Studies on epidemiology, molecular detection and genetic diversity of selected viruses infecting cassava and wine grapes

Cassava (Manihot esculenta Crantz) is an important staple food crop for people in Africa and grapevines (Vitis vinifera L.) are cultivated worldwide for multiple purposes, including consumption of its berry and processed products such as raisins and wine. The focus of this research was on begomoviruses associated with cassava mosaic disease (CMD) in Nigeria and grapevine rupestris stem pitting disorder of wine grape cultivars in the Pacific Northwest (PNW) of the United States of America.;Molecular characterization of DNA A genomic component of begomoviruses associated with CMD confirmed the occurrence of African cassava mosaic virus (ACMV) and East African cassava mosaic Cameroon virus (EACMCV) in Nigeria. Nucleotide sequence analysis of DNA A of ACMV and EACMCV isolates collected from different plant species confirmed two weed hosts (Senna occidentalis and Combretum confertum ) and three crop plants (Ricinus communis, Leucana leucocephala, and Glycine max) as potential alternative hosts for the two viruses. This information expanded our current knowledge of the ecology of cassava-infecting begomoviruses in Nigeria. A multiplex PCR assay in conjunction with simplified sample preparation method was developed for concurrent detection of ACMV and EACMCV in cassava infected with CMD. This technique facilitated high throughput diagnosis of CMD in epidemiological studies, crop improvement and phytosanitary programs in Nigeria.;Molecular diversity of field isolates of Grapevine rupestris stem pitting-associated virus (GRSPaV; genus Foveavirus) in wine grape cultivars grown in the PNW region was evaluated relative to virus isolates from other grape-growing regions. Assessment of the coat protein and a portion of the helicase region of the replicase using phylogenomic and population genetics approaches showed that genetic diversity of GRSPaV in the PNW vineyards is considerably greater than reported in other regions. The results are useful for developing improved diagnosis of different genetic variants of the virus in 'clean' plant programs. The study also showed putative recombination events in GRSPaV that contributed to an increased understanding of molecular population genetics of viruses infecting woody perennials.