United States

{,p$ Department of

#$ Argriculture

a

~~5 Forest Service Research Note

I* Southern Forest SO-306

Experiment Station February 1984

Testing for Seed Quality in Southern Oaks

F. T. Bonner

Along with this limited resource of seedlings, nurserymen face the fact that collection and care of acorns are

more difficult than for most tree seeds, so reliable data on

acorn quality becomes important in obtaining seedlings

efficiently. Some factors that contribute to this difficulty

are:

(1)

(2)

(3)

Bumper crops are erratic and greatly variable in

quality among seed lots.

Premature collection of acorns is very common

when collecting from logging slash; full maturity,

necessary for normal germination, may not be

apparent to the eye.

Post-collection care is difficult. Viability can be lost

quickly from excessive drying, freezing, or heating.

SUMMARY

Expressions of germination rate, such as peak value

(PV) or mean germination time (MGT), provide good estimates of acorn quality, but test completion requires a

minimum of 3 weeks. For more rapid estimates, tetrazolium staining is recommended. Some seed test results

were significantly correlated with nursery germination of

cherrybark and water oaks, but not with seedling growth.

Additional keywords: Acorns, germination, nursery

performance, Quefcus.

INTRODUCTION

Total production of bareroot seedlings of southern oaks

is not large, although most nurseries do grow some oak

seedlings. For the 1982-83 planting season, nine states

advertised seedlings from 1 to 3 species of oak (Monaghan 1982). While several industrial nurseries also grow

oak seedlings, their supply is destined to reforest their

own lands.

(4) Acorns must be stored above freezing at high

moisture contents.

These conditions also favor insects, disease, and early

sprouting.

OPTIONS FOR TESTING

Several options exist for evaluating acorn quality:

A. Standard laboratory germination test. Germination

tests can be run using the “cut and peel” method which

is very similar to techniques used for official seed tests

(Association of Official Seed Analysts 1978). The procedure is simple:

1.

2.

3.

4.

B.

Cut acorns in half (pruning shears are good for this)

and discard the half with the cup scar.

Peel the pericarp from the remaining half and place

it on moist blotter, Kimpak’, or similar material, cut

side down.

Incubate at alternating temperatures of 20” (16

hours)/30°C (8 hours, with light). Keep test surface

moist.

Count germination at desired intervals for up to 28

days. (Tests may be terminated early if germination

is complete.) An acorn is scored as germinated if

both radicle and shoot exhibit normal growth and

morphology.

Rapid viability tests. Because of time restrictions

mentioned earlier, seed managers may prefer one of

three rapid viability estimates:

1. Cutting test. Cross-section cuts will disclose damage due to insects, disease, and desiccation, but

‘Mention of trade names is for information only and does not imply

endorsement or recommendation by the US. Department of Agriculture over others not mentioned.

Southern Forest Experiment Stationm-102lO U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1
they may not always disclose loss of viability from

overheating or freezing.

EXPERIMENTAL RESULTS

2. Radiography. X-rays can provide a very quick,

non-destructive test for damage or incomplete

embryo development. Sample exposure and radiograph interpretation guides are available (Belcher

and Vozzo 1979).

3. Tetrazolium staining (TZ test). Tetrazolium chloride

is widely accepted as a vital stain in seed science.

The following procedure has been moderately

successful for acorns:

(a) Use two samples of 50 acorns each.

(b) Cut acorns in half with pruning shears. Remove

pericarp from the half containing the embryonic

axis, and discard the other half. Count and discard any rotten acorns.

Various experiments have been carried out on measurement of acorn vigor at the Forestry Sciences Laboratory in Starkville, Mississippi, since 1972. Some results

have been published previously for cherrybark oak (Bonner 1974). More recent results are herein summarized:

A. 1978 Water Oak Test Methods

Five lots of water oak collected from 1975 to 1978 were

randomly sampled for the following tests:

1. Standard laboratory germination test.

2. TZ test.

(c) Place acorn halves in a deep dish, micropyle end

down, and add TZ solution until the halves are

almost covered. Solution should be made from

2,3,5triphenyl tetrazolium chloride and should

have a pH of 7.0.

3. Nursery growth tests which measured:

a. bed germination.

b. bed survival at end of growing season.

c. seedling dry weight at end of growing season.

All lots had been cleaned and upgraded by water flotation at collection. Prior to testing they had been stored

moist at ‘2°C according to current recommendations

(Bonner 1973).

(d) Cover dishes and incubate in the dark for 24

hours at 21” to 25“. Break cotyledons apart to

study stain in each acorn. A good stain is bright

pink to red. Very dark red (as in blood) indicates

tissue damage.

(e) Score stain in 5 classes:

I. Cotyledon and embryonic axis both unstained.

Il. Axis stained, cotyledon unstained.

Ill. Cotyledon stained, axis unstained.

IV. Axis and cotyledon both unstained.

V. Rotten or insect damage beyond recovery.

Class I is best, of course, but many acorns in

Class II will also germinate. Class Ill acorns are

very weak, and they normally will not produce

plantable seedlings in nurseries. Some may

germinate in greenhouses. Classes IV and V will

not germinate, but inclusion of the counts can

show the reasons for poor quality.

C. Vigor tests. Germination or viability percentages

seldom give a completely accurate picture of acorn quality. Several other tests may be used:

1. Germination rate. Speed of germination may be

expressed as mean germination time (MGT), or

peak value (PV) where PV= maximum value of

cumulative percentage divided by days of test

(Czabator 1962).

The germination tests employed 4 samples of 50

unstratified acorns each. Germination was counted 3

times per week. TZ tests were carried out on 4 samples of

50 acorns each, except for lot 77-l 7, which had only 2

samples available. Nursery growth plots were four completely randomized plantings of 50 acorns each, which

had received 36 days of stratification at 3°C.

Results-All germination and TZ tests clearly showed

that lot 75-5 exhibited poorest quality and lot 77-17 was

the best (table 1). Values for the other 3 lots were intermediate with few significant differences. TZ results for lot 77-

17 were much higher (95%) than those of the other lots,

and TZ and germination capacity were about equal.

Nursery germination and survival were similar to the

laboratory germination test results, although lot 77-l 7 did

slip in final nursery survival (49.2%-third best). Mean

seedling dry weights were highest for 77-l 7 and 75-5 (the

lot of lowest quality). The high mean weights for lot 75-5

are thought to be related to low bed density resulting

from poor germination. No plots were thinned to a uniform density, a condition which was corrected in the next

nursery test.

2. Leachate conductivity. Immersion in distilled water

for various periods, followed by some measure of

solute leakage into the water, has been used successfully for many seeds. Electrical conductivity of

the leachate is the most popular method, and good

correlations between leachate conductivity and

seed vigor in water oak acorns have recently been

reported (Agmato 1982).

These results suggested that laboratory germination

capacity, germination rate (PV), and TZ test results were

all correlated with nursery germination and growth, but

the number of lots precluded a definitive test. The big differences between germination and TZ results for some

lots seemed inconclusive.

B. 1982 Test Methods

Multiple lots of white oak (12) cherrybark oak (15) and

water oak (15) were used to retest the relationship of seed

vigor estimates to seedling performance in nursery beds.

The following tests were run:

1. Standard laboratory germination test.

2. TZ test.

3. Nursery growth tests which measured:

-

F. T. Banner is Supervisory Plant Physiologist, Southern Forest Experiment Station, Forest Service-USDA, Starkville, Mississippi.

2
Table 1 .-Germination andseedling growth in 5 lots of water oak, 7978 test

Seed Germination TZ stain Nursery Nursery Seedling

Lot* PV capacity Class I germ. survival dry weight

._____....___ ___ _________________________ pet, _________......_______ _ . ..__________..._. g

75-5 4.0 a 58.2a** ll.Oa 32.8 a 30.8 a 2.1 a

77-6 5.8 b 84.0 b 44.0 b 46.0 ab 42.0 ab 1.3 b

78-7 5.8 b 90.8 b 61 .O c 56.8 bc 51.6 bc 1.7ab

76-10 6.6 bc 90.8 b 51.0 b 60.8 bc 60.0 c 1.3 b

77-17 7.0 c 98.0 c 95.0 d 65.6 c 49.2 bc 2.0 a

*The first two numbers in the lot designation refer to year of collection.

l *Lot means followed by the same letter did not differ significantly at the 5% level, based on Duncan’s

new Multiple Range test.

Table 2.-Laboraatory germination and TZ stain data for a// 3 species, 1982 test. Rate parameters (PV and MGT) were not

available for white oak

-

White oak Cherrybark oak Water oak

T Z Germination TZ Germination T Z Germination

Lot no. stain capacity stain capacity PV MGT stain capacity PV MGT

. ..~~~~~~~..~~~~~~~.....~~~~....~~~~ pet, ..__...._______...._..~...~.~~..... days . . . . .. .._.... p(y, _____...____. days

1 84 96.5 8 9 1.4 7.4 8 0 71.0 4.3 13.2

2. 83 90.5 89 83 11.2 5.9 6 4 94.0 10.9 7.9

3 71 81.5 94 86 10.4 5.9 4 5 52.0 4.7 9.8

4 90 96.5 86 93 14.4 4.4 8 5 83.5 4.3 15.3

5 82 84.0 86 93 12.7 5.0 7 1 71.0 6.1 8.6

6 88 80.0 48 37 4.0 6.9 6 5 87.5 5.1 13.7

7 78 70.0 97 92 10.0 7.1 8 2 93.5 11.4 4.8

8 96 83.5 86 77 5.9 12.4 7 0 89.0 10.2 8.4

9 75 62.0 88 77 8.2 6.9 8 9 87.5 5.0 13.5

1 0 84 84.5 90 82 8.2 7.1 8 6 83.5 8.4 8.7

1 1 77 67.0 80 84 12.0 5.3 8 3 87.0 9.0 8.3

1 2 78 67.0 7 5 92.5 6.1 12.8

1 3 89 89.0 7 8 94.5 6.6 11.3

1 4 86 75.0

1 5 82 65.0 :::: :::: ::::

7 6 81.0 10.1 7.8

6 6 92.5 7.6 10.0

a. weekly emergence.

b. number of plantable seedling produced.

c. mean seedling fresh weight, top length, stem

diameter, and volume (D2H).

Upgrading, storage, and sampling paralleled other tests.

Germination was tested with 4 samples of 50 acorns

each, TZ tests with 2 samples of 50 each, and nursery

growth with 4 samples of 50 each.

White oak acorns were planted in February without

stratification. Almost all acorns had emerging radicles visible at planting. Cherrybark and water oak acorns were

stratified for 32 days at 2”, then planted on March 24.

Many acorns had also started germinating by planting

time. In late May all plots were thinned to a density of 4 to

6 seedlings per square foot. Beds were not fertilized and

only moderately irrigated.

Correlation coefficients were calculated between all

seed vigor estimates and all seedling performance parameters.

Results-For white oak, laboratory germination capacities ranged from 62.0 to 96.5 percent, while the TZ percent (Class I only) ranged from 75 to 96 percent (table 2).

There was a significant positive correlation between the

two (r = 0.671).

Seedling growth data for white oak indicated two things

(table 3). First, once thinned to a good density, few

performance differences showed between seed lots.

Secondly, there were no significant correlations of seed

vigor estimates with seedling growth. For these 15 lots of

white oak, seedling performance could not be predicted

by measuring seed quality.

Cherrybark oak test data showed a greater range of

seed quality than that for white oak (table 2). Germination

capacity values were very close to the TZ results

(r= 0.965). Expressions of germination rate (PV and

MGT) varied widely between lots, the variation suggesting that the rate parameters are more sensitive to vigor

differences than are germination capacity percentages.

This same relationship can be shown with seeds of many

species.

Nursery growth results for cherrybark oak showed high

positive correlation (r=0.983) between TZ and nursery

germination (table 4). Other significant, but lower, correlations with nursery germination were obtained with PV and

3
germination capacity. These two expressions and TZ

were also significantly correlated with the number of

plantable seedlings. However, none of the seedling

growth parameters were correlated with estimates of

acorn vigor.

Water oak germination and TZ results were similar to

those in the 1978 test, because TZ was not significantly

correlated with germination capacity (table 2). The only

significant correlations between seed vigor estimates and

nursery performance occurred in measures of germination rate: PV and MGT (table 5). MGT was significantly

correlated with seedling size and weight, the only such

significant correlation of the entire test. TZ and germination capacity were not correlated with anything.

Table 3.-White oak seedling performance, 1982 test

DISCUSSION

Species differences cause some problems in TZ staining of acorns. Water oak cotyledons fit together very

tightly, thus restricting access of the TZ solution to the

embryonic axis. This species also has a tough testa next

to the cotyledons, which restricts entrance of the solution.

Similar problems have occurred in other tests with willow

oak and Nuttall oak acorns. Scraping the testa away from

the embryonic axis and removing more than one-half of

the cotyledons might improve the condition. The more

cotyledon removed, the more likely that the remaining

pieces will separate when imbibed.

Cherrybark oak acorns do not present the problems

described above. Their cotyledons readily separate when

Nursery Nursery Plantable*

Lot no. emergence germination seedlings

wks. pet no.

1 8.0 46.0 1 1

2 7.8 89.5 1 6

3 7 7 69.5 1 7

4 8.3 46.5 1 2

5 7.5 82.0 1 4

6 8.0 66.0 1 0

7 8.3 43.0 9

8 8 2 34.0 7

9 8.8 49.5 1 5

1 0 7.9 65.5 1 6

1 1 8.1 60.5 1 3

1 2 7 7 44.5 1 5

1 3 7.8 56.5 1 4

1 4 8.3 51.5 1 4

1 5 8.7 26.0 8

*Minimum top length of 30 cm.

**All roots pruned to a length of 15 cm before weighing.

Fresh* * Top Stem

weight length diameter D”H

cl cm mm cm3

51.1 4 6 8.8 38.6

65.0 5 8 9.2 56.6

71.2 6 0 9.6 59.4

57.0 4 8 8.4 36.1

70.2 5 5 9.6 54.6

57.4 3 9 8.2 26.4

35.0 4 0 6.8 21.0

46.6 3 9 8.5 30.0

66.5 6 1 9.6 61.3

56.3 5 6 9.0 48.4

57.8 5 1 8.8 42.1

65.4 5 5 9.5 52.8

54.4 5 6 8.9 48.5

75.7 6 6 9.8 71 .o

53.1 4 3 8.5 36.1

Table 4.-Cherrybark oak seedling performance, 1982 test

Nursery Nursery Plantable* Fresh * * Top Stem

Lot no. emergence germination seedlings weight length diameter D’H

1

2

3

4

6

7

8

9

1 0

1 1

1 2

wks. pet. n o g cm mm cm3

8.0 2.0 2 28.4 5 2 7.5 32.4

6.7 75.0 1 9 52.4 7 7 9.0 64.2

7.3 73.5 1 8 22.9 4 9 6.2 19.8

7.6 81.5 17 26.0 4 8 6.2 18.8

6.2 79.0 2 0 45.3 7 2 8.2 51.3

7.3 44.5 1 8 51.1 6 8 8.8 56.0

7.1 83.0 2 0 46.9 7 0 8.8 55.3

7.2 76.5 2 0 50.5 7 5 8.9 61.3

6.7 75.0 2 0 49.4 7 6 8.7 60.6

6.1 84.0 2 0 49.9 7 8 8.6 59.8

5.7 71.5 2 0 52.9 7 9 8.7 63.2

*Minimum top length of 30 cm.

**All roots pruned to a length of 15 cm before weighing.
Table 5.-Water oak seedling performance, 1982 test

Nursery Nursery Plantable*

Lot no. emergence germination seedlings

wks. pet. no.

1 9.8 35.5 1 6

2 8.1 67.0 2 0

3 7.6 45.5 1 8

4 10.2 22.5 1 2

5 7.8 59.5 2 0

6 9.7 44.0 1 8

7 8.4 62.0 1 9

8 8.2 75.0 1 9

9 10.1 33.0 1 5

1 0 9.0 60.5 1 9

1 1 7.2 64.0 2 0

1 2 10.0 46.5 1 7

1 3 8.7 58.5 1 8

1 4 8.8 69.0 1 9

1 5 9.2 60.5 1 8

*Minimum top length of 30 cm.

l *All roots pruned to a length of 15 cm before weighing.

Fresh * * Top Stem

weight length diameter D*H

g

cm mm cm’

39.1 6 5 7.6 40.8

50.0 7 1 8.9 60.0

52.8 7 4 8.4 57.8

26.7 5 2 6.6 25.1

63.4 7 6 9.6 74.8

27.0 5 7 6.6 27.4

42.9 6 7 8.3 48.6

37.2 6 0 7.5 36.7

32.2 5 9 7.4 36.4

56.8 7 4 8.9 61.9

62.0 8 1 10.2 90.6

37.7 6 0 8.0 40.2

53.0 7 8 9.0 67.2

41.6 6 6 7.8 42.8

57.2 7 3 9.0 64.2

imbibed, and the testa on cherrybark acorns is thinner.

Other red oak species that are more like cherrybark than

water oak are Shumard and scarlet oaks.

Cotyledon color also influences stain interpretation.

Healthy acorns with high lipid contents (water, willow,

cherrybark) are orange, and the stain will show reddishorange. Low-fat acorns (Shumard, all white oaks) have

white to pale yellow cotyledons; good stains in these

cases are typically pink to red.

Stain interpretation was also difficult on white oak

acorns, because the radicles were, in most cases already

protruding through the pericarp when the tests were run.

Rapid germination of this species is the rule, not the

exception. When white oak acorns are cut, the cotyledons frequently break apart and damage the axis.

In general, correlations between laboratory seed measurements and seedling growth in the nursery were poor.

Only MGT for water oak gave significant correlations with

seedling growth. The strongest relationships were

between nursery germination and the number of plantable seedlings. Once seedlings were established and bed

densities equalized, seed quality had little effect on seedling size. Had bed densities not been adjusted, though,

the best lots would have been too dense in these tests,

and seedling growth would have suffered.

It is also apparent that seed measurements that

express rate of germination were the best indicators of

nursery performance. This conclusion, consistent with

the bulk of seed research results, was reported by our

laboratory previously for cherrybark oak (Bonner 1974).

The major question remaining is: “Why weren’t the

seed measurements correlated with seedling performance?” Definitive answers are not apparent, but the

nature of the oak seed itself is influential. Acorns have an

abundant food supply within themselves. Much damage

can occur and can be reflected in TZ tests, yet the acorn

can still germinate and produce a normal seedling. This

has been observed many times in our laboratory and

nursery, and it could explain the germination capacities’

being much higher than the TZ values for water oak in

1978 (table 1).

Acorns are recalcitrant seeds with short life spans.

Once seed quality begins to decline, it declines very rapidly. The time course of acorn deterioration is so rapid

that seed lots are either good or very bad within three

years of collection.

CONCLUSIONS AND RECOMMENDATIONS

1. Several seed vigor tests were significantly correlated with nursery germination of cherrybark and water

oaks, but not for white oak. Tetrazolium (TZ) staining was

best for cherrybark oak; peak value (PV) was also good.

Germination rate expressions (PV and MGT) were best

for water oak.

2. Seed vigor tests could not predict oak seedling

performance, as measured by seedling growth parameters. Only mean germination time (MGT) for water oak

was significantly correlated with seedling growth, and

these coefficients were low (0.59 to 0.54).

3. TZ results were significantly correlated with germination capacity (lab test) for white oak and cherrybark

oak, but not for water oak. Cherrybark oak is welladapted to the TZ test, but water and white oaks present

minor problems.

4. In spite of mixed results just discussed, seed quality

tests are still definitely recommended for seed managers

and nurserymen who must make management decisions

or calculate sowing rates for seed lots of southern oaks. If

5
immediate decisions (those being made within 7 days)

are required, TZ tests should be made. The procedures

described in this paper are easily learned. If more time is

available (3 weeks or more), germination tests that allow

calculation of rate measures (PV or MGT) should be

used. As to “cut and peel” preparation, which is similar

to that for the TZ test, that method’s germination data

should be available in 14 to 21 days for most species.

LITERATURE CITED

Agmata, A. L. 1982. Physiological effects of drying Quercus nigra L. acorns. Unpubl. M.S. Thesis, Dept. Forestry, Miss. State Univ. 59 p.

Association of Official Seed Analysts. 1978. Rules for testing seeds. J. Seed Technol. 6(2): 1 - 126.

Belcher, E. and J. A. Vozzo. 1979. Radiographic analysis

of agricultural and forest tree seeds. Assoc. Off. Seed

Anal. Handb. on Seed Test., Contrib. No. 31. 29 p.

Bonner, F. T. 1973. Storing red oak acorns. USDA For.

Serv. Tree Planters’ Notes 24(3): 12 - 13.

Bonner, F. T. ,1974. Tests for vigor in cherrybark oak

acorns. Proc. Assoc. Off. Seed Anal. 64: 109 - 114.

Czabator, F. J. 1962. Germination value: an index combining speed and completeness of pine seed germination. For. Sci. 8: 386 - 396.

Monaghan, T. A. 1982. Seedlings available from state

nurseries. Miss. Coop. Ext. Serv. For. Res. Man. Tech.

Note MTN-4E. 8 p.

*U.S. GOVERNMENT PRINTING OFFICE: 1984-769-089: I.5