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Abstract
Screening for cassava mosaic begomoviruses (CMBs)-resistance using grafting and whitefly inoculation was performed with local and improved cassava. The onset of symptom appearance and the evolution of Cassava mosaic disease (CMD) varied in function of genotypes and virus inoculation techniques used. Grafting position using cassava as scion or rootstock does not affect CMD display and evolution. No relation was established between the number of whiteflies feeding on each genotype and viral inoculation technique tested. Detopping of young leaves induces triggering effect on CMD expression. PCR and ELISA confirmed the EACMV-UG's preferential transmission by whitefly. Hypothesis of virus replication and cultivars's susceptibility were supported by virus increasing particles in infected cassava. Cultivars Mvuazi (TMSI 95/0528) and 96/1089A are suggested field immune to CMBs; Disanka (TMSI 95/0211), Yauma, Timolo, Bangi, Mahungu (TMS 92/297), Mvuama (TMS 83/138), Lueki (TMS 91/377) and Zizila (MV 99/0038) are CMD-resistant; whereas Ponjo, Lofiongi, Ngonga and Mboloko are susceptible. Our results showed that resistant genotypes may express CMD under high inoculum pressure such as grafting.
Acknowledgements
We wish to thank the Belgian Cooperation for funding this study. Authors are grateful to Plant Pathology Laboratory, UCL Belgium, for molecular analysis, IFA-Yangambi for carrying out the field experiment, INERA-Yangambi and PIDR-Kisangani for the collection of local cassava cultivars, IITA and FAO-Kisangani for providing improved cassava varieties. The authors are also grateful to Prof. H. Maraite for critically reading the manuscript and suggesting improvements.