1.1 Background of study
Plant viruses are responsible for huge economic losses in many countries around the world.
A virus is an infection agent that typically consists of nuclei and molecule in a protein coat, it is too small to be seen by light microscopy, and is able to multiply only within the living cells of a host. (Holmes, 1939). Viruses can be spread by direct transfer of sap by contact of a wounded plant with a healthy one, such contact may occur during agricultural practices, as by damage caused by tools or hands, or naturally as by animal feeding on the plant. Most of the viruses infecting plants rely on insects to move from one host to another, some remain associated with the mouth parts and can be inoculated within seconds or minutes. (Martinus, 1898). This work those not cover insect transmission but basically mechanical inoculation.
1.2 Methods employed to control plant viruses
Plant viruses and virus diseases have been studied for more than 100 years and much attention has been given to their control. However, this has been difficult to achieve because of the lack of any effective means of curing virus-infected plants. Chemotherapy, thermotherapy and Meristem-tip culture can be successful but they cannot be used on a large scale. (Brook, 1964). The main approach has been to prevent or delay virus infection or to minimize its effect. Various means have been used to achieve these objectives, including phyto-sanitation. (Involving quarantine measures, crop hygiene use of virus-free plant materials and eradication) changes in crop practices, use of pesticide for control of vectors, mild strain protection and the employment of resistant or tolerant varieties. (Sarkar, 1995). Some viruses can be eliminated from infected plant by heat or meristem-tip therapy or by the use of chemicals (Faccioli and Marami, 1998) these methods are used widely to develop virus-free plants of vegetatively-propagated crops for further propagation. It prevents plants from becoming infected, delay infection to such a life stage of crop impaired and decrease the effects of infection. (Mink et al, 1998).
1.2.1 Ricinus Sp (Castor oil plant) has being classified as a member of the sponge family, Euphobiaceae. The seed from Ricinus sp plant contain in excess of 45% oil. The said oil is used widely for various purposes. It is used as a lubricant, in high speed engine and aeroplanes, in the manufacture of soap, transparent paper, printing ink, varnishings, linolilium and plasticizer. It is also used for medical and lighting purposes. It has antimicrobial activities against gram positive bacteria (Nuttall & Labuda, 2008).
1.2.2 Mirabilis Jalapa. (The four 0’clock plant) has being classified as a member of the Nyctaginaleae family the species mirabilis Jalapa is a commonly grown ornamental plant and is available in a range of colours. The flower of Mirabilis Jalapa is used for food colouring, and the leaves may be eaten cooked as food. It serves as emergency food. It is used for dye production for cakes and jellies. It is also used for cosmetics production. It has antiviral protein (MAP) which was demonstrated to possess abortificiant actively in pregnant mice, inhibitory effect on call-free protein synthesis and antiproliferative effect on tumor cells. (Wong et al, 2014).
1.2.3 Phyllanthus amerus: is a member of the Euphorbiaceae family, it is commonly called the stone breaker, the plant extract from Phyllanthus according to (Nicole, 1998) has being used for killing bacteria, expels stones, support kidneys and treat malaria.
1.2.4 Adansonia Digitata: Belongs to the family Malvaceae. This species is found in hot, dry savannahs’ of Sub-Saharan Africa. Common names, Baobab, monkey bread tree, dead-rat tree and cream of taster tree etc. The leaves are used either fresh as a cooked vegetable or dried and powered as an ingredient of soups and sauces. The shoots and roots of seedlings are eaten as well. The roots are boiled and eaten in West Africa in times of famine. It is used as functional food for the well being of the rural communities, food for livestock, shelter for the living and the dead, the bark of a digitata has been imported in the past into Europe by the packing and paper industry and for medicinal use. Under the name cortex Cael Cedra. It was used as a substitute for quinine to reduce fever (Jardin, 1968).
1.2.5 Acalypha Indica: belong to the family Euphorbialeae. It is a common herb growing up to 75cm tall with ovate leaves. The leaves are cooked and eaten as vegetable. This plant is held to high esteem in traditional medicine, as it is believed to rejuvenate the body. It is useful bronchitis pneumonia, ashma and pulmonary tuberculosis. It also has significant antibacterial and antifungal activities, both against human and plant pathogen. (Burkill, 1974).
1.3 Plant as reserviour Of Antiviral substance
Plants from Northern Nigeria with a history of use in both human and veterinary traditional medicine have been investigated for their antiviral activity and their hypotoxility determined. Most of the extracts have activity against more than one virus of a dose rate of between 100 and 400 microg/100 microl. (Mehesh, 2000).
Lawsonia Inermis: Popularly known as Hemma or mehindi in the oriental world, is an evergreen medium sized shrub belonging to the family hythraccere. This plant harbors a well documented folklore history for treating convulsion, jaundice and malignant ulcers. Phytochemical studies in henna plant have indicated the presence of several bioactive molecular like isophumpagin, hipeol, 30-norlupan -3-01-20-one betuhennan, betuhennamic acid and nstigmasterol in leaves and roots. Plant extract have been known to be depressing antimicrobial, antioxidant, wound healing, anti-inflammatory antipyretic, analgesis actions, (Keyvan, 2008).
1.4 Morocan water melon Mosaic virus :.