Plant Volatiles Reduce the Viability of the Root-Knot NematodeMeloidogyne incognitaEither Directly or When Retained in Water

Abstract

Volatile organic compounds (VOC) produced by green residues for the management of plant-parasitic nematodes are poorly studied for oilseed plants and some Brassica spp. To investigate the activity of VOC in vitro and as biofumigants, dry and aqueous macerates of broccoli (Brassica oleracea var. italica) shoots and sunflower (Helianthus annuus) seed were used against the root-knot nematode Meloidogyne incognita. VOC produced by sunflower seed caused higher mortality of M. incognita second-stage juveniles (J) than VOC produced by broccoli shoots but both plant species were equally effective in decreasing the infectivity and reproduction of this nematode. The number of galls and eggs produced by the nematode in tomato roots was reduced by 89 and 95%, respectively, on average, at the highest concentrations of broccoli and sunflower seed macerates tested as biofumigants. When nematodes were placed in water exposed to broccoli VOC, J immobility increased and the number of galls and eggs produced by the nematode in tomato roots decreased 80 and 96%, respectively. Water exposed to sunflower seed VOC had no effect on the viability of the nematode. Gas chromatography was used to identify five and six chemical groups in broccoli and in sunflower seed macerates, respectively, but only alcohols, sulfurated VOC, and terpenes were detected in the water exposed to these plant macerates. Sulfurated VOC from the water exposed to broccoli macerates were found to be involved in its activity against M. incognita. The purified VOC dimethyl disulfide (DMDS) and 3-pentanol were tested directly against J and showed a lethal concentration of 176 and 918 µg/ml (ppm), respectively, whereas dimethyl sulfide had no effect against M. incognita. Furthermore, DMDS and 3-pentanol retained in water killed J and reduced gall formation and the number of eggs of M. incognita on tomato roots. Both these plant species produced toxic VOC to M. incognita, whereas only VOC retained in water exposed to broccoli had activity against M. incognita.

Volatile emissions of watercress (Nasturtium officinale) leaves and passion fruit (Passiflora edulis) seeds against Meloidogyne incognita

“…Then, each well of the 96‐well polypropylene plate was filled with distilled water (100 μL), and the plates were incubated for an additional 24 h at 25 °C. After that, the J 2 that were still immobile were considered dead (mortality determination) …”

“…As a positive control, broccoli inflorescence ( B. oleracea var . italica ) applied at 1.5 g was used, which produces VOCs toxic to M. incognita . The percentages of mobile, immobile, and dead J 2 were quantified as described above.…”

“…exposure of M. incognita second‐stage juveniles (J 2 ) to 3‐methylbutyl acetate at 500 μg mL 1 for 1 h caused mortality above 84% . In recent years, studies on the use of plant VOCs against PPNs have expanded . Biofumigation, consisting of the incorporation of plant residues that slowly release their bioactive compounds into the soil, has been successfully used to control PPNs since the 19th century .…”

“…From a practical point of view, irrigation after plant residue incorporation temporarily holds the VOCs in the soil, avoiding losses to the atmosphere and increasing the chances of PPN control, mainly because the volatile molecules are diluted in water . In a previous study, the application of water with diluted VOCs to infested substrates reduced the infectivity and reproduction of M. incognita in tomato plants …”

“…7,13 In recent years, studies on the use of plant VOCs against PPNs have expanded. 6,7,[14][15][16] Biofumigation, consisting of the incorporation of plant residues that slowly release their bioactive compounds into the soil, has been successfully used to control PPNs since the 19th century. 17 Compounds resulting from field biofumigation have proven nematicidal activities, and the best example is isothiocyanates emitted by brassicas.…”