Remarkable Diversity and Prevalence of Dagger Nematodes of the Genus Xiphinema Cobb, 1913 (Nematoda: Longidoridae) in Olives Revealed by Integrative Approaches

Abstract

The genus Xiphinema includes a remarkable group of invertebrates of the phylum Nematoda comprising ectoparasitic animals of many wild and cultivated plants. Damage is caused by direct feeding on root cells and by vectoring nepoviruses that cause diseases on several crops. Precise identification of Xiphinema species is critical for launching appropriate control measures. We make available the first detailed information on the diversity and distribution of Xiphinema species infesting wild and cultivated olive in a wide-region in southern Spain that included 211 locations from which 453 sampling sites were analyzed. The present study identified thirty-two Xiphinema spp. in the rhizosphere of olive trees, ten species belonging to Xiphinema americanum-group, whereas twenty-two were attributed to Xiphinema non-americanum-group. These results increase our current knowledge on the biodiversity of Xiphinema species identified in olives and include the description of four new species (Xiphinema andalusiense sp. nov., Xiphinema celtiense sp. nov., Xiphinema iznajarense sp. nov., and Xiphinema mengibarense sp. nov.), and two new records for cultivate olives (X. cadavalense and X. conurum). We also found evidence of remarkable prevalence of Xiphinema spp. in olive trees, viz. 85.0% (385 out of 453 sampling sites), and they were widely distributed in both wild and cultivated olives, with 26 and 17 Xiphinema spp., respectively. Diversity indexes (Richness, Hill´s diversity, Hill´s reciprocal of D and Hill´s evenness) were significantly affected by olive type. We also developed a comparative morphological and morphometrical study together with molecular data from three nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S, ITS1, and partial 18S). Molecular characterization and phylogenetic analyses allowed the delimitation and discrimination of four new species of the genus described herein and three known species. Phylogenetic analyses of Xiphinema spp. resulted in a general consensus of these species groups. This study is the most complete phylogenetic analysis for Xiphinema non-americanum-group species to date.

Xiphinema japonicum n. sp. (Nematoda: Longidorinae) from the Rhizosphere of Japanese Podocarpus macrophyllus (Thunb.), a Cryptic Species Related to Xiphinema bakeri Williams, 1961

“…Species identification in genus Xiphinema is very difficult because of conservative and overlapping morphological and morphometric characters. These identification procedures are further complicated because of the morphological intraspecific variation and the presence of cryptic species that are morphologically indistinguishable but may be phylogenetically distant to one another (Brown and Topham, 1985;Guti errez-Guti errez et al, 2010Archidona-Yuste et al, 2016b). Because of the diversity of diagnostic/morphological characters, Xiphinema species are divided into two groups viz X. americanum group which contains more than 55 species and a second bigger group namely X. non-americanum group (Ghaemi et al, 2012;Guti errez-Guti errez et al, 2013).…”

Integrative taxonomy of Xiphinema histriae and Xiphinema lapidosum from Spain

“…The genus Xiphinema Cobb, 1913 is a large and morphologically diverse group of plant-parasitic nematodes comprising more than 275 species (Archidona-Yuste et al, 2016a, 2016b. The economic importance of this group of nematodes is not only because of its extensive range of host plants and worldwide distribution, but for the transmission of several important plant viruses (genus Nepovirus, family Comoviridae) that cause direct damage to a wide variety of crops (Taylor and Brown, 1997;Decraemer and Robbins, 2007).…”

“…The economic importance of this group of nematodes is not only because of its extensive range of host plants and worldwide distribution, but for the transmission of several important plant viruses (genus Nepovirus, family Comoviridae) that cause direct damage to a wide variety of crops (Taylor and Brown, 1997;Decraemer and Robbins, 2007). Due to their economic importance, complex identification because of the sharing of a variety or morphological characters and existence of cryptic species, it is essential to identify species accurately and developing integrative taxonomy methods to control such plant pathogenic species (Archidona-Yuste et al, 2016a, 2016b. Species identification in this group is complex because of the sharing of a variety of morphological characters and the existence of cryptic species (Archidona-Yuste et al, 2016a, 2016b.…”

“…Due to their economic importance, complex identification because of the sharing of a variety or morphological characters and existence of cryptic species, it is essential to identify species accurately and developing integrative taxonomy methods to control such plant pathogenic species (Archidona-Yuste et al, 2016a, 2016b. Species identification in this group is complex because of the sharing of a variety of morphological characters and the existence of cryptic species (Archidona-Yuste et al, 2016a, 2016b. According to the key for species of Xiphinema established by Loof and Luc (1990), the genus Xiphinema consists of X. americanum-group and X. non-americanum species.…”

“…Several authors have highlighted the great diversity of Xiphinema spp. detected in the Iberian Peninsula, in particular, around 40 species of the Integrative taxonomy of Xiphinema histriae and Xiphinema lapidosum from Spain genus Xiphinema have been reported in Spain, mainly associated with woody, ornamental, and vegetable plant species (Gutiérrez-Gutiérrez et al, 2010, 2016Archidona-Yuste et al, 2016a, 2016b.…”