Abstract:
Whiteflies, Bemisia tabaci, (Gennadius) are major insect pests that affect many crops such as cassava, tomato, beans, cotton, cucurbits, potato, sweet potato, various species of fruits and ornamental plants. Bemisia tabaci transmits viral diseases namely cassava mosaic and cassava brown streak diseases which are the main constraints to cassava production causing huge losses estimated in excess of US$ 100 Million annually among many small-scale farmers in East Africa. The current work aimed at determining the phylogenetic relationships and population genetic structure among whiteflies in major cassava growing areas of Kenya. Surveys were carried out between 2013 and 2015 in major cassava growing areas (Western, Nyanza, Eastern, and Coast regions). Adult whiteflies were collected from the five top most leaves of the cassava plants, and the samples from each field for DNA extraction and amplification of mitochondrial cytochrome oxidase I gene. The whitefly population is associated with the continued transmission and spread of the dual pandemic of cassava begomoviruses (CMD and CBSD). The amplified mtCOI gene sequences and phylogenetic trees were constructed using Bayesian methods to understand the genetic diversity across the study regions. The population genetic structure was analyzed by AMOVA that showed FST 0.2000. Phylogenetic analysis revealed two distinct Bemisia tabaci species present in Kenya, sub-Saharan Africa comprising five different clades (A-E) with percent sequence similarity ranging from 97.7 to 99.5%.Clades B, C, D and E are predominantly distributed in Western and Nyanza regions of Kenya whereas clade B is dominantly found along the Coast, Eastern and parts of Nyanza. Bemisia tabaci clade A clusters
together with sub-Saharan Africa 2-(SSA2) recorded a percent sequence similarity of 99.5%. The sub-Saharan Africa 2 is species associated with CMD and is found in western Kenya region that borders Uganda. This work also reports the identification of SSA2 after a 15 years break in Kenya. More information is needed to determine if these species are differentially involved in the epidemiology of cassava viruses.
Keywords: Bemisia tabaci; genetic diversity; mt-COI; cassava; Kenya
