Estrutura genética de uma população do begomovírus Bean golden mosaic vírus (BGMV) que infecta a fava (Phaseolus lunatus L.) no estado de Alagoas

Abstract

The lima bean (Phaseolus lunatus) is one of four cultivated species in the genus Phaseolus. The species was domesticated in South or Central America. It is one of the main cultivated legumes in the tropics and has a great potential as a source of vegetable protein to the population. Among its most important diseases are those caused by viruses, particularly by begomoviruses (family Geminiviridae). Infected plants display an intense yellow or golden mosaic, and have a drastically reduced yield. The objective of this work was to characterize the genetic structure of begomovirus populations infecting lima beans in the state of Alagoas, by analyzing complete DNA-A sequences. Lima bean plants with typical symptoms of begomovirus infection were collected in a number of areas around the states of Alagoas and Pernambuco during 2005. Total DNA was extracted and the presence of a begomovirus was confirmed by PCR. The viral genomic components were amplified using the DNA polymerase from phage phi29, and then cleaved with either BamH I or Hind III. Cleaved products were ligated to the pBluescript KS+ plasmid vector and the recombinant plasmids were transformed into Escherichia coli DH5α. Clones were submitted to cleavage with Hae III and, according to the obtained restriction pattern, 22 (20 from samples collected in Alagoas, and two from samples collected in Pernambuco) were selected for sequencing. Phylogenetic analysis was carried out with MEGA 4.0 using the Neighbour-Joining method. The genetic diversity of the population was evaluated using the DnaSP program, version 5. Analysis of the 22 sequences revealed that they all belonged to a single begomovirus species, Bean golden mosaic virus, with 90 to 94% nucleotide sequence identity with a BGMV isolate from soybean (access number FJ665283.1). All sequences clustered with other Brazilian BGMV isolates from common bean and soybean in the phylogenetic tree, although the two isolates from Pernambuco are closer to the soybean isolate than the 20 isolates from Alagoas. Thus, the lima bean isolates clustered based on their geographical origin. Analysis of the population indicated a high degree of genetic variability, significantly higher than that observed for two begomovirus populations from tomato obtained in the southeastern region of Brazil.