Sensibilidade a cúpricos e estrutura genética de populações de Xanthomonas campestris pv. viticola

Abstract

Bacterial canker is a disease of great economic importance for the grapevine, in the “Submédio” of the São Francisco Valley, Northeast of Brazil. To support strategies of disease control, copper sensitivity of Xanthomonas campestris pv. viticola (Xcv) and genetic structure of population must be studied. This research aimed to estimate the copper sensitivity of isolates obtained from this region; to compare the adaptability of sensitive and tolerant copper isolates; to perform analyzes on some of these isolates through the genes copA and copB; and to study the genetic structure of three populations using genomic profiles of rep-PCR. From 70 isolates analyzed, 23 (33 %) were classified as tolerant to copper hydroxide at 140 μg ml-1 Cu2+, and 21 (30 %) to copper oxychloride at 70 or 140 μg ml-1 Cu2+. Ten isolates of each reaction phenotype were selected for subsequent assays. When tolerant isolates were inoculated in grapevine seedlings sprayed with the copper, the incubation period of the disease was reduced by up to four days. CopA and copB genes were present in both phenotypes of the isolates. The analyzes performed with the copA gene showed a high shared genetic similarity of sharing between Xcv and X. alfalfae subsp. citrumelonis, X. citri subsp. citri and X. arboricola pv. juglandis. In the absence of copper, tolerant isolates did not exhibit reduced adaptability in relation to cultural characteristics, growth, tolerance to different temperatures, NaCl concentrations, pH levels, induction of hypersensitivity and biofilm production. The rep-PCR genomic profiles of Xcv isolates from Petrolina-PE (n = 60), Juazeiro-BA (n = 16) and Casa Nova-BA (n = 29) were analyzed to determine the intra- and inter- population diversity. ERIC and REP techniques showed high haplotype diversity in each population while BOX showed low, even though the values were close. The haplotype net detected an absence of structure in the population with few or none haplotype shared by isolates of the three populations. The haplotype differentiation analyzes among populations showed low index values demonstrating low genetic differentiation among them. Moreover, populations presented low global diversity.