Search

Aim: The production of healthy cuttings from a local cassava cultivar for cassava mosaic control. Study design: The study was carried out at the In Vitro Culture Laboratory using the techniques of thermotherapy and culture of tissues and explants in a specific medium. Place and duration: The study was carried out at the Laboratory of Biological and Agronomic Sciences for Development at the University of Bangui, Central African Republic from December 2017 to June 2018. Methodology: A variety of cassava called six-month very susceptible to mosaic was used for this work. The cuttings used were infected by Cassava Mosaic Begomoviruses (CMBs) with high severity. It were subcultured in a room under the heat of 37 ° C to 40 ° C for two weeks. Explants and meristems were taken from the stems and the apices, respectively. These collected materials were treated and seeded on appropriate culture media. After the plants produced in vitro were acclimatized and the leaves were removed to check their phytosanitary state by the PCR technique. Results: The rate of emergence of the acclimatized plants and the expression of the disease on the microplants were evaluated. The results show that 75% of the weaned vitro plants recovered under acclimatization. In addition, the acclimatized plants left growing in the greenhouse for four months remained asymptomatic. Molecular analysis by PCR showed that begomoviruses were not detected on meristem samples unlike samples from stem fragments. Conclusion: The combination of thermotherapy technique associated with the culture of meristems constitutes an effective means useful for the sanitation of infected plant material.

International audience; Eleven cassava genotypes were tested against cassava mosaic disease (CMD) and compared to a local susceptible cultivar in field conditions from June 2011 to July 2012 in Central African Republic (CAR) at two sites representative of the savanna (Damara) and forest (Pissa) zones of the country. The mean number of whiteflies observed on plants varied among genotypes within each site, but was found nearly three times higher at Damara than at Pissa, resulting in a CMD incidence nearly five times higher at Damara than at Pissa. However, no relation was observed between the number of insect on the plants and the level of susceptibility/resistance of the genotypes. The difference of disease pressure between the two sites revealed high level of resistance in several genotypes, while some other ones indicated rather only a partial resistance. Nevertheless, none of the genotypes tested was found immune, in the end, the virus being detected at least in one site in every genotype, including those ones presenting no symptoms in both sites. The impact of CMD on yield components was assessed on the local susceptible check and three partially resistant genotypes, showing that the disease has no significant effect on the tuberous roots number as well as their weight in both sites. The yield potential varied among different genotypes and between the two sites, the mean number of tuberous roots as well as their mean weight being higher in Damara than in Pissa. This study identified highly resistant genotypes such as 'Gabon' that performed well in both sites, and '91/02322' that was symptomless and presented a yield potential equivalent to the local check. These genotypes could be distributed to growers with the main advantage to be resistant to CMD and, therefore, reducing the risk to spread sources of inoculum all over the cassava cropping areas in the country. (Résumé d'auteur)

Cassava mosaic disease (CMD) is one of the main production constraints for cassava ( Manihot esculenta ) in Africa (Patil & Fauquet, 2009). The disease is caused by seven cassava mosaic geminiviruses (CMGs, genus Begomovirus ). A severe…