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Seed Dormancy - PowerPoint

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					     School of Agriculture,
     Policy and Development




Some implications of weed seed
ecology for weed management
  Alistair Murdoch
 EWRS conference , Santorini, September 2009
 Novel and sustainable weed management in arid and semi-arid agro-ecosystems
... Weeds are opportunists !!!




   Photo by Dannie Romney, International Livestock Research Institute, Kenya
   Prerequisites for invasive weeds
• Propagule dispersal to a new site during which…
   – Viability must be preserved
   – Growth must generally be prevented
   – Predation must be avoided
• After dispersal, invasion occurs if propagules can
   – Maintain viability
   – Prevent growth and
   – Avoid predation
  until conditions are suitable for growth
• Propagules must then be in the right physiological state
  to grow, reproduce and disperse progeny.
      Watch out!
We’ve got to stay alive




           http://www.filebuzz.com/software_screenshot/full/75438-Cartoon_Character_Screensaver.jpg
 Preserving viability
 Seed storage behaviour
• Most weeds have ‘orthodox’ seed storage behaviour:
   – Seeds survive better when dried to very low moisture
     contents and seeds can be frozen when dry
• Recalcitrant seeds:
   – Seeds cannot be dried without damage and some are
     damaged by chilling below 15ºC
  Loss of viability in dry storage

                                       Phelipanche aegyptiaca


                                            50°C, 80%rh



                         60°C, 75%rh




                                                                Weed Research 10, 447–457
                                                                Kebreab & Murdoch (1999)
Note seed to seed variation
within population
                                                                 Ph. aegyptiaca      O. crenata          O. minor


   Survival of
  Phelipanche/
                                                                                          20°C

     Orobanche                                                                                    30°C
  seeds after
  dry storage               Germination of dry stored seeds, %
    for up to
                                                                                                  40°C

  c. 400 days
   at various                                                                                     50°C
    temper-
   atures and
                                                                                                  60°C
    moistures
Kebreab & Murdoch (1999)
Weed Research 10, 447–457


                                                                                  Storage period, days
                  100
                                         Phelipanche aegyptiaca
                   90                    Orobanche cernua 
                   80                      O. crenata
Germination (%)




                   70

                   60
                                                                           Survival of
                   50
                                                                          seeds after
                   40                                                     wet storage
                   30                                                       for up to
                   20                                                     210 days at
                   10                                                         30°C
                    0
                        0   30     60    90    120    150     180   210

                                 Conditioning period (days)               Kebreab & Murdoch (1999)
                                                                          J Exp Bot 50: 211-219
How long can you
  live in soil?




       http://www.filebuzz.com/software_screenshot/full/75438-Cartoon_Character_Screensaver.jpg
Modelling seed depletion in soil
Negative exponential decay curve
  S = S0 e-gt   or      loge S = loge S0 - gt

   where S is the number of surviving seeds from an initial
     population S0 after t years. g is the annual rate of
     depletion.
This model is only valid on
   – a year-to-year basis, and
   – in the absence of seed influx.

If true, implications include that seed banks have:
    – a constant half life, and
    – a constant annual probability of depletion
                                          Depletion
       Predicting seed depletion          factors

    A depletion factor of 106 is like
       reducing the seed bank
 from 1000 seeds/m2 to 10 seeds/ha.
Elimination is therefore an unrealistic
outcome for invasive plant
management unless the
depletion rate is very high.
Say > 90% per annum
Don’t germinate all
together




        http://www.filebuzz.com/software_screenshot/full/75438-Cartoon_Character_Screensaver.jpg
    Germination prevention
• Dormancy
• Quiescence
                                                                                                                       Open symbols: 32/27ºC, 13h/11h day/night
                                                                                                           Spikelets
                                                                                                                       Closed symbols: 27/20ºC , 13h/11h day/night



                                                    Germination percentage (probability scale)
       Germination percentage (probability scale)
                                                                                                 93
                                                                                                                                  Water                                     Nutrient
                                                                                                 84

                                                                                                 69
                                                                                                                                                                          Drought

                                                                                                 50

                                                                                                 31

                                                                                                 16

                                                                                                  7
Seed                                                                                                                                          Note seed to seed variation
dormancy
                                                                                                  2                                           within population
varies with                                                                                           0          10        20         30        40        50         60
maturation
                                                                                                      After-ripening period (days) at 40ºC, 43% rh
conditions                                                                                                After-ripening period (days)


Cenchrus
ciliaris                                                                                                  Sharif Zadeh & Murdoch Seed Science Research (2000) 10, 447–457
  Dormancy varies with post-harvest
  dry storage (afterripening), Striga hermonthica
                    100
                              60 C
                     90
                                                  30 C                                          20 C
   Germination, %




                     80        50 C
                                      40 C
                     70
                     60
                     50
                     40
                     30
                     20
                     10
                      0
                          0     10     20    30   40     50   60   70   80    90   100   110   120   130

Sonko & Murdoch, unpublished
                                                          Afterripening period, days

  After dry storage, seeds were pre-conditioned for 14 d in water at 30ºC and then germinated at
      30ºC in 1ppm GR24. Seeds were collected in The Gambia from an infestation of millet.
 To germinate
        or
not to germinate
   that is the
    question
        -

 a balancing act
     for the
individual seed –
 How does this
 balance vary?
•   Jose L. Gonzalez      Andujar, Sevilla, Spain
•   Diane Benoit, Québec, Canada
•   Adam Davis,           Urbana, IL, USA
•   Frank Forcella,       Morris, MN, USA
•   Federica Graziani,    Perugia, ITALY
•   Andrea Grundy,        Warwick, UK


Regional variation of germination and dormancy of Chenopodium
album seedlots tested at Reading as part of EWRS WG joint
experiment. Seeds were obtained from most of those listed
                          •   Laila Karlsson ,   Linköping, Sweden
                          •   Per Milberg,       Linköping, Sweden
                          •   Paul Neve,         Warwick, UK
                          •   Ilse A. Rasmussen, Flakkeberg, Denmark
                          •   Jukka Salonen,     Jokioinen, Finland
                          •   Bozena Sera,       Czech Republic
                          •   Edite Sousa,       Tapada da Ajuda, Portugal
                          •   Francesco Tei,     Perugia, Italy
                          •              Collaborators and co-authors
                              Kirsten Tørresen,  Ås, Norway
                          •   Jose M. Urbano,    Sevilla, Spain
General correlation of viability and
“non-dormancy” of Chenopodium album
 with latitude of origin
       Viability or non-dormancy,




                                    90
                                    80                                        Viability (NS)
                                    70
                                    60
                  angles




                                    50
                                    40
                                              Non-dormancy (P<0.05)
                                    30
                                    20
                                    10
                                    0
                                         35       40     45      50      55       60       65
                                                       Latitude, degrees North
 Murdoch et al. unpublished
Optimum constant temperature
for germination of Chenopodium album
is correlated with “non-dormancy”

                                                                   Spearmann Rank
   Optimum temperature, deg C




                                30
                                                              Correlation Coefficient:
                                26                                 -0.752 (P=0.005)

                                22

                                18

                                14

                                10
                                     0.0   20.0    40.0      60.0      80.0      100.0
                                           Maximum germination on plate, %
Optimum constant temperature
for germination of Chenopodium album
is NOT correlated with latitude of origin
 Optimum temperature, deg C



                              30

                              26

                              22

                              18

                              14        Spearmann Rank Correlation
                                        Coefficient: -0.164 (P=0.56, NS)
                              10
                                   35        40       45      50       55     60   65
                                                    Latitude, degrees North
       Responses of common seed lot of
       Chenopodium album to 0.01 mol/L
       potassium nitrate in dark and light
                Germination, angles

                                      90
                                      80   Common Seedlot             Light
                                      70    LSD
                                      60
                                      50                              Dark
                                      40
                                      30
                                      20
                                      10
                                       0
Murdoch et al. unpublished
                                                  Water     Nitrate
Germination (angles) responses to KNO3 in darkness and light




                                                               Murdoch et al. unpublished
Chenopodium album :
Northern seed lots: additive effects of nitrate and light
Southern seed lots: positive interaction (synergism)
                            40
                                                             Interaction of light
                            35
                                                             and nitrate (P<0.05)
      Interaction, angles




                            30
                            25
                            20
                            15
                            10
                             5       Canada
                             0
                            -5 35   40         45       50        55     60         65
                                              Latitude, degrees North
Murdoch et al. unpublished
Germination (º) after chilling for various periods
70            Spain 37º                 70       Portugal 38º               70       USA-IL 40º                              70                        Italy 43º
60
              Negative slope            60
                                                 Slope not significant      60
                                                                                     Slope not significant                   60                        Negative slope
50                                      50                                  50                                               50
40                                      40                                  40                                               40
30                                      30                                  30                                               30
20                                      20                                  20                                               20
         LSD (P =0.05)
10                                      10                                  10                                               10
0                                       0                                   0                                                  0
     0   10     20       30   40   50        0   10   20   30     40   50        0    10   20   30   40       50                   0          10         20            30   40   50



70       Canada 45º                     70       USA-MN 45º                 70        Czech Rep. 48º                         70                       UK 52º
60       Slope not significant          60       Positive slope             60
                                                                                      Slope not significant                  60
                                                                                                                                                      Negative slope
50                                      50                                  50                                               50
40                                      40                                  40                                               40
30                                      30                                  30                                               30
20                                      20                                  20                                               20
10                                      10                                  10                                               10
0                                       0                                   0                                                  0
     0   10     20       30   40   50        0   10   20   30     40   50        0    10   20   30   40       50                   0          10         20            30   40   50



70                                      70                                  70                                               70
60                                      60                                  60       Norway 59º                              60
50                                      50                                  50       Slope not significant                   50
40       Common seed 55º                40       Denmark 55º                40                                               40
30       Slope not significant          30
                                                 Slope not significant
                                                                            30                                               30
20                                      20                                  20                                               20                    Finland 60º
10                                      10                                  10                                               10                    Negative slope
0                                       0                                   0                                                  0
     0   10     20       30   40   50        0   10   20   30     40   50        0    10   20   30   40       50                   0          10         20            30   40   50
                                                           Chilling period, days                     Chilled at 3.1ºC; germinated at 10º/20º C (12h/12h) with light;
                                                                                                     means of 4 replicates of 50 seeds; SED = 4.4, 249 df
For the population of seeds:
quantitative variation in behaviour
in populations tends to be normally distributed.
     But there can be qualitative differences …
                                            Chill out? I’m going back to                 Light AND nitrate
More light                                               sleep
 please                                                                                   AND alternating
                                                                                            temperature



                                         Non-dormant
                                                                                         Nitrate please




             Photo by Dannie Romney, International Livestock Research Institute, Kenya
Don’t get suppressed
     by a crop




         http://www.filebuzz.com/software_screenshot/full/75438-Cartoon_Character_Screensaver.jpg
Suppression of biomass of different weeds (%)
biomass of individual



                         100
Suppression of weed




                                                   low               Medium                High
                          90
    species (%)




                          80
                          70
                          60
                          50




                                                                                                      m
                                                                          m
                                  is




                                                             is
                                               a




                                                                                     ice
                                            tul




                                                           ns




                                                                                                   ru
                                                                      lbu
                               ns




                                                                                    ec
                                                         ve




                                                                                               nig
                                         co
                             e




                                                                       a
                          rv




                                                                                  sp
                                                         ar




                                                                    C.
                                       A.
                           a




                                                                                            S.
                                                                               P.
                                                    V.
                        C.




                                                                  Vigour

                                            Sed df 29
ividual
 weed




                        100                     Recommended                   Double
                         90            Spring wheat cv Axona. 2002 growing season.
 )
uctive                                                                                             Suppression of reproductive
 specie                                                                                              units of individual weed
                                                                                                            species (%)
                                                                                 C.                                                                     C.
                                                                                    a




                                                                  100
                                                                                                                                                           a




                                                                                                       50
                                                                                                            60
                                                                                                                 70
                                                                                                                      80
                                                                                                                           90
                                                                                                                                100
                                                                                        rv e                                                                                        rv e
                                                                                               ns
                                                                                                  is


                                                                                  A.                                                                                    A.
                                                                                         co                                                                                          co
                                                                                               tul
                                                                                                  a                                                                                        t
                                                                                                                                low




                                                                                 V.                                                                     V.
                                                                                      ar v                                                                                         ar v
                                                                                             en
                                                                                                sis                                                                                       e




                                                  Recommended
                                                                                   C.                                                                                     C.
                                                                                                                                         Rate




                                                                        Vigour        a      lbu                                                                             a            lb
                                                                                                 m
                                                                                                                                Medium
                                                                                                                                           Suppression of reproductive units (%)




                                                  Double                         P.                                                                             P.
                                                                                    spe                                                                            spe
                                                                                        c      ice                                                                     c
                                                                                                                                High




                                                                                  S.                                                                                 S.
                                                                                     nig                                                                                nig
                                                                                         ru      m
Spring wheat cv Axona. 2002 growing season. Doukali unpublished
                             Weed biomass suppression.
                             Weeds suppressed similarly by high and low
                             vigour crop seed lots if weeds emerged
                                      Pre HV             F.AtHV         At HV                        F. Syn
                             synchronously with crop. Effect of vigour
                                      PostLV             F.At LV        At LV
                             eliminated at a given crop density.
                             50

                             40                                             () Low vigour
                                                                            Asynchronous
                   (g/pot)




                             30
Weed dry matter, g per pot




                                      High () and low
                                             () vigour
                             20             synchronous

                             10                                         () High vigour
                                                                           Asynchronous
                              0
                                        0                 100         250                 400          550
                                                                 density, plants / m2
                                                            Croppopulation plant/m2
                                                           Crop
                                  Spring wheat cv Paragon. Unpublished results, Doukali and Murdoch 2006
                        Weed seed suppression.
                        Seed production suppressed similarly by
                        high and low vigour crop seed lots if weeds
                                                                  of
                        emerged synchronously with crop. Effect At HV
                                  Pre v1          F.AtHV                                              F.Syn
                        vigour eliminated at a given crop density.AtLV
                                  PostLV          F.AtLV

                        25

                        20                                                    () Low vigour
                                                                              Asynchronous
                                  High () and low
Weed seeds, g per pot
            (g/pot)




                        15               () vigour
                                        synchronous
                        10
                                                                         () High vigour
                        5                                                   Asynchronous
                        0
                                  0                   100              250                 400    550
                                                            Crop density, plants /   m2
                                                        Crop poulation plant/m2
                             Spring wheat cv Paragon. Unpublished results, Doukali and Murdoch 2006
Some concluding outcomes
for weed management
• Predicting population dynamics:
   – Quantify the life cycle
   – Quantify seed-to-seed variation in population
• Mitigate risk of sudden expansion of infestation
   –   Explore options for control at various stages of the life cycle
   –   Manage the crop to suppress weeds
   –   Consider the overall farming system
   –   Rarely find magic bullets!
   –   Integrate diverse options is a best
• Have rational expectations of control of invasions
   – Understand factors affecting seed germination, dormancy
     and longevity
          Watch out for new weed species
Take your eyes off the ball and before you know it, a new
               patch will have appeared.
        Acknowledgements
u   Several research students contributed to this work
    –   Farzad Sharifzadeh (Iran)
    –   Landing Sonko (The Gambia)
    –   Ermias Kebreab (Eritrea)
    –   Musa Doukali (Libya)
    –   Sophie Allen (UK)
u   EWRS Germination and Early Growth WG for
    seeds of Chenopodium album
                                       Aren’t these strange flowers
                                       pretty? I’m going to take some
                                       home!




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