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Prelecionista: Ms. Baltazar A. I. Chipiringo. Data: 01/06/2021, às 17:00 horas pelo ZOOM*. Orientador: Francisco Murilo Zerbini.

The begomoviruses constitute a group of plant viruses of great relevance to agriculture due to the severity of the diseases caused by them worldwide. Agriculture in Mozambique is moving towards “modernization”, with increased areas of monoculture, extended growing seasons, irrigation and mechanization replacing subsistence farming. However, changes in agricultural practices can also promote pathogen emergence. Understanding the emergence and evolution of plant viruses can provide beneficial information on management practices and the fight against these diseases in crops. This work aimed at the detection, identification and molecular characterisation of begomoviruses associated with legumes and weeds and is presented in two parts: i) A new recombinant begomovirus naturally infects Pyrenecantha sp. in Mozambique, and ii) Emergence of a bipartite begomovirus in Mozambique and its recombination-driven adaptation to legume crops.  In the first study, a weed plant later identified as Pyrenecantha sp. (Icacinaceae) with yellow mosaic symptoms typical of begomovirus infection was collected in a maize production field in the district of Malema, Nampula province. The viral genome was amplified using rolling-circle amplification (RCA), cloned and sequenced. The DNA-A sequence has higher nucleotide sequence identity (78%) with tomato yellow leaf curl Namakele virus, while the DNA-B sequence has higher nucleotide identity (70%) with Deinbolia mosaic virus. The two components have a genomic organization typical of Old World, bipartite begomoviruses. Alignment of their common regions (CR) indicated a 35-nt insertion in the DNA-A CR. The nt sequence identity between the CRs is only 83%, but increases to 96% when the 35-nt insertion is removed from the alignment. The CRs have identical iterons, and the amino acid sequence of the Rep protein contains the IRDs predicted to recognize these iterons. Together, these results indicate that the cloned DNA-A and DNA-B are cognate components of the same virus, and the 35-nt insertion suggests a recombination event in the DNA-A CR. The name Pyrenecantha yellow mosaic virus (PyYMV) is proposed for the new virus. For the second study, symptomatic samples of bean, soybean and cowpea plants were collected in central and northern Mozambique. Seven DNA-A components were cloned and sequenced. The seven sequences are 96% identical, indicating that they represent the same virus. The higher identity with other begomoviruses is 85% with cowpea golden mosaic virus. Eighteen DNA-B components were cloned and sequenced, with 93% identity amongst each other and a maximum of 72% sequence identity with cotton yellow mosaic virus. Alignment of the CRs and the identification of identical iterons indicate that the DNA-A and DNA-B components are cognate components of the same virus, for which the name Mozambique legume mosaic virus (MLMV) has been proposed. Three recombination events (including both intra- and interspecific events) were detected in the DNA-B. The intra- and interspecific nucleotide diversity of the DNA-B was higher in the MP gene and in the short intergentic region (SIR). The overall nucleotide diversity of the DNA-A and DNA-B components was similar. MLMV is an emergent begomovirus in legume crops in Mozambique, and its adaptation to the new hosts seems to be driven by recombination in the DNA-B.

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