Assessing whitefly diversity to infer about begomovirus dynamics in cassava in Brazil
Plant virus ecology is strongly dependent on that of its vector. The necessity of a competent vector for transmission is a primary ecological factor driving the host range expansion of plant arthropod-borne viruses, with vectors playing an essential role in promoting disease emergence. Cassava begomoviruses severely constrain cassava production in Africa. Curiously, begomoviruses have never been reported in cassava in South America, the center of origin for this crop. It has been hypothesized that the absence of a competent begomoviruses vector that efficiently colonizes cassava is the reason why begomoviruses have not emerged in South America. To test this hypothesis, we performed a country-wide whitefly diversity study in cassava in Brazil. Adults and/or nymphs of whiteflies were collected from sixty-six cassava fields across twelve states representing the main agroecological zones of the country. A total of 1,385 individuals were genotyped based on partial mitochondrial cytochrome oxidase I (mtCOI) sequences. A high species richness was observed, with five previously described species and two putative new ones. The most prevalent species were Tetraleurodes acaciae and Bemisia tuberculata, representing over 75% of the analyzed individuals. Although we detected, for the first time, the presence of Bemisia tabaci Middle East-Asia Minor 1 (BtMEAM1) colonizing cassava in Brazil, it was not prevalent. The species composition varied across regions, with fields in the Northeast region showing a higher diversity. These results expand our knowledge of whitefly diversity in cassava and support the hypothesis that begomovirus epidemics have not occurred in cassava in Brazil due to the absence of competent vector populations. However, they indicate an ongoing adaptation process of BtMEAM1 to cassava, increasing the likelihood of begomovirus emergence in this crop in the near future.