Efficiency of Different Methods of Breaking Dormancy and Seedling Development in Parkia biglobosa and Prosopis africana
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Date
2021-03
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UNIVERSITY OF ILORIN
Abstract
Seed dormancy is an inactive phase of plant life that is greatly influenced by environmental and physiological conditions. High level of dormancy displayed in seeds of Parkia biglobosa (PB) and Prosopis africana (PA) delay seed germination, growth and development of the plants. This study was carried out to assess the efficiency of different methods of breaking dormancy to enhance seed germination and seedling establishment of PB and PA. The objectives of the study were to: (i) determine the proximate composition and secondary metabolites of the collected seeds; (ii) investigate the effect of different methods of breaking dormancy on the germination capacity; (iii) quantify the generated Reactive Oxygen Species (ROS) in the seeds; (iv) evaluate the effect of germination on the enzyme activities; (v) examine the seed coat morphology; and (vi) determine the elemental constituents of the seed coats.
Fruits of PB were collected from Jigawa (PBJG), Kwara (PBKW), Kaduna (PBKD) and Katsina (PBKT) while PA were from Niger (PANG), Kwara (PAKW), Kaduna (PAKD) and Kebbi (PAKB) states respectively. Seeds from the fruits were subjected to chemical, mechanical and hormonal treatments to break the dormancy. Chemical scarification was carried out using concentrated HCl, HNO3 and H2SO4 for 5, 10, 15 and 20 minutes each. Mechanical scarification with sandpaper was used to remove part of the seed coat. Seeds were treated with auxin and gibberellin at 150, 200 and 250 mg/l for 12, 24 and 36 hours. Proximate composition, secondary metabolite, ROS levels, α-amylase, protease and lipase activities were evaluated using standard methods. Scanning electron microscope was used to examine the seed coat morphology. Elemental constituents of the seeds were determined using Electron Dispersive X-ray. Data were analysed using Analysis of Variance at p < 0.05.
The findings of the study were that:
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i. PBJG had the highest moisture content (9.29%) and crude fat (1.26%), PBKT produced the highest ash content (3.81%). Highest alkaloid (1.02%) and steroid contents (3.80%) were obtained in PBJG and PBKD, respectively;
ii. PBJG, PBKW and PBKD had 100% germination capacity (GC) at 15 and 20 minutes H2SO4 scarification, PAKB and PANG had the highest GC at 20 minutes of scarification (93.3%). Only PBKW displayed 100% GC with mechanical scarification. The PBJG and PAKB treated with 250 mg/l of gibberellin at 30 hours produced the highest GC (76.7% and 70.0%), respectively;
iii. hydrogen peroxide {32.72 μmol g/dry weight (DW)}, superoxide anion (23.66 μmol g DW-1) and hydroxyl radicals (82.72) were contained in PBJG and PBKD, respectively;
iv. activities of α-amylase (0.081μ/mol/min), protease (0.34μ/mol/min) and lipase (0.99×10-5 U/mol) were highest in the germinating seed of PBJG, PBKW and PBJG at 7 days of planting respectively;
v. seeds morphology was undulate and thin with raised seed coat sculpture; and
vi. calcium (29.6%) was the most abundant elemental constituents of the seed coat followed by potassium (26.2%) and antimony (23.4%).
The study concluded that dormancy breaking was most achieved using H2SO4 scarification. The study recommended that H2SO4 scarification be employed in the breaking of seed dormancy in PB and PA.
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Keywords
Breaking Dormancy, Seedling Development, Parkia biglobosa, Prosopis africana, Seed Dormancy