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Southern Forest SO-281

Experiment Station November, 1981

Nitric Acid Promotes Pine Seed Germination

Robert C. Hare

SUMMARY

Germination of a number of recalcitrant seed lots of loblolly, slash and longleaf pine was improved markedly following

treatment with 0.1 percent nitric acid for 4 hours or 10

percent for 10 minutes.

Additional keywords: Sexual propagation, progeny

testing, growth promoters.

INTRODUCTION

Slash (Pinus elliottii Engelm. var. elliottii,, longleaf (I?

palustris Mill.), and loblolly (/? taeda L.) pine seeds generally germinate satisfactorily following 4°C storage for 5 years

or more (Schopmeyer 1974). However, specific lots may be

difficult to germinate even when stratified. Although the

seeds appear sound when cut and examined, some type of

induced dormancy exists. A simple chemical method for

breaking dormancy of difficult-to-germinate seed lots would

be valuable in tree improvement operations such as progeny testing. Biswas et al. (1972) reported that potassium

nitrate, gibberellic acid, kinetin, and thiourea promoted loblolly pine seed germination. These chemicals and benzyladenine, hydrogen peroxide, boric acid, citric acid, and

nitric acid were applied to break dormancy, but in the present trials only HN03 consistently promoted germination.

This paper reports a series of experiments in which pine

seed germination was improved following treatment with

nitric acid.

MATERIALS AND METHODS

Unstratified seed lots of different ages and families were

treated with HN03 in 1980 and 1981. Most lots had a history

of poor germination following an overnight water soak.

Longleaf, loblolly, and slash were tested separately. Typically, 40 to 75 seeds per treatment were placed in a 125 ml

Erlenmeyer flask containing 40 ml water (control) or the

appropriate chemical solution. The flasks were gently

shaken for the specified length of time, the solutions were

decanted, and the seeds rinsed with water. Seeds were

sown, without drying, on moistened vermiculite and germinated in the greenhouse under intermittent mist or in a

closed container in the growth chamber (30” C, 16-hour day,

20” C night). To see whether the nitric acid effect was due to

the H+ ion or the N03- ion, the effects of water, HN03,

H2S04, and KN03 on seed germination were compared.

“Percent HN03” in this instance, refers to the percent of

concentrated stock nitric acid used (70 percent HN03 in HZ0

v/v).

RESULTS AND DISCUSSION

Nitric acid improved both the rate of seed germination and

the total germination of many family and bulk seed lots of

slash, loblolly, and longleaf pine (tables 1 and 2) but a few

lots still germinated unsatisfactorily following HN03 treatment. Poor germination of seed lots was related both to age

of seed within a family (table 1) and to specific families

where age was not a factor (table 2). In Trial 5 with slash

pine family 18-27, 23-year-old seed germinated poorly

even with HN03, and germination of controls, as well as

response to HN03 treatment, improved as time in storage

decreased. Overall, slash and loblolly pine seed germination was doubled by HN03 in the 18-day trial. With longleaf

pine, a lo-minute soak in 10 percent HN03 improved germination of 12 recalcitrant seed lots (table 2). Overall germination was increased fivefold at 10 days (not shown in

table) and threefold at 20 days.

Southern Forest Experiment Station/T-l0210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
Table 1 .-Percent germination of lob/o//y and slash pine seed, with and without 0.1 percent nitric acid

treatment

Species

Trial

number

Loblolly 4

Slash 1

2 18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

18-27 x wind

6 18-27 x wind

W-l-20 x wind

w-1-20 x W-l-5

18-27 x 9-2

18-27 x BC-1

18-27 x BC-2

Bulk 1968

Bulk 1972

1978

1978

1977

1977

1957

1957

1967

1972

1978

1979

1979

1979

1979

1979

1979

Mean

Family

Days after treatment

Collection 1 0 1 8

year Soak H,O HN03 H,O HNO,

hours _______________ percent ________________

4 5

4 5 6

4 1 5

4 5

4 0

2 0 0

4 0

1 6 0

4 3

4 8

4 3

2 4 4 1

2 4 4 4

2 4 .

2 4 7 0

2 4 7 5

2 4 6 0

2 4

2 0 3 5 6 0

8 0

7 0 4 5 8 0

4 5 6 0 8 5

3 7 1 2 6 5

5 3 1 2 8 0

0 8 1 5

8 8 2 8

5 3 2 4 5

2 5 3 7 6 2

3 3 4 2 7 2

8 4 5 4 8 6

7 8 7 3 7 9

4 6 7 9

9 1 8 1 9 5

9 0 8 4 9 2

8 5 7 1 8 7

5 1 4 2 6 7

Table 2.-Percent germination after 20 days with difficult-to-germinate

seed lots of longleaf pine treated with water or 10 percent nitric

acid 10 minutes. Seed collected in 1979 and 1980

Family Hz0 HN03

3 5

A-l

A-4

A-10

A-12

A-15

B-5

B-9

B-10

B-11

B-13

B-17

1 1 1 6

1 1 5 8

2 1 6

6 6 0

8 7 0

9 2 0

9 2 2

1 5 6 6

2 1 6

6 8

1 6 2 6

1 0 4 0

8.8 34.8

Generally, 0.1 percent HN03 for 4 hours was effective,

but a 16- or 20- hour soak was sometimes better with 0.1

percent HN03 (table 1). Apparently the effect is dosespecific; in another trial with longleaf pine 0.1 percent for

1,000 minutes, 1 percent for 100 minutes, and 10 percent for

10 minutes were equivalent. Germination at 18 days was 55,

60, and 60 percent respectively for the three HN03 treatments, compared to only 5 percent with water.

Efforts to determine whether the mechanism of HN03

stimulation is a hydrogen ion or a nitrate effect were unsuccessful. While HN03 improved germination of slash pine

seed, equimolar concentrations of H2S04, KN03, and

H2S04 + KN03 inhibited germination.

Although pine seed germination is generally not a problem, poor germination can seriously hamper progeny testing operations of certain lots. To avoid such problems,

soaking southern pine seeds for 10 minutes in 10 percent

HN03 followed by a water rinse may be helpful.

LITERATURE CITED

Biswas, P. K.; Bonamy, P. A.; Paul, K. B. Germination promotion of loblolly pine and baldcypress seeds by stratification and chemical treatments. Physiol. Plant. 27:71-

76: 1972.

Schopmeyer, C. S. Seeds of woody plants in the United

States. C.S. Schopmeyer, Technical Coordinator. Agric.

Handbook No. 450. Washington, DC: U.S. Department of

Agriculture Forest Service: 1974. 883 p.

Robert C. Hare is Plant Physiologist, Southern Forest Experiment Station, Forest Service-USDA, Gulfport, Mississippi.

2 *U.S. GOVERNMENT PRINTING OFFICE: 1981~569-082/16