Recent Studies on Molecular Characterization and Selection of Cassava Varietes Resistant to Xanthomonas axonopodis PV. Manihotis in Cote D’ivoire

Morpho-Molecular and symptomatic characterizations of strains of Xanthomonas axonopodis PV.
Manihotis in Côte D’ivoire.
In Côte d'Ivoire, cassava is the second food crop after yam, with an estimated yield of 2.8 million tons
per year. Cassava cultivation, however, suffers from many constraints that limit its productivity.
Cassava bacterial blight caused by Xanthomonas axonopodis pv. manihotis causes damage to
cassava crops in Côte d’Ivoire. In order to have a better understanding of the pathogen, 800 isolates
were collected from cassava diseased leaves and stems in six of the seven agroecological zones
(AEZ). Bacterial colonies of each isolate showing typical Xanthomonas axonopodis pv. manihotis
morphological characteristics were subjected to molecular analysis. Based on the count of the leaves
attacked by the disease, the sensitivity of eight cassava varieties was assesses under natural
infestation conditions in Ferkessédougou. The results showed, after 48 hours of incubation, colonies
with morphological characteristics, ivory-white, smooth, shiny, convex, with regular outline, non-stinky
and viscous appearance. PCR amplification of the DNA showed a single band profile of about 900 bp
characteristic of Xanthomonas axonopodis pv. Manihotis. Of the eight varieties tested, only the
improved varieties “Bocou 2” and “Yavo” were the least attacked. Xanthomonas axonopodis pv.
manihotis is of course the causal agent of the spots, burns and dieback observed on cassava
varieties in Côte d’Ivoire. Therefore, the varieties “Bocou 2” and “Yavo” can be recommended to
producers in areas where cassava bacterial blight is more rampant. Convincing results have appeared
at the end of this study, but for a better management of the disease, the virulent strains are also to be
identified for a good varietal selection.