Marine Organisms for the Sustainable Management of Plant Parasitic Nematodes

Algae and Their Metabolites as Potential Bio-Pesticides

An increasing human population necessitates more food production, yet current techniques in agriculture, such as chemical pesticide use, have negative impacts on the ecosystems and strong public opposition. Alternatives to synthetic pesticides should be safe for humans, the environment, and be sustainable. Extremely diverse ecological niches and millions of years of competition have shaped the genomes of algae to produce a myriad of substances that may serve humans in various biotechnological areas. Among the thousands of described algal species, only a small number have been investigated for valuable metabolites, yet these revealed the potential of algal metabolites as bio-pesticides. This review focuses on macroalgae and microalgae (including cyanobacteria) and their extracts or purified compounds, that have proven to be effective antibacterial, antiviral, antifungal, nematocides, insecticides, herbicides, and plant growth stimulants. Moreover, the mechanisms of action of the majority of these metabolites against plant pests are thoroughly discussed. The available information demonstrated herbicidal activities via inhibition of photosynthesis, antimicrobial activities via induction of plant defense responses, inhibition of quorum sensing and blocking virus entry, and insecticidal activities via neurotoxicity. The discovery of antimetabolites also seems to hold great potential as one recent example showed antimicrobial and herbicidal properties. Algae, especially microalgae, represent a vast untapped resource for discovering novel and safe biopesticide compounds.

Bioassay Directed Fractionation of Petroleum Ether Extract of Aerial Parts of Ceriops tagal: Isolation of Lupeol as the Nematicidal Agent against Cyst Nematode Heterodera zeae

Plant parasitic cyst nematode  Heterodera zeae  is a pest, causing substantial economic losses in agriculture. Organic pesticides, based on plant products have emerged as eco-benign nematicidal agents.  Ceriops tagal  is a well-known marine medicinal plant which has not been evaluated against any nematode. Petroleum ether extract of the aerial parts of the plant (CTP), exhibited promising activity against infective stage larvae of  H. zeae . On subjecting to classical solvent-solvent separation, it afforded petroleum ether soluble (CTP-S), methanol soluble ( CTPMS-1 , CTPMS-2) and insoluble (CTPM-IN-2) fractions, which exhibited activity against the cyst nematode within 24 h exposure. GC, GCMS and ESI-HRMS analyses of CTPMS-1 and CTPMS-2 fractions resulted in the identification of a number of compounds, including pentacyclic triterpenoids, lupeol ( 1 ), betunal ( 2 ), betulin ( 3 ), lupenone ( 4 ), betulonaldehyde ( 5 ), betulonic acid ( 7 ), methyl-3-acetoxy-27- O -(3,4-dihydroxy- E -cinnamoyl)-20(29)-lupen-28-oate ( 8 ) and  β -amyrin, along with phenylpropanoid esters, fatty acids and their derivatives, benzamide, and indole derivatives. CTPM-IN-2 which mainly contained lupeol ( 1 ) exhibited maximum nematicidal activity, with 91% and 93% mortality of the larvae of  H. zeae , after exposure for 72 h at the concentration of 0.5% and 1%, respectively. Its fractionation and purification through column chromatography resulted in the isolation and identification of four lupane-type triterpenoids  1 ,  3 ,  4  and betulinic acid ( 6 ). One of its most abundant column fractions CC-9-18 (145 mg) which exhibited substantial activity, with 81% mortality at the lowest concentration of 0.125% after 48 h of incubation mainly contained lupeol. It seems lupeol, a wide spread bio-privileged triterpenoid is the nematicidal principle of the plant as its authentic sample showed LC 50 value of 0.061 after 72 h exposure. It is for the first time that nematicidal activity is reported for any part of  C. tagal  and that of lupeol against  H. zeae.  Pentacyclic triterpenoids  1 - 8  are biosynthetically related. Of the twenty-four compounds isolated or identified in the present investigation only five constituents  1 ,  3 ,  6 ,  7  and palmitic acid have been isolated previously from  C. tagal .