BackgroundWithin-field multiple crop species intercropping is well documented and used for disease control, but the underlying mechanisms are still unclear. As roots are the primary organ for perceiving signals in the soil from neighboring plants, root behavior may play an important role in soil-borne disease control.Principal FindingsIn two years of field experiments, maize/soybean intercropping suppressed the occurrence of soybean red crown rot, a severe soil-borne disease caused by Cylindrocladium parasiticum (C. parasiticum). The suppressive effects decreased with increasing distance between intercropped plants under both low P and high P supply, suggesting that root interactions play a significant role independent of nutrient status. Further detailed quantitative studies revealed that the diversity and intensity of root interactions altered the expression of important soybean PR genes, as well as, the activity of corresponding enzymes in both P treatments. Furthermore, 5 phenolic acids were detected in root exudates of maize/soybean intercropped plants. Among these phenolic acids, cinnamic acid was released in significantly greater concentrations when intercropped maize with soybean compared to either crop grown in monoculture, and this spike in cinnamic acid was found dramatically constrain C. parasiticum growth in vitro.ConclusionsTo the best of our knowledge, this study is the first report to demonstrate that intercropping with maize can promote resistance in soybean to red crown rot in a root-dependent manner. This supports the point that intercropping may be an efficient ecological strategy to control soil-borne plant disease and should be incorporated in sustainable agricultural management practices.

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Background Soybean red crown rot is a major soil-borne disease all over the world, which severely affects soybean production. Efficient and sustainable methods are strongly desired to control the soil-borne diseases. Principal Findings We firstly investigated the disease incidence and index of soybean red crown rot under different phosphorus (P) additions in field and found that the natural inoculation of rhizobia and arbuscular mycorrhizal fungi (AMF) could affect soybean red crown rot, particularly without P addition. Further studies in sand culture experiments showed that inoculation with rhizobia or AMF significantly decreased severity and incidence of soybean red crown rot, especially for co-inoculation with rhizobia and AMF at low P. The root colony forming unit (CFU) decreased over 50% when inoculated by rhizobia and/or AMF at low P. However, P addition only enhanced CFU when inoculated with AMF. Furthermore, root exudates of soybean inoculated with rhizobia and/or AMF significantly inhibited pathogen growth and reproduction. Quantitative RT-PCR results indicated that the transcripts of the most tested pathogen defense-related (PR) genes in roots were significantly increased by rhizobium and/or AMF inoculation. Among them, PR2 , PR3 , PR4 and PR10 reached the highest level with co-inoculation of rhizobium and AMF. Conclusions Our results indicated that inoculation with rhizobia and AMF could directly inhibit pathogen growth and reproduction, and activate the plant overall defense system through increasing PR gene expressions. Combined with optimal P fertilization, inoculation with rhizobia and AMF could be considered as an efficient method to control soybean red crown rot in acid soils.

Bio-oil from the catalytic pyrolysis of algae biomass is an attractive energy source. To improve algae bio-oil properties for cofeeding applications in conventional oil refineries, bimetallic Ni–Cu/ZrO2 catalysts, with various Cu/Ni ratios (0.14 to 1.00 w/w) at a fixed total metal loading of 22 wt %, were synthesized and used for hydrodeoxygenation (HDO) of bio-oils via the catalytic pyrolysis of Chlorella and Nannochloropsis sp. at 350 °C and a hydrogen pressure of 2 MPa in a trickle-bed reactor. It was found that the Ni–Cu/ZrO2 catalysts were more attractive than Ni/ZrO2 catalysts in HDO, as the addition of copper could facilitate the reduction of nickel oxide. As the loading of Cu increased, the HDO efficiency of the Ni–Cu/ZrO2 catalyst for crude bio-oil increased and thereafter decreased. The 15.71Ni6.29Cu/ZrO2 catalyst showed the highest activity, with an HDO efficiency of 82% for Chlorella bio-oil. Moreover, the Ni–Cu/ZrO2 catalyst was stable with low sintering and little coking according to transmission electron microscopy (TEM), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) of the catalysts before and after reaction. In addition, this catalyst exhibited the favorable properties of product bio-oils. In particular, the cetane number of the upgraded bio-oil from Nannochloropsis sp. reached the EN 590-09 standard (specification of diesel fuel for vehicles).

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