Etude de l’effet d’une source d’inoculum externe sur la propagation du CABMV (Cowpea aphid – borne mosaic virus) selon la proximité des parcelles voisines et la variété de niébé

Un champ ensemencé avec des semences de qualité peut se retrouver voisin avec un autre ensemencé avec des semences infectées par le virus de la mosaïque du niébé. Ce virus est transmis par les semences à des taux de 0 à 40% selon les variétés. Ces semences infectées donnent des jeunes plantes virosées à partir desquelles les pucerons vont propager la maladie. Ce travail a été effectué pour déterminer la distance minimale permettant d’éviter des contaminations à partir d’inoculum externe suivant la sensibilité de la variété. Ainsi, deux parcelles centrales de 300 m2 ont été semées avec des graines de Gorom local contaminées à 0,5% par le virus. Autour de la première parcelle centrale, 4 parcelles de 200 m2 chacune ont été semées avec des graines de Gorom local indemnes de virus aux distances respectives de 10 m, 15 m, 20 m et 25 m. Autour de la deuxième parcelle centrale, des semences indemnes de virus de Kvx61-1 ont été utilisées. Un dispositif similaire a été constitué pour les parcelles témoins avec des semences indemnes de virus. La propagation de la maladie a montré qu’elle est liée à la variété, aux pucerons et à la distance avec la source d’inoculum.© 2015 International Formulae Group. All rights reserved.Mots clés: Semences indemnes de virus, semences contaminées, distance minimale, puceronsEnglish Title: Study of the effect of external inoculum source on CABMV (Cowpea aphid – borne mosaic virus) spread in relation to the proximity of neighboring plots and the cowpea varietyEnglish AbstractA field sown with quality seeds can be closed to another one sown with seeds infected by cowpea mosaic virus which is seed transmitted at rates ranging from 0 to 40% depending on cowpea varieties. Infected seeds germinate and grow into virus-infected seedlings from which aphids will spread the disease. This  research was carried out in order to determine the minimum distance needed for avoiding contaminations from external virus inoculum sources, in relation with the susceptibility of cowpea varieties. Thus, two central plots of 300 m² have been sown with contaminated seeds at 0.5% by CABMV of cowpea variety Gorom local. Around the first central plot, four plots of 200 m² each were sown with virus-free seeds of Gorom local at respective distances of 10 m, 15 m, 20 m and 25 m. Around the second central plot, virus-free seeds of Kvx61- 1 have been used. A similar layout was done for the control plots with virus-free seeds. It was found that the spread of the disease was related to the cowpea variety, the aphids and the distance from the inoculum source.© 2015 International Formulae Group. All rights reserved.Keywords: Virus-free seeds, contaminated seeds, minimum distance, aphid

Antifungal and Antiaflatoxinogenic Effects of Cymbopogon citratus, Cymbopogon nardus, and Cymbopogon schoenanthus Essential Oils Alone and in Combination

The antifungal and antiaflatoxinogenic activities of the essential oils (EOs) from the leaves of Cymbopogon schoenanthus, Cymbopogon citratus, Cymbopogon nardus, and their pair combinations were investigated. Antifungal susceptibility and the efficacy of paired combinations of EOs were assessed using agar microdilution and checkerboard methods, respectively. Identification and quantification of chemical components of the EOs were carried out by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector (GC-MS and GC-FID), respectively. Aflatoxins were separated and identified by High-Performance Liquid Chromatography (HPLC) and then quantified by spectrofluorescence. The EO of C. nardus exhibited the highest inhibitory activity against Aspergillus flavus and Aspergillus parasiticus. The combination of C. citratus and C. nardus and that of C. nardus and C. schoenanthus exhibited a synergistic effect against Aspergillus flavus and Aspergillus, respectively. Both C. citratus and C. schoenanthus EOs totally inhibited the synthesis of aflatoxin B1 at 1 µL/mL. C. citratus blocked the production of aflatoxins B2 and G2 at 0.5 µL/mL. Both C. citratus and C. schoenanthus totally hampered the production of the aflatoxin G1 at 0.75 µL/mL. The combination of C. citratus and C. schoenanthus completely inhibited the production of the four aflatoxins. The study shows that the combinations can be used to improve their antifungal and antiaflatoxinogenic activities