Source: QFM Radio [summ. Mod.DHA, edited]
The Zambian Ministry of Agriculture says that the government is concerned about cassava brown streak disease because it can cause losses of up to 100 percent in susceptible varieties. They say that it is a major constraint to cassava production in southern Africa.
The threat posed by the disease must be controlled in order to protect both farmers and the cassava industry. The media play a critical role in information dissemination and must provide factual information. It is hoped that training will raise awareness of the disease in an effort to eradicate it in the country.
[Cassava brown streak disease (CBSD; also called root rot) can be caused by _Cassava brown streak virus_ (CBSV) and the more recently identified _Ugandan cassava brown streak virus_ (UCBSV; both genus _Ipomovirus_). Coinfections of both viruses in the same plant also exist (ProMED post 20190214.6315604), but possible synergism or other interactions in the host still need to be clarified. Symptoms may include leaf chlorosis, stem necrosis, and yellow/brown corky necrosis in the starch-bearing tissue of roots. Leaves may appear healthy even when the roots have rotted away. Crop losses of 20 to 80%, depending on crop variety, have been reported earlier, the total crop loss mentioned above may be due to local varieties; losses in individual root weight of up to 70% have been observed in susceptible cultivars.
The viruses are transmitted by the whitefly vector _Bemisia tabaci_ (a serious crop pest in its own right) and are spread to new areas by infected cassava cuttings. Disease management includes pathogen exclusion, removal of infected plants, use of virus-free seed tubers for planting, as well as vector control. Resistant varieties are being developed for specific local requirements. Identification of alternative hosts from unrelated plant families for CBSV and UCBSV (ProMED post 20181223.6221346 and see link below) indicate that reservoir hosts may have an impact on the epidemiology of CBSD.
CBSD is considered a threat to the whole of sub-Saharan Africa where cassava is a major food crop. Recent outbreaks appear to indicate a westward spread of the viruses (ProMED post 20130508.1698543). CBSD poses a particular risk to new crop varieties developed with resistance to cassava mosaic disease (CMD; begomovirus species, spread like CBS; see previous ProMED posts in the archives). A new CBSV strain adapted to higher altitudes has emerged in eastern Africa and is affecting additional CMD-resistant cultivars (ProMED posts 20100525.1735, 20120706.1191742). Joint management of both diseases has become a major challenge in the region and globally (ProMED posts 20110829.2643, 20090709.2463).
In Zambia, a major outbreak of CBSD was reported in 2018 (ProMED post 20180920.6042364), but it is not clear if that was the first occurrence in the country. Several neighbouring countries had previously reported CBS on their territories (e.g. ProMED posts 20130508.1698543, 20110318.0857, and 20140306.2316298).
Zambia: https://promedmail.org/promed-post?place=8704650,170 and
http://ontheworldmap.com/zambia/zambia-political-map.jpg (with provinces)
http://cdn.wn.com/pd/85/4f/39ea54dafdb1c1843bd628b012e7_grande.jpg (tubers) and
Comparison CBS and CMD symptoms:
Information on cassava brown streak:
https://doi.org/10.1038/s41598-019-50259-0 (vector populations), and
CBS viral variants and strains:
CBS viruses reservoir hosts:
Information on cassava mosaic disease:
Virus taxonomy via:
_B. tabaci_ whiteflies, taxonomy and biotypes:
http://www.iucngisd.org/gisd/species.php?sc=106 (with pictures)