Phylogenetic position of Xiphinema americanum species (Nematoda: Longidoridae) associated with macadamia using mtDNA (cox1 region) from South Africa

Abstract

Plant parasitic nematodes belonging to the family Longidoridae live in the soil, causing crop yield loss. Nematodes of the genus Xiphinema, commonly called dagger nematodes, parasitize various plants. Many of these nematodes, the majority of them belonging to the Xiphinema americanum group, can transfer viruses to plants during feeding and cause yield loss. This species is indicated to be highly risky to plants and must be identified correctly, and it is associated with macadamia as one of the most important crops in Limpopo Province in South Africa. Therefore, this molecular study was conducted in 2023 at the Limpopo University to identify the Xiphinema from South Africa's soils using the cox1 region of mtDNA marker. The recovered nematode was extracted using the tray method, and then its DNA was extracted using the Chelex method. The nematode was identified as Xiphinema americanum. Afterwards, cox1 of mtDNA was amplified using specific primers to identify the nematode. The Nblast analysis based on the mtDNA showed South African X. americanum had 99% similarity (AM086690) with the South African population. Additionally, it showed 99% similarity with a population of X. americanum (KX263061) from the USA. Phylogenetic analysis using maximum likelihood placed this species with those molecularly identified as X. americanum in the same clade with highly supported 100 bootstrap values. In conclusion, this species was determined using cox1 of mtDNA; however, other rDNA markers, such as ITS and rDNA, were recommended to understand Xiphinema phylogeny better.