Abstract
Black spot is a major foliar disease of sweet basil (Ocimum basilicum) present in a typical cultivation area of northern Italy, including the Liguria and southern Piedmont regions, where this aromatic herb is an economically important crop. In this study, 15 Colletotrichum isolates obtained from sweet basil plants with symptoms of black spot sampled in this area were characterized morphologically and by nuclear DNA analysis using internal transcribed spacers (ITS) and intervening 5.8S nrDNA as well as part of the β-tubulin gene (TUB2) regions as barcode markers. Analysis revealed all but one isolate belonged to the recently described species C. ocimi of the C. destructivum species complex. Only one isolate was identified as C. destructivum sensu stricto (s.s.). In pathogenicity tests on sweet basil, both C. ocimi and C. destructivum s.s. isolates incited typical symptoms of black spot, showing that although C. ocimi prevails in this basil production area, it is not the sole causal agent of black spot in northern Italy. While no other hosts of C. ocimi are known worldwide, the close related species C. destructivum has a broad host range, suggesting a speciation process of C. ocimi within this species complex driven by adaptation to the host.
Highlights
Sweet basil (Ocimum basilicum L.), a species of the Labiatae family, is an economically important herb crop in several Mediterranean countries and other parts of the world, including France, Israel, Italy, and United States [1]
The phylogenetic analysis of the combined data set of sequences from internal transcribed spacers (ITS) and tubulin 2 gene (TUB2) regions of all 15 representative Colletotrichum isolates collected from basil in northern Italy and included in the present study, along with reference sequences of Colletotrichum species separated within the C. destructivum complex, produced a phylogenetic tree with a similar topology and high concordance with those reported in previous studies by other authors who revised the systematics of Colletotrichum acutatum, C. boninense, and C. destructivum species complexes using multigene sequence analysis [12,13,24]
All but one isolates from basil were identified as C. ocimi because they clustered with the ex-type isolate of this species and were clearly distinct from C. destructivum s.s
Summary
Sweet basil (Ocimum basilicum L.), a species of the Labiatae family (tribe Ocimoideae), is an economically important herb crop in several Mediterranean countries and other parts of the world, including France, Israel, Italy, and United States [1]. It is used both as a fresh and dried food spice as well as in traditional medicine. Black spot is the common name for anthracnose disease of sweet basil and Plants 2020, 9, 654; doi:10.3390/plants9050654 www.mdpi.com/journal/plants
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