Espécies de begomovírus infectando cnidoscolus urens e estudo da transmissão de cnidoscolus mosaic leaf deformation virus por sementes.

Abstract

Species of the genus Begomovirus (family Geminiviridae) cause damage to crops of economic importance around the world. However, non-cultured hosts play a relevant epidemiological role, acting as a viral reservoir. These viruses are transmitted by a complex of cryptic species of the whitefly Bemisia tabaci, with rare cases of transmission via seeds. Interestingly, Cnidoscolus urens plants exhibiting typical symptoms of begomovirus infection are often observed under field conditions even in the apparent absence of the insect vector. In this context, the objective of the present study was to molecularly characterize the begomovirus species infecting C. urens, as well as to evaluate the possible transmission of these viruses via seeds. Leaf samples of C. urens showing symptoms indicative of begomovirus infection were collected in the states of Pernambuco (PE) and Rio Grande do Norte (RN) between 2019 and 2020. Total DNA was extracted from the leaf tissue and subsequently used as a template for viral genome amplification by rolling circle amplification (RCA), followed by enzymatic digestion, cloning and primer walking sequencing. Samples of leaves, flowers and seeds were also collected from symptomatic plants of C. urens in Paripueira, state of Alagoas (AL). For transmission tests, seedlings were obtained from seeds collected from symptomatic plants and positive, via PCR, for cnidoscolus mosaic leaf deformation virus (CnMLDV). Leaf samples were collected from C. urens plants 60 days after germination (dag), and CnMLDV infection was evaluated, via PCR, using species-specific primers. A total of six clones of the DNA-A genomic component and two clones of the DNA-B were obtained. DNA-A from the isolate from Paulista (PE) shared a higher percentage of nucleotide identity (79,9%) with tomato common mosaic virus (ToCmMV; accession number KC706579), while DNA-A from the isolate from Cabo de Santo Agostinho (PE) showed a higher percentage of nucleotide identity (88,9%) with CnMLDV (NC_038982). The DNA-A component of the isolate from Goianinha (RN) also shared a higher percentage of nucleotide identity (82,8%) with CnMLDV (NC038982). Based on the species demarcation criteria for the genus Begomovirus, three possible new species were characterized infecting C. urens, and, adopting the binomial system, the following names are proposed, Begomovirus paulitiensis, Begomovirus caboniensis and Begomovirus goianiensis, respectively. The results of CnMLDV detection in different tissues of symptomatic plants of C. urens revealed that 62% of the sepals, 79% of the androecium and 83% of the flowers, petals and gynoecium were infected. More than 90% of seeds collected from symptomatic C. urens infected with CnMLDV tested positive via PCR. CnMLDV was also detected from tegument, endosperm and embryo. However, C. urens seedlings did not show typical symptoms of viral infection 60 dag, and were PCR negative for CnMLDV. These results suggest that CnMLDV is not seed-transmitted in C. urens. Keywords: no-cultivated plants; Euphorbiaceae; transmissibility.