BACTERIAL LEAF BLIGHT, RICE – MADAGASCAR: FIRST REPORT’

Tuesday, 02 January 2024 12:26:34

Grahame Jackson posted a new submission ‘

Submission

BACTERIAL LEAF BLIGHT, RICE – MADAGASCAR: FIRST REPORT

ProMED
http://www.promedmail.org

Source: European Plant Protection Organisation (EPPO) Reporting Service 11/2023/253 [summ. Mod.DHA, edited]
https://gd.eppo.int/reporting/article-7735

Bacterial leaf blight of rice caused by _Xanthomonas oryzae_ pv. _oryzae_ (EPPO A1 List) was considered to be absent from Madagascar, as shown by regular monitoring for rice diseases carried out since the 1980s. In December 2019, symptoms resembling those of bacterial leaf blight were observed in 2 rice (_Oryza sativa_) fields in the Central Highlands of Madagascar. Affected plants showed yellow to greyish, water-soaked lesions starting from the leaf tip and progressing along the central vein or leaf margin. At a later stage, leaves became completely desiccated and sometimes had droplets of yellow exudate at the leaf margin.

Symptomatic leaf samples were collected from both fields. Laboratory analysis (morphological, PCR, pathogenicity tests) confirmed the presence of _X. oryzae_ pv. _oryzae_. Further surveys from 2020 to 2022 confirmed the presence of the bacterium in Madagascar and a sharp increase in disease incidence.

Communicated by:
ProMED

[Bacterial leaf blight (BLB) of rice caused by _Xanthomonas oryzae_ pv. _oryzae_ (Xoo) causes yellowing and drying of leaves, as well as wilting of seedlings. Blight lesions caused by severe strains elongate over the entire length of the flag leaf, giving a striped appearance. Severe strains may also affect panicles. Mild strains cause only small leaf lesions and may not lead to any detectable yield loss. Various saprophytic fungi may invade the lesions, contributing to the damage. Field patches infested with bacterial blight have a whitish, ragged appearance. In Asia, for example, millions of hectares of rice paddies are severely affected by Xoo every year, with reported yield losses of up to 60%.

BLB is favoured by rain, high levels of fertilizer, high humidity, standing pools of water and warm temperatures. The bacterium is short-lived in soil and suspected to be seed borne but also to be short-lived in seeds. Grassy weeds, infected plant material (such as rice stubble or ratoons) and contaminated irrigation systems are thought to be primary pathogen reservoirs. The disease spreads by windblown rain and mechanical means (for example when transplanting seedlings or by high insect activity).

Disease management usually includes phytosanitation (control of weed and volunteer rice reservoir hosts, removal of contaminated materials), cultural measures (optimal plant spacing and fertilisers) and use of resistant crop varieties. Control of insect populations by insecticides may help reduce the unspecific spread of bacteria via their scratching and sucking wounds. Antibacterial sprays containing antibiotics are rarely used because they often provide little benefit; furthermore, agricultural application of antibiotics is strictly regulated in most countries. The related _X. oryzae_ pv. _oryzicola_ causes bacterial leaf streak of rice.

More recently, another bacterial leaf blight of rice caused by _Pantoea ananatis_ has also been identified (see links below).

Pictures
BLB symptoms on rice leaves:
http://agropedia.iitk.ac.in/sites/default/files/uas%20raichur/diseases%20of%20paddy/blb00.jpg and
http://www.knowledgebank.irri.org/images/stories/bacterial-leaf-blight-4.JPG
BLB affected rice plants:
http://www.invasive.org/images/768×512/0162037.jpg
Droplets of Xoo exudate on leaf:
http://www.invasive.org/images/768×512/0162038.jpg

Links
Source publication:
https://doi.org/10.1094/PDIS-03-23-0411-PDN
BLB of rice, disease & pathogen information:
http://www.knowledgebank.irri.org/decision-tools/rice-doctor/rice-doctor-fact-sheets/item/bacterial-blight,
https://gd.eppo.int/taxon/XANTOR (with distribution map),
https://doi.org/10.1079/cabicompendium.56956,
http://www.apsnet.org/publications/PlantDisease/BackIssues/Documents/1993Articles/PlantDisease77n01_5.pdf and via
http://www.oisat.org/pests/diseases/bacterial/bacterial_leaf_blight.html
_X. oryzae_ pv. _oryzae_ taxonomy:
http://www.uniprot.org/taxonomy/64187
_P. ananatis_ leaf blight of rice:
https://doi.org/10.1094/PDIS-08-22-2014-PDN and
https://doi.org/10.1007/s42161-023-01514-x
EPPO A1 quarantine list:
https://www.eppo.int/ACTIVITIES/plant_quarantine/A1_list
– Mod.DHA