Diagnosis and control of plant diseases in northern Vietnam

• Hanoi Agricultural University, Vietnam
• National Institute of Plant Protection, Vietnam
• Queensland University of Technology, Australia

Disease is a major constraint to crop production in tropical and subtropical regions. In Vietnam, agriculture is thought to suffer considerably from plant disease, with losses around 50% reported for tomatoes in the Hanoi region. However, it was hard to gather accurate data on the range and impact of plant diseases, mainly because of inadequate facilities and expertise in the country. Thus, two problems needed to be tackled: the loss of agricultural production through disease and poor capacity to develop suitable control strategies for the diseases.
Furthermore, fungal damage of crops such as peanuts and maize can have serious health implications when consumed by humans or domestic animals because the product may be contaminated with fungal toxins that are dangerous even in minute quantities.
This project helped to build the capacity of research workers in Vietnam so that they could define problems, diagnose plant diseases accurately and start implementing control methods. The crops for study were chosen because of their importance in the country and also because of expertise available from Australia.

The main aim of the project was to develop the capacity within Vietnam to control plant diseases, in particular viral diseases of bananas, cucurbits and papaya, and fungal diseases of maize, peanuts and tomatoes. The secondary aim was to improve knowledge of the epidemiology of diseases relevant to crops in Australia and elsewhere in the region.

The project fell into two parts - one dealing with viral diseases and the other with fungal diseases. Extensive surveys established the incidence and likely type of viral disease in bananas, cucurbits (cucumbers and related types) and papaya. The researchers then used diagnostic tests to identify the specific viruses. New tests were developed when they were not already commercially available.
The second part of the virus work concentrated on banana bunchy top virus (BBTV). The rate of virus movement and the severity of symptoms were known to vary between Vietnam and Australia. The researchers investigated potential differences in the strains of viruses and effects on a range of banana cultivars. A set of virus-free banana cultivars was established in tissue culture and made available for planting. Strategies for the control of viruses in bananas and papaya were trialed.
The project component on fungal disease started with a survey of tomatoes, peanuts and maize. Fungi were sampled from diseased plants in the field, isolated in the lab, and then developed as pure cultures. Fungal identification involved tests of disease-causing ability. The patterns of disease spread and severity were studied by collecting data on cultivars grown, agronomic practices, and the history of previous crops. An important part of this work examined the effect of paddy rice on soil-borne fungal pathogens.
Finally, a survey of growers was carried out to establish the level of their knowledge of the diseases and crops and find out what management practices they used to try to reduce the spread and severity of these fungal diseases.

The project had a major impact on the soilborne fungal and viral disease diagnostic capability in Vietnam. However it was over ambitious - although crops were surveyed and diseases identified, which met the first objective of both the viral and fungal disease components, the epidemiology studies (second objectives), loss assessment of particular diseases (first objectives) and development of control strategies were not developed for most of the original target crops of the project. The decision to include soilborne fungi meant that air and seedborne fungi and most bacterial diseases were excluded.

The project contributed to the Vietnamese scientific capacity in disease diagnostics, pathogen reference collections, pathogenicity testing, development of a disease control research capability, development of future integrated pest management (IPM) strategies for viral and soil borne fungal diseases, and international refereed publications.

Specialist knowledge in diagnosis of fungal pathogens in pineapple, cabbage, coffee and lychee and virus in banana, papaya, tomato and cucurbits has increased the Vietnamese capacity for disease diagnosis. This will make possible future diagnostics of emerging diseases in important horticultural crops.

Vietnam has been expanding its coffee production hugely to gain export earnings, but many of the coffee bushes developed a 'decline' that was reducing yields and then killing the plants. This problem was referred to the ACIAR project, which discovered the causal factors and recommended remedies, which have now been applied to solve the problem.

There was also a similar problem with a lychee decline, in an area northeast of Hanoi where the government was promoting lychees as a cash crop for poor farmers. The project also looked at this problem and has almost sorted out the multiple causal factors (it is more complex than the coffee one). Recommended remedial actions were successfully applied.

The project implemented a state-of-the-art molecular disease diagnostic laboratory at Hanoi Agricultural University. A team of plant protection experts from Agriculture, Fisheries and Forestry - Australia undertook a survey of such facilities in Vietnam and acknowledged the new laboratory as one of the two best such facilities in Vietnam. A number of young Vietnamese scientists have been trained to a high standard in the use of the equipment and application of the techniques.