Further developments in the redrying and storage of prechilled beechnuts (Fagus sylvatica L.): effect of seed moisture content and prechilling duration

HAL Id: hal-00883252

https://hal.archives-ouvertes.fr/hal-00883252

Submitted on 1 Jan 1999

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Further developments in the redrying and storage of

prechilled beechnuts (Fagus sylvatica L.): effect of seed

moisture content and prechilling duration

Claudine Muller, Elyane Laroppe, Marc Bonnet-Masimbert

To cite this version:

Original

article

Further

_developments

in the

_redrying

and

_storage

of prechilled

beechnuts

_(Fagus

_sylvatica

_L.):

effect

of

seed

moisture

content

and

_prechilling

duration

Claudine Muller

_{Elyane Laroppe}

_a

Marc

Bonnet-Masimbert

a

Inra Centre de

_Nancy

54280

_Champenoux,

France

b

Inra Centre d’Orléans 45160 Ardon, France

(Received 11

_February

1998;

accepted July

1998)

Abstract -

_Techniques

for

_{breaking dormancy}

of beechnuts _(Fagus

_sylvatica)

have been

_{greatly improved}

over the last 20 years. A

major improvement

has been the introduction of a new

_{procedure involving prechilling}

after

_rehydration

of the seeds to a

_precise

mois-ture content (m.c.) (28-30 %). This allows

_long-term

_storage of non-dormant beechnuts. This

_study

aimed to: i)

optimize prechilling

conditions

_{by prechilling}

seeds at a _{range of moisture} contents (28-34 %) for different durations (X to X+6, where X is the duration necessary to obtain the

_germination

of 10 % of the viable seeds under stratification in a wet medium at 3 °C); ii) follow

changes

in

the

_{germination ability}

of

_prechilled

seeds

_during

_{3 years of} storage. The

_{germination capacity}

of beechnuts was tested

_just

after

prechilling,

after

_prechilling

and

_drying

down to 8 %, and after

_prechilling,

then

_drying

and storage. The best maintenance of the ger-mination _percentage

_during

_storage was obtained when seeds were

_prechilled

at 30 % m.c. for X+2 weeks. A

_damaging

effect of

dry-ing

was observed when the moisture content of the seeds

_{during prechilling}

was

_high

_{(34 %)} and the duration

long

(X+6). When

prechilling

was

_applied

after _storage the best results were obtained at 32 % m.c. _{(© Inra/Elsevier, Paris.)}

Fagus

sylvatica

/ beechnut / seed /

_dormancy

/ _storage

Résumé -

Progrès

dans la conservation des faines

_{(Fagus sylvatica}

L.)

prétraitées :

influence de la teneur en eau des faines et

de la durée de

_{prétraitement.}

Les

_techniques

de levée de dormance des faines _(Fcagus

_sylvatica)

ont été

_grandement

améliorées au cours des

_vingt

dernières années. Un

_{progrès majeur}

a résulté de l’introduction d’une

technique

de

_{prétraitement après réhydratation}

des semences à un niveau de teneur en eau _(TE) contrôlé (28-30 %). De

_plus,

ceci a ouvert la voie à la conservation à

_long

terme des faines dans un état non-dormant. Notre étude visait à : i)

optimiser

les conditions du

_{prétraitement :}

TE des faines variant entre 28 et

34 % et durées variant entre X et X+6 (où X

_représente

le nombre de semaines _permettant la

_germination

de 10 % des faines viables,

en condition de stratification dans un milieu humide à _{3 °C) ;} ii) suivre

_pendant

trois années de conservation l’évolution de la faculté

germinative

des faines ainsi

_{prétraitées.}

Des tests de

_germination

ont été effectués

_{juste après}

le

_{prétraitement, après prétraitement}

et

séchage

à TE 8 %, et

_{après prétraitement, séchage}

et conservation.

Le meilleur maintien de la faculté

_germinative

est obtenu à la suite d’un

_{prétraitement}

à TE 30 %

_pendant

X+2 semaines. Le

_séchage

occasionne une baisse de faculté

_{germinative lorsque}

le

_{prétraitement}

a été effectué à TE 34 % et _{pour la durée la}

_{plus longue}

(X+6).

Lorsque

le

_{prétraitement}

est

_{appliqué après}

_{conservation,} les meilleurs résultats sont obtenus à TE 32 %. _(© Inra/Elsevier, Paris.)

Fagus sylvatica

/ faines / semence / dormance / conservation

*

Correspondence

and

_reprints

1. INTRODUCTION

The

_European

beech

_(Fagus

_sylvatica

L.)

is an

impor-tant timber

_species

often used in

_forestry.

Beechnuts,

like

many other forest

seeds,

possess

embryo dormancy

which

responds

to cold. The

_dormancy

can be

_{particularly deep}

because it _may

_require

4 to 20 weeks of

_prechilling

at a

temperature of 1 to 5 °C before it is broken

_{[6, 12,}

_{18, 23].}

This

_dormancy

can _vary

_greatly

from year to year, from

one seedlot to another

and,

even within a

_seedlot,

from

one seed to another.

Traditionally,

beechnuts are

_prechilled

at 3 °C in a

moist medium

_{(cold stratification)}

but the seeds will also

germinate

at this _temperature as soon as

_dormancy

is

bro-ken

_{[ 16].}

This

_premature

_{germination during chilling}

cre-ates

_problems

for

_sowing.

_Therefore,

Suszka and Zieta

[20]

proposed

a modification to the traditional treatment

by

interrupting

the _pretreatment when 10 % of nuts have

germinated.

This

duration,

expressed

in weeks, is

desig-nated as ’X’. It is clear that after X weeks of

_chilling,

dor-mancy is not

_completely

released and so

_seedling

emer-gence is

generally

neither uniform nor

_complete.

Moreover,

since

_germination

is considered an irreversible

process, there is no _way to

_dry

the seed after

_prechilling

without serious

_damage

to seeds in the

_early

_stages

of

germination.

In

_1975,

to overcome the drawbacks of the classical

cold stratification with a

_medium,

a new

_procedure

of

prechilling,

based on the control of seed moisture content

(m.c.)

without a medium was

_developed

for beechnuts in Poland

_[17]

and further elaborated in France

[11, 12].

In this

_procedure

seeds are moistened

_{during prechilling}

to a m.c. of 28-30 % and then maintained at 3 °C for 2 weeks

longer

(i.e.

X+2

_weeks)

than for classical stratification. This

_precise

m.c. is

_enough

for

_{dormancy breaking}

to be

achieved,

but it does not allow seeds to

_germinate.

As a

consequence, seeds can be dried without

_damage

after the

prechilling

which can be

_{applied immediately}

after

har-vest, or after a

_period

of _storage and before

_sowing

_[10].

Since 1976 we have conducted _many

_experiments

and

obtained _very

_promising

results for

_storing

non-dormant beechnuts for _up to 8 _years

_{[11, 12, 14, 22, 23].}

In recent

years the new

_methodology

has been

_applied

in France on a

_large

scale

_by

the ’Office National des Forêts’ and

_by

seed

_companies.

In 1990 one of the

_largest

French seed

companies

(Vilmorin,

Angers)

applied

the

_procedure

to

10 tons of beechnuts and achieved an _average

germina-tion

_(among

different

_seedlots)

of 60-70 %. These

non-dormant beechnuts were

_successfully

used over the next

18 months.

The purpose of this

study

was:

_i)

to

_optimize

prechilling

conditions,

with _respect to both seed moisture

content and the duration of

_chilling

and

_ii)

to follow

changes

in the

_{germination of prechilled}

_{seeds for 3 years}

of _storage in relation to these conditions.

In addition, we tested whether the same

_dormancy

breakage

conditions would be

_equally

effective before or

after _storage, i.e. whether seeds were stored in a

non-dor-mant or dormant state.

2. MATERIALS AND METHODS

2.1. Seed material

A Danish seedlot

₍₄₅

_{kg), supplied by}

the Tree

Improvement

Station

_(Humlebaek)

was used for the

experiments. Upon

arrival, in December

_1993,

seed m.c.

was 21.6 % and

_viability

77 %. The

_degree

of

_dormancy

(X)

was determined in stratification

_just

after arrival

(before

and after

_drying):

6 weeks were _necessary to

obtain 10 % of

_germination

at 3 °C for wet beechnuts and

only

4 weeks for dried beechnuts.

2.2.

_{Prechilling, drying}

and

_storage

conditions

A _part of the seedlot

₍₂₅

_kg)

was

_{prechilled just}

after

arrival. The

_following

m.c. and

_prechill

durations were

applied

in a factorial

_design:

28, 30,

32 and 34 % m.c. and

X, X+2, X+4 and X+6 weeks for the durations

(X

= ₆

weeks).

The

_longest

duration thus

_corresponds

to 12 weeks of _{pretreatment.} In _{this paper}

_{’prechilling’}

will

designate prechilling

without medium in contrast to

’stratification’ which

_designates

a

_prechilling

into a wet

medium. After

_pretreatment

this first lot was dried at

room _temperature to 7-8 % m.c. and stored at -7 °C. The remainder

₍₂₀

_kg)

of the seedlot was stored in a dormant

state for 18 months at 7-8 % m.c. and -7

°C;

they

were

then

_prechilled

at

30,

32 and 34 % m.c. for

_{X+2, X+4,}

X+6 and X+11 weeks

_just

before

_sowing.

2.3. Germination tests

Germination tests were

_performed

on four

_replicates

of

50 seeds

_(randomized

block

_design),

in

darkness,

in the

laboratory

on moist filter _paper at 3°/20 °C

₍₁₆

h + 8

_h).

These

_{alternating temperatures}

are

_generally

used in our

laboratory

because

_they

have shown a

_good

correlation

with

_germination

_{in nursery} conditions.

(or coefficient of

_velocity)

_[9]

calculated with the formula:

with _ni = number of

_germinated

seeds after

ti

days

and N = total

germinated

seeds at the end of the test.

The seeds were tested in the

_laboratory,

after

_receiving

the

_{dormancy breaking}

treatments, before and after

dry-ing

and after 1, 2 and 3 years of _storage.

After 18 months of _storage, the

_germination

and

nurs-ery emergence of seeds that had been

prechilled

before storage was

_compared

with those

_pretreated

after _storage. In the nursery

only

the best treatments

_(according

to the

laboratory

test _{after I year of}

_storage)

were sown, i.e. 30 and 32 % m.c.

_during

X+2 and X+4 weeks for seeds stored

_prechilled;

32 and 34% m.c.

_during

X+2 weeks for

seeds

_prechilled

after _storage.

2.4. Statistical

_analyses

Statistical differences for the number of

_germinated

seeds per

replicate

and MGT were submitted to

_analysis

of variance

_according

to a _two-way classification with

interaction

_(procedure

_{ANOVA, SAS).}

Bonferroni’s

mul-tiple

range test at 0.05 level of

_probability

was

_applied

to

compare means of

_significant

main factors or interaction.

3. RESULTS

The results will be

_presented

in three _stages:

₁₎

_just

after

_prechilling,

₂₎

after

_prechilling

and

_drying

and

3)

after

_{prechilling, drying}

and _storage for 18 months in

comparison

to

_{non-prechilled}

seeds also stored for 18 months.

3.1. Effect

_{of prechilling}

conditions: moisture content and duration

Two series of tests were

_{performed immediately}

after

the arrival of the seeds in the

_laboratory.

3.1.1. Results

_{obtained just}

_{after prechilling}

The results are

_given

in table I. Germination was

sig-nificantly higher (average

80

_%)

at m.c.

_varying

between

30 and 34 % than at 28 % m.c. where GP was 64.3 %.

There was no

_significant

difference between either

aver-age GP or MGT at

_30,

32 and 34 % m.c. For a short

dura-tion of

_prechill,

such as X

weeks,

good germination

was

already

obtained at 30 and 32 % m.c. which _suggests that

breaking

of

_dormancy

starts earlier at 30 and 32 % m.c.

than at the other m.c.

₍₂₈

and 34

_%).

However, X weeks

(GP

61.2 % on

_average)

was not sufficient to

_completely

break the

_dormancy.

No

_significant

difference was

observed between

X+2,

X+4 and X+6 weeks

_(GP

around 80

%).

For the

_speed

of

_germination,

the best results were

obtained at 30-32 % m.c. and with the duration X+4 weeks

_(individual

treatment values not

_shown).

3.1.2. Results obtained

_{after drying}

The results are

_given

in table II. The GP before and after

_{drying, averaged}

for the factors ’duration’ and

’moisture

_content’,

are also summarized in

_figure

1.

Immediately

after

_drying,

we

_generally

observed a

_slight

but

_significant

decrease of GP: 5 to 10 % on _average,

depending

on the treatment - _except for X weeks where

there was a

_systematic

increase

_(compare

tables I and

_II).

The decrease was

_greater

at the

_{longest prechill}

duration,

X+6 weeks and the m.c.

_high

_{(34 %).}

It is

_possible

that

that the

_higher

the m.c., the stronger the

negative

effect of

drying.

After

_drying

_(table

_II)

there was no effect of

_prechill

duration in the _range of X to X+4 weeks whatever the moisture content. The best values for GP and MGT were

always

obtained in the range of 30-32 %

(even

34

_%)

for the m.c., and

X,

X+2 and X+4 for the duration: GP

var-ied between 74.5 and 79.5 % and MGT was around 12

days

(individual

treatment values not

shown).

3.2.

_Storage

for 18 months:

comparison

of seeds

_prechilled

before

_storage

and seeds

_prechilled

after

_storage

3.2.1.

_Laboratory

tests

With

_regard

to the GP of seeds

_prechilled

before

stor-age

(table III),

the best results were obtained at 30 and 32

% m.c. for X+2 and X+4 weeks. GP was

_{significantly}

lower at 28 % m.c. whatever the duration. At 34 % m.c.,

GP decreased

_by

48 % at the

_longest

duration of

prechilling

(X+6).

For seeds

_pretreated

after

_storage

(table V),

the

_{highest Gps}

were obtained at a moisture

content

_{slightly higher}

than for seeds

_prechilled

before

storage i.e. 32 and 34 % m.c. The duration X+2 seems to

be sufficient but X+4 weeks and even

_{longer periods}

can

be used without _any

_significant

decrease in

_germination

as

_opposed

to what we observed for

_prechilling

before

storage.

In case of the MGT

_(tables

IV,

VI),

the

_longer

the

pre-treatment the faster the

_germination.

MGT was

particu-larly

low for seeds

_prechilled

after _storage, most

_probably

because

_they

were sown moist

_{(30-34 % m.c.)}

as

opposed

to seeds

_prechilled

before _storage which were

3.2.2. Results in the _nursery

Results for

_seedling

_emergence obtained in the _nursery

(figure

2)

were similar to those obtained in the

_laboratory

(tables III-VI).

Even if there were no

_significant

differ-ences in SEP between the six treatments

_(applied

before

or after

_storage),

overall the behaviour of seeds stored after

_{being prechilled}

seemed

_slightly

better than that of

seeds

_{classically prechilled just}

before

_sowing.

_However,

the rate of

_seedling

_emergence was

_slightly

faster with the seed

_prechilled

after storage

(MGT

=

_16.6)

than with seed

prechilled

before _storage

_(MGT

=

_17.7),

_probably

because

_they

were sown at a

_higher

m.c.

3.3. The

_changes

in

_germination

of

_prechilled

seeds

_during

_storage

Figure

3 shows all the results obtained in the

laborato-ry

during

the 3 _years of _storage. Good

_stability

was

obtained at 30 and 32 % m.c. with durations X and X+2 weeks with no

_significant

loss of

_germination

after 3

was obtained with a

_{prechilling performed}

at 30 % m.c.

for X+2 weeks. When the duration was

_longer

than X+2

weeks,

there was a

_large

decrease of GP after the 2nd _year of _storage, which was

_significant

at 32 and 34 % m.c. At

28 % m.c., even

_though

GP was never

_high,

it did not

decline.

Poor results were

_generally

obtained for X+6 weeks of

prechilling

and to some extent for X+4

weeks,

especially

at 32 and 34 % m.c. This decrease was

_already

noticeable

after

_{1 year}

of

_storage.

4. DISCUSSION

Following

the ideas of Suszka

[ 17, 20],

beechnuts have

now been

_{successfullly}

stored

_prechilled

for up to 30

months

_[11],

42 months

_{[12, 14]}

and even 6 to _{8 years}

_[5,

10, 13].

Since the

1990s,

the

_drying

and _storage

_{of prechilled}

seeds has also been

_{successfully developed}

for seeds of

other hardwood

_{species, particularly}

Fraxinus excelsior

[25]

and Prunus avium

[ 14].

In the case of

conifers,

stor-age of

prechilled

seeds has been

difficult,

particularly

when

_they

were redried to a m.c. of 10 % or less

[ 1,

3, 4,

7, 27].

In

1995,

Jones

_[8]

succeeded in

_redrying

Picea

sitchensis seeds to 7% _{without any loss of}

_viability

but

some

_dormancy

was reinduced

_{during storage. Recently,}

we have obtained

_positive

results with

_{prechilled Douglas}

fir seeds stored at 6 % m.c.

_(Muller,

_unpublished

_results);

neither

_{re-imposition}

of

_dormancy

nor loss of

_viability

were _{observed after 2 years of storage.}

In the case of

beechnuts,

the

_key

is in

_prechilling

at a

controlled moisture content which

_permits

the

_breaking

of

_dormancy

without

_allowing

the

_germination.

_The

pro-posed

prechilling

m.c. have varied from one author to

another. However, in all cases, the values range between 28 and 32 %

[2, 5, 12, 13, 18, 20, 21, 23].

In the _present

_study,

our first

objective

was to

_optimize

prechilling

conditions before

_drying

and _storage. Just

after

_prechilling

_{(table I),}

the

_high

GPs

(around

80

%)

were obtained at m.c. between 30 and 34 % m.c. At 28 %

m.c., GP was

_{significantly}

lower

_{(64.3 %),}

which

sug-gests that at this m.c. not all the seeds have had their dor-mancy broken.

Therefore,

the

prechilling

moisture

con-tent must not

_drop

below 30 %.

To take into account the

_{heterogeneity}

of the

seedlot,

the

_prechilling

duration can be varied for different

pro-posed. Recently,

Derkx and Joustra

_[2]

_reported

that a

cold

_prechilling

of 16-20 weeks is

_required

to obtain the

optimal dormancy breakage

in

_freshly

harvested

beech-nuts. Gille and

_Nowag

_[5],

advocated 14 weeks for all seedlots. Other authors

_{[12, 18, 20], however,}

_prefer

to

adjust

the duration of the

_prechilling

to the estimated

degree

of

_dormancy

of each seedlot. As

_already

men-tioned,

this estimate refers to an X value

_{(in weeks) [20]}

where X

is,

for a

_given

seedlot,

the duration _necessary to

obtain 10 % of

_germination

of viable seeds under

condi-tions of stratification in a wet medium. In our

experi-ments, increased

_germination

was obtained between X+2 and X+6 weeks

_{(table I)}

with no

_significant

difference in this _range of durations if there was no further _storage.

When _storage is

_planned,

it is _necessary to

_dry

the seeds. We have shown here that this

_drying

causes a

decrease

_(table

II,

_figure

1)

of the GP. However, for the shortest duration

_(X),

which was

_clearly

insufficient for

full

_{dormancy breakage,}

an increase of GP was observed

after

_drying.

Similar stimulation of seed

_{germination by}

reducing

water content has also been observed in the

mature or immature seeds of _many

_species

_(see

review

_by

Thomsen

_[24]).

It has also been observed in dormant tree

seeds,

Aesculus

_{hippocastanum}

_[15]

and

_Fagus

_sylvatica

[17].

According

to Thomsen

[24],

drying

can

_replace

_part

of the cold

_requirement

for beechnuts. In her case

_drying

the beechnuts to 8 % m.c. _{gave the} same results as 3 to 4 weeks of cold stratification.

Our

_experiment

confirms that

_drying

after

_prechilling

has the same

_positive

effect on the seeds whose

dorman-cy was

_incompletely

eliminated after X weeks. In our

case, such treatment

_replaced

two weeks of cold and therefore no

_significant

difference was observed between

X and X+2 weeks after

_drying

_{(table II)}

as

_opposed

to a

significant

difference before

_drying

_{(table I).}

On the other

sig-nificantly

suffered from

_drying,

_especially

if it was

com-bined with a

_high

m.c.

_{(34 %).}

In the latter case, a loss of

about 40 % GP is observed.

_According

to Derkx and Joustra

_[2],

it is

_possible

that

_early

_germinative

events,

which start at the end of

_{dormancy breaking,}

reduce the

tolerance to dessication.

After

_prechilling,

the beechnuts were dried at a

mod-erate temperature

(around

18-20

_°C)

down to 7-8 % m.c.

Prechilled beechnuts seem to be more sensitive to drastic

drying

(e.g.

drying

to moisture content around 5

_%)

than dormant beechnuts

_(Muller,

_unpublished

_results).

However this needs further

_{investigation.}

The current

_experiments

demonstrated that beechnuts

can be

_successfully

stored in sealed containers at -7 °C for at least _{3 years}

_(figure

_3).

If

_they

are to be stored in a

non-dormant state, the best maintenance of GP was

observed after a

_prechill

at 30 % m.c. for X+2

weeks,

which confirms

_previous

results

_{[5, 12, 13].}

Another outcome of our

_experiments

concerns the

comparison

between conditions for

_{dormancy breakage,}

when the treatment is

_applied

before or after _storage. In

fact,

several

_possible

combinations between

_prechilling

and _storage have been

_proposed

for beechnuts

[10, 14]:

prechilling

before _{storage, during storage}

_[21].

Until now,

the same

_prechill

conditions have been

_proposed

for these

different cases: 30-32 % m.c. for X+2 weeks

_{[19, 22, 23].}

In the

_present

_{experiment, prechilling,}

whether it was

applied

before or after _storage, led to

_relatively

similar

results,

in the

_{laboratory (tables}

_III-VI)

and in the _nursery

(figure 2),

after 18 months of

_{storage. However,}

when

prechilling

was

_applied

after

_{storage (table}

V and

VI),

there was some

_advantage

from

_increasing

the moisture

content to 32-34 % m.c., i.e. 2 %

higher

than when seeds

were

_prechilled

before _storage

_(table

III and

_IV).

In

conclusion,

the

_ability

to

_dry

and store non-dormant seeds has

_definitely

_opened

new

_{possibilities}

in the

han-dling

and

_preparation

of dormant

_species.

The

_integration

of

_dormancy

release treatments with seed _storage for

deep

dormant hardwood seeds ensures the

_availability

of non-dormant seeds that are able to

_germinate

_{without any}

further

_pretreatment

even after

_long

_storage.

It

_brings

a

flexibility

to a situation where the constraints

_(including

the _necessary

_variability

of the seeds from _very diverse

trees)

are numerous and _represents an

_important

advance

in the

_technology

of

_forestry

seeds.

Acknowledgements:

This work was

_{supported by}

the

European

Union

_through

the

_project

AIR2-CT93-1667:

’A

_{multidisciplinary approach}

to the

_{understanding}

and

efficient

_handling

of seed

_dormancy

in tree

_species’.

The

authors are

_grateful

to Simon Hawkins for critical

_reading

of the

_manuscript.

REFERENCES

[1] Barnett J.P., Germination _temperatures for conifer

cul-ture of southern

_pines,

Southern J.

_Appl.

For. 3 (1979) 13-14.

[2] Derkx M.P.M., Joustra M.K.,

Dormancy breaking

and short term _storage of

_pretreated

_Fagus

_sylvatica

seeds, in: Ellis

R.H., Black M., Murdoch A.J., Hong T.D. (Eds.), Basic and

Applied Aspects

of Seed

_{Biology, Proceedings}

of the Fifth International

_Workshop

on _Seeds,

_Reading,

_1995, Kluwer Academic Publishers _{Dordrecht/Boston/London, 1997, pp.} 270-278.

[3] Edwards _D.G.W.,

_Storage

of

_prechilled

Abies seeds. Proc. IUFRO Int.

_Symp.

Forest Tree Seed

_Storage,

PNFI, Ontario, Canada, 23-27

_September

_{1980, 1980, pp. 195-203.}

[4] Edwards _D.G.W.,

_{Special prechilling techniques}

for tree

seeds, J. Seed Technol. 10 (2) (1986) 151-171.

[5] Gille K.,

_Novag

A.,

Storage

of beech seeds,

Allg.

Forst. Zeitschrift 50 (18) (1995) 960-961.

[6]

Gosling

PG., Beechnut _storage: a review and

_practical

interpretation

of the scientific literature,

Forestry

64 (1991)

51-59.

[7] Hedderwick GW.,

Prolonged drying

of stratified

Douglas

fir seeds affects

_{laboratory germination,}

New Zealand For. Serv., For. Res. Instit. Research Leaflet no. _19, 1968.

[8] Jones SK., Sitka spruce (Picea sitchensis) seed

germina-tion in relagermina-tion to seed

_{development, dormancy}

and _storage, PhD thesis,

Department

of

_{Agriculture, Earley}

Gate,

Reading,

1995, pp. 62-86.

[9] Kotowski F.,

Temperature regulation

to

_germination

of

vegetable

seeds, Proc. Am. Soc. Hortic. Sci. 23 (1962) 176-184. [10] Muller C., Combination of

_{dormancy breaking}

and

storage for tree seed: new

_strategies

for hardwood

_species,

In: Edwards D.G.W. (Ed.),

Dormancy

and Barriers to Germination,

Proc. Intern.

_Symp.

of IUFRO

Project Group

P2-04-00 (Seed Problems), Victoria, BC, Canada, 1993, pp. 79-85.

[11] Muller C., Bonnet-Masimbert M., Levée de dormance des faines avant leur conservation: résultats

_{préliminaires,}

Ann. Sci. For. 42 (1985) 385-396.

[12] Muller C., Bonnet-Masimbert M.,

Breaking dormancy

before _storage: an

_improvement

to

_processing

of beechnuts

(Fagus

sylvatica L.), Seed Sci. Technol. 17 (1989) 15-26.

[13] Muller C., Bonnet-Masimbert M.,

Storage

of

non-dor-mant hardwood seeds: new _trends, Ann. Sci. For. 46

_(Suppl.)

(1989) 92s-94s.

[14] Muller C., Bonnet-Masimbert M.,

Laroppe

E.,

Nouvelles voies dans le traitement des

graines

dormantes de certains feuillus: Hêtre, Frêne, Merisier, Rev. For. Fr. 42 (1990)

329-345.

[15] Suszka B., Conditions for the

_breaking

of

_dormancy

and

_germination

of the seeds of Aesculus

hippocastanum

L.,

Arbor. Kornickie 11 (1966) 203-220.

[16] Suszka B.,

Dormancy,

storage and

_germination

of

Fagus sylvatica

L., Arbor. Kornickie 11 (1966) 221-240. [17] Suszka B., Cold _storage of

_{after-ripened}

beech _(Fagus

[ 18] Suszka B.,

Seedling

emergence of beech (Fagus

syl-vatica L.) seed

_pretreated

by

chilling

without medium at

con-trolled

_hydrations

_levels, Arbor. Kornickie 24 ₍₁₉₇₉₎ 11-135.

[19] Suszka B.,

Kluczynska

A.,

Seedling

emergence of stored beech (Fagus

sylvatica

L.) seed

_prechilled

at a controlled

hydration

level and

_{pregerminated}

in cold moist _conditions, Arbor. Kornickie 21 ₍₁₉₈₀₎ 231-255.

[20] Suszka B., Zieta L., Further studies on the

_germination

of beech _(Fagus

_sylvatica

_L.) seed stored in an

_already

after-ripened

condition, Arbor. Kornickie 21 ₍₁₉₇₆₎ 279-296.

[21] Suszka B., Zieta L., A new

_presowing

treatment for cold stored beech _(Fagus

_sylvatica

_L.) seed, Arbor. Kornickie 22 ₍₁₉₇₇₎ 237-255.

[22] Suszka B., Muller C., Bonnet-Masimbert M., Graines des feuillus forestiers de la récolte au _semis, Inra Editions, Paris ISBN 2-7380-0516-0, 1994, pp. 175-211.

[23] Suszka B., Muller C., Bonnet-Masimbert M., Seeds of forest broadleaves: from harvest to

_sowing,

Inra Editions, Paris ISBN 2-7380-0659-0, 1996, pp. 75-211.

[24] Thomsen K.A., The effect of harvest time and

_drying

on

_dormancy

and

_storability

in beechnuts, in: Ellis R.H., Black

M., Murdoch A.J.,

_Hong

T.D. _(Eds.), Basic and

_Applied

Aspects

of Seed

_{Biology, Proceedings}

of the Fifth International

Workshop

on _Seeds,

_Reading,

_1995, Kluwer Academic Publishers Dordrecht/Boston/London, 1997, pp. 45-51.

[25]

Tylkowski

T., Mediumless stratification and

_dry

stor-age of

after-ripened

seeds of Fraxinus excelsior L., Arbor. Kornickie 35 ₍₁₉₉₀₎ 143-152.

[26] Vanesse R., Influence du

_séchage

secondaire des

graines

de

_Pseudotsuga

menziesii (Mirb) Franco sur leur

germi-nation à 20 °C, Bull. Rech.

_Agron.

Gembloux 2 (1967)