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Vetiver, a nonhost grass for certain nematodes, was studied for the production of compounds active against the southern root-knot nematode, Meloidogyne incognita. In laboratory assays studying the effects on second-stage juvenile (J2) activity and viability, crude vetiver root and shoot extracts were nematotoxic, resulting in 40% to 70% J2 mortality, and were also repellent to J2. Vetiver oil did not exhibit activity against J2 in these assays. Gas chromatography-mass spectrometry analyses of three crude vetiver root ethanol extracts and a commercial vetiver oil determined that two of the major components in each sample were the sesquiterpene acid 3,3,8,8-tetramethyltricyclo[5.1.0.0(2,4)]oct-5-ene-5-propanoic acid and the sesquiterpene alcohol 6-isopropenyl-4,8a-dimeth yl-1,2,3,5,6,7,8,8a-octahydronaphthalen-2-ol. The acid was present in higher amounts in the extracts than in the oil. These studies demonstrating nematotoxicity and repellency of vetiver-derived compounds to M. incognita suggest that plant chemistry plays a role in the nonhost status of vetiver to root-knot nematodes, and that the chemical constituents of vetiver may be useful for suppressing nematode populations in the soil.

The rice root nematodes, Hirschmanniella oryzae and H. mucronata, are serious and widespread threats to global rice production, especially in tropical and subtropical zones. Reliable and efficient identification of these nematodes is vital to nematode control and management. In this current study, 36 soil or rice root samples were collected from rice fields located in Pathum Thani province and used for nematode extraction. The results demonstrated that Hirschmanniella sp. was found in all paddy fields, especially in Muang District, where RD47 rice cultivars were grown at soil pH of 5.9. Molecular identification based on the analysis of 28S rRNA and 18S-ITS1-1.58S genes revealed 98 – 99 % similarity to H. mucronata, and its phylogenetic trees were grouped with H. mucronata from Cambodia and Philippines. Likewise, the morphometric characterization revealed remarkable features of H. mucronata with long body (1,639 - 2,329 µm), long stylet (24 - 27 µm) and an obvious mucron at the end of terminus. Therefore, the main rice root nematode species found in Pathum Thani’s rice fields were H. mucronata. HIGHLIGHTS The rice root nematodes, Hirschmanniella, are presented the predominant plant-parasitic nematodes in rice cultivated areas of Pathum Thani province, Thailand Population densities of Hirschmanniella are encountered in rice roots than in soil, especially in RD47 rice cultivars grown in Muang District Both of morphological and molecular characterization illustrating the species of rice root nematodes were mucronate This is a first description on the molecular characterization of mucronata from rice fields in Thailand GRAPHICAL ABSTRACT

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Summary The legume cavalcade, Centrosema pascuorum, is used extensively as a cover crop and as a component of conservation agriculture systems. It is also an attractive rotation or cover crop for the management of root-knot nematodes (RKN; Meloidogyne spp.) as it is a non-host. RKN are persistent pests that are well known to be difficult to control. However, the mechanisms governing the non-host status of cavalcade is unknown. The current study established that cavalcade leaves are toxic to RKN as either aqueous extracts or soil amendments. Bioassays conducted using Meloidogyne javanica showed that a 90% concentration of aqueous extract derived from 1-month-old cavalcade leaves (89 mg crude extract ml−1) suppressed nematode hatch (82.9%) and killed infective second-stage juveniles of M. javanica (85.3%). Soil amendments with 1% (w/w) of 1-month-old cavalcade leaves (0.99 mg crude extract g−1 soil) also provided effective control of M. javanica in the glasshouse on okra. One-month-old leaves appeared more effective than 2- or 3-month-old leaves. The soil amendments had no adverse phytotoxic effect on okra seed germination. Our study demonstrates the potential for using cavalcade leaves or extracts to manage RKN. This may be due to the nematicidal activity of the various compounds in the leaves, such as flavonoids, phenols and terpenoids, which should be further assessed.