Detection and strain differentiation of plant pathogenic mycoplasma-like organisms in the Australasian/Pacific region

• Prince of Songkla University, Thailand
• Department of Agriculture and Livestock, Papua New Guinea
• Malaysian Agricultural Research and Development Institute, Malaysia
• Bogor Agricultural University, Indonesia

MLOs are responsible for a number of serious plant diseases in the Asia-Pacific region. In Australia, MLOs are associated with important diseases in tomato, potato, sweet potato, papaya and tropical legumes.

MLOs are associated with witches' broom disease of peanut, soybean and sweet potato in Indonesia; phyllody diseases of sesame, soybean, mungbean, peanut and wing bean in Thailand; yellow dwarf and orange leaf diseases of rice in Malaysia, Taiwan and Indonesia; and little leaf of sweet potato throughout the Pacific.

MLOs cause significant reduction in yields in Australia's and PNG's sweet potato industries. Possible infections of MLOs in PNG's sweet potatoes prevent distribution of their many valuable cultivars.

Crop losses due to the organism are difficult to quantify as other diseases or pests may be present in the crop. Without a reliable assay it has been difficult to determine the number of infected plants, or the distribution and spread of the organism.

This project aims to:

develop a routine method to detect Mycoplasma-like organisms (MLOs) and the taxonomic significance of this study the variability between MLO strains;

examine the nature of the MLOs chromosome(s) and the component DNA;

identify and analyse different MLO strains and the crops they are associated with;

compile a map of MLO strains for the Australasian/Pacific region;

study the relationship between the spread of MLO strains, the numbers of insects that carry them and insect distribution. Develop a model to predict the spread of MLO related diseases; and

increase the capacity of participating countries to detect and identify different MLO strains using molecular tools.

The normal way to study MLOs in the region has been to examine diseased plants under the transmission electron microscope. This method can not detect differences between strains and is not widely used as it is difficult to gain access to an electron microscope in many regions.

The main techniques used in the study will involve the manipulation of DNA from the different strains. These techniques will include:

DNA extraction;

duplication of DNA sequences through cloning of DNA fragments and polymerase chain reactions (PCR); and

analysing the differences in the DNA from different strains by mapping different restriction sites along the DNA and sequencing DNA fragments.