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Source: Plant Disease [edited]

[Ref: Diallo A et al. (2021) First report of Bacterial Leaf Streak disease of rice caused by _Xanthomonas oryzae_ pv. _oryzicola_ in Ivory Coast. Plant Dis 105, First Look;]
Bacterial leaf streak (BLS) of rice caused by _Xanthomonas oryzae_ pv. _oryzicola_ (Xoc) is considered an emerging disease of rice in Africa. [It] is now present in at least 8 African countries including Burundi [ProMED post 20150327.3258500], Burkina Faso, Kenya, Madagascar, Mali, Nigeria, Senegal, and Uganda. Yield loss by BLS is estimated at 20 to 30%. BLS has not been described in adjacent rice-growing Ghana and Liberia. Xoc samples collected between 2003 and 2011 in [neighbouring] Burkina Faso and Mali have been characterized.

Xoc is transmitted through seeds. Given the extensive rice trade between Burkina Faso, Mali, and Côte d'Ivoire [IC], we hypothesized that BLS might also be present in IC. Field surveys were carried out across IC in 2018. Typical BLS symptoms were observed in Korhogo [Savanes District]. Colonies characteristic of Xoc were purified from 6 individual samples from 2 distinct sites. PCR for identification of _X. oryzae_ pathovars revealed for all the isolates the characteristic amplicons of 324 and 691 base pairs.

[In] pathogenicity tests, all [inoculated rice] plants developed water-soaked lesions. [Reconfirmation of Xoc by] PCR fulfilled Koch's postulate. 3 isolates were sequenced [for] gene gyrB. Analysis revealed 100% identity with the gyrB sequence of Xoc reference strain BLS256 and 10 polymorphic nucleotides compared to reference strain PXO99A. This is the 1st report of BLS in Côte d'Ivoire. Surveys in IC and neighboring countries where the disease has not been reported will allow us to assess disease incidence as part of future control strategies.

Communicated by:

[Bacterial leaf streak (BLS) of rice is caused by _Xanthomonas oryzae_ pv. _oryzicola_ (Xoc). The bacteria can also affect a number of grasses which may serve as pathogen reservoirs. Symptoms include translucent interveinal streaks extending into orange lesions which can kill the leaf. Yellowish bacterial exudates may be seen. Bacteria can enter through small wounds on the leaf surface, including insect damage. Plants are susceptible at all stages, but infection is most damaging at the tillering stage. BLS is more prevalent during rainy seasons.

The pathogen survives between crop cycles on volunteer rice plants, leaf debris, and infected stubble. BLS is seed-borne; it can also be spread with infected plant and other materials; by water; and by mechanical means (including human and insect activity). Disease management is difficult and may include phytosanitation (control of reservoir hosts, removal of contaminated materials); cultural measures (optimal plant spacing and fertilisers); bacteriocides (such as copper compounds); and use of resistant crop varieties.

Diagnostic sequences identified earlier in some African isolates were identical to several Asian strains (see ProMED post 20150327.3258500 and link below). The bacteria may have entered the region with contaminated seed from those areas, but that would remain to be verified.

A different strain of the pathogen (_X. oryzae_ pv. _oryzae_) causes bacterial leaf blight (BLB). Symptoms are similar to BLS, but BLB is generally considered more invasive. Another member of the genus (_X. translucens_ pv. _undulosa_) causes leaf streak of wheat, rye, and barley (ProMED post 20210604.8422632).

Côte d'Ivoire:,, and (districts)
Africa (overview):

Bacterial leaf streak on rice:,, and
Comparison of BLS and BLB symptoms:

Information on bacterial leaf streak of rice:,, and
Xoc sequences in Burundi strains:
_X. oryzae_ pv. _oryzicola_ taxonomy:
Genus _Xanthomonas_ taxonomy:
- Mod.DHA]


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