The phytoecdysteroid, 20-hydroxyecdysone (20E), is a major molting hormone of invertebrates, possibly including nematodes. As 20E is inducible in spinach, the defensive role against plant-parasitic nematodes was investigated. The effects of direct application on nematodes was assessed by treating cereal cyst nematode, Heterodera avenae, juveniles with concentrations of 20E from 8.2 x 10(-8) to 5.2 x 10(-5) M before applying to Triticum aestivum growing in sand. H. avenae, Heterodera schachtii (sugarbeet cyst nematode), Meloidogyne javanica (root-knot nematode), and Pratylenchus neglectus (root lesion nematode) were treated with 5.2 x 10(-5) 20E and incubated in moist sand. To test the protective effects of 20E in plants, the latter three nematodes were applied to Spinacia oleracea in which elevated concentrations of 20E had been induced by methyl jasmonate. Abnormal molting, immobility, reduced invasion, impaired development, and death occurred in nematodes exposed to 20E either directly at concentration above 4.2 x 10(-7) M or in plants. Phytoecdysteroid was found to protect spinach from plant-parasitic nematodes and may confer a mechanism for nematode resistance.
The induction of defense compounds in oats (Avena sativa) in response to invasion by parasitic nematodes and to application of the wound hormone methyl jasmonate was examined. Oats cv. Quoll seedlings were challenged with Pratylenchus neglectus, Heterodera avenae, and Ditylenchus dipsaci and treated with 1 x 10(-4) M methyl jasmonate. Three compounds, isolated in methanolic root and shoot extracts of oats, exhibiting an absorbance spectrum typical of flavone glycosides, were induced by nematode invasion and methyl jasmonate. These were identified as flavone-C-glycosides by mass spectrometry. The effect of the flavone-C-glycosides on the invasion by and development of cereal cyst nematode H. avenae was assessed using methanolic extracts of shoots and roots from methyl jasmonate-treated plants. Both extracts impaired nematode invasion and development. When the extracts were fractionated by high voltage paper electrophoresis, only one flavone-C-glycoside, O-methyl-apigenin-C-deoxyhexoside-O-hexoside, inhibited nematode invasion. The protective effect of the induction of flavone-C-glycosides in oats by methyl jasmonate was evaluated against H. avenae and P. neglectus. Treatment with methyl jasmonate reduced invasion of both nematodes and increased plant mass, compensating for damage caused by the nematodes, and is attributed to the active flavone-C-glycoside. The active compound, O-methyl-apigenin-C-deoxyhexoside-O-hexoside, has not been implicated previously in plant defense against any pest or pathogen, and appears to provide protection against the major cereal nematodes Heterodera and Pratylenchus.
Accessions of Oryza longistaminata and O. glaberrima, two rice species from Africa, and O. sativa were screened to identify sources of resistance to Meloidogyne graminicola. An initial population of 6000 J2/plant was inoculated to cuttings of the African rice species and 5-day-old seedlings of O. sativa. Root nematode densities were estimated 60 days after the last inoculation. O. sativa entries were all susceptible to the rice root-knot nematode. One accession of O. longistaminata represented by two individuals (WL02-2 and WL02-15) and three accessions of O. glaberrima (TOG7235, TOG5674 and TOG5675) were resistant to M. graminicola. DL01-1, an O. longistaminata accession, was susceptible to the rice root-knot nematode. Identification de sources de resistance a Meloidogyne graminicola chez Oryza longistaminata et O. glaberrima - Plusieurs accessions d'Oryza longistaminata et d'O. glaberrima, deux riz africains, et d'O. sativa ont ete criblees pour trouver des sources de resistance a Meloidogyne graminicola. Des inoculums de 6000 J2 par plante ont ete inocules sur des boutures des deux riz africains et sur des plantules de 5 jours d'O. sativa. Les populations presentes dans les racines ont ete evaluees 60 jours apres l'inoculation. Toutes les varietes testees d'O. sativa etaient sensibles. Une accession d'O. longistaminata, representee par deux individus (WLO2-2 et WLO2-15), et trois accessions d'O. glaberrima (TOG7235, TOG5674 et TOG5675) etaient resistantes.
Meloidogyne graminicola, the rice root-knot nematode, has become a constraint on Asian rice production due to rice cropping intensi cation and increasing scarcity of water. This work relates to the assessment of crop rotation, fallow and nematicide treatments in naturally infested elds to manage M. graminicola populations and prevent yield losses. One or two consecutive crops of cowpea or seasons of fallow before a rice crop lowered nematode populations and improved rice yield by 30-80%. Methyl bromide was used to determine yield potential and almost eradicated the nematode, trebling rice yield. Carbofuran improved yield of the rst rice crop but did not affect the second rice crop. Due to its short life cycle, M. graminicola populations were similar after only a single rice crop and after three consecutive crops. It is recommended that, to ensure higher rice yields, M. graminicola populations should be maintained at low density by non-host crop rotations or fallows, ideally for two seasons before planting rice.
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