Improvement of 'King' mandarin {Citrusnobilis) cultivation techniques in southern Vietnam

摘要

Huanglongbing (HLB) is the most devastating disease in citriculture of southern Vietnam, where 'King' mandarin, Citrus nobilis, is commonly cultivated. Japan International Cooperation Agency (JICA) conducted the international cooperative project withSouthern Horticultural Research Institute (SOFRI) to enhance the technical transfer system of local government to citrus growers for increasing fruit yields in this region. The main techniques in the project were 1) planting trees at a wider distance (4.0 m) instead traditional planting distance, <1.5 m; 2) training and pruning of trees to shape the canopy in spherical form; and 3) HLB management developed by SOFRI. In the project farms where the techniques have been introduced, fruits were first harvested 26 months after planting, and the yield was 25.2 kg tree1 on average. This was nearly three times higher than the average yield by traditional cultivation, 10 kg. In this period, 4.3% trees were infected by HLB in the project farms, whereas the infection proportion was 56% in the traditional farms. Owing to the low occurrences of HLB infection, the project farms attained much higher income from 'King' mandarin. Analysing the conditions of farms and the growers' economy, it was found that sufficientincome from high fruit yields depended on how frequently extension officers visited farms for technique transfer on-time and how diligently growers followed the suggestions of the officers.