Neck orange (Citrus reticulata Blanco) decline: Causal pathogens and factors enhancing disease severity
1994
Sdoodee, R. (Prince of Songkla Univ., Songkhla (Thailand). Faculty of Natural Resources. Dept. of Pest Management)
Neck orange decline is a fatal disease which has reduced the neck orange production area in Songkhla but the cause has not been identified. Serological assays of the declining trees grown at Prince of Songkla University by ELISA, immunogold-labelling and immunoblotting technique indicated that the trees were infected with citrus tristeza viruses (CTV) and/or greening bacteria. The infection rates were higher than 80 percent. The incidence of CTV was confirmed by the presence of aggregated thread like particles in a phloem cell as determined by electron microscopy (EM). However, EM did not reveal greening organisms in ultrathin-section of neck orange midribs. Subsequently, tristeza viruses and greening bacteria were successfully transmitted from the infected trees to their specific indicator plants by side-grafting. It is evidence that the declining disease of neck orange was caused by the infection of the tristeza virus and/or the greening bacteria. Observation on symptom development during 1990-1994 confined that factors enhancing disease severity were early and mixed infections of CTV and greening bacteria, and the infection of tristeza stem pitting strain with combination of the use of calamondin root stock.
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