Reducing plant pathogens could increase crop yields after plastic film mulching.

Soil fungi are closely associated with crop growth in agricultural ecosystems through processes such as nutrient uptake and pathogenesis. Plastic film mulching (PM) plays a dominant role in increasing crop yields in dryland agriculture worldwide. The functional guilds of soil fungi under PM and their effects on crops remain unclear. In this study, we explored the absolute abundance, diversity, community composition, and functional guilds of soil fungi after short-term (2 years) and long-term (10 years) mulching experiments. Short-term mulching caused a 37 %-51 % decrease in absolute fungal abundance owing to abrupt changes in the microenvironment. The response of the fungal community to PM varied with sites, with the effect being more pronounced under poor hydrothermal conditions (314 mm). The abundance of potential fungal pathogens decreased under PM; for example, Gibberella (maize ear rot) abundance was 45 % and 72 % lower under short- and long-term mulching, respectively, when compared with that in control. In contrast, the abundance of plant biocontrol fungi increased under PM; for instance, Glomeromycota abundance increased twofold under long-term mulching. Although PM did not alter the complexity and stability of fungal co-occurrence network, competition among fungi increased in the absence of sufficient carbon (C) sources. Long-term mulching reduced phytopathogen guilds by 12 %-77 % and increased arbuscular mycorrhizal fungi (AMF) guilds by 89 %-94 %. Structural equation modeling suggested that PM altered fungal functional guilds mainly by shaping the structure of the fungal community, and fungal pathogens decreased with increased AMF functional guilds, inducing higher maize yields. These results showed for the first time, from a microbial perspective, that pathogens reduction owing to PM could explain 4.4 % of maize yield variation, providing theoretical guidance to accomplish sustainability of continuous maize mulching.

Allelochemicals from the Rhizosphere Soil of Potato (Solanum tuberosum L.) and Their Interactions with the Soilborne Pathogens.

To reveal the allelopathic effects of potato, seven compounds were isolated from the rhizosphere soil: 7-methoxycoumarin (1), palmitic acid (2), caffeic acid (3), chlorogenic acid (4), quercetin dehydrate (5), quercitrin (6), and rutin (7). Bioassays showed that compounds 1, 2, 4, and 6 had inhibitory effects on the growth of L. sativa and tissue culture seedlings of potato. The existence of the allelochemicals was confirmed by HPLC, and their contents were quantified with a total concentration of 9.02 µg/g in the rhizosphere soil of replanted potato. Approaches on the interactions of the allelochemicals and pathogens of potato including A. solani, B. cinerea, F. solani, F. oxysporum, C. coccodes, and V. dahlia revealed that compound 1 had inhibitory effects but compounds 2-4 promoted the colony growth of the pathogens. These findings demonstrated that the autotoxic allelopathy and enhancement of the pathogens caused by the accumulation of the allelochemicals in the continuously cropped soil should be one of the main reasons for the replant problems of potato.

Identification of Pathogenic Fusarium spp. Responsible for Root Rot of Angelica sinensis and Characterization of Their Biological Enemies in Dingxi, China.

Root rot is a serious disease in plantations of Angelica sinensis, severely reducing yield and quality and threatening sustainable production. Fusarium isolates (n = 32) were obtained from field samples of root rot tissue, leaves, and infected soil. Isolates were identified by comparison of the sequences of their internal transcribed spacer region and translation elongation factor 1-α to sequences of known species in the National Center for Biotechnology Information database. These Fusarium isolates include Fusarium tricinctum (43.75%), F. equiseti (31.25%), F. solani (9.37%), F. oxysporum (6.25%), F. acuminatum (6.25%), and F. incarnatum (3.12%). For pathogenicity testing under greenhouse conditions, seven isolates were selected based on a phylogenetic analysis, including four strains of F. tricinctum and one strain each of F. solani, F. oxysporum, and F. acuminatum. The seven isolates were all pathogenic but differed in their ability to infect: The four F. tricinctum strains were capable of causing root rot in A. sinensis at 100% incidence and were highly aggressive. Furthermore, the symptoms of root rot induced by those seven isolates were consistent with typical root rot cases in the field, but their disease severity varied. Observed histopathological preparations of F. tricinctum-infected seedlings and tissue slide results showed that this fungal species can penetrate epidermal cells and colonize the cortical cells where it induces necrosis and severe plasmolysis. Plate confrontation experiments showed that isolated rhizosphere bacteria inhibited the Fusarium pathogens that cause root rot in A. sinensis. Our results provide timely information about the use of biocontrol agents for suppression of root rot disease.

Bacillus amyloliquefaciens Rescues Glycyrrhizic Acid Loss Under Drought Stress in Glycyrrhiza uralensis by Activating the Jasmonic Acid Pathway.

Drought is a major factor limiting the production of the perennial medicinal plant Glycyrrhiza uralensis Fisch. (Fabaceae) in Northwest China. In this study, 1-year-old potted plants were inoculated with the strain Bacillus amyloliquefaciens FZB42, using a gradient of concentrations (CFU), to test for microbe-induced host tolerance to drought condition treatments in a greenhouse experiment. At the concentration of 108 CFU ml-1, FZB42 had significant growth-promoting effect on G. uralensis: the root biomass was 1.52, 0.84, 0.94, and 0.38 times that under normal watering and mild, moderate, and severe drought stress conditions, respectively. Under moderate drought, the positive impact of FZB42 on G. uralensis growth was most pronounced, with both developing axial and lateral roots strongly associated with indoleacetic acid (IAA) accumulation. An untargeted metabolomic analysis and physiological measurements of mature roots revealed that FZB42 improved the antioxidant system of G. uralensis through the accumulation of proline and sucrose, two osmotic adjustment solutes, and by promoting catalase (CAT) activity under moderate drought stress. Furthermore, significantly higher levels of total flavonoids, liquiritin, and glycyrrhizic acid (GA), the pharmacologically active substances of G. uralensis, were found in the roots of inoculated plants after FZB42 inoculation under all imposed drought conditions. The jasmonic acid (JA) content, which is closely related to plant defense responses and secondary metabolites' production, was greatly increased in roots after the bacterial inoculations, indicating that FZB42 activated the JA pathway. Taken together, our results demonstrate that inoculation with FZB42 alleviates the losses in production and pharmacological metabolites of G. uralensis caused by drought via the JA pathway's activation. These results provide a developed prospect of a microbial agent to improve the yield and quality of medical plants in arid and semi-arid regions.