Sustainable strategies for management of the "false root-knot nematode" Nacobbus spp.

The genus Nacobbus, known as the false root-knot nematode, is native to the American continent and comprises polyphagous species adapted to a wide range of climatic conditions. Alone or in combination with other biotic and abiotic factors, Nacobbus spp. can cause significant economic yield losses on main food crops such as potato, sugar beet, tomato, pepper and bean, in South and North America. Although the genus distribution is restricted to the American continent, it has quarantine importance and is subject to international legislation to prevent its spread to other regions, such as the European Union. The management of Nacobbus spp. remains unsatisfactory due to the lack of information related to different aspects of its life cycle, survival stages in the soil and in plant material, a rapid and reliable diagnostic method for its detection and the insufficient source of resistant plant genotypes. Due to the high toxicity of chemical nematicides, the search for alternatives has been intensified. Therefore, this review reports findings on the application of environmentally benign treatments to manage Nacobbus spp. Biological control strategies, such as the use of different organisms (mainly bacteria, fungi and entomopathogenic nematodes) and other eco-compatible approaches (such as metabolites, essential oils, plant extracts, phytohormones and amendments), either alone or as part of a combined control strategy, are discussed. Knowledge of potential sources of resistance for genetic improvement for crops susceptible to Nacobbus spp. are also reported. The sustainable strategies outlined here offer immediate benefits, not only to counter the pathogen, but also as good alternatives to improve crop health and growth.

Screening and identification of horticultural soil fungi for their evaluation against the plant parasitic nematode Nacobbus aberrans.

The plant-parasitic nematode Nacobbus aberrans is an endoparasite causing severe losses to a wide range of crops from North to South America. The use of native antagonistic fungi may be considered as a possible biological control alternative to reduce the damages caused by this species. Antagonistic effects of 66 potential nematophagous fungi against eggs (J1) and second-stage juveniles (J2) of N. aberrans, were evaluated in vitro on water agar. DGC test showed significant differences (p < 0.0001) in the efficacy of some fungal isolates tested, with parasitism levels for J1 and J2 of 0-95 and 1-78%, respectively. Five isolates of Purpureocillium lilacinum, Metarhizium robertsii and Plectosphaerella plurivora appeared as the most effective antagonists of N. aberrans, relying on hyphae and adhesive conidia in host infection processes.

Efficacy of epiphytic bacteria to prevent northern leaf blight caused by Exserohilum turcicum in maize / Eficacia de bacterias epifíticas en la prevención del tizón foliar del maíz causado por Exserohilum turcicum

Eight potential biological control agents (BCAs) were evaluated in planta in order to assess their effectiveness in reducing disease severity of northern leaf blight caused by Exserohilum turcicum. The assay was carried out in greenhouse. Twenty-six-day-old plants, V4 phenological stage, were inoculated with antagonists by foliar spray. Only one biocontrol agent was used per treatment. Ten days after this procedure, all treatments were inoculated with E. turcicum by foliar application. Treatments performed were: C-Et: control of E. turcicum; T1: isolate 1 (Enterococcus genus) + E. turcicum; T2: isolate 2 (Corynebacterium genus) + E. turcicum; T3: isolate 3 (Pantoea genus) + E. turcicum; T4: isolate 4 (Corynebacterium genus) + E. turcicum; T5: isolate 5 (Pantoea genus) + E. turcicum; T6: isolate 6 (Bacillus genus) + E. turcicum; T7: isolate 7 (Bacillus genus) + E. turcicum; T8: isolate 8 (Bacillus genus) + E. turcicum. Monitoring of antagonists on the phyllosphere was performed at different times. Furthermore, the percentage of infected leaves and, plant and leaf incidence were determined. Foliar application of different bacteria significantly reduced the leaf blight between 30-78% and 39-56% at 20 and 39 days respectively. It was observed that in the V10 stage of maize plants, isolate 8 (Bacillus spp.) caused the greatest effect on reducing the severity of northern leaf blight. Moreover, isolate 8 was the potential BCA that showed more stability in the phyllosphere. At 39 days, all potential biocontrol agents had a significant effect on controlling the disease caused by E. turcicum.

Se evaluó a 8 potenciales agentes de control biológico (ACB) en un ensayo in planta, con el objetivo de probar su efectividad en la reducción del daño provocado por Exserohilum turcicum, agente causal del tizón foliar del maíz. El ensayo se llevó a cabo en invernadero. Plantas de maíz de 26 días, en estadio fenológico V4, se inocularon con los potenciales antagonistas por aplicación foliar como espray. Solo un agente de biocontrol fue usado por tratamiento y todos los tratamientos se inocularon con E. turcicum 10 días después, también por aplicación foliar. Los tratamientos desarrollados fueron los siguientes: C-Et: control de E. turcicum; T1: aislamiento 1 (género Enterococcus) + E. turcicum; T2: aislamiento 2 (género Corynebacterium) + E. turcicum; T3: aislamiento 3 (género Pantoea) + E. turcicum; T4: aislamiento 4 (género Corynebacterium) + E. turcicum; T5: aislamiento 5 (género Pantoea) + E. turcicum; T6: aislamiento 6 (género Bacillus) + E. turcicum; T7: aislamiento 7 (género Bacillus) + E. turcicum; T8: aislamiento 8 (género Bacillus) + E. turcicum. La monitorización en la filosfera de los antagonistas se llevó a cabo a diferentes tiempos. Además, se determinó el porcentaje de hojas infectadas y la incidencia en plantas y hojas. La aplicación foliar de diferentes bacterias redujo significativamente la gravedad del tizón del maíz: entre el 30 y el 78% a los 20 días y entre el 39 y el 56% a los 39 días. En el estadio V10 de las plantas de maíz se observó que el aislamiento 8 (Bacillus spp.) causó el mayor efecto de reducción del tizón foliar. Además, dicho aislamiento fue el potencial agente de biocontrol que mostró mayor estabilidad en la filosfera. A los 39 días, todos los potenciales agentes de biocontrol demostraban un efecto significativo sobre el control de la enfermedad causada por E. turcicum.

Efficacy of epiphytic bacteria to prevent northern leaf blight caused by Exserohilum turcicum in maize.

Eight potential biological control agents (BCAs) were evaluated in planta in order to assess their effectiveness in reducing disease severity of northern leaf blight caused by Exserohilum turcicum. The assay was carried out in greenhouse. Twenty-six-day-old plants, V4 phenological stage, were inoculated with antagonists by foliar spray. Only one biocontrol agent was used per treatment. Ten days after this procedure, all treatments were inoculated with E. turcicum by foliar application. Treatments performed were: C-Et: control of E. turcicum; T1: isolate 1 (Enterococcus genus)+E. turcicum; T2: isolate 2 (Corynebacterium genus)+E. turcicum; T3: isolate 3 (Pantoea genus)+E. turcicum; T4: isolate 4 (Corynebacterium genus)+E. turcicum; T5: isolate 5 (Pantoea genus)+E. turcicum; T6: isolate 6 (Bacillus genus)+E. turcicum; T7: isolate 7 (Bacillus genus)+E. turcicum; T8: isolate 8 (Bacillus genus)+E. turcicum. Monitoring of antagonists on the phyllosphere was performed at different times. Furthermore, the percentage of infected leaves and, plant and leaf incidence were determined. Foliar application of different bacteria significantly reduced the leaf blight between 30-78% and 39-56% at 20 and 39 days respectively. It was observed that in the V10 stage of maize plants, isolate 8 (Bacillus spp.) caused the greatest effect on reducing the severity of northern leaf blight. Moreover, isolate 8 was the potential BCA that showed more stability in the phyllosphere. At 39 days, all potential biocontrol agents had a significant effect on controlling the disease caused by E. turcicum.

Evaluation of the control ability of five essential oils against Aspergillus section Nigri growth and ochratoxin A accumulation in peanut meal extract agar conditioned at different water activities levels.

Essential oils (EOs) from boldo [Pëumus boldus Mol.], poleo [Lippia turbinata var. integrifolia (Griseb.)], clove [Syzygium aromaticum L.], anise [Pimpinella anisum] and thyme [Thymus vulgaris]) obtained by hydrodistillation were evaluated for their effectiveness against the growth of Aspergillus niger aggregate and A. carbonarius and accumulation of ochratoxin A (OTA). The evaluation was performed by compound dissolution at the doses of 0, 500, 1500 and 2500µL/L in peanut meal extract agar (PMEA) and exposure to volatiles of boldo, poleo (0, 1000, 2000 and 3000µL/L) and clove oils (0, 1000, 3000 and 5000µL/L), taking into account the levels of the water activity of the medium (a(W) 0.98, 0.95, 0.93). Statistical analyses on growth of Aspergillus strains indicated that the major effect was produced by oil concentrations followed by substrate a(W), and that reductions in antifungal efficiency of the oils tested were observed in vapor exposure assay. At all a(W) levels, complete fungal growth inhibition was achieved with boldo EO at doses of 1500 and 2000µL/L by contact and volatile assays, respectively. Contact exposure by poleo and clove EOs showed total fungal inhibition at the middle level tested of 1500µL/L, regardless of a(W), while their antifungal effects in headspace volatile assay were closely dependent on medium a(W). The fumigant activity of poleo (2000µL/L) and clove oils (3000µL/L) inhibited growth rate by 66.0% and 80.6% at a(W) 0.98 and 0.93, respectively. OTA accumulation was closely dependent on a(W) conditions. The antiochratoxigenic property of the volatile fractions of boldo, poleo and clove EOs (1000µL/L) was more significant at low a(W) levels, inhibition percentages were estimated at 14.7, 41.7 and 78.5% at a(W) 0.98, 0.95 and 0.93, respectively. Our results suggest that boldo, poleo and clove oils affect the OTA biosynthesis pathway of both Aspergillus species. This finding leaves open the possibility of their use by vapor exposure as effective non-toxic biopreservatives against OTA contamination in stored peanuts.

Postharvest control of peanut Aspergillus section Flavi populations by a formulation of food-grade antioxidants.

The effect of a formulation containing butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl paraben (PP) on total mycoflora and Aspergillus section Flavi populations in natural and inoculated stored peanuts was evaluated. A survey of 480 peanut samples was carried out from July to December 2006. Two experimental units (silos 1 and 2) contained 200 kg of natural peanuts, while the other two (silos 3 and 4) had 200 kg of peanuts inoculated with Aspergillus flavus/A. parasiticus mixture (2 x 10(4) spores g(-1)). Silos 2 and 4 were treated with BHA-PP-BHT mixture (1802+1802+2204 microg g(-1)). Fungal counts were significantly affected (P<0.001) by Aspergillus section Flavi inoculum, tissue type, sampling period, antioxidant treatment and their interactions. Penicillium, Aspergillus and Fusarium spp. were the most common genera identified from both peanut tissues. Aspergillus flavus was the most frequently isolated species and there were significant differences (P<0.05) between its population in the control and treated peanuts. No aflatoxins were detected in any of the control or treated samples during storage. The development of natural peanut mycoflora and particularly Aspergillus section Flavi populations was inhibited by the ternary mixture of food-grade antioxidants.

Antiaflatoxigenic property of food grade antioxidants under different conditions of water activity in peanut grains.

Analytical grade (AG) and industrial grade (IG) of three-food grade antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and propyl paraben (PP) were analyzed to prove their fungitoxic effect on Aspergillus section Flavi strains. The effect of interactions among 10 antioxidant treatments at water activity levels (0.982, 0.955, 0.937 a(W)) for 11 and 35 days of incubation and at 25 degrees C in peanut grains on mycelial growth (CFU g(-1)) and aflatoxin B(1) (AFB(1)) accumulation were evaluated. Both antioxidant grade treatments had a significant effect (P<0.001) on fungal count. All antioxidant treatments showed the highest effectiveness on control of growth of peanut aflatoxigenic strains at 0.937 a(W) and at 11 days of incubation. Overall, AG and IG binary mixtures M3 (20+10 mM), M4 (20+20 mM) and ternary mixtures M5 (10+10+10 mM), M6 (10+20+10 mM), M7 (20+10+10 mM) and M8 (20+20+10 mM) were the treatments most effective at inhibiting growth of Aspergillus section Flavi strains. Industrial grade BHA 10 and 20 mM, binary mixtures M1 (10+10 mM), M2 (10+20 mM), M3 (20+10 mM), M4 (20+20 mM) and ternary mixtures M5 (10+10+10 mM), M6 (10+20+10 mM), M7 (20+10+10 mM) and M8 (20+20+10 mM) completely inhibited AFB(1) production. The studied results suggest that IG antioxidant mixtures have potential for controlling growth of these mycotoxigenic species and prevent aflatoxin accumulation at the peanut storage system.