Pot studies on the effects of mycorrhizal root colonization on plant growth and nematode reproduction in tomato-Meloidogyne incognita and carrot-Pratylenchus penetrans pathosystems were carried out. The mycorrhizal fungus Glomus mosseae did not protect tomato plants inoculated with the pathogen M. incognita when it was inoculated simultaneously with the mycorrhiza, as plants inoculated with M. incognita died before harvest. On the other hand, when tomato seedlings were inoculated with the nematode three weeks after mycorrhization, colonization of tomato roots by G. mosseae compensated for the reduction of plant growth caused by M. incognita infection. Tomato shoot weight was 24% greater and gall index 33% lower than plants inoculated with the nematode alone, and final soil densities of M. incognita were reduced by 85% when tomato roots were colonized by the mycorrhiza. Root infection by P. penetrans reduced carrot growth, but soil inoculation with Glomus sp. spores compensated for the damage caused by P. penetrans. Addition of Glomus spores to soil reduced P. penetrans soil densities by 49%.
The root-knot nematode (RKN) is one of the most devastating parasitic nematodes of plants. Although some secondary metabolites released by the host plant play roles as defense substances against parasitic nematodes, the mechanism underlying the induction of such defense responses is not fully understood. We found that sclareol, a natural diterpene known as an antimicrobial and defense-related molecule, inhibited RKN penetration of tomato and Arabidopsis roots. Sclareol induced genes related to ethylene (ET) biosynthesis and signaling and phenylpropanoid metabolism in Arabidopsis roots. In roots of ein2-1, an ET-insensitive mutant line, both sclareol-induced inhibition of RKN penetration and sclareol-induced enhancement of lignin accumulation were abolished. A mutant defective in lignin accumulation did not exhibit such inhibition. Sclareol also activated MPK3 and MPK6, Arabidopsis mitogen-activated protein kinases whose activation is required for triggering ET biosynthesis. Sclareol-induced inhibition of RKN penetration was exhibited by mutants of neither MPK3 nor MPK6. Treatment with a biosynthetic precursor of ET was insufficient compared with sclareol treatment to inhibit RKN penetration, suggesting the existence of an ET-independent signaling pathway leading to RKN resistance. These results suggested that sclareol induced resistance to RKN penetration partially through ET-dependent accumulation of lignin in roots.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.