Assessing root nodule microsymbionts in healthy and declined rooibos (Aspalathus linearis burm f.) at a plantation in South Africa

Abstract

Aspalathus linearis (burm f.), commonly known as rooibos, grows in nutrient and organic matter poor sandy soils that limit its growth. In this study, samples of nodules from both declined and healthy rooibos plants were collected to determine the frequency of nodule nitrogen-fixing and endophytic bacteria. Standard microbiological procedures as well as sequence analysis of the 16S rRNA revealed that more than 75% of the bacterial isolates from the healthy plants contained microsymbionts belonging to the Rhizobium group and the remaining 25% were characterized as Pseudomonas and Burkholderia spp. The nodule from the declined plants lacks a sufficient number of rhizobia and was mostly white in color, small and contains the free-living endospore-forming Bacillus and other endophytic Burkholderia and Pseudomonas spp. The results provide a baseline data on the microsymbionts of rooibos nodules in Citrusdal and highlighted the need for further investigation using additional techniques. ARTICLE HISTORY

Rhizobium-Linked Nutritional and Phytochemical Changes Under Multitrophic Functional Contexts in Sustainable Food Systems

“…Non-pathogenic parasites of Rhizobium-legume symbioses comprise a wide range of microbes that draw resources from symbiotic systems without causing disease to rhizobia or the host plant. These include non-pathogenic non-symbiotic bacteria and fungi that live endophytically in root nodules and other plant tissues without causing disease (Omar and Abd-Alla, 2000;Mrabet et al, 2006;Selvakumar et al, 2013;De Meyer et al, 2015;Martínez-Hidalgo and Hirsch, 2017;Hassen et al, 2018;Muresu et al, 2019). Besides the non-pathogenic bacteria, root nodules of leguminous plants such as Hedysarum species and Vicia faba host human pathogens such as Enterobacter cloacae, Enterobacter kobei, Escherichia vuneris, Pantoea agglomerans, and Leclercia adecarboxylata (Muresu et al, 2010;Saïdi et al, 2013;Selvakumar et al, 2013).…”