Variation in seed production and germination in 22 rare and threatened Western Australian Verticordia (Myrtaceae)



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97

Journal of the Royal Society of Western Australia, 84:103-110, 2001

© Royal Society of Western Australia 2001

Variation in seed production and germination in 22 rare and threatened

Western Australian Verticordia (Myrtaceae)

A Cochrane

1

, K Brown



2

, S Cunneen

3

 & A Kelly



4

1

Threatened Flora Seed Centre, Department of Conservation and Land Management, Locked Bag 104,



Bentley Delivery Centre, Perth WA 6983

2

Environmental Weeds Action Network, 108 Adelaide Terrace, East Perth WA 6000



3

CSIRO Centre for Mediterranean Agricultural Research, Floreat WA 6014

4

24 Carnarvon St, East Victoria Park WA 6100



email: annec@calm.wa.gov.au

Manuscript received August 2000, accepted March 2001

Abstract

This study investigates the reproductive potential of 22 rare and threatened Western Australian

taxa in the genus Verticordia (Myrtaceae) over a 5-year period. Considerable inter- and intra-specific

variation in both seed production and germinability was demonstrated for the majority of taxa. The

seed to flower ratio, or “seed set”, ranged from 0% to 68% with an overall mean of 21% in 82

accessions representing seed from 48 populations of the 22 taxa. Percentage germination ranged

from 7% to 100% with an average of 49% for 68 accessions. The precariously low annual

reproductive capacity of some of the more restricted and critically endangered taxa threatens their

survival and unexpected disturbance events may result in population decline or even localised

extinction. Mitigation measures such as the reintroduction of plant material into new sites and the

enhancement of existing populations through additional plantings may be warranted for many of

Western Australia’s rare and threatened Verticordia.

Keywords: Verticordia, seed production, germination

Introduction

Verticordia (family Myrtaceae, sub-family

Leptospermoideae) consists of woody perennials largely

endemic to the South West Botanical Province of Western

Australia. This genus occupies a prominent place in

many shrub and heathland communities along with other

myrtaceaous genera such as Beaufortia, Calytrix, Agonis,



Leptospermum, Melaleuca, Chamelaucium and Calothamnus.

There has been a considerable increase in our taxonomic

understanding of the genus in the past decade, and a

revision in 1991 identified 3 subgenera, 24 sections, 97

species, and 62 subspecies and varieties (George 1991).

Material was later re-examined and 100 species and 43

infraspecific taxa were described for the genus (George &

George 1994). Many taxa in the genus are considered of

high conservation value. There were 76 taxa of Verticordia

on the Western Australian Department of Conservation

and Land Management’s Declared Rare and Priority

Flora List (Atkins 1998). Seventeen of these were declared

rare (WA Government Gazette 1999), and five of these

were ranked under IUCN criteria as Critically

Endangered by CALM’s Western Australian Threatened

Species and Communities Unit (Anon 1998b). Many

populations are at risk of local extinction in the near future

due to a range of threatening processes. These include

disease, weed invasion, salinity, small population sizes,

habitat fragmentation and/or continued land clearing.

The genus possesses many species with great potential

for ornamental horticulture (George 1990). The often

prominently displayed feathery flowers are borne singly

but appear as heads or spikes and are generally brightly

coloured, ranging from yellow to red to purple. The

flowers are long lasting, and can be picked for the cut

flower market. Between 1996 and 1998 over 1 million

flowering stems of 23 taxa of Verticordia were bush picked

from private, crown lands and cultivated stands for the

cut flower industry (L Rohl, CALM, unpublished data).

Over-picking of flowers from the wild has been

impacting on wild populations of a number of species

(e.gV. eryocephala) with detrimental effects (McEvoy &

True 1995).

Although there have been a number of studies on

pollen germination and tissue culture propagation in



Verticordia (McComb et al. 1986; Tyagi et al. 1992), there

has been limited research conducted on the reproductive

biology of particular species in the genus. Seed appears

to be of the dependent embryo type (small embryos

relative to the endosperm) according to classification by

Atwater & Vivrette (1987). Tyagi et al. (1991) reported

that in Verticordia only a single seed is set despite ovule

numbers of up to 13 in some taxa. Our experience has

shown that on rare occasions 2 and 3 seed per flower

may form in taxa with multiple ovules (A Cochrane,

personal observations). Houston et al. (1993) report seed

set (based on seed to flower ratio) for V. nitens averaging

27% with a range from 0.6% to 54% and 36% for V. aurea.

Tyagi et al. (1991) also reported low seed set for a range

of taxa in the genus.

Holm (1988) considered that pollinators for this genus

were likely to be unspecialised insects, but postulated


98

Journal of the Royal Society of Western Australia, 84(3), September 2001

that V. grandis may be bird pollinated due to the flower

structure. Houston et al. (1993) reported apparent

pollinator mutualism in V. nitens and possibly in V. aurea.

Profuse flowering in some species of Verticordia pointed

towards intense competition for pollinators (Holm 1988),

and given the great range of floral morphology, scent,

colour and flowering times, it is possible that many

pollinators will be found to be highly specific.



Verticordia have indehiscent fruits (nuts) that usually

contain a single seed and are shed annually. They are

never discharged but the entire flower dries and breaks

off below the receptacle. It is thought that dormancy in

some members of the Myrtaceae (for example in

Chamelaucium, Verticorida and Darwinia) is controlled by

the seed coat inside the fruit that breaks down in time

due to weathering and soil disturbance (Beardsell et al.

1993a). Verticordia plants for the nursery industry have

traditionally been propagated vegetatively due to

inadequate knowledge of seed collection and germination

techniques (Watkins & Shepherd 1984). Relatively few

studies have been undertaken on seed germination in this

genus, although Ashby (1961) reported some success with

V. picta, V. chrysantha and V. brownii. Over the past 5

years considerable developments have been made in the

techniques required for successful germination of a range

of Western Australian species (see review by Bell et al.

1993; Cochrane & Kelly 1996). Smoke responsiveness has

been demonstrated in the genus (Dixon et al. 1995) and

after-ripening requirements can be overcome with the

addition of the growth hormone gibberellic acid

(Cochrane et al. unpublished observations).

Over the past 5 years, seeds of a large range of

threatened taxa in the genus Verticordia have been

collected for conservation in Western Australia’s ex situ

program. The aim of this program is to conserve the

genetic diversity of threatened taxa under low moisture

and low temperature conditions for long periods of time

(> 50 years) until material is required for recovery

purposes (Cochrane & Coates 1994).

This present study assessed the reproductive potential

of a range of rare and threatened taxa in the genus

Verticordia through an analysis of seed set and

germination data collected over a 5 year period. These

data are useful as a basis for recommendations for

conservation and management of the populations. Sound

knowledge of germination mechanisms will enable

adequate monitoring of seed viability in storage and

enhances the opportunity to provide whole plants for

recovery.



Methods

All Verticordia seeds used in this study were collected

from wild populations between January 1994 and

December 1998. Site names have been abbreviated due to

the confidentiality of locational information for

conservation flora. Seed stocks are held ex situ at the

Department of Conservation and Land Management’s

Threatened Flora Seed Centre, a seed-based genebank for

the conservation of genetic material from rare and

threatened taxa. Seeds were tested for germinability

freshly collected and, in many cases, after moisture

content reduction and storage at –20 

o

C for periods of up



to 5 years.

Seed set was assessed by sectioning 3 replicate

samples of 100 old flowers (fruits) through the

hypanthium to establish the presence or absence of a

healthy seed (swollen, moist, white embryo). Calculation

of seed set by the cut test method was based on the

proportion of seeds to old flowers rather than the seed to

ovule ratio. Seed to flower ratio was considered to be a

more useful indicator of reproductive potential than seed

to ovule ratio as rarely did more than 1 ovule per flower

set. “Seed set” was therefore defined as the number of

intact and healthy seeds for a given number of flowers.

Some predation of developing ovules was observed

during cut tests, although the level of predation was not

quantified.

Seed germination trials were conducted under

laboratory conditions. Seed sample sizes were dependent

on the number of old flowers (fruits) collected, as well as

the number of seeds obtained by the cut test (seed set)

and ranged from 5 to over 1000 seeds (x– 61). To aid

germination, seeds were completely excised from the old

flowers with a scalpel under a dissecting microscope.

Prior to seed coat removal, flowers were soaked in

distilled water for a minimum of 2 hours to soften the

seed coat. Seeds were germinated in 90 mm glass Petrie

dishes on a 0.75% (w/v) agar solution in temperature

and light controlled incubation cabinets, using a 12-hour

photoperiod. Cabinets were set at a constant 15 

0

C. A 2%


solution of Previcure fungicide was added to the agar

solution to inhibit fungal growth. Seeds were not surface

sterilised prior to incubation. Petrie dishes were checked

twice weekly and germination was determined by radicle

emergence.

Previous research (A Cochrane, unpublished data) has

indicated that many species of Verticordia are smoke

responsive, and the seeds of those species requiring

aqueous smoke treatment for optimum germination were

soaked for 24 hours in a smoke solution obtained from

Perth’s Kings Park and Botanic Gardens and produced

according to Dixon et al. (1995). After soaking, seeds were

rinsed with distilled water prior to incubation. Growth

promoters have been found to be necessary to cue

germination in fresh seed of Verticordia, and the growth

hormone gibberellic acid (GA

3

) was added to the agar



medium at either 25 mg L

-1

 or 10 mg L



-1

.

Results

The number of ovules per flower in the genus

Verticordia varies between species and ranges from 1 to 8

for the 22 taxa studied (Table 1). Rarely did more than 1

seed per flower reach maturity and as such the seed to

ovule ratio ranged from 0.125 to 1 (Table 1). There was a

broad range of inter- and intra-specific variation in seed

set and germination within the genus (Table 2). The mean

seed set for all collections was 21% (± 1.85) with a range

from 0 to 68%. Population seed set was never greater

than 68%, although seed set for a single individual within

a taxon did reach 90% in V. staminosa subsp cylindraceae

var erecta (see Fig 1). The mean percentage germination

was 49% (± 2.96), range 7-100%, for 68 accessions.

Fourteen taxa are known to be obligate seeders; 4 are

respouters, with 3 considered to have the potential to

both resprout and seed. Information on the reproductive


99

A Cochrane et al.: Seed production and germination in Verticordia



Table 1

Fire response, number of ovules per flower, seed to ovule ratio, and percentage seed set and germination for 22 rare and threatened taxa

in the genus Verticordia.

Species


Fire

Ovules


Seed/

% seed set

% seed germination

Response


per

ovule


(± se, range)

(±  se, range)

(Seeder/

flower


ratio

Resprouter)

Subgenus Chrysoma

V. endlicheriana Schauer var angustifolia AS George (sect Chrysoma)

Both


2

0.5


11 (11)

24 (24)


V. staminosa ssp cylindracea AS George var cylindracea (sect Synandra)

Resprouter

2

0.5


58.0 ± 3.6 (53-65)

79.4 ± 11.6 (57-96)



V. staminosa ssp cylindracea AS George var erecta (sect Synandra)

Resprouter

2

0.5


33.5 ± 25.5 (8-59)

84.5 ± 3.5 (81-88)



V. staminosa C Gardner & AS George ssp staminosa  (sect Synandra)

Resprouter

2

0.5


32.0 ± 6.1 (20-40)

76.7 ± 12.0 (60-100)

Subgenus Eperephes

V. albida AS George (sect Pennuligera)

Seeder


7 or 8

0.125-0.14

43.8 ± 5.02 (20-68)

30.4 ± 8.6 (10-87)



V. comosa AS George (sect Pennuligera)

Seeder


8

0.14


17 (17)

47 (47)


V. attenuata AS George (sect Verticordella)

Seeder


6

0.17


22.8 ± 8.9 (8-48)

37.5 ± 5.9 (26-54)



V. bifimbriata  AS George (sect Verticordella)

Seeder


6

0.17


33.5 ± 16.5 (17-50)

68 (68)


V. carinata  Turcz (sect Verticordella)

Seeder


6

0.17


16.0 ± 2.1 (13-20)

34.7 ± 11.9 (11-48)



V. hughanii  F Muell (sect Verticordella)

Both


8

0.143


15.0 ± 9 (6-24)

63.0 ± 6.0 (57-69)



V. spicata ssp squamosa  F Muell (sect Verticordella)

Seeder


6 or 7

0.17-0.14

8.6 ± 2.1 (0-19)

43.0 ± 8.6 (7-86)

Subgenus Verticordia

V. densiflora Lindley var caespitosa Turcz (sect Corymbiformis)

Seeder


1 or 2

1-0.5


25 (25)

73 (73)


V. densiflora Lindley var pedunculata AS George (sect Corymbiformis)

Seeder


1 or 2

1-0.5


25 (25)

78 (78)


V. dasystylis ssp oestopoia AS George (sect Penicillaris)

Unknown


2

1-0.5


6 (6)

75 (75)


V. fimbrilepis ssp australis Trucz (sect Verticordia)

Seeder


2

0.5


22.7 ± 4.5 (14-29)

56.7 ± 21.5 (15-87)



V. fimbrilepis ssp fimbrilepis  Trucz (sect Verticordia)

Seeder


2

0.5


24.0 ± 2.5 (15-39)

53.8 ± 6.5 (25-86)



V. harveyi  Benth (sect Verticordia)

Seeder


2

0.5


11.5 ± 3.1 (3-25)

33 (33)


V. helichrysantha  F Muell Ex Benth (sect Verticordia)

Both


4 or 5

0.25-0.2


19.3 ± 8.4 (4-33)

47.3 ± 9.940 (29-63)



V. pityrhops  AS George (sect Verticordia)

Seeder


2

0.5


5 (5)

-

V. plumosa var ananeotes  (Desf) Druce (sect Verticordia)

Resprouter

4

0.25



5.4 ± 1.6 (2-11)

26.0 ± 7.0 (11-42)



V. plumosa var pleiobotrya (Desf) Druce (sect Verticordia)

Seeder


4

0.25


24 (24)

72 (72)


V. plumosa var vassensis (Desf) Druce (sect Verticordia)

Seeder


4

0.25


7.7 ± 2.6 (0-17)

46.0 ± 8.7 (25-75)

strategy for one taxon (V. dasystylis subsp oestopoia) was

not known.

Seed production and germinability for the 82

collections of Verticordia exhibited year to year (Fig 2A-

C), population to population (Fig 3), plant to plant (Fig 4)

and seasonal (Figs 5, 6) variation. The mean seed set and

germination for each taxon was calculated (Table 1);

however, the wide spatial and temporal variation make

these figures somewhat misleading. Nonetheless these

data provide a reference point to illustrate the variation

between taxa. There were no apparent trends evident for

seed set and germination or for reproductive strategy

within the different subgenera or sections (Table 1). There

was also no correlation between condition of the

population as determined by location (road verge versus

reserve or bushland) and health of population (degraded

or healthy) and reproductive potential (Table 2). In

addition, there was no correlation between intra-specific

population size and levels of seed set (Table 2).

Discussion

Seed Production

It would appear from this study that rare and

threatened taxa within the genus Verticordia exhibit

excess flower production and a corresponding low seed

to flower ratio, in keeping with previous results for

common taxa in the genus (Tyagi et al. 1991; Houston et



al. 1993). Lee & Bazzaz (1982) consider it more cost

beneficial for plants to produce excess flowers and only

allocate energy for seed production to those flowers with

a minimal level of surviving embryos. Flower production

is less energy draining than the necessary proteins and

lipids required for seed production. Surplus flower

production may enable plants to exploit favourable

conditions such as increased resources or pollinator

activity that occur unpredictably. Seasonal and yearly

changes in seed set may be due to changes in flower

density during the flowering period that may in turn

affect pollinator assemblages, abundance and behaviour.

It may also give a plant the opportunity to increase its

Figure 1.

 Differences in seed set between individual plants for V.



staminosa subsp cylindracea var erecta 1995 Site MG.

100

Journal of the Royal Society of Western Australia, 84(3), September 2001



Table 2

Site location, condition (D=degraded H=healthy RV=road verge P=reserve, park, remnant bush), population size, time of collection,

number of plants sampled, percentage seed set, and germination for 22 rare and threatened taxa in the genus Verticordia.

Species


Location

Condition

Population

Time of


Plants

%

% germi-



Seeds

size


collection

sampled


seed set

nation


 used in

germi-


nation

trials


V. albida

Site L


H RV

16

Jan-96



16

24

19



54

V. albida

Site L


H RV

16

Jan-97



12

20

30



53

V. albida

Site S


D RV

<20

Jan-96


5

50

87



8

V. albida

Site S


D RV

<20

Jan-97


7

56

12



50

V. albida

Site TSE


D RV

<50

Jan-96


10

42

27



15

V. albida

Site TSE


D RV

<50

Jan-97


20

38

10



50

V. albida

Site WW


H P

1000+


Jan-95

8

46



-

-

V. albida

Site WW

H P


1000+

Jan-96


500

68

29



78

V. albida

Site WW


H P

1000+


Jan-97

25

50



29

31

V. attenuata

Site BH

D RV


<100

Mar-94


30

13

36



47

V. attenuata

Site E


D RV

<50

Mar-94


20

22

34



35

V. attenuata

Site E


D RV

<50

Feb-95


30

48

26



66

V. attenuata

Site R


D RV

1000+


Mar-94

50

8



54

28

V. bifimbriata

Site D

H P


<30

Jan-95


12

50

-



-

V. bifimbriata

Site D


H P

<30

Feb-99


15

17

68



28

V. carinata

Site NIT


H P

1000+


Apr-96

100


20

48

23



V. carinata

Site NIT


H P

1000+


Apr-97

400


13

45

38



V. carinata

Site NIT


H P

1000+


Apr-98

100


15

11

36



V. comosa

Site NETS

H RV/P

100+


Jan-97

30

17



47

19

V. dasystylis ssp oestopoia

Site BC

D RV


8

Nov-97


8

6

75



16

V. densiflora var caespitosa

Site FNR


H P

100+


Feb-99

20

25



73

22

V. densiflora var pedunculata

Site WLH

D RV


<50

Feb-99


20

25

78



18

V. endlicheriana var angustifolia

Site MB


H P

1000+


Feb-95

50

11



24

17

V. fimbrilepis ssp australis

Site KR

H P


500+

Jan-95


200

14

15



13

V. fimbrilepis ssp australis

Site KR


H P

500+


Feb-96

200


29

87

45



V. fimbrilepis ssp australis

Site KR


H P

500+


Feb-97

100


25

68

63



V. fimbrilepis ssp fimbrilepis

Site AT


D P

<50

Mar-97


25

15

30



40

V. fimbrilepis ssp fimbrilepis

Site AT


D P

<50

Feb-98


15

20

25



48

V. fimbrilepis ssp fimbrilepis

Site AT


D P

<50

Jan-96, Feb-96

8

39

79



168

V. fimbrilepis ssp fimbrilepis

Site J4


D RV

<50

Mar-97


40

17

62



29

V. fimbrilepis ssp fimbrilepis

Site J4


D RV

<50

Jan-98


30

20

32



54

V. fimbrilepis ssp fimbrilepis

Site J4


D RV

<50

Jan-96, Feb-96

30

31

56



168

V. fimbrilepis ssp fimbrilepis

Site J7


D RV

100+


Mar-97

50

32



73

81

V. fimbrilepis ssp fimbrilepis

Site J7

D RV


100+

Jan-96, Feb-96

150

28

86



99

V. fimbrilepis ssp fimbrilepis

Site JNR


H P

300+


Feb-98

250


15

82

71



V. fimbrilepis ssp fimbrilepis

Site NH


D RV

13

Jan-96



10

20

46



63

V. fimbrilepis ssp fimbrilepis

Site R


D RV

10

Jan-98, Feb-98,



10

19

30



23

Mar-98


V. fimbrilepis ssp fimbrilepis

Site TR


H P

100


Jan-99

100


37

44

1470



V. harveyi

Site BP


H P

1000+


Apr-94

16

13



-

-

V. harveyi

Site BP

H P


1000+

Apr-96


30

10

-



-

V. harveyi

Site BP


H P

1000+


Apr-97

50

11



-

-

V. harveyi

Site EPT

H P


1000+

Apr-95


200

7

-



-

V. harveyi

Site EPT


H P

1000+


Apr-97

50

3



33

9

V. harveyi

Site SET

H P


1000+

Apr-96


500

25

12



25

V. helichrysantha

Site CR


H P

1000+


Nov-94

200


33

63

104



V. helichrysantha

Site CR


H P

1000+


Oct-95

1000


21

50

54



V. helichrysantha

Site TB


H P

1000+


Nov-98

50

4



29

14

V. hughanii

Site A

H P


1000+

Mar-99


60

24

69



58

V. hughanii

Site HNR


D P

<30

Mar-99


8

6

57



21

V. pityrhops

Site EMB


H P

500+


May-99

200


5

-

-



V. plumosa var ananeotes

Site ANR


H P

<100

Mar-94


10

11

11



9

V. plumosa var ananeotes

Site ANR


H P

<100

Mar-94


20

3

18



11

V. plumosa var ananeotes

Site ANR


H P

<100

Feb-95


30

5

-



-

V. plumosa var ananeotes

Site ANR


H P

100+


Feb-98

150


6

42

19



V. plumosa var ananeotes

Site ANR


H P

100+


Feb-99

30

2



33

24

V. plumosa var pleiobotrya

Site M

D RV


500+

Feb-95


27

24

72



64

V. plumosa var vassensis

Site APV


D RV

50+


Feb-97

40

5



53

15


101

offspring vigour through selective abortion. Surplus

flower production may also provide an ovary reserve in

case of mortality of flowers, or may provide a buffer

during adverse weather conditions or during competition

that may reduce pollen flow (Lee & Bazzaz 1982).  The

interacting factors of pollination failure, resource

deficiency, predation and genetic defects causing

developmental failure may cause pre-dispersal seed and

ovule mortality (Fenner 1985; Wallace & O’Dowd 1989).

A range of biological constraints can also lead to

reductions in seed production (Owens 1995). These

include (1) periodic or inadequate floral initiation, (2)

asynchronous development and flowering, (3) floral

abortion, (4) ovule abortion, (5) embryo abortion, and (6)

failure of seeds and fruits to mature and our inability to

determine maturity. Constraints and their importance

will vary among species, sites and years and occur

throughout all stages of development. Stephenson (1981)

reports that whole fruit abortion is common among

outcrossing perennials and that a low fruit to flower ratio

(i.e. seed set) is observed in many species. Similarly,

Wiens et al. (1987) noted that reproductive success as

measured by seed to ovule ratio in outcrossing plants

was considerably lower (22%) than in inbreeding plants

(90%).


V. plumosa var vassensis

Site APV


D RV

50+


Jan-98

30

9



44

27

V. plumosa var vassensis

Site E

D RV


<20

Feb-99


10

0

-



-

V. plumosa var vassensis

Site FR


H P

1000++


Feb-98

1000


0

-

-



V. plumosa var vassensis

Site FR


H P

1000++


Feb-99

90

7



75

8

V. plumosa var vassensis

Site GBR

H RV


100+

Feb-98


20

17

48



44

V. plumosa var vassensis

Site WLH


D RV

50+


Feb-99

17

16



33

82

V. spicata ssp squamosa

Site C

H P


11

Jan-96


5

18

52



46

V. spicata ssp squamosa

Site C


H P

11

Jan-97



10

7

29



21

V. spicata ssp squamosa

Site C


H P

11

Feb-98



11

19

24



54

V. spicata ssp squamosa

Site CR


D RV

1

Jan-97



1

4

60



5

V. spicata ssp squamosa

Site CYM


D RV

1

Jan-96



1

0.35


-

-

V. spicata ssp squamosa

Site CYM2

D RV


1

Jan-97


1

0

-



-

V. spicata ssp squamosa

Site NETS

D RV

1

Jan-97



1

1

-



-

V. spicata ssp squamosa

Site S


D RV

2

Jan-96



2

8

36



22

V. spicata ssp squamosa

Site S


D RV

1

Jan-97



1

14

50



6

V. spicata ssp squamosa

Site TSM


D RV/P

15

Jan-96



15

11

86



7

V. spicata ssp squamosa

Site TSM


D RV/P

15

Jan-97



13

12

7



31

V. staminosa ssp cylindraceae

var cylindraceae

Site PG

H P


30

Dec-95


7

53

57



14

V. staminosa ssp cylindraceae

var cylindraceae

Site PR

H P


200

Dec-98


33

65

96



100

V. staminosa ssp cylindraceae

var cylindraceae

Site VR

H P


50

Dec-98


12

56

85



103

V. staminosa ssp cylindraceae

var erecta

Site MG

H P


200+

Dec-95


10

59

88



40

V. staminosa ssp cylindraceae

var erecta

Site MG

H P


200+

Dec-98


50

8

81



21

V. staminosa ssp staminosa

Site MH


H P

500+


Oct-95, Nov-95

20

36



60

45

V. staminosa ssp staminosa

Site MH

H P


500+

Oct-97


30

40

70



50

V. staminosa ssp staminosa

Site MH


H P

500+


Oct-96, Oct-96,

50

20



100

24

Nov-96



Species

Location


Condition

Population

Time of

Plants


%

% germi-


Seeds

size


collection

sampled


seed set

nation


 used in

germi-


nation

trials


Table 2 (continued)

A number of researchers have reported that self-

incompatibility in the family Myrtaceae contributed to

low seed set (e.g. Briggs 1962, 1964; Prakash 1969; Rye

1980; Barlow & Forrestor 1984; Griffin et al. 1987;

Beardsell et al. 1993b, Sedgley & Granger 1996). Despite

widespread self-incompatibility within the family, recent

research into the mating system of the rare Verticordia



fimbrilepis subsp fimbrilepis has established that inbreeding

rates are very high (J Samson, CALM, personal

communication). Rye (1980) and Tyagi et al. (1991) also

noted self-compatibility in a number of species in the

genus. Tyagi et al. (1991) considered that low seed set in

field populations of some species of Verticordia was

determined by factors such as efficiency of pollen

transfer, genetic diversity within populations and

physiological constraints rather than loss of pollen

fertility. They were unable to demonstrate that seed

produced by inbreeding was viable, although recent

studies (J Samson, CALM, personal communication) have

now shown that 78% of seeds of V. fimbrilepis subsp

fimbrilepis produced as a result of self-fertilisation were

viable. McEvoy (1995) also reported that seed viability

was not reduced by selfing in the common V. eriocephala.

These data suggest that inbreeding depression is unlikely

to be a cause of low seed set in this genus.

A Cochrane et al.: Seed production and germination in Verticordia



102

Journal of the Royal Society of Western Australia, 84(3), September 2001

Environmental stress and demographic structure of

the population have also been known to contribute to

low seed production (Jordano 1992) and can account for

some of the wide variation in seed set noted between

individuals, populations and years. However, this study

demonstrated that smaller populations of Verticordia

located on degraded road verges did not necessarily

exhibit lower seed set than larger populations occurring

in remnant bush or in reserves or bushland (Table 2).

There appeared to be no difference in seed set between

healthy and degraded sites indicating that environmental

Figure 6.

 Seasonal differences in seed set and germination for V



staminosa subsp staminosa Site MH 1996 collections.

Figure 2.

 Difference in seed set and germination between years

for V. carinata Site NIT, V. spicata subsp squamosa Site C, and V.

staminosa subsp staminosa  Site MH.

Figure 3.

 Differences in seed set and germination between sites

of collection for V albida 1997 collections.

Figure 4.

 Differences in seed set and germination between

individual plants for V fimbrilepis subsp fimbrilepis Site A, 1998.

Figure 5.

 Seasonal differences in seed set and germination for V



fimbrilepis subsp fimbrilepis 1996 collections.

stress at a gross level may not be impacting on the

reproductive capacity of those taxa studied. It is possible

that reproductive success may be a function of plant

maturity, although at the time of this study the age

structure of each population was unknown. Another

significant factor affecting seed set is the presence and

health of pollinators, which may in part be related to the

health of the site and opportunities for supporting

pollinators.

Various studies have reported a relationship between

seed set and life history (Wiens 1984; Ehrlen 1991;

Time During Season

Percentage



103

A Cochrane et al.: Seed production and germination in Verticordia

Richmond & Chinnock 1994; Meney et al. 1997). It

appears that reproductive success in some genera may in

part be determined by the internal allocation of resources

as dictated by the plants’ regenerative mode (Carpenter

& Recher 1979; Hansen et al. 1991; Ladd & Wooller 1997;

Meney et al. 1997). In this study, there was no evidence to

suggest that seed set in Verticordia varied between

obligate seeding and resprouting species. The wide intra-

specific variation in seed set makes it difficult to

determine relationship between levels of seed set and

regenerative mode and further investigations are

required.



Seed Germination

The breakdown of seed dormancy in Verticordia

appears to require not only the removal of the seed coat,

which acts as a barrier to water uptake, but also the

addition of growth hormones to overcome an after-

ripening requirement. It is possible that the hypanthium

and perianth might help protect the seed from

weathering, thus maintaining dormancy. This has been

observed in Thrytomene calycina (Beardsell et al. 1993c).

Recent work on other genera in the family Myrtaceae

(Darwinia and Chamelaucium) has also established the

need for hypanthium removal and the application of

growth hormones to aid germination (A Cochrane,

unpublished data). Despite considerable inroads into

understanding the germination requirements of the

genus Verticordia, we are not achieving maximum

germination in most cases from what appears to be

healthy, mature seed. It is obvious that there is still a

great deal more to be understood about the germination

requirements of particular taxa. Further research is

required to determine whether this incomplete

germination is due to after-ripening requirements, to

maturity of seed, to inadequate dormancy breaking

treatments and/or to genetically related defects.

Given that sampling of material for ex situ

conservation occurs on a random basis to enable the

range of genetic characters and reproductive potential to

be represented, it is not unexpected to find such intra-

and inter-specific variability in germination.

Germinability of seed will be affected by the

environmental conditions under which the seed

developed. It will also be affected by the timing of

collection (see Figs 5, 6) and post-harvest conditions prior

to germination. Germination differences among

individuals have important fitness consequences and

germination differences between populations could well

be reflecting inbreeding depression (Menges 1991). There

have been suggestions that there is a relationship

between population size and germinability in species,

with larger populations exhibiting higher germination

than smaller populations (Menges 1991). Our data on

Verticordia indicate no such relationship (Figure 3).

This study has demonstrated considerable variation in

seed set and germinability in a range of taxa in the genus

Verticordia. The precariously low annual reproductive

success of some of the taxa studied indicates a need for

considerable monitoring of the health and biology of

these taxa over the long-term. Continued disturbance

such as clearing, disease or fire may result in population

decline or even localised extinction of some of the more

critically endangered taxa. Changes in population size,

degree of isolation and fitness are warning signs that

populations may be vulnerable (Ellstrand & Elam 1993)

and should cause concern to conservation managers.

Regeneration plays a major role in the composition and

floral diversity of plant communities. The regeneration

potential of a population depends on the proportions of

germinable seed successfully growing, maturing and

attaining reproductive status, as well as the reproductive

potential determined by seed set and germination. For

most taxa the effective size of the soil seedbank remains

unknown. Seedling survival through summer months is

also unknown. Further stresses due to post-dispersal

factors (seed predation and seedling mortality) in species

that already exhibit low pre-dispersal reproductive

success will critically restrict the ability of the taxon to

reconstitute populations from seed, or to maintain levels

of plants in the face of disturbance and senescence.

Seed set in plants occurring in intact vegetation is no

greater than in plants located in degraded sites, but the

ability of populations to attract and support pollinators

may be dependent on the condition of the site and its

associated vegetation. Despite the ability of plants to self-

pollinate, the impact of reducing population size and

health on the survival of plants and their reproductive

capacity is unknown. Mitigation measures such as the

reintroduction of material into new sites and the

enhancement of existing populations may be warranted

for many of Western Australia’s rare and threatened

Verticordia. The observed year to year and site to site

variations in seed set and germination suggest a cycle of

alternating high and low reproductive activity which

may be affected by seasonal influences on fruit survival

and maturation. Reproductive success in terms of seed to

flower ratio may be a function of size, age, condition and

genetic make-up of the plants, as well as seasonal factors

and pollinator activity. Research into spatial and

temporal factors (e.g. climatic data, nutrient status of sites,

pollinator visitors, pollen loads, age structure and genetic

variability within each population) affecting seed

production and germinability in Verticordia is considered

necessary to ensure local extinction of small isolated

populations does not occur.



Acknowledgments: 

The authors wish to acknowledge the assistance of E

George for identification of specimens and for the provision of

information on ovule numbers and regenerative mode for the taxa utilised

in this present study. Between 1992 and 1998 the Threatened Flora Seed

Centre was funded by the Threatened Species and Communities Section,

Biodiversity Group, Environment Australia.

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