Carbohydrate and lipid balances in the positive plant phenotypic response to arbuscular mycorrhiza: increase in sink strength.

The exchange of phosphorus (P) and carbon (C) between plants and arbuscular mycorrhizal fungi (AMF) is a major determinant of their mutualistic symbiosis. We explored the C dynamics in tomato (Solanum lycorpersicum) inoculated or not with Rhizophagus irregularis to study their growth response under different NaH2 PO4 concentrations (Null P, 0 mM; Low P, 0.065 mM; High P, 1.3 mM). The percentage of AMF colonization was similar in plants under Null and Low P, but severely reduced under High P. However, the AMF mass biomarker 16:1ω5 revealed higher fungal accumulation in inoculated roots under Low P, while more AMF spores were produced in the Null P. Under High P, AMF biomass and spores were strongly reduced. Plant growth response to mycorrhiza was negative under Null P, showing reduction in height, biovolume index, and source leaf (SL) area. Under Low P, inoculated plants showed a positive response (e.g., increased SL area), while inoculated plants under High P were similar to non-inoculated plants. AMF promoted the accumulation of soluble sugars in the SL under all fertilization levels, whereas the soluble sugar level decreased in roots under Low P in inoculated plants. Transcriptional upregulation of SlLIN6 and SlSUS1, genes related to carbohydrate metabolism, was observed in inoculated roots under Null P and Low P, respectively. We conclude that P-limiting conditions that increase AMF colonization stimulate plant growth due to an increase in the source and sink strength. Our results suggest that C partitioning and allocation to different catabolic pathways in the host are influenced by AMF performance.

Arsenic and mercury tolerant rhizobacteria that can improve phytoremediation of heavy metal contaminated soils.

Background: Mining deposits often contain high levels of toxic elements such as mercury (Hg) and arsenic (As) representing strong environmental hazards. The purpose of this study was the isolation for plant growth promoting bacteria (PGPBs) that can improve phytoremediation of such mine waste deposits. Methods: We isolated native soil bacteria from the rhizosphere of plants of mine waste deposits and agricultural land that was previously mine tailings from Tlalpujahua Michoacán, Mexico, and were identified by their fatty acid profile according to the MIDI Sherlock system. Plant growth promoting traits of all bacterial isolates were examined including production of 3-indoleacetic acid (IAA), siderophores, biofilm formation, and phosphate solubilization. Finally, the response of selected bacteria to mercury and arsenic was examined an in-vitro assay. Results: A total 99 bacterial strains were isolated and 48 identified, representing 34 species belonging to 23 genera. Sixty six percent of the isolates produced IAA of which Pseudomonas fluorescens TL97 produced the most. Herbaspirillum huttiense TL36 performed best in terms of phosphate solubilization and production of siderophores. In terms of biofilm formation, Bacillus atrophaeus TL76 was the best. Discussion: Most of the bacteria isolates showed high level of tolerance to the arsenic (as HAsNa2O4 and AsNaO2), whereas most isolates were susceptible to HgCl2. Three of the selected bacteria with PGP traits Herbispirillum huttiense TL36, Klebsiella oxytoca TL49 and Rhizobium radiobacter TL52 were also tolerant to high concentrations of mercury chloride, this might could be used for restoring or phytoremediating the adverse environmental conditions present in mine waste deposits.

Cellulase and chitinase activities and antagonism against Fusarium oxysporum f.sp. cubense race 1 of six Trichoderma strains isolated from Mexican maize cropping.

OBJECTIVE: To evaluate the enzymatic and biocontrol capacity of native Trichoderma strains isolated from corn crops in Irapuato (state of Guanajuato) and Napízaro (state of Michoacán), Mexico. RESULTS: Six native strains from Irapuato and Napízaro were tested, with five of them identified as T. harzianum and one as T. tomentosum. The six strains qualitatively and quantitatively showed enzyme activity for cellulase and chitinase. The best results were obtained for strains IrV6SIC7 and MichV6S2C2 with 878 IU L-1 of chitinase and 1323 IU L-1 of cellulase, respectively. All Trichoderma strains acted antagonistically toward Fusarium oxysporum f.sp. cubense race 1 (FocR1), with percentages of inhibition that ranged from 9 to 54%. In addition, the microscopic analysis allowed visualizing the mechanisms of mycoparasitism and antibiosis by either IrV6SIC7 or MichV6S2C2. The latter effects indicate that the tested native Trichoderma strains isolated from corn crops possessed enzymatic mechanisms as a strategy for biocontrolling FocR1 strains. CONCLUSION: The enzyme production by the Trichoderma strains represents a potential biotechnological utilization for either agricultural or industrial purposes.

Maize mycorrhizas decrease the susceptibility of the foliar insect herbivore Spodoptera frugiperda to its homologous nucleopolyhedrovirus.

BACKGROUND: The multiple nucleopolyhedrovirus of Spodoptera frugiperda (SfMNPV) plays an important role in regulating its natural host and has high potential for use as a bioinsecticide. However, information about how agricultural practices such as fertilization and plant biotic interactions affect the biocontrol efficacy of SfMNPV is limited. In this study, we examined how multitrophic maize-mycorrhiza-insect herbivore interactions affect the biocontrol efficacy of SfMNPV against S. frugiperda under full and reduced mineral nitrogen fertilization. Two fully factorial greenhouse pot experiments with three factors were performed: (i) arbuscular mycorrhizal fungi (AMF) (with and without AMF), (ii) nitrogen fertilization (50% and 100% N), and (iii) insect (with and without of S. frugiperda). The biocontrol efficacy of SfMNPV against S. frugiperda was examined using detached leaves under controlled environmental conditions. RESULTS: Associating maize with AMF resulted in multitrophic cascade effects. Plants with AMF showed suppression of plant growth and increased leaf N and P content, which coincided with increased foliar herbivory and larval biomass that finally reduced the susceptibility of S. frugiperda to SfMNPV. Reduced levels of N fertilization mitigated these observed cascade effects on the biocontrol efficacy of SfMNPV with maize mycorrhizas. CONCLUSION: Our results show that AMF can modulate S. frugiperda-SfMNPV interactions via plant-mediated phenotypic responses to the mycorrhizal association and are most likely linked with increased leaf food quality for S. frugiperda. These results call for further studies to address the mode of interaction and possible implications for pest management in maize agroecosystems. © 2021 Society of Chemical Industry.

In a belowground multitrophic interaction, Trichoderma harzianum induces maize root herbivore tolerance against Phyllophaga vetula.

BACKGROUND: Trichoderma spp. are soil fungi that interact with plant roots and associated biota such as other microorganisms and soil fauna. However, information about their interactions with root-feeding insects is limited. Here, interactions between Trichoderma harzianum and the root-feeding insect Phyllophaga vetula, a common insect pest in maize agroecosystems, were examined. RESULTS: Applications of T. harzianum and P. vetula to the root system increased and decreased maize growth, respectively. Induced tolerance against herbivore attack was provided by T. harzianum maintaining a robust and functional root system as evidenced by the increased uptake of Cu, Ca, Mg, Na and K. Herbivore tolerance also coincided with changes in the emission of root volatile terpenes known to induce indirect defense responses and attract natural enemies of the herbivore. More importantly, T. harzianum induced de novo emission of several sesquiterpenes such as ß-caryophyllene and δ-cadinene. In addition, single and combined applications of T. harzianum and P. vetula altered the sucrose content of the roots. Finally, T. harzianum produced 6-pentyl-2H-pyran-2-one (6-PP) a volatile compound that may act as an antifeedant-signaling compound mitigating root herbivory by P. vetula. CONCLUSION: Our results provide novel information about belowground multitrophic plant-microbe-arthropod interactions between T. harzianum and P. vetula in the maize rhizosphere resulting in alterations in maize phenotypic plant responses, inducing root herbivore tolerance.

Increased maize growth and P uptake promoted by arbuscular mycorrhizal fungi coincide with higher foliar herbivory and larval biomass of the Fall Armyworm Spodoptera frugiperda.

Most plant species naturally associate with arbuscular mycorrhizal fungi (AMF), which are known to promote crop nutrition and health in agroecosystems. However, information on how mycorrhizal associations affect plant biotic interactions that occur aboveground with foliar herbivores is limited and needs to be further addressed for the development of pest management strategies. With the objective to examine the influence of maize mycorrhizas on foliar herbivory caused by larvae of Spodoptera frugiperda, a serious pest in maize agroecosystems, we performed a fully factorial greenhouse pot experiment with three factors: Maize genotype (Puma and Milpal H318), AMF (with and without AMF, and without AMF with mineral P) and Insect herbivory (with and without S. frugiperda). Main results showed that inoculation with AMF improved plant growth and foliar P concentration, which coincided with increased foliar damage from herbivory and higher biomass of S. frugiperda larvae. A significant positive correlation between shoot P concentration and larval biomass was also observed. Finally, foliar herbivory by S. frugiperda slightly increased and decreased AMF root colonization in Puma and H318, respectively. In conclusion, our results show that maize plant benefits from AMF in terms of promotion of growth and nutrition, and may also increase the damage caused from insects by improving the food quality of maize leaves for larval growth, which seems to be linked to increased P uptake by the maize mycorrhizal association.

Bacillus cabrialesii sp. nov., an endophytic plant growth promoting bacterium isolated from wheat (Triticum turgidum subsp. durum) in the Yaqui Valley, Mexico.

Strain TE3T, an endophytic plant growth promoting bacterium, was isolated from wheat (Triticumturgidum subsp. durum) sampled in the Yaqui Valley, Mexico. Biochemical, phenotypic and genotypic approaches were used to clarify the taxonomic affiliation of this strain. Based on analysis of its full-length 16S rRNA gene, strain TE3T was assigned to the genus Bacillus (similarity ≥98.7 %). This finding was supported by morphological and metabolic characteristics, such as rod shape, strictly aerobic metabolism, spore formation, Gram-positive staining, catalase-positive activity, reduction of nitrate to nitrite, starch and casein hydrolysis, growth in presence of lysozyme and 2 % NaCl, citrate utilization, growth pH from 6.0 to 8.0, and acid and indole production from glucose and tryptophan, respectively. The whole-genome phylogenetic relationship showed that TE3T formed an individual clade with Bacillus tequilensis KCTC 13622T, distant from that generated by all Bacillus subtilis subspecies. The maximum values for average nucleotide identity and in silico DNA-DNA hybridization were 93.85 and 54.30 %, respectively, related to Bacillus subtilissubsp. inaquosorum KCTC 13429T. Analysis of its fatty acid content showed the ability of strain TE3T to bio-synthetize fatty acids that are not present in closely related Bacillus species, such as C12 : 0, C12 : 0 2OH, C12 : 0 3OH, C17 : 0, iso-C17 : 0 3OH and C18 : 1ω9c. These results provide evidence that strain TE3T is a novel species of the genus Bacillus, for which the name Bacilluscabrialesii sp. nov. is proposed. The type strain of Bacilluscabrialesii is TE3T (CM-CNRG TB54T=CCStamb A1T).

Alterations in honey bee gut microorganisms caused by Nosema spp. and pest control methods.

BACKGROUND: Honey bees are associated with gut microorganisms essential for their nutrition and health. The composition of the microbial community can be used as a biological health indicator and is characterized using biomarker fatty acids. Commonly, gut microorganisms are exposed to pathogens and to an array of chemical and biological pest control methods. RESULTS: We found a strong negative effect on microbial gut community composition when exposed to the bee pest control chemicals oxytetracycline, oxalic acid and imidacloprid, and when inoculated with the bee pest Nosema spp. and the potential bee pest biocontrol agent Lactobacillus plantarum. Results from the in vitro test with bee pest chemicals showed a differential response of Lactobacillus spp. At the community level, some taxonomic groups were more affected depending on treatment, but sharp changes in the microbial structure were caused by compounds generally considered as bee safe. CONCLUSION: Our results show that pests such as Nosema spp. and pest control methods alter the composition of bee gut microorganisms, which may have severe consequences for pathogen defense, physiology and general honey bee health. In addition, L. plantarum has potential as a biocontrol agent against Nosema spp. © 2018 Society of Chemical Industry.