Onion is a widely cultivated crop, proper seed germination and sowing techniques play an important role in obtaining a healthy onion crop. Testing the germination percentage or germination rate of onion seeds is an important process for determining the viability of seeds, this article provides information about onion seed germination testing methods in a lab and we also discuss normal and abnormal seedlings.
Materials for onion seed germination test
Working Sample: Take 400 pure seeds, which means they must be free from impurities like debris, dirt, and seeds from other plants.
Substrate: In a germination test, two sheets are used the bottom sheet is 12’’×18’’×78’’ size and the upper sheet is ” 12×18” ×38’’ size.
Water: Soak both the top and bottom germination papers in water for a few seconds until they’re fully wet. They squeeze out the excess water from the paper and wet germination paper should be 80 grams.
Incubation chamber: The incubation chamber temperature should be maintained at 20℃. This specific temperature is ideal for onion seeds to germinate properly.
Tools: Label, Pen marker, Tray, Forceps, Zip lock bag, Sprayer, Stand, etc.
Procedure for germination test
Preparation of working sample: Take 400 number pure seeds as a working sample.
Preparation of substrate: Germination paper of 12’’×18’’×78’’ sized bottom sheet and 12” ×18” ×38’’ sized upper or covering sheet used for germination test in between paper (BP) method of each replication.
Treatment for breaking dormancy (Pre-treatment): Pre-chilling treatment for dormant seeds at 5℃ for 7 days. Between paper containing seeds are stored in a refrigerator for seven days at 5°C for breaking dormancy.
Sowing: Soaking two germination papers in water and squeeze out the excess water to reach 80g weight of each replication and place the 100 seeds of 4 replications on the germination paper bottom paper and cover the seeds by using upper germination paper and rolling of germination papers containing seeds and put the rolled between paper in a zip lock bag by giving some gap in the lock for aeration.
Incubation: Placing of zip lock bag as upright position in a stand into the incubation chamber and allow it for germination. The temperature should be maintained at 20℃ in the incubation chamber.
Seedling Evaluation
First count: The first seed count should be taken on the 6th day. On first the count, entirely normal seedlings will be evaluated.
Final count: The final count should be taken on the 12th day. On the final count normal, abnormal, hard, fresh, and dead seeds are evaluated.
Normal seedlings:
Normal seedlings should show the capacity for continued development into normal plants under favorable conditions and should have all essential structures.
- An intact seedling which possesses all the following essential structure:
- Primary roots with intact or small defects such as discolored or necrotic spots on primary roots are acceptable.
- Primary root is essential.
- Cotyledon is intact or small defects as discoloration or necrotic spots are acceptable.
Also, visit Seed testing QA, Seed Storage, Seed Dormancy, Seed Pelleting
Abnormal Seedlings:
The seedlings that do not have all essential structures (missing root and shoot) or are deformed or damaged or decayed that prevent the normal development of seedlings.
Damaged seedlings: Seedlings with no cotyledons, seedlings with constriction, split, crack, missing some essential parts, broken seedlings. During harvesting or some other mechanical activities, seed embryos may get damaged due to this some seedlings show abnormal growth like stunted, short primary roots, etc.
Deformed seedlings: Seedlings with weak or unbalanced development of the essential structures as twisting, stunted cotyledons, glassy seedlings, stunted roots, and swollen shoots.
Decayed seedlings: Seedlings with any of the essential structures diseased or decayed, due to this normal development of seedlings will be prevented.
Characteristics of Abnormal seedlings:
- Abnormal seedlings include deformed, fractured, cotyledons emerge before the primary root emergence, yellow or white colour seedlings, necrotic, decayed as a result of primary infection, glassy and spindle formation of seedlings.
- Primary root is missing, weak, stunted, stubby, retarded, broken, split from the tip, spindle formation of primary roots, and deformed and decayed as a result of primary infection.
- Cotyledons are too short and thick, broken, cracked, the shoot will form like a loop or bent over, twisted, spindly, glassy, deformed, and decayed as a result of primary infection.
Hard seeds: The seeds remain hard at the end of the test period because their impermeable seed coats prevent the absorption of water. Hard seed is also a type of seed dormancy, as it prevents the germination of viable seeds.
Fresh seeds: The seeds that have imbibed water but failed to germinate under favorable conditions may be due to dormant. These seeds will germinate after some treatment for breaking dormancy.
Dead seeds: The dead seeds that are neither hard nor dormant or have not produced any part of the seedling.
Germination Calculation
To calculate the germination percentage, use the following formula:
Germination %= Number of normal seedlings/Total number of seeds tested X 100
Factors Influencing Onion Seed Germination
Several factors can influence onion seed germination, such as seed moisture, temperature, moisture, light, and fungal growth.
