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Background 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 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 vector in cassava is the reason why begomoviruses have not emerged in South America. Methods 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 in the main agroecological zones of the country. A total of 1,385 individuals were genotyped based on mitochondrial cytochrome oxidase I sequences. Results A high species richness was observed, with five previously described species and two putative new ones. The 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.

Soybean stem necrosis is caused by cowpea mild mottle virus (CPMMV), transmitted by the whitefly Bemisia tabaci. CPMMV has already been recorded in all major soybean-producing areas of Brazil. The impacts caused by CPMMV to the current Brazilian soybean production are unknown, thus the main objective of this study was to evaluate the effects of CPMMV infection on the main important soybean cultivars grown in the Southern and Midwestern regions of Brazil. Although asymptomatic in some of the tested cultivars, CPMMV infection significantly reduced the plant height, the number of pods per plant and the 1,000-grain weight. In addition, estimated yield losses ranged from 174 to 638 kg ha−1, depending on the cultivar. Evidence of seed transmission of CPMMV was observed in the BMX POTÊNCIA RR cultivar. These results suggest that CPMMV could have an important role in the reduction of soybean productivity in Brazil, but symptomless infections might be hiding the actual impact of this pathogen in commercial fields and infected seeds could be the primary inoculum source of the virus in the field.

Cassava is a staple food crop in sub-Saharan Africa; it is a rich source of carbohydrates and proteins which currently supports livelihoods of more than 800 million people worldwide. However, its continued production is at stake due to vector-transmitted diseases such as Cassava mosaic disease and Cassava brown streak disease. Currently, the management and control of viral diseases in cassava relies mainly on virus-resistant cultivars of cassava. Thus, the discovery of new target genes for plant virus resistance is essential for the development of more cassava varieties by conventional breeding or genetic engineering. The chloroplast is a common target for plant viruses propagation and is also a potential source for discovering new resistant genes for plant breeding. Non-infected and infected cassava leaf samples were obtained from different locations of East Africa in Tanzania, Kenya and Mozambique. RNA extraction followed by cDNA library preparation and Illumina sequencing was performed. Assembling and mapping of the reads were carried out and 33 partial chloroplast genomes were obtained. Bayesian phylogenetic analysis from 55 chloroplast protein-coding genes of a dataset with 39 taxa was performed and the single nucleotide polymorphisms for the chloroplast dataset were identified. Phylogenetic analysis revealed considerable genetic diversity present in chloroplast partial genome among cultivated cassava of East Africa. The results obtained may supplement data of previously selected resistant materials and aid breeding programs to find diversity and achieve resistance for new cassava varieties.