Dual and Single-species Nematode Infections Distinctly Modulate Defense Metabolism in Brassica nigra Roots

Plant roots are exposed to various organisms that significantly impact plant productivity. Plant-parasitic nematodes (PPNs) such as Meloidogyne spp. and Pratylenchus spp. are microscopic roundworms that damage several crops. In natural populations, M. incognita and P. penetrans were found to infest black mustard (Brassica nigra) plants simultaneously. Considering their different feeding strategies and contrasting effects on plant defense responses, we hypothesized that dual infection may affect each nematode's performance via changes in the root metabolome. Using untargeted and targeted metabolomics, we evaluated how single and dual nematode infections affected B. nigra root metabolome. We combined these metabolic data with measures of early infection success. At three days post-inoculation, dual infection increased M. incognita penetration success, while that of P. penetrans remained unaffected. Compared to single-species infections, dual infections resulted in distinct root metabolic changes by reducing indole glucosinolates (GSL), gluconasturtiin, lignans, and phenylpropanoids. Dual and single-species infections affected different GSL classes. The allyl GSL, sinigrin and its breakdown products increased in P. penetrans-infected plants, while gluconasturtiin and 2-phenylethyl ITC increased in M. incognita-infected plants. This shows that plant defense response to dual nematode infection differ from those of single species, which has consequences to the early infection success of each nematode species.