Plant-parasitic nematodes associated with bush tea (Athrixia phylicoides) in South Africa and their relationship with physico-chemical soil properties

Bush tea (Athrixia phylicoides) is an aromatic, perennial, leafy shrub that is endemic to the northeastern mountain ranges of South Africa and has a high potential for commercialisation as an alternative to caffeine-containing tea. During the summer and winter of 2018-2019, a survey was carried out at nine localities in the northeastern regions of South Africa to study the diversity of nematodes associated with bush tea and, in terms of frequency of occurrence and abundance, identify the dominant plant-parasitic nematodes. Twenty-one plant-parasitic nematode species belonging to 14 genera were identified in 90 rhizosphere soil and root samples. Meloidogyne and Helicotylenchus were the dominant plant-parasitic nematode genera. Meloidogyne javanica and Scutellonema brachyurus were found at all localities, followed by M. enterolobii, Pratylenchus brachyurus, Rotylenchulus parvus, H. martini and S. truncatum (found at 7-8 localities). Other species identified included Criconema corbetii, C. sphaerocephalus, C. xenoplax, Criconemoides ihlathum, C. parvus, Discocriconemella glabrannulata, H. dihystera, H. erythrinae, H. paraplatyurus, Hemicycliophora typica, M. hapla, M. incognita, Rotylenchulus unisexus and R. clavicaudatus. Individuals of Crossonema, Paratylenchus, Ogma, the Xiphinema americanum-group and X. americanum sensu lato could not be identified to species level due to the low number of specimens present in the samples. Comparison of the two methods used to identify the Meloidogyne populations to species level shows that morphological identification (particularly perineal pattern morphology) provided a more complete picture of the Meloidogyne species present in the samples compared with the molecular SCAR-PCR technique. High levels of Cu, K and pH were associated with the highest relative population densities (RPD% = average population density of a nematode genus/total nematode population density × 100) of Meloidogyne, whilst high levels of Al and soil resistivity were associated with the lowest RPD% of Meloidogyne. By contrast, high levels of K and pH were associated with the lowest RPD% of Helicotylenchus, whilst high levels of Al and soil resistivity were associated with the highest RPD% of Helicotylenchus.