Germ & dormancy - generic practical

Improving the identification, handling 

and storage of “difficult” seeds 

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Germination / dormancy Practical Exercise 

Introduction 

Physiological and physical dormancy are the two most important constraints to the 

successful germination testing of conservation collections. Disruption of the covering 

structures surrounding seeds and fruits can be a very effective means of overcoming 

both forms of dormancy. However, there are important differences in the way the 

treatment is performed: 

Physical dormancy: The most effective way to treat small samples of seeds is to nip 

(chip) or file a small portion of seed coat to enable water uptake. Care is taken to 

position the treatment away from the underlying embryo to avoid damage. 

Physiological dormancy: Seeds with physiological dormancy often fail to germinate 

because the embryo does not have the growth potential to break through the covering 

structures. To alleviate this constraint, a portion of seed / fruit coat is carefully 

removed close to the embryo. 

Chemicals such as nitrate and gibberellins can also be effective in removing 

physiological dormancy. However, the effects of these and other germination 

promoters can be very dependent on the concentration used and method of 

application. For example, continuous exposure to GA during a germination test can 

result in weak, elongated seedlings that would be difficult to establish if they were 

required for regeneration. 

Objective 

After this practical you will understand the important differences between 

scarification treatments to overcome physical dormancy and surgical treatments aimed 

at removing the constraint to embryo growth when seeds have physiological 

dormancy. You will also understand that seed responses to promoting factors such as 

gibberellins are dependent on concentration and method of application. 

You will also learn the importance of the ‘cut test’ in the evaluation of ungerminated 

seeds at the end of germination tests. 

Materials 

• Seeds of physically dormant species eg Corchorus sp, Abelmoschus esculentus, 

• Seeds of physiologically dormant species eg Cleome gynandra, wild sorghum, 

Eragrostis pallens, Panicum coloratum, Vernonia galamensis 

• Potassium nitrate 

• Gibberellic acid (GA) 

• Appropriate germination media, eg 1% water agar, paper, sand 

• Petri dishes 

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• Forceps 

• Scalpel 

Method/Procedure 

Depending on time, species available and the particular dormancy issues you want to 

better understand, the following treatments may be tried. 

1. GA experiment 

Draw three samples of 40 seeds each of a physiologically dormant species. Subdivide 

each sample into four replicates of ten seeds. Sow the first, second and third set of 

replicates on 1% water agar containing 0mM, 0.7mM and 10mM GA respectively (or 

on paper wetted with GA solutions) and incubate at 25 o C. Score for germination after 

7 – 8 days of incubation. Use protrusion of the radicle as measure of germination. 

2. Requirement for alternating temperature 

Draw two samples of 40 seeds each of a physiologically dormant species. Subdivide 

each sample into four replicates of ten seeds. Sow the first and the second set of 

replicates on appropriate media and incubate at 25 o C and 30/25 o C respectively. Score 

for germination after 7 – 8 days of incubation. Use protrusion of the radicle as 

measure of germination. 

3. Surgical treatment 

Draw three samples of 40 seeds each of a physiologically dormant species. Subdivide 

each sample into four replicates of ten seeds. Surgically expose the embryo of the 

seeds of the second set of replicates carefully to avoid damaging the embryo. Nip 

away from embryo, the seed coat of the seeds of the third set of replicates Sow the 

three sets of replicates on on appropriate media and incubate at 35/15 o C. Score for 

germination after 7 – 8 days of incubation. Use protrusion of the radicle as measure of 

germination. 

4. Nipping experiment 

Draw two samples of 40 seeds each of a physically dormant species. Subdivide each 

sample into four replicates of ten seeds. Nip away from the embryo, the seed coat of 

the seeds of the second set of replicates to avoid damaging the embryo. Sow both the 

first and second set of replicates on on appropriate media and incubate at 25 o C. Score 

for germination after 7 – 8 days of incubation. Use protrusion of the radicle as 

measure of germination. 

5. Potassium nitrate treatment 

Draw two samples of 40 seeds each of a physiologically dormant species.. Subdivide 

each sample into four replicates of ten seeds. Sow the first and second set of replicates 

on 1% water agar containing 0% and 0.2% Potassium nitrate (or on paper wetted with 

0.2% nitrate solution) respectively and incubate at 25 o C. Score for germination after 7 

– 8 days of incubation. Use protrusion of the radicle as measure of germination. 

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6. Physical Scarification 

Scarify physically dormant legume seeds by rubbing the seeds on sand paper avoiding 

the region of the hilum. The seeds should be rubbed until a small portion of cotyledon 

tissue is revealed. Sow the seeds using the rolled towel method. Use two layers of 

base paper, and one layer of paper placed on top of the seeds 

Results 

See table below 

Questions 

These should encourage reflection/review of what trainees have learnt from the 

practical exercise and the associated lecture. 

The following questions may be adapted, depending on the species and treatments 

tested. 

1. Is there evidence that GA promotes the germination of the seeds of 

………………..? 

2. Explain the observed differences in germination among the three treatments in 

experiment 1. 

3. Are the seeds of ……………………………….sensitive to alternating 

temperature? What is the ecological explanation? 

4. Explain the effect of surgical operation in the germination of …………………. 

5. Is there evidence that the position of the nip has affected germination in 

experiment 2 ? 

6. The seeds of …………………… and ………………. have physical dormancy. 

True or false? 

7. Does KNO 3 promote germination in ………………………? 

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Improving the identification, handling and storage of “difficult” seeds 

Results 

Rep I Rep II Rep III Rep IV TOTAL 

Treatment N A F D N A F D N A F D N A F D N A F D E 

Experiment 

1 Effect of levels of GA on the germination of ……………………. 

0mM 

0.7mM 

10mM 

Experiment 

2 Effect of alternating temperatures on ……………………. 

25 o C 

30/20 o C 

Experiment 

3 Effect of surgical treatment on ……………………. 

Nip 0 

Nip 1 

Nip 2 

Experiment 

4 Effect of nipping on the germination of ……………………. 

Nip 0 

Nip 1 

Experiment 

5 Effect of KNO 3 on the germination of ……………………. 

0% KNO 3 

0.2% KNO 3 

Experiment 

6 Effect of scarification on the germination of ……………………. 

Intact 

Scarified 

Key: N: Normal seedlings A: Abnormal seedlings F: Fresh seeds D: Dead seeds 

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Germ & dormancy - generic practical

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