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A Rapid, Less-costly and Accurate Detection of Citrus Greening (HLB) Pathogen in the Asian and Pacific Region

In recent decades, citrus greening disease (Huanglongbing, HLB) has been devastating citrus orchards in the Asian and Pacific region, and giving destructive damage to the citrus industry in these areas. HLB was also found in USA and Brazil, and has been spreading there since then. In 1988, HLB was first identified in Okinawa, and has taken route throughout the prefecture. HLB has been spreading up to the north, and could be confirmed in Yoron and Amami-ohshima islands, Kagoshima Prefecture. It is considered to be a matter of time that HLB shall invade the Japan mainland because of global warming. Hence, the MAFF puts highest alert on HLB invasion into the Japan mainland, and enforces a variety of the water's edge countermeasures to keep HLB at bay.

However, the infection of HLB disease is very difficult to identify because of its similarity with symptoms of such nutrient deficiencies as Zn and Fe, and its pathogens, Diaphorina citri, cannot be cultivated on an artificial culture medium. In addition, no effective agrochemicals to control this disease are available. The only useful countermeasure to cope with the HLB infection is to cut down the infected citrus trees. In this regard, the earlier the infection is identified, the less damage is brought about. Currently, PCR and grafting of an indexing plant to the trees examined are the most common methodologies to check the disease infection, but both have a couple of disadvantages such being costly and time consuming. It is urgently needed to develop a rapid, less costly and accurate method to detect the HLB pathogens.

Objectives

  • To develop a rapid, less-costly and accurate detection technology of citrus greening pathogen (HLB) on would-be HLB infected citrus trees, and minimize HLB damages in major citrus production areas in the Asian and Pacific region.

Description of major activities (Year 2)

  • An analytical method, which is more rapid and cheaper than PCR, but possesses similar accuracy to the latter, will be developed for identification of HLB infected citrus trees. Some new technologies have been proposed and proved to be promising in a preliminary application. For instance, LAMP (Loop-mediated isothermal amplification) can be used as a better replacement of the PCR for HLB pathogen strains isolated in Japan. In this cooperative research, a four-primer-combination, which proved to be promising for the detection of the Japanese HLB isolates, is also useful for the isolates collected from Taiwan and other countries in the Asian and Pacific region. In case the combination does not work, better combinations shall be searched in a trial-and-error manner.
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