Erwinia carotovoravar.carotovora, Causal Agent of Bacterial Stem Rot of Cassava: Etiology, Epidemiology and Control

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Abstract
In Colombia a bacterial disease of cassava associated with cassava fruitfly (Anastrepha spp.) damage has been observed within the past four years. Etiological studies show that the bacterium is similar to Erwinia carotovora var. carotovora. Following stem damage by Anastrepha spp. larvae the pathogen enters the plant. The symptoms are internal rotting of the stem and wilting of young shoots or branches, followed by tip collapse and dieback or canker formation of lignified stem parts. The etiology is described in detail. The cassava stem rot bacterium (CSRB) is a slender Gram-negative rod with an average size of 2.4 × 1.2 μm. The cells are motile and possess 4–8 peritrichous flagella. In 48 hour-old cultures the cells are single or in chains of 2–3 cells, unencapsulated and non-spore forming. The results of artificial inoculations are given. Biochemical, physiological and cultural characteristics of CSRB are presented. It is concluded that CSRB is a close relative of the E. carotovora group and is indistinguishable from E. carotovora var. carotovora. Conversely, a comparison between E. cassavae and CSRB shows that they are different species. As a result cassava is now reported as a host of E. carotovora var. carotovora. The insect vector of CSRB and its epidemiology are then discussed. Recommendations are made for the control of CSRB and its insect vector. The use of clean, CSRB-uninfected cuttings of cassava varieties resistant to the insect seems to be the most promising control measure. Other methods are the use of insecticides and/or attractants.