Papaya's

They are useful crops but they are susceptible to disease. They are a good food source as they are high in vitamin A, C and K, complex B vitamins, potassium, calcium, iron and dietary fibre. They are a brightly coloured fruit whose seeds can be dispersed in many ways such as: fruit can be dropped and some seeds can survive passage through an animal's gut and be deposited in a heap of fresh fertiliser. Unripe papayas contain a proteolytic enzyme called papain which acts as a meat tenderiser.

Growing Papayas

The papaya tree grows up to 9 metres tall. The leaves and flowers emerge directly from the stem. The variety is chosen for its suitability for the particular environment that it is to be grown in or the fruit type needed. The papayas sent abroad tend to be smaller and are shipped green as the ripe skin is easily damaged. Papaya trees are common in gardens and small farms as the trees are relatively small and need little looking after.

Ringspot disease

Papaya plants are subject to attack by pests. Such as fungal and viral diseases. Papaya ringspot virus consists of single-strand of RNA protect by a coating of proteins. It is transmitted by the stylet of aphids. There are two different strands: P and W, but its only P that infects the papaya family. The virus causes oily streaks, chlorosis and distortion of leaves. The disease causes devastation for a farm - it affects fruit quality and yield. The only way to remove it from the farm is to uproot and burn the infected plants. Attempts at developing resistance have had limited success. The only improvement comes from inserting a mild strand of the virus in young trees which reduces the severity of the disease in the future.

A GM solution?

Scientists are attempting to develop papayas with pathogen-derived resistance. Breeders have tried to develop resistant plants. Transgenic plants have been modified to include genes from the pathogen. PDR interferes with this hijack of the plant. A technique called particle bombardment doesn't insert the DNA to the necessary cells. Therefore the cells have to be separated so you can identify which have the new DNA. Cells which have the DNA can be selected using their antibiotic resistance. The antibiotic will only kill the cells without the DNA. Tissue culture is then used to grow the plants. Monoculture is a risk