VARIABILITY AND CORRELATION STUDIES IN BASIL SCENT LEAF (Ocimum gratissimum)

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Ocimum gratissimum belongs to the mint family (Lamiaceae) and grows naturally in tropical and warm temperate regions. It is commonly called scent leaf, African basil or shrubby basil. In Nigeria it is known as efinrin in Yoruba, daidoya in Hausa and nchuanwu in Igbo. The genus Ocimum contains more than 60 herbaceous and bush species that differ widely in growth habit, yield traits and essential oil composition. Plants in the genus are used for flavouring and perfumery, and in traditional medicine for conditions that include diabetes (Kumar et al., 2012). Leaf extracts of O. gratissimum contain a range of phytochemicals with antioxidant activity (Igbinosa et al., 2013).

Many studies in rats report that O. gratissimum lowers blood glucose (Aguiyi et al., 2000; Owoyele et al., 2005; Egesie et al., 2006; Okoduwa et al., 2017). It has also been reported to improve insulin sensitivity in insulin-resistant rats (Shittu et al., 2021), and phenolic substances from Ocimum species have been found to enhance glucose-stimulated insulin secretion in mouse pancreatic islets (Casanova et al., 2017). At the same time, one study raised concern about reproductive safety, because a leaf extract may precipitate infertility in male diabetic rats (Shittu et al., 2019). Information on its effects during pregnancy is therefore important.

Because medicinal plants vary from one plant to the next, the quality and quantity of their useful traits depend on the genetic make-up of the plant, the environment and the interaction between them. Variability studies show how much difference exists among plants for important traits, which is the raw material for selection and improvement. In Ocimum, genetic variability has been found for traits such as essential oil yield, leaf length, leaf width and oil content, and accessions of O. gratissimum are particularly rich in phenylpropanoids (Patel et al., 2018). Other work found considerable variability in morphometric traits among accessions, with high heritability and genetic advance for oil yield and herb yield per plant (Lal et al., 2017).

Correlation studies add information by showing how traits are related. For example, herb yield and oil content have been found to be strongly associated with oil yield in Ocimum species (Kumar et al., 2012), and leaf-to-stem ratio has been found to correlate with oil content (Lal et al., 2017). Correlation alone can mislead, because two traits may appear related only because both are related to a third. Path-coefficient analysis therefore separates the direct and indirect effects of each trait (Kumar et al., 2012). Such information helps breeders choose traits for indirect selection.

Despite its importance in Nigerian diet and medicine, little is known about the variability and trait relationships of O. gratissimum in Nigeria. This study investigates that variability and the correlations among its traits. It also examines the effect of an aqueous leaf extract on pregnancy and its outcome in alloxan-induced diabetic pregnant rats.

1.2 Justification of the Study

Diabetes is a growing concern in Nigeria, which increases the need for safe and effective alternative treatments. Pregnant women who develop diabetes are often advised to be careful with drugs because of possible risks to the mother and the developing fetus, so options that are known to be safe are needed. O. gratissimum is widely eaten and used as a herbal remedy, yet there is little literature on its effects on pregnancy in diabetic animals, and almost nothing on how its traits vary and relate to one another. This study addresses both gaps. Knowing which traits vary and how they are associated will help in selecting superior plants. Testing the extract on weight gain, fasting blood glucose and pregnancy outcome will add safety and efficacy information.

1.3 Aim of the Study

The study aims to carry out variability and correlation studies in scent leaf (Ocimum gratissimum) and to determine the effect of an aqueous leaf extract on pregnancy and its outcome in diabetic pregnant rats.

1.4 Objectives

1. To assess the variability among O. gratissimum plants or accessions for growth and yield traits.
2. To determine the correlations among these traits.
3. To determine the effect of the aqueous leaf extract on pregnancy and weight gain in diabetic pregnant rats.
4. To determine the effect of the extract on fasting blood glucose in diabetic and non-diabetic pregnant rats.
5. To determine the effect of the extract on pregnancy outcome in diabetic and non-diabetic pregnant rats.

REFERENCES

Aguiyi, J. C., Obi, C. I., Gyang, S. S., & Igweh, A. C. (2000). Hypoglycaemic activity of Ocimum gratissimum in rats. Fitoterapia, 71(4), 444–446. https://doi.org/10.1016/S0367-326X(00)00143-X

Casanova, L. M., Gu, W., Costa, S. S., & Jeppesen, P. B. (2017). Phenolic substances from Ocimum species enhance glucose-stimulated insulin secretion and modulate the expression of key insulin regulatory genes in mice pancreatic islets. Journal of Natural Products, 80(12), 3267–3275. https://doi.org/10.1021/acs.jnatprod.7b00699

Egesie, U. G., Adelaiye, A. B., Ibu, J. O., & Egesie, O. J. (2006). Safety and hypoglycaemic properties of aqueous leaf extract of Ocimum gratissimum in streptozotocin induced diabetic rats. Nigerian Journal of Physiological Sciences, 21, 31–35.

Igbinosa, E. O., Uzunuigbe, E. O., Igbinosa, I. H., Odjadjare, E. E., Igiehon, N. O., & Emuedo, O. A. (2013). In vitro assessment of antioxidant, phytochemical and nutritional properties of extracts from the leaves of Ocimum gratissimum (Linn). African Journal of Traditional, Complementary and Alternative Medicines, 10(5), 292–298.

Kumar, R. R., Reddy, L. P. A., & Patel, R. P. (2012). Genetic association for oil yield and its component traits in different Ocimum species. Electronic Journal of Plant Breeding, 3(2), 794–799.

Lal, R. K., Singh, S., Gupta, P., Dhawan, S., Sarkar, S., & Verma, R. (2017). Quantification of ursolic acid, correlations and contribution by other traits towards accumulation of ursolic acid in six Ocimum species. Trends in Phytochemical Research, 1(1), 39–46.

Okoduwa, S. I. R., Umar, I. A., James, D. B., & Inuwa, H. M. (2017). Anti-diabetic potential of Ocimum gratissimum leaf fractions in fortified diet-fed streptozotocin treated rat model of type-2 diabetes. Medicines, 4(4), 73. https://doi.org/10.3390/medicines4040073

Owoyele, B. V., Funsho, M. A., & Soladoye, A. O. (2005). Effect of aqueous leaves extract of Ocimum gratissimum (sweet basil) on alloxan induced diabetic rats. Pharmacognosy Magazine, 1, 62–63.

Patel, R. P., Singh, R., Lal, R. K., Gupta, P., Kesarwani, A., & Goyal, N. (2018). Genetic variability of agronomic traits and biodiversity in the genus Ocimum. Trends in Phytochemical Research, 2(2), 103–110.

Shittu, S. T. T., Lasisi, T. J., Shittu, S. A. S., Adeyemi, A., Adeoye, T. J., & Alada, A. A. (2021). Ocimum gratissimum enhances insulin sensitivity in male Wistar rats with dexamethasone-induced insulin resistance. Journal of Diabetes & Metabolic Disorders, 20(2), 1257–1267. https://doi.org/10.1007/s40200-021-00850-y

Shittu, S. T., Shittu, S. A., Olatunji, A. A., & Oyeyemi, W. A. (2019). Ocimum gratissimum leaf extract may precipitate infertility in male diabetic Wistar rats. JBRA Assisted Reproduction, 23(1), 37–44.