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Research Note

so-341

Experiment Station June 1987

Cone Storage and Seed Quality in Longleaf Pine

F.-T. Bonner

SUMMARY

Immature cones of longleaf pine (Pinus palustris Mill.)

can be stored for at least 5 weeks without adversely

affecting‘.extraction or seed quality. Cone moisture

should be below 50 percent before using heat to open

cones.

INTRODUCTION

Early collection and storage of cones prior to seed

extraction is common for all southern pines, including

longleaf (Pinuspalustris Mill.). A study by McLemore (7)

found that careful cone storage for up to 5 weeks could

increase seed yield of longleaf pine, although germination of seeds from cones collected when cone specific

gravity averaged 0.99 was decreased by 5 weeks of

storage.

Barnett (2) confirmed that cone storage for 5 weeks

would increase longleaf seed yield, but found that germination was decreased if the stored cones were immature

when collected. He recommended that cones of longleaf

be collected only when mature (specific gravity less than

0.90) to avoid loss of seed quality.

Preliminary tests at our laboratory have indicated that

cone storage can be beneficial to seed quality of several

pines, including longleaf (4). The previous studies by

McLemore (7) and Barnett (2) used unheated indoor

storage. Most of the cone storage in the South today is

outdoors in unprotected burlap bags or 20-bushel wirebound boxes. A comparison of these two methods of

longleaf pine cone storage seemed warranted.

METHODS

Immature cones of longleaf pine were collected from 5

to 10 trees in southern Mississippi from September 14 to

16, 1984, by a contractor and delivered to the Forestry

Sciences Laboratory at Starkville, Mississippi, the following day in a mixed lot. Samples were immediately

taken to determine cone specific gravity (10 cones) and

moisture content (10 cones). Other samples of 10 cones

each were placed in laboratory ovens at 3543, or 49 “C

to extract seeds for germination tests.

The remaining cones were placed in small burlap bags

for storage under the following conditions: (1) outdoors

without protection, (2) outdoors with overhead cover,

but exposed to blowing rains, and (3) inside small, unheated sheds with complete protection.

There were four replications of each storage condition.

Outdoor cones (condition 1) were sprayed with hoses

every 3 or 4 days to simulate occasional rainfall when

natural rainfall did not occur.

Each week for 5 weeks, 12 cones were removed from

each bag. Three were used for specific gravity and cone

moisture determinations, and three were dried at each of

three extraction temperatures (35, 43, and 49 “C) in

forced-draft ovens.

The cones were dried in small trays for 48 hours, then

hit against a table top to remove easily extracted seeds.

The cones were then carefully torn apart by hand to

recover all other seeds. The number of easily extracted

seeds were expressed as a percentage of the total

seeds for a measure of extraction efficiency.

The seeds were dewinged by hand, and germination

Southern Forest Experiment Stationfi-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

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was tested according to standard procedures (7). Germination percentages were based on filled seeds only.

Analyses of variance were carried out using arcsin transformations of both extraction efficiency and percent normal germination; germination rate was expressed by

Peak Value (5).

Cone specific gravity was measured by water displacement (3). Moisture contents were determined by

weight loss of cones dried for 24 hours at 105 “C and

were expressed as a percentage of fresh weight. Each of

these cones was cut into four pieces with a cone cutter

for moisture determinations.

RESULTS AND DISCUSSION

The cones were definitely immature when delivered;

specific gravity averaged 0.98 + 0.01, and cone moisture content was 56.3 percent. Seeds immediately extracted also indicated immaturity in their sensitivity to

drying temperatures (table 1). Drying at 49 “C yielded

seeds with a 14:3 percent germination, while drying at

35 “C yielded seeds with a 66.1 percent germination.

Cones lost moisture at different rates under the three

storage conditions (table 2). Moisture loss was slowest

in the indoor storage. The two outdoor conditions were

about equal in drying rate, except for extended rains

during weeks 3 and 5, which raised moisture levels in the

outdoor storage without protection.

Extraction efficiency was not significantly influenced

by storage condition, storage time, or drying temperature

(table 3). Five weeks of storage dropped cone moisture

contents as low as 18 percent, but did not improve extraction efficiency. For cones stored indoors, increasing

drying temperature from 35 to 49 “C improved extraction

efficiency, but this was not true for the other storage

conditions. Cones exposed to the weather opened

sooner in the ovens than cones from indoor storage, but

after 48 hours of drying there was little difference in cone

opening. It should be noted that a three-cone sample is

small, but drying facilities were limited. Sample size undoubtedly contributed to the variability of the results

(table 3).

Table 1 .-Germination of seeds extracted at three temperatures from

immature cones

Drying temperature Germination

“C Percent

3 5 66.1

4 3 48.3

4 9 14.3

Peak value

Percent/day

3.7

2.2

0.8

Table 2.-Average cone moisture content during storage under three

conditions

Storage

period Outdoors

Storage condition

Outdoors. covered Indoors

Weeks ___________________ percent _______________---

0 56.3 56.3 56.3

1 48.2 47.9 51.7

2 32.4 39.3 41.5

3 29.1 20.8 29.8

4 19.0 17.2 24.3

5 35.5 18.1 19.4

These results suggest that a cone moisture level of 50

percent is the critical point for drying longleaf pine cones.

Once cone moisture is below this level, extraction should

be successful. Results of previous tests (4) support this

conclusion, as do the results of Barnett (2).

Total germination was not affected by any of the

storage-extraction treatments (table 4). While the values

were not especially high, they were consistent across all

treatments.

The most important finding, however, was the effect of

cone storage on the rate of germination, normally considered a sensitive index of seed quality. In this study,

cone storage significantly increased germination rate

(table 4). Peak Value averaged 5.3 after 1 week of cone

storage, 6.0 after 3 weeks, and 7.6 after 5 weeks. This

leads to the conclusion that the storage conditions stimulated the internal processes leading to germination.

Prolonged warm, moist storage environments could also

cause germination in the cones, which has been observed after longleaf cone storage for several months in

20-bushel boxes at one southern extractory. Longleaf

cones could obviously be held too long before opening,

but this study did not determine the limit. McLemore (6)

suggested 60 days as a maximum for storage.

Seeds brought close to germination in prolonged cone

storage should be used as soon as possible and not

stored to carry over to later years. If storage of a portion

of the lot is required, then those seeds extracted first

should probably be stored. This point is currently under

study with samples from all cone storage/extraction

treatments.

Drying temperatures also had a significant effect on

germination rate (table 4). The lower the temperature,

the better the seed quality. This result underscores the

danger of using seed yield or percent germination alone

to evaluate cone handling and seed extraction procedures. Extraction was equal for all temperatures, but the

two higher temperatures damaged seed quality.

F. T. Bonner is supervisory plant physiologist at the Forestry Sciences Laboratory, maintained by the Southern Forest Experiment Station, Forest

Service-USDA, Starkville, MS.

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Table 3.-Extraction efficiency for longleaf cones stored under different conditions and

dried at three temperatures

Storage Drying Weeks of storage

conditions temoerature 1 2 3 4 5 Mean

“C _____________ percent ________------

Outdoors, Uncovered 3 5 9 6 6 2 4 3 3 8 9 4 4

4 3 6 3 5 7 4 2 6 8 8 7 6 4

4 9 4 1 6 2 4 2 7 3 5 4 5 5

Mean 36 62 36 58 78 54

Outdoors, Covered 3 5 7 5 5 3 3 7 1 9 3 4 4 3

4 3 1 3 6 4 2 2 2 4 3 0 2 9

4 9 3 7 7 4 2 4 4 6 3 2 4 3

Mean 4 1 6 4 2 8 2 9 3 2 3 8

Indoors 3 5 2 2 4 8 5 2 6 4 6 7 5 0

4 3 4 9 3 8 5 0 6 3 6 4 5 3

4 9 3 3 3 4 7 6 6 6 7 5 5 7

Mean 34 40 60 64 69 54

Table 4.-Germination of seeds extracted from cones stored under different conditions and dried at three temperatures

Storage

condition

Drying Weeks of storage

temperature 1 2 3 4 5 Mean

“C _______________ percent ________--------

Total germination

Outdoors 3 5 83.0 74.5 79.3 84.5 80.4 80.4

4 3 78.1 75.9 81.8 90.0 82.3 81.9

4 9 75.0 85.8 86.4 79.6 82.3 82.0

Mean 78.8 79.0 82.6 85.0 81.7 81.5

Outdoors, Covered 3 5 82.9 79.5 82.9 81.3 86.3 82.9

4 3 88.7 81.2 87.5 83.7 80.8 84.5

4 9 76.9 87.2 91.9 84.5 93.0 87.2

Mean 83.5 82.8 87.7 83.2 87.1 84.9

Indoors 3 5 84.2 68.9 85.9 76.4 93.4 82.6

4 3 86.9 90.7 84.4 84.1 85.2 86.4

4 9 92.3 80.6 86.5 55.5 80.9 80.4

Mean 88.0 80.9 85.6 72.8 87.0 83.2

Peak Value

Outdoors 3 5 5.9 4.4 5.6 7.4 8.0 6.3

4 3 4.0 5.1 5.7 6.2 7.0 5.6

4 9 4.1 5.8 5.6 5.8 7.2 5.7

Mean 4.6 5.1 5.6 6.4 7.4 5.8

Outdoors, Covered .35 7.0 6.0 6.0 6.6 7.2 6.6

4 3 5.6 5.9 6.7 6.6 7.2 6.4

4 9 3.8 5.7 5.8 6.2 7.9 5.9

Mean 5.4 5.9 6.2 6.5 7.4 6.3

Indoors 3 5 6.1 4.2 6.4 5.1 9.7 6.3

4 3 5.6 5.8 6.4 5.4 7.5 6.2

4 9 5.6 4.8 5.6 4.5 6.9 5.5

Mean 5.8 4.9 6.2 5.0 8.1 6.0

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CONCLUSIONS

Results of this study indicate that immature longleaf

pine cones can be stored for at least 5 weeks without

adversely affecting extraction or seed germination. The

maturation effect during storage actually enhances seed

quality as reflected in germination rate. Cone moisture

should be below 50 percent (0.80 specific gravity) before

drying is begun, and drying should be at temperatures of

about 35 “C. Under some conditions, higher temperatures might be useful, but 43 “C should be the maximum.

Storage of cones longer than 5 weeks may be possible

without seed damage, but extreme care should be used.

Extraction efficiency and seed quality were equal for

cones stored indoors or outdoors, but cones stored outdoors, which had alternate wetting and drying, seemed

to open sooner. If storage for later years is planned,

seeds from the earliest extraction (shortest storage),

should probably be chosen. Seeds from cones stored

the longest should be planted first.

LITERATURE CITED

1. Association of Official Seed Analysts. Rules for testing seeds. Journal of Seed Technology. 6(2): l126: 1981.

2. Barnett, James P. Cone and seed maturation of

southern pines. Res. Pap. SO-122. New Orleans,

LA: U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station; 1976. 11 p.

3. Barnett, James P. An easy way to measure cone

specific gravity. In: Proceedings of the seed collection workshop; 1979 May 16-18; Macon, GA. SATP-8. Atlanta, GA: U.S. Department of Agriculture,

Forest Service, State and Private Forestry; 1979:

21-23.

4. Bonner, F. T. Effects of seed extraction on the quality

of southern pine seeds. Proceedings: 1984 southern nursery conference; 1984 July 24-27;

Asheville, NC. Atlanta, GA: U.S. Department of

Agriculture, Forest Service, Southern Region;

1984:111-120.

5. Czabator, Felix J. Germination value: an index

combining speed and completeness of pine seed

germination. Forest Science. 8:386-396; 1962.

6. McLemore, B. F. Prolonged storage of longleaf cones

weakens seed. Southern Forestry Notes. New Orleans, LA: U.S. Department of Agriculture, Forest

Service, Southern Forest Experiment Station;

1961; 132: 3.

7. McLemore, B. F. Collection date, cone-storage period

affect southern pine seed yields, viability. Tree

Planters’ Notes. 26( 1):24-26; 1975.

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