Plant parasitic nematodes cause significant crop damage globally. Currently, many nematicides have been banned or are being phased out in Europe and other parts of the world because of environmental and human health concerns. Therefore, we need to focus on sustainable and alternative methods of nematode control to protect crops. Plant roots contain and release a wide range of bioactive secondary metabolites, many of which are known defense compounds. Hence, profound understanding of the root mediated interactions between plants and plant parasitic nematodes may contribute to efficient control and management of pest nematodes. In this review, we have compiled literature that documents effects of root metabolites on plant parasitic nematodes. These chemical compounds act as either nematode attractants, repellents, hatching stimulants or inhibitors. We have summarized the few studies that describe how root metabolites regulate the expression of nematode genes. As non-herbivorous nematodes contribute to decomposition, nutrient mineralization, microbial community structuring and control of herbivorous insect larvae, we also review the impact of plant metabolites on these nontarget organisms.1 study on effect of both plant and specific metabolites detected in root exudates of the plant, 2 study on effect of plant, 3 study on effect of synthetic compound on nematodes, NA indicate not applicable.

Phyllanthus emblica L. belonging to the family Euphorbiaceae is a common medicinal plant in Bangladesh. In order to evaluate the phytoconstituents and bioactivity of various parts of P. emblica, both the wild type (i.e., small) and cultivated (i.e., big) fruits were collected from the local market of Bangladesh and six ethanolic extracts were prepared from various parts of the collected fruits for this current study. A comparative analysis of the phytochemical compositions and various bioactivities especially antibacterial, antifungal, and antioxidant activity of the six ethanolic extracts were accomplished. The qualitative phytochemical analysis of plant extracts revealed the presence of large amounts of proteins, carbohydrates, phenolic compounds, glycosides, alkaloids, coumarins, flavonoids, tannins, saponins and resins etc. The maximum antioxidant activity was observed for wild type P. emblica seed extracts and the minimum activity was observed for cultivated flesh extracts. Moreover, among the samples the wild type P. emblica extracts have excellent amount of total phenol contents and the highest free radical scavenging activity. It is also found that P. emblica samples were active against both gram-positive (i.e., B. subtilis) and gram-negative (i.e., E. coli, and S. typhi) bacteria. The highest antibacterial activity was achieved in the wild type P. emblica seed extracts against both pathogenic (S. typhi) and non-pathogenic bacterial strains (E. coli, and B. subtilis). These samples showed almost no activity against Fusarium sp. fungus.

Although the effects of plant secondary metabolites on plant defense have been studied for decades, the exact roles of secondary metabolites in shaping plant-associated microbial and nematode communities remain elusive. We evaluated the effects of benzoxazinoids (BXs), a group of secondary metabolites present in several cereals, on root-associated nematodes. We employed 18S rRNA metabarcoding to compare maize root-associated nematode communities in a bx1 knock-out maize line impaired in BX synthesis and in its parental wild type (WT). Both genotype and plant age affected nematode community composition in the roots, and the effects of BXs on nematode communities were higher in the roots compared to the rhizosphere. Differential abundance analysis and quantitative PCR showed that the root lesion nematode Pratylenchus neglectus was enriched in the bx1 mutant line, while another root lesion nematode Pratylenchus crenatus was reduced. Correlation analysis showed that BX contents in maize roots mostly correlated negatively with the relative abundance of nematode reads. However, positive correlations between BXs and nematode taxa, including several plant parasitic nematodes, were also identified. Our detailed nematode community analysis suggested differential and selective effects of BXs on soil nematodes depending on both the nematode species and BX compound.