Phenotypic Evaluation of Cassava (Manihot esculenta Crantz) Genotypes to Cassava Mosaic Virus by Mechanical Methods of Transmission

Abstract

Aims: Cassava (Manihot esculenta Crantz), subsistence crop in sub-Saharan Africa was threatened by cassava mosaic virus that caused a devastated disease. This study aims to test thermotherapy as sanitation method in mechanical transmission study of cassava mosaic virus. Methodology: Cuttings of different cultivars were treated by heating during two hours and twenty four hours at 50°C before potting. Four mechanical techniques of virus transmission were used. Contact technique consisting to put an infected plant with a healthy plant together by one junction point and the graft technique involved the grafting of axillary buds of diseased plants to healthy plants. Latex technique consisted of passing the latex from the infected plants on the injured healthy plants several times and sap technique involved the injection of inoculum prepared from the infected leaves to the healthy plants. Results: Four cultivars had a sprouted rate superior to 80% by two hours of heating and less than 50% by 24 hours of heating. The bands related to ACMV or EACMV were not observed in the samples of different cultivars. Seventy five per cent (75%) of plants inoculated by contact technique had a perfect adhesion with 65% of plants expressing the mosaic symptoms. Six plants out of fourteen (6/14) of the plants of Hombete inoculated with latex expressed the disease symptoms and three plants out of ten (3/10) of the plants of Ornania expressed the disease symptoms. Hundred per cent (100%) of the plants of Djadjakor inoculated by grafting expressed the disease symptoms. Any plants of Atinwewe and Adjatidaho inoculated by Sap technique did not express the disease symptoms. Conclusion: These results suggest that heat is effective for virus elimination and grafting constitutes the mechanical transmission technique which can be used to screen cassava germplasm for virus resistance.