CARICA PAPAYA:The papaya is a large tree with a single stem

growing from 5 to 10m tall.The leaves are large, 50–70 cm in diameter.Papaya is the fruit of the Carica papaya plant.Papayas can be used as a food, a cooking aid and in traditional medicine. The stem and bark may be used in rope production.

BACTERIAL DISEASE OF PAPAYA: BACTERIAL WILT: CAUSATIVE AGENT: Ralstonia solanacearum Ralstonia solanacearum is an aerobic non-sporing,

Gram-negative plant pathogenic bacterium. R. solanacearum is soil-borne and motile with a

polar flagellar tuft. It colonises the xylem, causing bacterial wilt in a

very wide range of host plants.

Culture of Ralstonia solnacearum

HOSTS Plant hosts that R. solanacearum infects

includes: Crops: Papaya (Carica papaya); Potato

(Solanum tuberosum); Tomato (Lycopersicum esculentum); Aubergine (egg plant) (Solanum melongena); Banana, (Musa spp).

 Wild hosts: Woody nightshade (Solanum dulcamara)

SYMPTOMSWilting begins with lower leaves and petioles

and works its way up the plant. Wilted leaves with chlorotic, wedge-shaped

areas or chlorotic and/or necrotic leaf margins.

No leaf spots are evident. Eventually entire plant collapses on the

medium White runny ooze from cut stems.

BACTERIAL WILT IN PAPAYA

DISEASE CYCLE:High temperatures and high soil moisture generally

favors Ralstonia solanacearum.The bacteria can survive for a long time in water (up to 40

years at 20–25 °C in pure water) and the bacterial population is reduce d in extreme conditions (temperature, pH, salts, e.g.).

DISPERSALR. solanacearum causes wilting at high population and

disperses in several routes. The large number of R. solanacearum can shed from roots of symptomatic and non-symptomatic plants. Beside that, bacterial ooze (which is usually used as a sign for detection) on plant surfaces, can enter the surrounding soil or water.

INFECTION:R. solanacearum usually enter the plant via a wound.

Natural wounds as well as unnatural ones, would become entry sites for Ralstonia solanacearum. The bacteria get access to the wounds partially by flagellar-mediated swimming motility.

After invading a susceptible host, R. solanacearum multiplies and moves systematically within the plant before bacterial wilt symptoms occur. When the pathogen gets into the xylems through natural openings or wounds, tyloses may form to block the axial migration of bacteria within the plant.

The primary factor contributing to wilting is probably blocking of pit membranes in the petioles and leaves.

POTENTIAL SOURCES OF INOCULUM:

Contaminated irrigation pond and equipment

Infested soil

Latently infected weeds in and around fields

GENERAL MANAGEMENT:Commercial chemicals have generally proven

to be ineffective in controlling the pathogen and are not recommended as a means of control.

Using pathogen-free planting materials is a necessity.

Planting resistant cultivars minimizes the ill effects of the pathogen.

VIRAL DISEASE OF PAPAYA:PAPAYA LETHAL YELLOWING:CAUSATIVE AGENT: Papaya lethal yellowing Virus

Papaya Lethal Yellowing Virus (PLYV) is an isometric viral plant pathogen of the Tombusviridae family that causes lethal yellowing disease.

The virus infects only C. papaya, and some other members from the family Caricaceae.

PLYV consists of a capsid protein, a single strand of RNA, and causes progressive leaf yellowing and greenish circular spots on the fruits.

PAPAYA YELLOW LETHAL VIRUS:

 Large numbers of isometric virus particles can be observed by electron microscopy in cytoplasm and vacuoles of cells from leaves and fruits of infected plants.

 PLYV particles are isometric and 30nm in diameter.

HOST:Like the name implies, the host of PLYV is

very specific. Inoculation studies indicate that the

Caricaceae was the only family of plants affected by the virus.

SYMPTOMS:Symptoms of PLYV are very straightforward. The signs of the virus begin to become visible when the leaves at the top of the plant begin turning yellow and eventually falling off. This usually occurs in the upper third of the canopy and death of the plant is usually soon after the leaves wilt and die.

SYMPTOMS:

DISEASE CYCLE:PLYV was first recognized in the 1980's, and has always

been restricted to a relatively small geographical area. It is more likely that the virus was present in wild hosts

and jumped to papaya plants once this crop became widely cultivated in that area.

While no known biological vector is know for PLYV is known, it is known to be spread by human actions, including contaminated hands, agricultural tools, soil, and contaminated water.

The virus can be detected on the surface of seeds of infected fruits, but it is not detected in the embryo or in seeds harvested from infected roots.

MANAGEMENT:There are various ways that PLYV can be

controlled.

1. Virus-free plantlets: A large reason for the spread of PLYV is the use of infected Papaya plantlets for Papaya growth. In order to prevent the further spread of PLYV, it is helpful to start by growing new Papaya in orchards far away from PLYV infected orchard.

MANAGEMENT:2. Eradication of virus-infected plants:Any plants that show symptoms of PLYV or are suspected of having

the virus should be removed from growing orchards to prevent viral transmission.

3. Disinfecting agricultural tools:Just as infected plants can spread the virus, infected agricultural tools can too. The recommended method for disinfecting trimming or harvesting tools is to immerse them in 10% commercial household bleach solution for five minutes.Also clean properly the shoes and tyres of the tractors.

FUNGAL DISEASE OF PAPAYA:DAMPING OFF:CAUSATIVE AGENT: Pythium aphanidermatum

''Pythium aphanidermatum'' is a soil borne plant pathogen. Pythium is a genus in the class Oomycetes, which are also known as water molds. Also, they reproduce asexually with motile biflagellate zoospores that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridium, oogonium, and oospores.

DAMPING OFF:Culture of Pythium aphanidermatum:

HOSTS:Pyhtium aphanidermatum has a wide host

range, and is of economic concern to beets, peppers, chrysanthemum, cucurbits, cotton and turf grasses, however, because P. aphanidermatum requires warmer temperatures. It is a major cause of root rot in papaya production in subtropical areas.

SYMPTOMS:

Pythium aphanidermatum is responsible for pre and post emergence damping off.

Pre-emergence damping off is when the seed is infected prior to germination. This can result in poor or no germination, and is observable as a browning or rotting of the seed.

Post emergence damping off takes place after germination and results in a thinning, water-soaked stem near the plant collar, which eventaully causes the collapse of the plant.

SYMPTOMS:P. aphanidermatum can also cause root rot. Symptoms of root rot include stunted growth,

chlorotic leaves, leaf drop, and wilting.

DISEASE CYCLEPythium aphanidermatum survives in the soil as oospores,

hyphae and/or sporangia. Oospores can produce a germ tube and infect the plant

directly, or, if the environment is favorable the oospore may produce

sporangia, which in turn produce motile, biflagellate zoospores that swim to the host plant, encyst, and germinate. This infection can occur on seeds, which can rot, or produce a weak seedling. If it infects the roots of a seedling, the mycelium will grow throughout the plant tissue, releasing digestive enzymes which break down plant cell walls allowing the pathogen to absorb the nutrients, effectively killing the plant overtime.

P. aphanidermatum is a polycyclic disease. A polycyclic plant pathogen has several life cycles during a season.

MANAGEMENT:Several cultural management methods can be effective in

avoiding disease caused by Phythium aphanidermatum. The pathogen thrives in a moist environment, so it is important to prevent an excessive amount of moisture from building up in the plant media.

Irrigation that is too frequent and usage of soil that has poor drainage increase its growth.

In addition, poor ventilation and insufficient exposure to sunlight can cause the plants themselves to accumulate moisture, potentially spreading disease.

Several chemical types can be used to manage the pathogen including acylalanines, thiadiazoles, carbamates, cinnamic acid derivatives.