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Details of Canola Flowering and the Effect of Heatand the Effect of Heat

Murray Hartman

Oilseed Specialist

ARD, Lacombe

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flower bud initiation

Shift from vegetative to reproductive stage in the apicalreproductive stage in the apical bud is visible by 3-4 leaf stage– Buds vary in maturity on same

raceme and different branches have different maturity

(Canola Council of Canada)

(Valipour et al)

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(Valipour et al)

Argenine canola (B. napus) can self- pollinate whereas Polish canola (B. rapa) can’t

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Anther Development

Late green bud stage

Hormone balance needed for filament elongation, pollen viability, anther dehiscence

25 to 100,000 pollen grains per flower

Copyright ©2004 American Society of Plant BiologistsScott, R. J., et al. Plant Cell 2004;16:S46-S60

, p g preleased gradually over several days after flower opening

•More in warm dry weather

•Pollen grains generally in clumps

•Mature pollen semi-desiccated

Pollen grain coating from tapetum determines compatability with stigma

rain

s pe

r st

igm

a

Spring sown B. napus in England

50% of ovules fertilized

Pol

len

g

anth

ers

50% of ovules fertilized in first hour after flower opening

Lots of pollen!

Pol

len

grai

ns in

a

Hayter and Cresswell, 2006

J. Appl. Ecol. 43:1196-1202

Lots of pollen!

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Brassica flowers are structured for insect pollination

•Bright petals, nectaries etc

•B. napus capable of self-fertilization minimizes need for insect pollinators

•Studies on bee hives and canola yield in B. napus have shown varied results•Range from no yield effect to almost 50% higher yield

•UK study found bees only contributed about 1% of the pollen for a canola stigma

UV photo showing “bee guide” to nectaries (Sasaki and Takahashi, 2002)

Pollen recognition

compatible then water

...

...

2 sperm cells

and nutrients flow to pollen grain

Pollen tube guided to

.

(Wilhelmi and Preuss, 1999)

micropyle

ovary and ovules

Double fertilization

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~ 160 pollen grains needed an a B. napus stigma to fertilize all the ovules and have full seed set in a pod

Arabidopsis

Kemp and Doughty 2003

J. Exp. Biol. 54:157-168Elleman et al, 1992

New Phytol. 121: 413-424

Arrival 45 min 90 min

Dearnaley et al. 2001. Sex Plant Reprod. 13:265-271

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Arabidopsis

~ 20-30% of ovules aren’t fertilized

Weterings and Russell, Plant Cell, 2004 16:S107-118

even under optimal conditions

•Defective – lack embryo sac

•Complete ovule determined by 1 week before flower opening

Post-fertilization• Pods elongate from 2 to 8 days• Pods increase in girth

– Normally only when seed is presentNormally only when seed is present– Fertilized seeds produce hormones to stimulate pod

growth, speed death of flower parts no longer needed (stamens etc)

• Cumulative effect of fertilized ovules begin to suppress later reproductive structures

• Seed abortion occurs 4 – 8 days after flowering– More immature ovules– Ovules furthest down the pistil– Ovules in later flowers such as terminal ends of

raceme

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Stress!

• Canola flowers are most vulnerable to t d i b d (b lti ) t 1 kstress during green bud (bolting) to 1 week

after flower opening

• Over-production of flowers to allow for defects and stress losses– ~ 50% flowers set pods and seeds 50% flowers set pods and seeds

– Canola can compensate for poor early conditions with more branching, late flowers

Polowick, 1988 Annals Bot.90%

‘Westar’, 32 C day / 26 C night from 1st true leaf

Normal

23/18

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Polowick, 1988 Annals Bot. 62:83-86

Parthenocarpy and abnormal reproductive structures

Hot, dry and windy combined!

Premature pistil emergence with normal sized stamens and petals: genetic abnormality

Very short stamens due to male sterility

All flowers on this plant will be pabnormal

Photo: John van Dam

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Compensatory late flowers and pods

1 or 2 weeks starting early flower Heat treatment 35 C 4 hours, ramped from 23 C for 6 hours 18 C for 6 hours at night

Heat treatment

50% pod set

Heat affected fertilized flowers up to 4 days old and for 1 week after heat stress stopped

Compensatory late flowers and pods didn’t recover full seed number or yield

Young et al 2004 J. Exp. Bot. 55:485-495

y

Reciprocal crosses made 4th day of heat treatment

Young et al 2004 J. Exp. Bot. 55:485-495

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Aborted pistils (blanks)

Parthenocarpic (empty) pods

Young et al 2004 J. Exp. Bot. 55:485-495

1 week heat shock at early flower or early pod

35/15 vs 28/15

Control 20/15

EndWeird bloated pod with some seed sprouting, pistil like structures

Angadi et al 2000 CJPS 80:693-701

Start of heat 35/15

Hormones???

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Plants transferred to other temperature regime (shock) before, during and after flowering

27/17 and 22/15

Only looked at main d b hraceme and branches

were removed

Bud to late flower stages were most sensitive

Both male and female flower parts affected

62% parthenocarpic pods

Morrison 1993 Can J Bot 71:303-308

in heat treatment

Researchers Temperature duration timing and degrees

Damaging temperature

Polowick and Sawhney 1987 Continuous @ 18/15 or 28/23 None, although stamens slightly shorter at 28

Fan and Stefansson 1986 7 days after bolting @ 22/16 up to 30/24 None

Polowick and Sawhney 1988 Continuous @ 23/18 or 32/26 32/26 almost complete sterility

Morrison et al 1989 Continuous temperatures ramped up and Maximum temps of 27 and 30 (2Morrison et al 1989 Continuous, temperatures ramped up and down gradually 15/5 up to 30/20

Maximum temps of 27 and 30 (2 hours) reduced pod and seed set

Morrison and Stewart 1992 Field study with 3 different seeding dates at Ottawa and related to temp

Seeds per pod and yield affected when temp >29 at flowering

Morrison 1993 Plants transferred to other temp at different growth stages 27/17 or 22/15

Almost complete sterility at 27/17 from early growth stages

Angadi et al 2000 7 days at early flower or early pod @ 20/15 or 28/15 or 35/15

28/15 starting to suffer less seeds/ pod and yield loss

Aksouh et al 2001 29 days after flowering temp ramped up to Yield loss due to seed size at high 40 C or shock vs 21/16 temp

Gan et al 2004 10 days at bud, early flower or pod @ 20/18, 28/18 or 35/18

Slight yield loss at 28 and many sterile pods at 35

Young et al 2004 1 or 2 weeks at early flower @ 23/18, or 35/ 18 (4 hours, temp ramped up and down)

Pollen & pistil fertility, yield affected by 35

Aksouh – Harradj et al 2006 20-25 days after flowering, 1 day acclimation at moderate temp then either 28/23 or 38/23

Seed weight of sensitive variety affected most affected

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Summary• Heat stress will affect both male and female flower parts,

and the fertilization process– Temperatures 27-30 C

• Will affect already fertilized flowers that are 4 or 5 days old (sterile / parthenocarpic pod, aborted seeds)

• Will affect young pods through seed abortion up to 8 days old and seed size

• Will affect subsequent flowers for about 1 week –pod parthenocarpy / deformation, abortion or “blanks”

• Not known how many days of heat stress before injury or how wind / humidity affects the response

– Probably acts through hormone signals– Other stresses (drought, salinity) will affect plant in similar

fashion through hormones also• But not as dramatic as temperature