ABSTRACT

This study which is titled the photochemical screening and nutrient evaluation of paw paw leaves extract is aimed at evaluating the phytochemical screening and nutrient of methanolic extract of C. papaya. The powdered leaf of C. papaya was extracted with methanol. The concentrated crude methanolic extract was then evaluated for phytochemical screening. Phytochemical screening was performed to determine the presence of carbohydrate, and various secondary metabolites such as alkaloids, flavonoids, steroids, tannins and saponins. Phytochemical screening revealed the presence of carbohydrate, tannin and saponin.

The antimicrobial activities of methanolic solvent extract of Carica papaya leaf were tested against the gram-positive and gram-negative bacterial strains and fungus by observing the zone of inhibition. The antimicrobial test was performed by disc diffusion method. The gram- positive bacteria used in the test were Staphylococcus saprophyticus, Streptococcus pyogenes, Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, β-hemolytic streptococcus, Bacillus megaterium and the gram-negative bacteria were Escherichia coli, Shigella dysenteriae, Salmonella paratyphi, Shigella boydii and fungus like Asperllius niger and Candida albicans were also used.

The crude methanolic extract of Carica papaya leaf showed mild to moderate antimicrobial activities against the microorganisms at different concentrations of 50 µg/disc, 100 µg/disc and 150 µg/disc. However, no activity was found against Streptococcus pyogenes and Shigella boydii.

CHAPTER ONE

INTRODUCTION

1.1 The Plants Role in Human

Medicinal plants have always been associated with cultural behaviours and traditional knowledge. The renaissance of interest in plant products has been stimulated by the use of plant extracts in chronic conditions for which conventional drugs is perceived to offer very little specificity in its target (Rhiouani et al., 1999). This has resulted in the use of large number of medicinal plants with curative properties to treat various diseases (Verpoorte, 1998). Nearly 80% of the world‘s population relies on traditional medicines for primary health care, most of which involve the use of plant extracts (Akindele and Adeyemi, 2007).

The blind dependence on synthetics is over and people are returning to the naturals with hope of safety and security. Also, the development of adverse effects and high microbial resistance to the chemically synthesized drugs, has forced men into ethnopharmacognosy. More so, in our local situation, degree of ignorance and illiteracy had forced many to abandon or neglect pharmaceutically formulated drugs in favour of locally prepared herbal remedies coupled with the fact that pharmaceutical products are increasingly being faked. Thus, the herbal products today symbolise safety in contrast to the synthetics that are regarded as unsafe to human and environment (Joy et al., 2001). Herbs are staging a comeback, herbal ‗renaissance‘ is happening all over the globe and people returning to the naturals with hope of safety and security. By and large, the public is gradually drifting towards acceptance and usage of herbal preparations.

In Africa, traditional healers and remedies made from plants play important role in the health of millions of people (Adotey et al., 2012). The users of these remedies, found literally thousands of phytochemicals from plants as safe and broadly effective alternatives with less adverse effects. The Pharmacognosy Society of Nigeria supports the acceptance of herbal remedies or treatment of ethnomedicinal practice along with conventional orthodox health care system (Ndukwe, 2004). This is largely due to the fact that plants used for traditional medicine contain a wide range of substances that can be used to treat chronic as well as infectious diseases (Duraipandiyan et al., 2006).

Biological organisms particularly plants produce two distinctly different types of chemical products. The first type, primary metabolites, which consists of compounds such as sugars and proteins that are common to most organisms and are essential for functional metabolism. Secondary metabolites, on the other hand, are chemicals unique to a single species or related group of organisms. Not until the 1990s that scientists fully realize that these secondary metabolites are more than mere leftovers from an organisms metabolic processes. These chemicals can function as communications tools, defense mechanisms or sensory devices. The biological activity of these chemicals is beneficial to the organism that produces them, but it is often harmful to other species, including humans (Swerdlow, 2000). This toxicity can adversely affect the functions of the entire human body or only a specific biological process, such as the growth of cancer cells (Yoder, 2005). Also, many beneficial biological activity such as anticancer, antimicrobial, antioxidant, antidiarrheal, analgesic and wound healing activity of plants have been reported. In this way, certain foreign, naturally produced chemicals can act as powerful drugs when administered at the proper concentration (Yoder, 2005).

Natural products are important in health care. They can be used as starting materials for semisynthetic drugs. The main examples are plant steroids, which led to the manufacture of oral contraceptives and other steroidal hormones. Today, almost every pharmacological class of drugs contains a natural product or natural product analog (Eba, 2005). Similarly, it represents an excellent resource for the identification of new lead structures (Newman and Cragg, 2007).

It is estimated that 25% of all prescriptions dispensed in the USA contained a plant extract or active ingredients derived from plants. It is also estimated that 74% of the 119 currently most important drugs contain active ingredients from plants used in traditional medicine for health care (Farnsworth et al., 1985), these traditional medicines are primarily plant-based (De-Pascual-Teresa et al., 1996). Another study of the most prescribed drugs in the USA indicated that a majority contained either a natural product or a natural product was used in the synthesis or design of the drug (Wakelin, 1986). Similarly, about 121 drugs prescribed in USA today come from natural sources, 90 of which come either directly or indirectly from plant sources (Benowitz, 1996). Forty-seven percent of the anticancer drugs in the market come from natural products or natural product mimics (Newman and Cragg, 2007).

Tropical and subtropical Africa contain between 40,000 – 45,000 species of plants with a potential for development and out of which 5,000 species are used medicinally (Van Wyk, 2008). Still there is a paradox that in spite of this huge potential and diversity, the African continent has only contributed 83 out of the 1100 classic drugs globally (Van Wyk, 2008).

It is a fact that traditional systems of medicine have become a topic of global importance. Although modern medicine may be available in many developed countries, people are still turning to alternative or complementary therapies including medicinal herbs. Yet, few plant species that provide medicinal herbs have been scientifically evaluated for their possible medical applications (Adotey et al., 2012). Herbs had been priced for their medicinal and therapeutic effects, flavouring and aromatic qualities for centuries (Joy et al., 2001). Similarly, the herbal drugs contain many chemical compounds naturally. In many cases, traditional healers claim the good benefit of certain natural or herbal products. But, it is only a few herbs, their extracts and active ingredients and also, the preperation containing them that their safety and efficacy data are available (Adotey et al., 2012). No dought, plants extracts either as pure compounds or as standardized extracts, provide unlimited opportunities for new drug discoveries because of the unmatched availability of chemical diversity (Cosa et al., 2006). However, it is a common practice among chemists that the content of any unlabelled bottle in the laboratory should be discarded. In this way, a truelly practicing chemist should dissociate himself or herself from uncharacterized drug no matter how effective the drug may be (Ndukwe, 2004). As such, It is therefore essential to separate out those compounds which are responsible for therapeutic effect and characterise them. They are called active constituents or principles.

Phytochemical screening is very important in identifying new sources of therapeutically and industrially important compounds such as alkaloids, flavonoids, phenolic compounds, saponins, steroids, tannins, terpenoids etc (Akindele and Adeyemi, 2007). Also, Isolation is a part of natural product chemistry, through which it is possible to separate different components and biologically active ones which can be incorporated as ingredients in the modern system of medicine. Modern medicine has largely confined itself to the isolation or synthesis of single active ingredient for the treatment of spercific disease (Shoge, 2010). Chromatographic techniques are widely used for the separation, isolation and purification of chemical constituents from natural drugs (Devi et al., 2012).

1.2 Objective of the Research Study

The objective of this study was to assess chemical and biological activity of Carica papaya

leaf using selected bench top bioassays, including antibacterial and antioxidant tests.

In addition to identifying phytomedicines, it can offer solutions to modern day diseases like AIDS and certain cancers.

Increased knowledge about phytomedicines can:

Serve as alternative solutions where orthodox medicines have limitations, for examples antibiotics (in case of antibacterial-drug resistance), anticancer drugs from plants, like tubulin polymerization inhibitors (which is less toxic than current anti- cancer drugs such as Actinomycin D).
Provide man with necessary knowledge to avoid or minimize unwanted side effects from toxicities resulting from use of herbal
To determine plants extraordinary ability to synthesize secondary metabolites:

Plants defense mechanisms are sophisticated which allow them to survive. They do this with an enormous variety of secondary metabolites that they synthesize. Several types of thousands of secondary metabolites have already been isolated and their structures were elucidated

The main roles of secondary metabolites have been identified to be:

Defense against herbivores (insects, vertebrates),
Defense against fungi and bacteria,
Defense against viruses,
Defense against other plants competing for light, water and nutrients,
Signal compounds to attract pollinating and seed dispersing animals,
Signals for communication between plants and symbiotic microorganism (N-fixing Rhizobia or mycorrhizal fungi) and
Protection against UV-light or physical stress. [Wink, 1999]

Medicinal plants have played an essential role in the development of human culture, for example religions and different ceremonies. (E.g. Dutura has long been associated with the worship of Shiva, the Indian god). Plants are directly used as medicines by a majority of cultures around the world, for example Chinese medicine and Indian medicine. Many foods crops have medicinal effects, for example garlic.

With onset of scientific research in herbals, it is becoming clearer that the medicinal herbs have a potential in today‟s synthetic era, as numbers of medicines are becoming resistant.

1.3 Bioactive properties derived from Plants

Large numbers of surveys have been conducted in which plant extracts have been evaluated for various biological activities. Only a small sample of species are listed are in Table 1.1:

Table 1.1: Plants with medicinal uses indicating Biological activity, Drug name, Type of extract or plant part, Plant species

Biological activity	Drug/extract/plant part	Plant name	Reference
Antineoplastic	Combretastatin A-4 and B-1	Combretum caffrum Combretum kraussi	Pettit et al. (1987) Pettit et al. (1995)
Antibacterial	Juice	Vacccinium spp. (cranberry)	Ofek et al. (1996)
Antifungal	Grapefruit peel	Citrus paradisa	Stange et al. (1993)
Antiviral – AIDS	Glycyrrhizin (Flavonoid)	Glycyrrhiza rhiza	Watanbe et.al (1996)
Antimalarial (plasmodium)	Solvent extract	Mahonia aquifolia	Omulokoli et al. (1997)
Insecticide	Phenantrenes	Combretum apiculatum	Malan and Swinny (1993)
Molluscicide	Mollic acid	Combretum molle	Rogers (1989)

Schistisomiasis
Hypoglycemic	Leurosine sulphate (alkaloid)	Catharanthus roseus	Svoboda et al. (1964)
Cardiotonic activity	Extract	Carissa sp.	Thorpe and Watson (1953)
Andro-or estrogenic	Extract	Butea superba	Schoeller et al. (1940)
CNS	Morphine	Papaver somniferum	Schmitz (1985)
Antihelminthic	Dried nuts	Quisqualis indica Combretum molle	Ladion (1985) Rogers and Verotta (1997)

Traditional Medicine Practice In Bangladesh

Traditional Medicine is the medicine or treatment based on traditional uses of plants, animals or their products, other natural substances (including some inorganic chemicals). Bangladesh possesses a rich flora of medicinal plants. Most probably 5000 species of different plants growing in this country in which more than a thousand are regarded as having medicinal properties. Although the use of traditional medicine is so deeply rooted in the cultural heritage of Bangladesh the concept, practice, type and method of application of traditional medicine vary widely among the different ethnic groups. Traditional medical practice among the tribal people is guided by their culture and life style and is mainly based on the use of plant and animal parts. Among the largest ethnic group, the Bangalees on the main land, there are two distinct forms of Traditional medicine practice:

1. One is the old and original form based on old knowledge, experience and belief of the older generations. This includes:

Folk medicine, which uses mainly plant and animal parts and their products as medicines for treating different diseases and also includes treatments like blood- letting , bone-setting, , hot and cold baths, therapeutic fasting and

Religious medicine, which includes use of verses from religious books written on papers and given as amulets, religious verses recited and blown on the face or on water to drink or on food to eat, sacrifices and offerings in the name of God and gods, etc. and
Spiritual medicine, which utilizes methods like communicating with the supernatural beings, spirits or ancestors through human media, torturous treatment of the patient along with incantations to drive away the imaginary evil spirits and other similar

2. The other is the improved and modified form based on the following two main traditional systems:

Unani-Tibb or Graeco-Arab system, which has been developed by the Arab and Muslim scholars from the ancient Greek system, and
Ayurvedic system, which is the old Indian system, based on the Vedas the oldest scriptures of the Hindu saints of the Aryan age.

Both the Unani and Ayurvedic systems of traditional medicine have firm roots in Bangladesh and are widely practiced all over the country. Apparently the recipients of these systems of medicine appear to be the rural people, but practically a good proportion of the urban population still continues to use these traditional medicines, although organized modern health care facilities are available to them.

Plant materials are used in these preparations in a variety of forms, such as small pieces, coarse powders, as their extracts, infusions, decoctions or distillates. They are dispensed as broken pieces, coarse and fine powders, pills of different sizes, in the form of compressed tablets, as liquid preparations, as semi-solid masses and in the form of ointments and creams, neatly packed in appropriate sachets, packets, aluminium foils, plastic or metallic containers and glass bottles. The containers are fully labeled with indications/contra-indications, doses and directions for use and storage, just like modern allopathic medicinal preparations.

The plant Carica papaya (Linn.) belongs to the family Caricaceae, is used a medicinal agent in Bangladesh. Medicinal plants are an important therapeutic aid for various ailments. Today, there is widespread interest in drugs deriving from plants. This interest primarily stems from the belief that green medicine is safe and dependable, compared with costly synthetic drugs that have adverse effects. Medicinal plants are potential sources of medicine in developing countries to treat serious diseases. About 80% people of the rural areas of underdeveloped countries still depend on medicinal plants. Studies revealed that there are more traditional medicine providers than the allopathic practitioners especially in the rural areas (WHO, 2002). Bangladesh has a good number of medicinal plants and these plants have many biologically active compounds.

Researchers now become concerned about natural products of higher plants due to novel source of antimicrobial agents. Plants have developed sophisticated active defense mechanisms against infectious agents [Barz et al., 1990]. The main aim of these reactions appears to be inhibition of microorganisms with antibiotic compounds, hydrolytic enzymes, and inactivation of microbial exoenzymes with specific inhibitors and isolation of lesions. These defense mechanisms operate at different stages of infection [Kuc, 1990a]. The external plant surfaces are often covered with biopolymers (fatty acid esters) that are difficult to penetrate. In addition, external surfaces can be rich in compounds (phenolic compounds, alkaloids and steroid glycoalkaloids) that will inhibit the development of fungi and bacteria [Reuveni et al., 1987]. Once pathogens have passed the external barriers, they may encounter plant cells that contain sequestered glycosides [Kuc, 1990b]. The glycosides may be antimicrobial per se or may be hydrolyzed to yield antimicrobial phenols; these in turn may be oxidized to highly reactive quinones and free radicals [Noveroske et al., 1964].

Damage to a few cells may rapidly create an extremely hostile environment for a developing pathogen. This rapid, but restricted disruption of a few cells after infection can also result in the biosynthesis and accumulation of low molecular weight antimicrobial, liphophylic compounds, called phytoalexins. Phytoalexins differ in structure, with some structural similarities within plant families [Carr and Klessig, 1989]. Some are synthesized by the malonate pathway, others by the mevalonate or shikimate pathways, whereas still others require participation of two or all three of the pathways [Kuć, 1990b]. Phytoalexins can induce constitutive or other secondary metabolite pathways and link to various metabolic pathways [Barz et al., 1990]. Since phytoalexins are not translocated, their protective effect is limited to the area of the infection, and their synthesis and regulation are accordingly restricted. Phytoalexins are degraded by some pathogens and by the plant; thus, they are transient constituents and their accumulation is a reflection of both synthesis and degradation. Often associated with phytoalexin accumulation is the deposition around sites of injury or infection of biopolymers, which both mechanically and chemically restrict further development of pathogens [Hammerschmidt and Kuć, 1982]. These biopolymers include: lignin, a polymer of oxidized phenolic compounds; callose, a polymer of β-1, 3-linked glucopyranose; hydroxy-proline-rich glycoproteins, and suberin. The macromolecules produced after infection or some forms of physiological stress include enzymes, which can hydrolyze the walls of some pathogens [Carr and Klessig, 1989], including chitinases, β-1, 3- glucanases and proteases.

Unlike the phytoalexins and structural biopolymers, the amounts of these enzymes increase systemically in infected plants even in response to localized infection. They are often found intercellular where they would contact fungi and bacteria. These enzymes are part of a group of stress or infection-related proteins commonly referred to as pathogenesis-related (PR) proteins. The function of many of these proteins is unknown. Some may be defense compounds; others may regulate the response to infection [Tuzun et al., 1989]. Another group of systemically produced biopolymer defense compounds comprises the peroxidases and phenoloxidases [Hammerschmidt et al., 1982]. Both can oxidize phenols to generate protective barriers to infection, including lignin. Phenolic oxidation products can also cross- link to carbohydrates and proteins in the cell walls of plants and fungi to restrict further microbial development [Stermer and Hammerschmidt, 1987]. Peroxidases also generate hydrogen peroxide, which is strongly antimicrobial. Association with peroxidative reactions after infection is the transient localized accumulation of hydroxyl radicals and superoxide anion, both of which are highly reactive and toxic to cells. Both plant and microbial compounds regulate the expression of genes that encode products that contribute to disease resistance. The speed and degree of gene expression and the activity of the gene products (and not the presence or absence of genes for resistance mechanisms) determine disease resistance in plants [Kuć, 1990b]. The future will probably see the restriction of pesticide use and a greater reliance on resistant plants generated using immunization and other biological control technologies, genetic engineering and classical plant breeding. However, as with past and current technology, we may create unique problems. The survival of our planet may significantly depend upon anticipating these problems and meeting the challenge of their solution.

1.5 The Medicinal Plants contribution in the New World

Just Before Modern Medicine: At the early of modern medicine the Muslim physicians were done a great job. The Arabian Muslim physicians, like Al-Razi and Ibn Sina (9^th to 12^th century AD), brought about a revolution in the history of medicine by bringing new drugs of plant and mineral origin into general use. Al Razi‟s important books are: Qitab-al-Mansuri, Al-Hawai, Qitab-al-Muluki, Qitab-al-Judari-wal-Hasabah, Maan La Yahoduruho Tibb etc. The famous medical book, Al-Kanun, of Ibn Sina was the prescribed book of medicine in the schools of western medicine for several centuries [Mian & Ghani., 1990].

The use of medicinal plants in Europe in the 13^th and 14^th centuries was based on the Doctrine of Signatures or Similar developed by Paracelsus (1490-1541 AD), a swiss alchemist and physician [Murray, 1995]. The South American countries have provided the world with many useful medicinal plants, grown naturally in their forests and planted in the medicinal plant gardens. Use of medicinal plants like coca (Erythroxylum species) and tobacco (Nicotiana tabacum) was common in these countries in the 14^th and 15^th centuries. The earliest mention of the medicinal use of plants in the Indian subcontinent is found in the Rig Veda (4500-1600 BC). It supplies various information of the medicinal use of plants in the Indian subcontinent [Hill, 1972]. Medicinal plants used by the Australian aborigines many centuries ago tremendously enriched the stock of medicinal plants of the world. The current list of the medicinal plants growing around the world includes more than a thousand items [Sofowora, A., 1982].

1.6 Modern Prescription Drugs

To make prescriptions easily understandable by the patients, Paracelsus (1493 AD) started to use German instead of traditional Latin language used in medicine. His book On Diseases of Miners was very important at that time. Nuremburg Pharmacopoeia was published in 1546. First London Pharmacopoeia published in 1618. Later on its name became the British Pharmacopoeia. Many of the remedies employed by the herbalists provided effective treatments. Studies of foxglove for the treatment of dropsy (congestive heart failure) set the standard for pharmaceutical chemistry. In the 19th century, scientists began purifying the active extracts from medicinal plants (e.g. the isolation of morphine from the opium poppy). Advances in the field of pharmacology led to the formulation of the first purely synthetic drugs based on natural products in the middle of the 19th century. In 1839, for example, salicylic acid was identified as the active ingredient in a number of plants known for their pain-relieving qualities; salicylic acid was synthesized in 1853, eventually leading to the development of aspirin. It is estimated that 25% of prescriptions written in the U.S. contain plant-derived ingredients (close to 50% if fungal products are included); an even greater percentage are based on semi synthetic or wholly synthetic ingredients originally isolated from plants [Hill, A., 1972].

1.7 Plant Medicines, Safer and Time Tested

Plant medicines are far and away safer, gentler and better for human health than synthetic drugs. This is so because human beings have co-evolved with plants over the past few million years. We eat plants, drink their juices, ferment and distill libations from them, and consume them in a thousand forms. Ingredients in plants, from carbohydrates, fats and protein to vitamins and minerals, are part of our body composition and chemistry.

1.8 Drug Discovery from Medicinal Plants

Drug discovery from medicinal plants involves a multifaceted approach combining botanical, phytochemical, biological, and molecular techniques. Medicinal plant drug discovery continues to provide new and important leads against various pharmacological targets including cancer, HIV/AIDS, Alzheimer’s, malaria, and pain. Several natural product drugs of plant origin have either recently been introduced to the United States market, including arteether, galantamine, nitisinone, and tiotropium, or are currently involved in late-phase clinical trials. As part of our National Cooperative Drug Discovery Group (NCDDG) research project, numerous compounds from tropical rainforest plant species with potential anticancer activity have been identified. Our group has also isolated several compounds, mainly from edible plant species or plants used as dietary supplements that may act as chemo preventive agents. Although drug discovery from medicinal plants continues to provide an important source of new drug leads, numerous challenges are encountered including the procurement of plant materials, the selection and implementation of appropriate high- throughput screening bioassays, and the scale-up of active compound. [Hill, A., 1972]

1.9 Description on Carica papaya

Carica papaya is an evergreen shrub or small tree that grows best in full sun to light shade. The papaya plant has been described with a large variety of adjectives, which acknowledge the structural and functional complexity of this giant tropical herb. Carica papaya, with a somatic chromosome number of 18, is the sole species of this genus of the Caricaceae, a family well represented in the Neotropics, which includes six genera with at least 35 species [Fisher, 1980; Ming et al, 2008; Carvalho and Renner, 2013)].

Papayas have always held an attraction for people. It is a power house of nutrients and is available throughout the year. Papaya as well the leaf is a good source of Vitamin A (Catotene), Vitamin B1 (Thiamine), Vitamin B2 (Riboflavin), Vitamin C (Ascorbic acid), Vitamin E, Niacin, Minerals such as Calcium, Iron, Phosphorous, Potassium, Proteins, Fats, Calories, Carbohydrates, β-carotene, Fibers and Folate that helps to boost the number of platelets present on the blood.

Papayas may be very helpful for the prevention of atherosclerosis and diabetic heart disease. Papayas are an excellent source of vitamin C as well as a good source of vitamin E and vitamin A (through their concentration of pro-vitamin A carotenoid phytonutrients), three very powerful antioxidants. These nutrients help prevent the oxidation of cholesterol. Only when cholesterol becomes oxidized is it able to stick to and build up in blood vessel walls, forming dangerous plaques that can eventually cause heart attacks or strokes. One way in which dietary vitamin E and vitamin C may exert this effect is through their suggested association with a compound called paraoxonase, an enzyme that inhibits LDL cholesterol and HDL cholesterol oxidation. Papayas are also a good source of fiber, which has been shown to lower high cholesterol levels. The folic acid found in papayas is needed for the conversion of a substance called homocysteine into benign amino acids such as cysteine or methionine. If unconverted, homocysteine can directly damage blood vessel walls and, if levels get too high, is considered a significant risk factor for a heart attack or stroke. [Whfoods, 2013]

The nutrients in papaya have also been shown to be helpful in the prevention of colon cancer. Papaya’s fiber is able to bind to cancer-causing toxins in the colon and keep them away from the healthy colon cells. In addition, papaya’s folate, vitamin C, beta-carotene, and vitamin E have each been associated with a reduced risk of colon cancer. These nutrients provide synergistic protection for colon cells from free radical damage to their DNA. Increasing the intake of these nutrients by enjoying papaya is an especially good idea for individuals at risk of colon cancer. [Aravind et al, 2013]

Papaya effectively treats and improves all types of digestive and abdominal disorders. It is a medicine for dyspepsia, hyperacidity, dysentery and constipation. Papaya helps in the digestion of proteins as it is a rich source of proteolytic enzymes. Even papain-a digestive enzyme found in papaya is extracted, dried as a powder and used as aid indigestion. Ripe fruit consumed regularly helps in habitual constipation. [Aravind et al, 2013]

The enzymes papain and chymopapain and antioxidant nutrients found in papaya have been found helpful in lowering inflammation and healing burns. That is why people with diseases (such as asthma, rheumatoid arthritis, and osteoarthritis) that are worsened by inflammation, find relief as the severity of the condition reduces after taking all these nutrients. [Aravind et al, 2013]

It has been reported that papaya helps in the prevention of diabetic heart disease and also prevents premature aging. The skin of papaya works as a best medicine for wounds.

The milky juice of Carica papaya when extracted and dried, is used as chewing gum, medication for digestion problems, toothpaste and meat tenderizers. It has been used to treat digestive problems and intestinal worms as well as warts, sinusitis, eczema, cutaneous tubercles and hardness of the skin. [Aravind et al, 2013]

Green fruits are used to treat high blood pressure, round worm infection, dyspepsia, constipation, amenorrhoea, skin disease, general debility and genitor-urinary disorders [Burkhill, 1985].

Carica papaya plants produce natural compounds (annonaceous acetogenins) in leaf bark and twig tissues that possess both highly anti-tumour and pesticidal properties. Carica papaya L. leaf tea or extract has a reputation as a tumour-destroying agent. [Last, 2008]

The seed is used for intestinal worms when chewed. The root is chewed and the juice swallowed for cough, bronchitis, and other respiratory diseases. The unripe fruit is used as a remedy for ulcer and impotence. [Elizabeth, 1994)]

Fresh, green papaya leaf is an antiseptic, whilst the brown, dried papaya leaf is the best as a tonic and blood purifier [Atta, 1999]. Chewing the seeds of ripe papaya fruit also helps to clear nasal congestion, [Elizabeth, 1994]. The green unripe pawpaw has a therapeutic value due to its antiseptic quality. It cleans the intestines from bacteria, more so that (only a healthy intestine is able to absorb vitamin and minerals, especially vitamin B12).

Because of all the abundant nutrients, papaya was reputably called “The Fruit of Angels” by Christopher Columbus in the 20^th century. Today, papaya is considered one of the famous fruits in the world. [Morton, J., 1987]

1.10 General characteristics of Carica papaya

Scientific Names: Carica papaya Linn, Carica hermaphrodita Blanco, Carica cubensis Solms, Carica sativa Tussac, Carica mamaja Vellero, Carica papaya Karsten [StuartXchange, 2013]

Family: Caricaceae

Bengali Name/Vernacular Name: Pepe, Papeya; Koiya (Chittagong). [Dr. Uddin, S. B., 2013]

Tribal Name: Pepo, Cokia (Tipra), Ptega (Rakhaing), Somphula (Khumi), Kamco (Bawm). [Dr. Uddin, S. B., 2013]

English Name: Papaya, Papaya tree, Melon tree, Papaia, Pawpaw, Papaw, Papau

Other Vernacular Names:

Arabic: Fafay, Babaya
Assamese: Omita
Burmese: Thimbaw
Czech: Papaja
French: Papaye, Papayer
German: Melonenbaum, Papayabaum
Hindi: Papeeta, Papiitaa
Italian: Papaia
Japanese: Motukuwa, Papaia, Popoo
Korean: Pa pa ya
Portugese: Ababaia, Mamao, Papaia, Fruto de Mamoeiro, Papaeira
Russian: Papaia
Spanish: Fruta bomba, Lechosa, Melon zapote, Papayero, Papayo, Papaya
Thai: Loko, Malako
Urdu: Papiitaa, Pappeeta
Vietnamese: Du Du [StuartXchange, 2013]

Type: Broad leaf evergreen

Zone: 10 to 12

Height: 6.00 to 20.00 feet

Spread: 3.00 to 15.00 feet

Bloom Time: Seasonal bloomer Bloom Description: Yellowish-white Sun: Full sun; Water: Medium

Parts Used: Leaves, fruit, roots and latex of trunk [Missouri botanical garden]

1.11 Botanical description of the plant

Carica papaya is an evergreen, tree-like herb, 2-10 m tall, usually unbranched, although sometimes branched due to injury, containing white latex in all parts.

Leaves: Leaves spirally arranged, clustered near apex of trunk; petiole up to 1 m long, hollow, greenish or purplish-green; lamina orbicular, 25-75 cm in diameter, palmate, deeply 7-lobed, glabrous, prominently veined; lobes deeply and broadly toothed.

The leaf contains beta-carotene, calcium, carpaine, fats, flavonols, niacin, papain, tannins, and vitamin C (in higher concentration in the leaf than in the fruit). The leaf, unlike the fruit, is not a source of the protein-dissolving enzyme papain, but the latex (sap) in the leaf stem is [Orwa et al. 2009]

Stem: The stem is cylindrical, 10-30 cm in diameter at the base to 5-10 cm at the crown, hollow with prominent leaf scars and spongy fibrous tissue. It has an extensive rooting system. Stem density is only 0.13 g cm^-3. The single stem provides structural support, body mass, storage capacity, defense substances, height, and competitive ability, and carries a bidirectional flow of water, nutrients, various organic compounds, and chemical and physical signals that regulate root and shoot relations. [Morton, J., 1987]

Fruits: The papaya fruit is pear-shaped with a bright golden-yellow skin. The flesh of the fruit is a brighter orange-yellow, juicy and silky smooth, with a sweet and sour flavor. The shiny gray or black seeds in the interior of the fruit have a peppery taste and are edible, although they are usually discarded.

The fruit yields an enzyme, papain, best known as a digestive aid but most commonly used to “clear” freshly brewed beer. This enzyme is especially concentrated in the fruit when it is unripe. [Morton, J., 1987]

Flowers: The 5-petalled flowers are fleshy, waxy and slightly fragrant. Some plants bear only short-stalked pistillate (female) flowers, waxy and ivory-white; or hermaprodite (perfect) flowers (having female and male organs), ivory-white with bright-yellow anthers and borne on short stalks; while others may bear only staminate (male) flowers, clustered on panicles to 5 or 6 ft (1.5-1.8 m) long.

Hermaphrodite (bisexual) papaya flowers are slender and thin and they are attached close to the stem. Male flowers will not be able to become a papaya fruit. Female flowers that are not pollinated will drop off from the tree. Hermaphrodite flowers are most sought after by growers. They are self pollinating and can give you a papaya fruit. [Morton, J., 1987]

Seeds: Seeds are numerous in central cavities, rounded, blackish, about 0.6 cm in diameter, each enclosed in a gelatinous membrane (aril). [Morton, J., 1987]

Roots: The papaya root is predominately a non-axial, fibrous system, composed of one or two 0.5–1.0 m long tap roots. Secondary roots emerge from the upper sections and branch profusely. [Jimenez et al, 2013]

1.12 Taxonomic hierarchy of the investigated Plant Kingdom: Plantae

Subkingdom: Viridaeplantae Infrakingdom: Streptophyta Division: Tracheophyta Subdivision: Spermatophytina Infradivision: Angiospermae Class: Magnoliopsida Superorder: Rosanae

Order: Brassicales Family: Caricaceae Genus: Carica L. Species: Carica papaya L. [ITIS Report, 2013]

The Plant Family: Caricaceae

The Caricaceae are a family of flowering plants in the order Brassicales, found primarily in tropical regions of Central and South America and Africa. They are short-lived evergreen pachycaul shrubs or small trees growing to 5–10 m tall. Many bear edible fruit.

The family comprises six genera and about 34-35 species:

Carica – one species, Carica papaya (Papaya), Americas
Cylicomorpha – two species, Africa
Horovitzia – one species, Mexico
Jacaratia – eight species, Americas
Jarilla – three species, Americas
Vasconcellea – twenty species, Americas [Carvalho, F.A., 2013]
- Origin and Distribution of Carica papaya

Though the exact area of origin is unknown, the papaya is believed native to tropical America, perhaps in southern Mexico and neighboring Central America. It is recorded that seeds were taken to Panama and then the Dominican Republic before 1525 and cultivation spread to warm elevations throughout South and Central America, southern Mexico, the West Indies and Bahamas and to Bermuda in 1616. Spaniards carried seeds to the Philippines about 1550 and the papaya traveled from there to Malacca and India. Seeds were sent from India to Naples in 1626. Now the papaya is familiar in nearly all tropical regions of the Old World and the Pacific Islands and has become naturalized in many areas. Seeds were probably brought to Florida from the Bahamas. Up to about 1959, the papaya was commonly grown in southern and central Florida in home gardens and on a small commercial scale.

In the 1950’s an Italian entrepreneur, Albert Santo, imported papayas into Miami by air from Santa Marta, Colombia, Puerto Rico and Cuba for sale locally as well as shipping fresh to New York, and he also processed quantities into juice or preserves in his own Miami factory.

Successful commercial production today is primarily in Hawaii, tropical Africa, the Philippines, India, Ceylon, Malaya and Australia, apart from the widespread but smaller scale production in South Africa, and Latin America. It is also widely cultivated throughout Bangladesh. [Morton, J., 1987]

Table 1.2: Documented Species Distribution [Orwa et al. 2009]

Native

Costa Rica, Mexico, US

Exotic

Antigua and Barbuda, Australia, Bahamas, Barbados, Brazil, Cambodia, Cameroon, Chile, Colombia, Cuba, Democratic Republic of Congo, Dominica, Dominican Republic, Ecuador, Eritrea, Fiji, Grenada, Guadeloupe, Haiti, India, Indonesia, Jamaica, Kenya, Laos, Malaysia, Martinique, Montserrat, Myanmar, Netherlands Antilles, New Zealand, Nicaragua, Nigeria, Papua New Guinea, Peru, Philippines, Puerto Rico, Samoa, Singapore, Solomon Islands, South Africa, Sri Lanka, St Kitts and Nevis, St Lucia, St Vincent and the Grenadines, Sudan, Tanzania, Thailand, Tonga, Trinidad and Tobago, Uganda, Venezuela, Vietnam, Virgin Islands (US), Zanzibar.

Ecology/ Cultivation of Carica papaya

Carica papaya thrives in warm areas with adequate rainfall and temperature range of 21- 33^oC. Its altitude range is similar to that of the banana, from sea level up to elevations at which frost occurs (often around 1600 m). Frost can kill the plant, and cool and overcast weather delays fruit ripening and depresses fruit quality. Fruit tastes much better when grown during warm sunny season, but yield can be very high at elevations around 1000 m, which is the altitude for papaya production in East Africa in the 1960_S. Evenly distributed annual rainfall of 1200 mm is sufficient if water conservation practices are employed. Plantations should be in sheltered locations or surrounded by windbreaks; strong winds are detrimental, particularly on soils, which cannot make up for large transpiration losses. Carica papaya grows best in light, well-drained soils rich in organic matter with soil p^H 6.0-6.5. It can tolerate any kind of soil provided it is well-drained and not too dry. The roots are very sensitive to water logging and even short periods of flooding can kill the plants [globinmed, 2013]

1.16 Plant Growth and Development

Under appropriate conditions of water availability, light, oxygen, air temperature, and humidity, papaya seeds undergo epigeal germination (Fig. 1.1a); emergence is typically completed in 2–3 weeks [Fisher 1980]. Primary leaves of young seedlings are not lobed (Fig. 1.1b) but become so after the appearance of the second leaf (Fig. 1.1c). Papaya leaves of adult plants are simple, large, and palmate (Fig. 1.1b). In tropical conditions, approximately two leaves emerge at the apex of the plant in a 3/8 spiral phyllotaxy every week (Fisher 1980). Leaf life commonly spans for 3–6 months under tropical conditions and persistent scars remain on the trunk as they abscise (Fig. 1.1e). The loss of leaves on the lower section of the plant and the continuous emergence of new ones at the apex give the canopy a sort of umbrella shape that casts a considerable amount of shade. The papaya plant develops very fast, taking 3–8 months from seed germination to flowering (juvenile phase) and 9–15 months for harvest [Paterson et al. 2008]. The plant can live up to 20 years; however, due to excessive plant height and pathological constraints, the commercial life of a papaya orchard is normally 2–3 years. [Jimenez et al. 2013]

Fig 1.1: Papaya seedlings and root system. (a) Germinating papaya seed. (b) Ten-day-old papaya seedling showing cotyledonary leaves and first true leaves. (c) Three-week-old papaya seedling with six true leaves. (d) Side view of an excavated 5-month-old papaya root system, showing the main and secondary roots. (e) Upper view of the same root system, showing horizontal distribution of secondary roots. [Jimenez et al. 2013]

1.17 Morphology, Architecture, and Anatomy of the Adult Plant

Papaya is usually a single-stemmed, semi-woody giant herb with fast, indeterminate growth (1-3 m during the first year). The plants may attain up to 10 m, although under modern cultivation height vegetative growth may induce axillary bud break and branching at the lower portions seldom surpasses 5–6 m. Occasionally, vigorous vegetative growth may induce axillary bud break and branching at the lower portions of the plant, which rarely exceeds a few centimeters in length. Some branching may also occur if apical dominance is lost due to tip damage, and, in tall plants, “distance” may release the lower buds from the dominant effect of the apex [Morton, J., 1987].

The plant produces large palmate leaves (~0.6 m²), with five to nine pinnate lobes (Fig. 1.2b) of various widths (40–60 cm), arranged in a spiral pattern (Fig. 1.2e) and clustered in the upper section of adult individuals [Morton 1987; Ming et al. 2008]. Leaf blades are dorsiventral and subtended by 30–105 cm long, hollow petioles that grow nearly horizontal, endowed with a starch-rich endodermis, perhaps important for cavitation repair [Bucci et al. 2003; Posse et al. 2009; Leal-Costa et al. 2010]. The leaf epidermis and the palisade parenchyma are composed of a single cell layer, while the spongy mesophyll consists of four to six layers of tissue. Reflective grains and druses are abundant throughout the leaf [Fisher, 1980]. Papaya leaves are hypostomatic, with anomocytic (no subsidiary cells) or anisocytic (asymmetric guard cells) stomata [Carneiro and Cruz 2009; Leal-Costa et al. 2010]. Stomatal density of sunlit leaves is approximately 400/ mm², which can adjust readily to environmental conditions of light, water, and heat. Important biologically active compounds have been identified in papaya leaves [Canini et al. 2007 ; Zunjar et al. 2011], where they function in metabolism, defense, signaling, and protection from excess light, among others [El Moussaoui et al. 2001 ; Konno et al. 2004]. Adult plants may have three possible sexual forms: female, male, and hermaphroditic (Figs. 1.2a–d and 1.3a–f).

Fig. 1.2: Types of papaya plants according to sex forms. (a) Female. (b) Hermaphroditic.

(c) Male. (d) Male fruit- bearing plant.

Fig. 1.3: Papaya flowers with one petal removed to show internal parts (a – c) and inflorescences (d-f). (a) Staminate flower showing stamens (st), pistillode (pi) and corolla tube (ct). (b) Perfect flower showing st, ct, stigmata (sa), petal (p) and an elongated ovary (o).

(c) Pistillate flowers showing sepals (sp), petals and round ovary (o). (d) Long male inflorescence with dozens of staminate flowers. (e) Andromonoecious cyme showing one dominant perfect (pf) and five secondary staminate flowers (sf). (f) Female cyme with three pistillate flowers. [Jimenez et al. 2013]

1.18 Sex Expression

Papaya has three sex forms (female, male, and hermaphrodite), regulated by an incipient X–Y chromosome system. Papayas can be either dioecious (with male and female plants) or gynodioecious (with hermaphrodite and female plants). Several studies suggest that the Y chromosome contains a small specific region that controls expression of male (Y) or hermaphrodite (Y^h) types. Female plants are of the XX form. All combinations among the Y and/or Y^h chromosomes are lethal; therefore, the male and hermaphrodite types are heterozygous (XY and XY^h, respectively) [Jimenez et al. 2013].

1.19 Pests and Diseases

A white scale, Pseudaulacspis pentagona, thickly encrusts young
Xyleborus beetles bore into weak stems and kill the
Fruit flies (Diptera) lay eggs in ripening fruits, causing them to
Several mites attack C. papaya; the mites, Hemitarsoneumus latus and several species of Tetranychus, cause leaves to yellow and shed and damage the
Root-knot nematodes Meloidogyne spp. and Rotylenchulus reniformis may be serious pests.
Beetles (Coleoptera) make holes on the trunk.
Polyphagous grasshoppers and mole crickets cut seedlings at ground
Numerous fungi cause diseases on C. papaya. The disease anthracnose is caused by pathogens Colletotrichum gloeosporioides and Glomerella
Pythium spp., Rhizoctonia spp. and Fusarium spp. cause damping-off in
Phytophthora spp. cause root, foot and trunk rots.
Aphids transmit a virus that causes ring spots; symptoms include chlorosis in younger leaves, vein clearing, mottling of laminae and shortened
A virus related to the cucurbit mosaic and transmitted from cucumbers and watermelons by the green peach aphid (Myzus persicae) causes a bitter flavour in the fruit.
A tree infected by the pathogen Cercospora papayae shows symptoms of round, grey- white lesions on leaves and black, sunken lesions on the fruit.
The disease, known as cercospora leaf spot attacks leaves of seedlings under humid, poorly ventilated
Bunchy-top, a mycoplasma disease, is transmitted by a hopper (Empoasca ).
Other diseases cause seed rot, premature shedding of leaves and dropping of flowers and young fruit. [Orwa et al. 2009]

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