Doctoral Degrees (Plant Sciences)

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Browsing Doctoral Degrees (Plant Sciences) by Author "Benesi, Ibrahim R. M."

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    Quantification of cassava mosaic geminiviruses and cassava brown streak viruses
    (University of the Free State, 2016-01) Musopole, Hastings Twalie; Labuschagne, Maryke T.; Gowda, Maruthi M.N.; Benesi, Ibrahim R. M.; Minnaar-Ontong, Adré
    English: Cassava (Manihot esculanta Crantz) is a perennial woody plant which is cultivated in Africa, Asia and Latin America. It is tolerant to drought and grows in poor soils. It is a source of carbohydrates, vitamins and small quantities of proteins. In Malawi, it is the most important root crop and it is grown across the country. It is consumed as a staple food by 30% of the people living along the central and northern part of Lake Malawi. Its production is constrained by among others, diseases CMD and CBSD. These two diseases are known to spread through white flies. The magnitude of attack by the two diseases depends on the genotype and the environment. No released genotypes in Malawi have ever been evaluated in seed transmission of viruses’ studies. The experiment on the quantification of F1 cassava progenies from open pollinated F1 progeny crosses revealed that genotypes which show high severity of CMD are likely to allow rapid multiplication of EACMMV and SACMV. However, it has been proven that this might not always be the case as some genotypes may have higher virus quantities while showing slightly less severe symptoms. Genotypes which succumb to high disease symptom severity are likely to have high incidence of the disease. CMD symptom severity and incidence were positively correlated. The experiment on determination of virus quantities in different tissues has provided information that virus quantities in particular tissues depend on the cultivar used. The viruses can spread to all the tissues analysed in this research. It was shown that root parenchyma and leaf tissues accommodated most of CBSV and UCBSV in the cultivars used. When there was co-infection, CBSV and UCBSV were positively correlated. EACMMV and SACMV quantity can vary in cassava tissues depending on the cultivar. Leaves have shown to contain a relatively high quantity of the viruses. CBSV, UCBSV, EACMMV and SACMV symptoms were not observed in seedlings grown from seeds which were obtained from diseased plants. The virus species were also not detected using Real-time PCR. This suggests that these virus species are not transmitted from diseased plants through seeds.