the LAI value at maximum tillering
…the time of panicle initiation
…the internode elongation starting date
Cessation of emergence of secondary and tertiary tillers occurs later than that of primary tillers
Desire traits of China’s super rice:
- 3-4 leaf tips above the panicle - low position of the panicle - erect tillers and leaves - delayed leaf senescence - moderate plant height
Days after sowing
40 50 60 70 80 90 100 110 Pan icl e DW per producti v e till er, g 0 1 2 3 SCL (cm/g) 20 40 60 80 100 120 140 mean-H mean-I China: increasing biomass accumulation PC to Culm -0.4 -0.2 0.0 0.2 0.4
EGrFil MdGrFil LGrFil
Pa n P C 0.7 0.9 1.1 1.3 ns * ns * * *
Stronger stem and higher reserves storage
Stronger remobilization from culm to panicle
Tropical conditions: improving remobilization SCL stronger stem of hybrid at flowering lighterstem of hybrid at maturity Stronger remobilization with hybrid
In subtropical conditions in China, the main objective is to increase biomass accumulation during grain filling
In tropical conditions, is sink regulation the main improvement to focus on?
Year/ Season GY (t/ha) ShDW m-2 HI SSI (g cm g-1) 2007 DS H (7) 11.03 a 2108 a 0.54 a 175 a Transplanting I (6) 9.48 b 1932 b 0.50 b 145 b 2006 DS H (3) 8.45 a 1780 a 0.51 a 150 a Staggered I (3) 7.53 b 1634 a 0.45 b 102 b 2006 DS H (2) 8.49 a 1587 a 0.55 a 156 a AWD genotypes I (3) 8.44 a 1611 a 0.52 b 133 b 2005 DS H (2) 7.16 a 1959 a 0.45 a 114 a Braodcasting I (2) 5.94 b 1820 a 0.42 a 93 b 2004 WS H (5) 5.93 a 1885 a 0.45 a 140 a Wet season I (7) 5.35 b 1748 b 0.42 b 117b
Comparing the main traits supporting higher hybrid rice performance in the tropics in contrasted conditions: shoot biomass or harvest index (or sink strength index, SSI)?
The partitioning efficiency (SSI) is significantly higher with hybrids in all the
situations while the shoot biomass is higher only in 2 of the 5 situations
SSI at maturity can be used more acurately than harvest index to discriminate plants in their ability to partition biomass efficiently
In tropical conditions, sink regulation seems to play a major role in supporting higher hybrid performance
Tillering efficiency (TilE): TilE = productive tillers
total tillers
non-productive tillers Transplanting young
seedlings is associated with higher tiller
mortality because of higher maximum tillering Tiller origin T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 P e rcentage of unproductiv e tillers per colony of pr im ary tiller ( % ) 0 20 40 60 80 100 120 Primary tillers Sec+ tert tillers
Tiller mortality concerns:
- young tillers, then low plant biomass
- small tillers, then low-competitive tillers for access to light with the taller tillers
- green tillers intercepting light inside the canopy for their own use
Is a low ratio of tiller efficiency correlated with lower grain yield?
Days after sowing (days)
0 40 80 120
Prod tiller no per plant
0 10 20 30 40 transplanted at 7 d transplanted at 14 d transplanted at 21 d
2007 DS IRRI Tillering efficiency 0.3 0.4 0.5 0.6 0.7 0.8 Grain y ield (t ha-1) 4 6 8 10 12 2004 WS IRRI-APA Tillering Efficiency 0.4 0.5 0.6 0.7 0.8 SB 25 Tiller Efficiency 0.4 0.5 0.6 0.7 0.8 2005 DS Muñoz Transplanting, IRRI, dry season Transplanting, IRRI, wet season Broadcasting, PhilRice, dry season
No positive correlation is observed between grain yield and TilE across genotypes
Are non-productive tillers useful to crop production by remobilizing substrates before getting senescent?
0 500 1000 1500 2000 2500
H1 H5 H6 H7 H8 H12 H13 H14 I1 I4 I9 I10 I11 I12 I13
Genotype Fi ll e d G ra in num be r pe r pl a nt 0 5 10 15 20 25 30
H1 H5 H6 H7 H8 H12 H13 H14 I1 I4 I9 I10 I11 I12 I13
Genotype 1000 Filled Gr ain d w (g) Control Tiller removal Manual removal of about 1/3 of the tillers per plant 11 days after panicle initiation
Grain size was not
affected but a strong
reduction in filled
grain number per
plant was reported
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
Unproductive tillers more efficient use of biomass Plant height more efficient use of biomass Biomass remobilization higher tolerance to lodging Grain filling duration more harvested grains Unfilled spikelets more efficient use of biomass Leaf senescence higher light interception higher biomass remobilization higher light interception higher light interception higher grain filling higher sink allowance higher biomass accumulation
Selecting for individual traits: dealing with the mutual benefit of opposite traits
IR72 NPT HYB1 HYB2 Target 1 Target 2 Grain yield, t ha-1 8.5 8.2 10.1 9.7 12.0 11.9 Total panicles/m2 400 250 450 600 350 250 Total spikelets/pan. 100 150 80 65 150 200 % filled spikelets 85 80 74 67 80 80 1000 FiGrDW, g 22 24 26 21 25 26
Examples of measured field data and possible target components:
High compensation between yield components (panicle number, grain number per panicle, grain size) indicates that many combinations can produce the same grain yield
Fixing a quantitative target for a single yield component should not be a strategy for increasing yield potential
In the objective of designing ideotypes for yield potential, it is needed to combine integrated approaches for complex traits with single-trait approaches for well-recognized traits of interest
Fille d g rain nu mber pe r p rod uctiv e tille r w ithin e a ch c o lony 0 20 40 60 Tiller colony MT T3 T4 T5 T6 T7 T8 T9 1000 f illed gr ain d ry w e ight (g) 0 6 12 18 24 Filled g rain n u mber per pr imary tille r 0 40 80 120 160 200 240 280 7 days old 21 days old P rod uct iv e ti ller pe r pl ant 4 6 8 10 12 14 16 NR TR Fi lled grai n numb e r pe r pl an t 400 450 500 550 H a rv est i nde x 0.15 0.20 0.25 0.30 0.35 H a rv es t i nde x of e a c h prim a ry t ill e r 7 an d 8 0.15 0.20 0.25 0.30 0.35 NR TR Tiller 7 Tiller 8 Fer ti lity rat e ( % ) of eac h prim ary ti lle r 7 and 8 0.20 0.25 0.30 0.35 0.40 0.45
Old seedlings transplanting and mechanical removal of early tillers reduced the productive tiller number but increased the number of filled grain per tiller
Selecting for yield components: high compensation at tiller level
Mechanical removal of early tillers also increased ‘harvest index’ and fertility rate at
Outline
•
Early tillering
•
Rapid tillering
•
Early cessation in tillering emergence
•
Tillering plasticity at later stage
•
Tillering and the unknown
•
Compensation and selecting for yield
components
General conclusion
• Early and rapid tiller production as an essential plant trait for high
yield
– through appropriate plant types (high-yielding hybrid rice and improved
inbreds in contrast to NPT and LTG introgressed lines)
– through appropriate crop management (direct-seeding, transplanting young seedlings)
– opportunity to increase SLA at early stage (high plasticity under shading) and
strong correlation reported between SLA and leaf area tend to indicate there is possibility to improve the early dynamics of tillers
– some genes of interest (Oshox gene and free lysin gene, Inez Loedin et al, and AtHOG1 gene, Prakash Kumar et al, University of Singapore) may
promote earlier tillering and improved nutrition. This needs to be investigated
• No architectural plasticity (tiller angle) was observed among high-
yielding genotypes for adaptation to contrasting planting design and uneven plant distribution like under broadcasting
– it appears necessary to run breeding programs for direct-seeding: this is now
the case under the CSISA project
– this could be a strong justification to screen for plasticity in tiller angle within the gene bank accessions
General conclusion
• Earlier cessation in tillering as a potential trait to increase carbohydrate storage in culms and subsequent remobilization to during grain filling
– this is already observed with hybrid rice, compared to inbreds, and under continuous flooding compared to alternate and drying
– the cessation in tillering could be associated with the initiation of new sinks that are
observed about simultaneously, like the start in internode elongation, the development of the panicle and the storage of reserves. However, no correlation has been reported yet. More investigation is needed
– it seems reasonable to investigate and look for a proof of concept if earlier cessation in tillering can trigger significant increase in carbohydrate storage. This can be done
experimentally as cessation in tillering in cereals is sensitive to change in red/far-red ratio inside the canopy (Ballaré and Casal, 2000). This can also be investigated through
simulation modelling via a mechanistic crop model
– the strategy to breed for New Plant Types (IRRI) and Low Tiller Gene Genotypes (Japan) with the aim at reducing significantly the number of non-productive tillers could have been successful if it would have reduced the number of tillers through an earlier cessation in tillering rather than a reduction in tiller emergence rate
• Non-productive tillers appear as an important trait of the rice crop in contributing to high yield
– no correlation between grain yield and tillering efficiency was reported when looking at many different situations (comparing genetic variability and also crop management practices)
– non-productive tillers are the smallest ones, the youngest ones, so they are not that competitive against the productive tillers. They are also green which means they are photosynthetically active. They may intercept light that productive tillers cannot access to
– non-productive tillers may be useful in contributing to high yield if a substantial amount of their biomass is remobilized towards the productive tillers. Remobilization from one tiller to another could be a high value trait for high yield. Such process should be investigated
General conclusion
• High plasticity of the rice crop is a remarkable trait to
compensate against unexpected stress conditions
– SLA plays the role of a buffer and is rapidly modified at the plant level to enhance tillering and leaf area production, like in the case of
reduction in access to radiation
– new productive tillers are developed to overcome tiller loss due to stress damages like in the case of heat and pest injury
– sink size and fertility rate are increased at individual tiller level to overcome the consequences of an earlier stress on tiller production
– the rice crop may also be too sensitive to changes in growing
conditions: initiation of new tillers under alternate wetting and drying conditions is not a desire trait. If the processes involved in the many responses of tiller plasticity to environmental conditions are different, then some could be blocked while the other would remain untouched
• Improving the sink regulation to partition the shoot biomass
even more efficiently seems to be the main option to increase grain yield of the C3 rice in tropical conditions
•
The assistant scientists:
– Estela Pasuquin, Crisanta Bueno, Brenda Tubana
•
The technicians:
– Pete Gapas, Rene Carandang, Vic Lubigan, Luis
Malabayabas, Andrew Revilleza, Elmer Duque, Rechelle Angeles, Julius Ranada
•
The secretaries:
– Bing Laude, Jennifer Hernandez, Emma Fabian
•
The scholars:
– Bancha Wiangsamut, Jessica Bertheloot, Célia Seassau, Marie Bucourt, Zuziana Susanti, Tapeshwar Shah
‘It is those scientists that have the understanding of interactions
within plants and between plants and dynamic environments that
can provide the key link between gene activity and crop yield’
