The mediterranean biotypes of Tylenchulus semipenetrans in Spanish citrus orchards

Les capacités de reproduction de quatorze populations du nématode des citrus (#Tylenchulus semipenetrans$) collectées dans la principale zone de citriculture de l'Espagne ont été comparées sur oranger amer et citrange Carrizo. Toutes les populations ont été identifiées comme appartenant au biotype méditerranéen. La capacité de reproduction varie considérablement en fonction des populations. Le pouvoir infestant et le taux de reproduction des populations collectées dans la rhizosphère des porte-greffes citranges Troyer ou Carrizo sont plus élevés (P supérieur ou égal à 0,05) que ceux des populations collectées sur oranger amer. (Résumé d'auteur

Trifoliata hybrids rootstocks for 'Lane Late' navel orange in Spain

Carrizo citrange [Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] and Cleopatra mandarin (C. reshni Hort. ex Tan.) are the most important rootstocks used in Spain, but they are problematic and it is necessary to search for new rootstocks with better all-round performance. The performance of 'Lane Late' navel orange [Citrus sinensis (L.) Osb] on ten rootstocks was determined in the South of the province of Alicante (Spain). They are Carrizo citrange, Cleopatra mandarin and eight new hybrids obtained at the Instituto Valenciano de Investigaciones Agrarias in Valencia (Spain): 020324 [Troyer citrange (C. sinensis × P. trifoliata) × Cleopatra mandarin], Forner-Alcaide 418 (F&A 418) [Troyer citrange × common mandarin (C. deliciosa Ten.)], Forner-Alcaide 13 (F&A 13), 030118, 030127 and 030131 (Cleopatra mandarin × P. trifoliata) and 030212 and 030230 (Cleopatra mandarin × Troyer citrange). Soil is clay loam, with pH 8.5 and electric conductivity in the saturation extract at 25ºC of 5.79 mS cm-1. Yield was weighed during the first nine harvests, fruit quality was determined in the last three. Pre-harvest fruit-drop was controlled for the 4th until 9th harvests. The trees of 'Lane Late' navel budded on Cleopatra mandarin were the tallest (2.5 m) and F&A 418 (1.6 m) the shortest of all rootstocks tested. Trees on 030131 hybrid and Carrizo citrange rootstocks had the highest mean yield (81.2 and 80.3 kg per tree per year respectively), while trees on F&A 418 produced the lowest mean yield (22.3 kg per tree per year). Trees on 030131, 020324 and 030212 had the highest yield efficiency as total cumulative yield per cubic meter of canopy volume (62.1, 58.7 and 55.9 kg m-3 respectively) whereas trees on 030127, F&A 418 and Cleopatra mandarin had lower yield efficiencies (45.0, 44.4 and 38.6 kg m-3, respectively). Pre-harvest fruit-drop was lower in trees grafted on Cleopatra mandarin (24.62 %) and on 030212 (26.61 %), and was also low on F&A 418 (27.76 %), 020324 (28.14 %) and 030230 (29.18 %) rootstocks. Trees on Carrizo citrange and 030127 experienced important fruit-drop (40.24 % and 38.27 % respectively). Trees on F&A 418 had the highest fruit weight and fruit size whereas trees on 030118 induced the lowest ones. The ripeness index was the highest on F&A 13 (18.3) and lowest on F&A 418 (15.3), 030212 (15.3)

Nematicidal activity of fervenulin isolated from a nematicidal actinomycete, Streptomyces sp. CMU-MH021, on Meloidogyne incognita

An isolate of the actinomycete, Streptomyces sp. CMU-MH021 produced secondary metabolites that inhibited egg hatch and increased juvenile mortality of the root-knot nematode Meloidogyne incognita in vitro. 16S rDNA gene sequencing showed that the isolate sequence was 99% identical to Streptomyces roseoverticillatus. The culture filtrates form different culture media were tested for nematocidal activity. The maximal activity against M. incognita was obtained by using modified basal (MB) medium. The nematicidal assay-directed fractionation of the culture broth delivered fervenulin (1) and isocoumarin (2). Fervenulin, a low molecular weight compound, shows a broad range of biological activities. However, nematicidal activity of fervenulin was not previously reported. The nematicidal activity of fervenulin (1) was assessed using the broth microdilution technique. The lowest minimum inhibitory concentrations (MICs) of the compound against egg hatch of M. incognita was 30 μg/ml and juvenile mortality of M. incognita increasing was observed at 120 μg/ml. Moreover, at the concentration of 250 μg/ml fervenulin (1) showed killing effect on second-stage nematode juveniles of M. incognita up to 100% after incubation for 96 h. Isocoumarin (2), another bioactive compound produced by Streptomyces sp. CMU-MH021, showed weak nematicidal activity with M. incognita

Evaluación de filtrados de cultivos fúngicos de hongos por su actividad frente a Tylenchulus semipenetrans

Culture filtrates of 20 fungi isolated from citrus soils were screened for their activity against Tylenchulus semipenetrans in both in vitro and greenhouse tests. The filtrates of Talaromyces cyanescens (isolates 2-4 and 2-5), Paecilomyces lilacinus, Chaetomium robustum, Acremonium strictum, Engyodontium album, Myrothecium verrucaria, Emericella rugulosa, and Tarracomyces gigaspora consistently inhibited the motility of second-stage juveniles at various concentrations of the filtrate. Dose-response models were used to determine the filtrate concentration required to inhibit the motility of 50% of the juveniles (CI50). The culture filtrate of P. lilacinus showed the highest activity with a CI50 value of 58% that differed from that of C. robustum (CI50 = 68%), and A. strictum CI50 = 82%. The culture filtrates of P. lilacinus, E. album, and T. cyanescens 2-5 maintained their activity when autoclaved at 120 deg C for 20 min. The autoclaved filtrate of T. cyanescens 2-4 was more effective at inhibiting juvenile motility (CI50 = 28%) than that of T. cyanescens 2-5 (CI50 = 80%), C. robustum (CI50 = 72 %) and P. lilacinus (CI50 = 72%). The culture filtrate of T. cyanescens 2-4 also inhibited egg hatching. Nematode reproduction on Cleopatra mandarin and Carrizo citrange were respectively reduced by the culture filtrate of P. lilacinus and the autoclaved filtrate of T. cyanescens 2-4. These results support the hypothesis that soil fungi may contribute to regulate nematode densities by the production of secondary metabolites with nematicidal activity.Se evaluó la actividad de filtrados de cultivos de 20 hongos aislados del suelo en parcelas de cítricos frente a Tylenchulus semipenetrans mediante ensayos in vitro y en invernadero. Los filtrados de Talaromyces cyanescens (aislados 2-4 y 2-5), Paecilomyces lilacinus, Chaetomium robustum, Acremonium strictum, Engyodontium album, Myrothecium verrucaria, Emericella rugulosa, y Tarracomyces gigaspora inhibieron consistentemente la movilidad de los juveniles de segundo estadio del nematodo a varias concentraciones del filtrado. Se utilizaron modelos de dosis-respuesta para determinar la concentración del filtrado que inhibía la movilidad del 50% de los juveniles (CI50). El filtrado del cultivo de P. lilacinus mostró la máxima actividad entre todos los ensayados con un valor de CI50 del 58%, la cual era superior a la de los filtrados de C. robustum (CI50 = 68%) y A. strictum (CI50 = 82%). Los filtrados de P. lilacinus, E. album, y T. cyanescens 2-5 retenían su actividad después de autoclavarlos a 120 grados C durante 20 min. La inhibición de la movilidad de los juveniles obtenida con el filtrado autoclavado de T. cyanescens 2-4 (CI50 = 28%) fue superior a la de los filtrados de T. cyanescens 2-5 (CI50 = 80%), C. robustum (CI50 = 72%), ó P. lilacinus (CI50 = 72%). El filtrado de T. cyanescens 2-4 también inhibió la eclosión de los huevos del nematodo. La reproducción del nematodo en mandarino Cleopatra y citrange Carrizo fue menor cuando los juveniles se incubaron en el filtrado de P. lilacinus y en el filtrado autoclavado T. cyanescens 2-4, respectivamente. Estos resultados apoyan la hipótesis de que los hongos del suelo pueden contribuir a la regulación de las poblacionales de los nematodos mediante la producción de metabolitos secundarios con acción nematicida