Abstract
<p class="1Body">The seed dormancy of <em>Senna obtusifolia</em> was investigated through various methods, namely pretreatments in concentrated sulfuric acid, 2% potassium nitrate (KNO<sub>3</sub>), 99% ethanol, 99% methanol, and in hydrogen perioxide; examination of the seed coverings; and the determination of water uptake by the seeds in order to ascertain the most effective technique for breaking dormancy and also determine the dormancy type. The results showed that sulfuric acid treatment recorded the highest germination (100%); followed by 2% hydrogen peroxide treatment (24%) in 15minutes immersion. The methanol and ethanol pretreatments gave 18.33% and 16.5% germinations respectively. Pretreatment in 2% potassium nitrate gave the lowest germination (8.50%), while the intact seeds of <em>S. obtusifiolia</em> (control) gave 0% germination. The anatomy of the seed coat indicated the presence of hard, thickened and specialized cells of cuticle, macrosclereids, osteoscereids, and disintegrated parenchyma layers. The water uptake of intact seeds was low (13.5%) after 24 hr imbibitions. These findings revealed that the seed coat acts as barrier to germination by preventing water absorption, possibly gaseous diffusion in and out of the seed and conferring mechanical resistance to the protrusion of embryo. Pretreatments, such as immersion in H<sub>2</sub>SO<sub>4 </sub>will soften the seed coat and permit germination. Seed dormancy in <em>S. obtusifolia </em>can be considered of physical nature and classified as physical dormancy. The results obtained in this study may serve as useful information in the production and improvement of <em>S. obtusifolia </em>seedlings, as knowledge on seed dormancy and germination is a critical factor and requirements to the understanding of the propagation of this plant either in situ or ex-situ, in view of the economic potentials/attributes of this species.</p>
Highlights
The results showed that for the durations of pretreatment, the germination percentage in concentrated H2SO4 increased with increasing time and there is significant difference in the percentage germination (Table 1)
Tambari and Aminu (2015) noted 73.32% germination in seeds of S. obtusifolia after 15mins of pre-treatment in H2SO4, Afshar et al(2014) noted that the dormant seeds of Canna indica L. (Cannaceae) when pretreated with H2SO4 showed maximum germination of 95% after three and four hours pretreatment
Mensah and Agbagwa (2004) reported that chemical scarification with concentrated H2SO4 was very potent in breaking seed dormancy of Gmelina arborea
Summary
S. obtusifolia is native to southern USA, Mexico and tropical America. It grows in disturbed sites, waste area, riparian zone banks of watercourses), floodplains, drainage channels, open woodlands, fallow land, crops and pastures in wetter tropical and subtropical environments (Harry-O’kuru, Payne-Wah, & Busman, 2012; Irwin & Barneby, 2016). Phytochemical investigations of the plant parts revealed the presence of medicinal compounds (phenolic compound anttraquinone, naphthopyrone glycosides) used for the treatment of eye inflammation, phtophobia, lacrimation, lowering of blood pressure, reduction of cholesterol level, bacterial and fungal infections, gonorrhoea, pneumonia, urinary tract infections and mycotic infections (Ettu, Senjobi, & Ilusanya, 2011; El-Morsy, 2013; Sushma & Sardana, 2013; Kim et al, 2011). Extracts from the plants have been reported to inhibit some bacteria strains and fungal species (Ettu et al, 2011; El-Morsy, 2013; Sushma & Sardana, 2013; Kim et al, 2011)
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