Effect of Inoculation with Arbuscular Mycorrhizal Fungi and Fungicide Application on the Secondary Metabolism of Solanum tuberosum Leaves

Arbuscular mycorrhizal fungi promote growth and enhance the accumulation of bioactive compounds in Tomato (Solanum lycopersicum L.)

Arbuscular mycorrhizal fungi (AMF) have been known to enhance plant growth and nutrient uptake. In this study, we investigated the effects of Funneliformis mosseae, Rhizophagus intraradices, and their co-inoculation on the growth and biochemical composition of tomato (Solanum lycopersicum L.) plants. The findings demonstrated that the inoculation of AMF significantly enhanced shoot and root length, shoot and root dry weight, number of fruits per plant, as well as concentrations of anthocyanin, phenolic compounds, and antioxidants in tomato plants. Both individual and co-inoculation of AMF also significantly increased nitrogen, phosphorus, and potassium concentrations in tomato plants. Our findings suggest that AMF can be used as a potential biofertilizer to enhance the growth and biochemical composition of tomato plants.

Physiological and Enzymatic Antioxidant Responses of Solanum tuberosum Leaves to Arbuscular Mycorrhizal Fungal Inoculation under Water Stress

Solanum tuberosum is one of the most widely cropped plant species worldwide; unfortunately, drought is one of the major constraints on potato productivity because it affects the physiology, biochemical processes, and yield. The use of arbuscular mycorrhizal fungi (AMF) has exhibited beneficial effects on plants during drought. The objective of this study was to analyse the effect of AMF inoculation on two genotypes of potato plants exposed to water stress, and the photosynthetic traits, enzymatic antioxidant activity, and exudation of low-molecular-weight organic acids (LMWOAs) of potato plants inoculated with two strains of AMF, Claroideoglomus claroideum (CC) and Claroideoglomus lamellosum (HMC26), were evaluated. Stomatal conductance exhibited a similar trend in the CC and HMC26 treatments for both potato genotypes; moreover, the photosynthetic rate significantly increased by 577.9% between the 100% soil humidity (S0) and 40% soil humidity (S2) stress levels for the VR808 genotype under the CC treatment. The activities of the enzymes catalase (CAT) and ascorbate peroxidase (APX) showed similar trends. In this study, there were different responses among genotypes and treatments. Inoculation with CC under S2 stress levels is a promising potential approach for improving potato growth under drought conditions.

Enhancing Water Status and Nutrient Uptake in Drought-Stressed Lettuce Plants (Lactuca sativa L.) via Inoculation with Different Bacillus spp. Isolated from the Atacama Desert

Drought is a major challenge for agriculture worldwide, being one of the main causes of losses in plant production. Various studies reported that some soil's bacteria can improve plant tolerance to environmental stresses by the enhancement of water and nutrient uptake by plants. The Atacama Desert in Chile, the driest place on earth, harbors a largely unexplored microbial richness. This study aimed to evaluate the ability of various Bacillus sp. from the hyper arid Atacama Desert in the improvement in tolerance to drought stress in lettuce (Lactuca sativa L. var. capitata, cv. "Super Milanesa") plants. Seven strains of Bacillus spp. were isolated from the rhizosphere of the Chilean endemic plants Metharme lanata and Nolana jaffuelii, and then identified using the 16s rRNA gene. Indole acetic acid (IAA) production, phosphate solubilization, nitrogen fixation, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity were assessed. Lettuce plants were inoculated with Bacillus spp. strains and subjected to two different irrigation conditions (95% and 45% of field capacity) and their biomass, net photosynthesis, relative water content, photosynthetic pigments, nitrogen and phosphorus uptake, oxidative damage, proline production, and phenolic compounds were evaluated. The results indicated that plants inoculated with B. atrophaeus, B. ginsengihumi, and B. tequilensis demonstrated the highest growth under drought conditions compared to non-inoculated plants. Treatments increased biomass production and were strongly associated with enhanced N-uptake, water status, chlorophyll content, and photosynthetic activity. Our results show that specific Bacillus species from the Atacama Desert enhance drought stress tolerance in lettuce plants by promoting several beneficial plant traits that facilitate water absorption and nutrient uptake, which support the use of this unexplored and unexploited natural resource as potent bioinoculants to improve plant production under increasing drought conditions.

Antioxidant Response, Phenolic Compounds and Yield of Solanum tuberosum Tubers Inoculated with Arbuscular Mycorrhizal Fungi and Growing under Water Stress

Solanum tuberosum (potato) is one of the most common crops worldwide; however, it is sensitive to water stress, which necessitates the identification of alternative tools to improve their production. Here, we evaluated the inoculation of two arbuscular mycorrhizal fungi (AMF) strains, Claroideoglomus claroideum (CC), Claroideoglomus lamellosum (HMC26), and the MIX (CC + HMC26) in yield and phenolic and antioxidant response using chromatographic and spectroscopic methods in potato crops, at increasing levels of water stress, namely, with 100% (0), 70% (S1), and 40% (S2) soil humidity. Two caffeoylquinic acid isomers were detected and their levels showed a tendency to increase under stress together with the AMF inoculation, reaching up to 19.2 mg kg-1 of 5-caffeoylquinic acid and 7.4 mg kg-1 of caffeoylquinic acid isomer when CC was inoculated, and potato plants grew at the highest water starvation condition (S2). Regarding antioxidant activities, a differentiated response was detected depending on the AMF strain, highlighting the effect of HMC26 on Trolox equivalent antioxidant capacity (TEAC) method and CC in cupric reducing antioxidant capacity (CUPRAC) method, reaching up to 1.5 μmol g-1 of TEAC in plants inoculated with HMC26 and 0.9 μmol g-1 of CUPRAC in plants inoculated with CC, both in potato tubers of plants growing under the S2 stress condition. Meanwhile, the use of AMF did not influence the number and biomass of the tubers, but significant changes in the biochemical properties of tubers were observed. The results suggest that specific AMF adaptations to water stress must be considered when inoculation procedures are planned to improve the yield and quality of tubers in potato crops.

The Impact of 2-Ketones Released from Solid Lipid Nanoparticles on Growth Modulation and Antioxidant System of Lactuca sativa

2-Ketones are signal molecules reported as plant growth stimulators, but their applications in vegetables have yet to be achieved. Solid lipid nanoparticles (SLNs) emerge as a relevant nanocarrier to develop formulations for the controlled release of 2-ketones. In this sense, seedlings of Lactuca sativa exposed to 125, 375, and 500 µL L-1 of encapsulated 2-nonanone and 2-tridecanone into SLNs were evaluated under controlled conditions. SLNs evidenced a spherical shape with a size of 230 nm. A controlled release of encapsulated doses of 2-nonanone and 2-tridecanone was observed, where a greater release was observed as the encapsulated dose of the compound increased. Root development was strongly stimulated mainly by 2-tridecanone and leaf area (25-32%) by 2-nonanone. Chlorophyll content increased by 15.8% with exposure to 500 µL L-1 of 2-nonanone, and carotenoid concentration was maintained with 2-nonanone. Antioxidant capacity decreased (13-62.7%) in L. sativa treated with 2-ketones, but the total phenol concentration strongly increased in seedlings exposed to some doses of 2-ketones. 2-Tridecanone strongly modulates the enzymatic activities associated with the scavenging of H2O2 at intra- and extracellular levels. In conclusion, 2-ketones released from SLNs modulated the growth and the antioxidant system of L. sativa, depending on the dose released.

Evaluation of the Antifungal Potential of Grape Cane and Flesh-Coloured Potato Extracts against Rhizoctonia sp. in Solanum tuberosum Crops

Potato (Solanum tuberosum) is one of the most important food crops worldwide, and Rhizoctonia solani infection is one of the most common diseases. The objective of this study was to evaluate the antifungal activity of Vitis vinifera byproducts (VIDES) and flesh-coloured potato (FCP) extracts against Rhizoctonia sp. in potato crops. Photosynthetic traits, phenolic profiles, and antioxidant and enzymatic activities were determined. The VIDES extract showed a 151.4% improvement in stomatal conductance and a 258.5% improvement in the photosynthetic rate compared to the plants without infection. Regarding the enzymatic antioxidant activity, the best response was found in the FCP treatments with 30 min of application, with increases of 25%, 161%, and 450% in ascorbate peroxidase, catalase (CAT), and glutathione reductase (GR) activities, respectively, compared to plants without infection. For the VIDES extract, a 15 min application produced an 83% increase in CAT activity, whereas a 181% increase in GR activity compared to plants without infection was produced after a 30 min application. A similar behaviour was observed for antioxidant compounds, where FCP had a higher concentration of compounds and antioxidant activity. This finding suggests that FCP and VIDES promote the synthesis of plant-defence compounds against Rhizoctonia sp. in potato crops, in which the application time is a determining factor.

Inoculation with Actinobacteria spp. Isolated from a Hyper-Arid Environment Enhances Tolerance to Salinity in Lettuce Plants (Lactuca sativa L.)

Irrigated agriculture is responsible for a third of global agricultural production, but the overuse of water resources and intensification of farming practices threaten its sustainability. The use of saline water in irrigation has become an alternative in areas subjected to frequent drought, but this practice affects plant growth due to osmotic impact and excess of ions. Plant-growth-promoting rhizobacteria (PGPR) can mitigate the negative impacts of salinity and other abiotic factors on crop yields. Actinobacteria from the hyper-arid Atacama Desert could increase the plant tolerance to salinity, allowing their use as biofertilizers for lettuce crops using waters with high salt contents. In this work, rhizosphere samples of halophytic Metharme lanata were obtained from Atacama Desert, and actinobacteria were isolated and identified by 16S gene sequencing. The PGPR activities of phosphate solubilization, nitrogen fixation, and the production of siderophore and auxin were assessed at increasing concentrations of NaCl, as well as the enhancement of salt tolerance in lettuce plants irrigated with 100 mM of NaCl. Photosynthesis activity and chlorophyll content, proline content, lipid peroxidation, cation and P concentration, and the identification and quantification of phenolic compounds were assessed. The strains S. niveoruber ATMLC132021 and S. lienomycini ATMLC122021 were positive for nitrogen fixation and P solubilization activities and produced auxin up to 200 mM NaCl. In lettuce plants, both strains were able to improve salt stress tolerance by increasing proline contents, carotenoids, chlorophyll, water use efficiency (WUE), stomatal conductance (gs), and net photosynthesis (A), concomitantly with the overproduction of the phenolic compound dicaffeoylquinic acid. All these traits were positively correlated with the biomass production under saltwater irrigation, suggesting its possible use as bioinoculants for the agriculture in areas where the water resources are scarce and usually with high salt concentrations.

Characterization and control of Rhizoctonia solani affecting lucky bamboo (Dracaena sanderiana hort. ex. Mast.) using some bioagents

In a survey conducted during the period of March-May 2019 in nurseries, warehouses, and shops at three governorates (Alexandria, El-Behera, and Giza governorates, Egypt), symptoms of root rot, basal stem rot, and wilt disease complex were observed in the lucky bamboo (Dracaena sanderiana hort. ex. Mast.). The highest disease infection percentage was found in lucky bamboo collected from Alexandria City (47.67%), while the highest disease severity was in lucky bamboo collected from El-Behera Governorate (35.19%). Rhizoctonia solani, Fusarium oxysporum, F. solani, Aspergillus niger, and Alternaria alternate were isolated and identified in the infected lucky bamboo samples. R. solani isolates were the most dominant among the recovered fungal species with a percentage of 80.89% of the total isolates (246). Pathogenicity tests showed that R. solani was the most pathogen with 100% disease infection and 76.67% disease severity. Molecular identification characterized R. solani isolate as R. solani AUMC 15120, MZ723906. Meanwhile, four biological control agents (bioagents) were isolated from the healthy lucky bamboo samples and identified based on cultural, morphological, microscopic characteristics, and the molecular phylogenetic analysis as Clonostachys rosea AUMC 15121, OL461708; Bacillus circulans TAG1, MW441316; B. siamensis TAP1, MW441318 and Ochrobactrum anthropi TAM1, MW441317. The four bioagents showed potential inhibition of R. solani in vitro as well as in vivo on lucky bamboo plants in vase treatments compared to the untreated inoculated control as well as certain fungicides and biocides used (Moncut, Rizolex-T, Topsin-M, Bio-Zeid, and Bio-Arc). The bioagent O. anthropi showed the highest inhibition growth (85.11%) of the in vitro R. solani colony, which was not significantly different from the biocide Bio-Arc (83.78%). However, C. rosea, B. siamensis and B. circulans showed inhibition values of 65.33, 64.44, and 60.44%, respectively. On the other hand, the biocide Bio-Zeid showed less inhibitory effect (43.11%), while the lowest growth inhibition was recorded by Rizolex-T (34.22%) and Topsin-M (28.67%). Furthermore, the in vivo experiment supported the in vitro results for the most effective treatments, where all the treatments significantly decreased the percentage of infection and disease severity compared to the inoculated untreated control. Additionally, the bioagent O. anthropi showed the highest effect, i.e., the lowest disease incidence and disease severity being 13.33% and 10%, compared to 100% and 75%, respectively, in the untreated inoculated control. This was not significantly different from the fungicide Moncut (13.33% and 21%) and from the bioagent C. rosea (20% and 15%) treatments for both parameters, respectively. In conclusion, the bioagents O. anthropi MW441317 at 1 × 10⁸ CFU/ml as well as C. rosea AUMC15121 at 1 × 10⁷/ml proved to be efficient to control R. solani causing root rot, and basal stem rot on lucky bamboo, compared to fungicide Moncut and can be used for disease management without the negative impact of the chemical control. Furthermore, this is the first report of the isolation and identification of Rhizoctonia solani, a pathogenic fungus, and four biocontrol agents (Bacillus circulans, B. siamensis, Ochrobactrum anthropi and Clonostachys rosea) associated with the healthy lucky bamboo plants.

AMF species do matter: Rhizophagus irregularis and Funneliformis mosseae affect healthy and PVY-infected Solanum tuberosum L. in a different way

Arbuscular mycorrhizal fungi (AMF) were documented to positively influence plant growth and yield, which is extremely important for the production of many crops including potato. However, the nature of the interaction between arbuscular mycorrhiza and plant virus that share the same host is not well characterized. In this study, we examined the effect of different AMF, Rhizophagus irregularis and Funneliformis mosseae, on healthy and potato virus Y (PVY)-infected Solanum tuberosum L. The analyses conducted included the measurement of potato growth parameters, oxidative stress indicators, and photosynthetic capacity. Additionally, we evaluated both the development of AMF in plant roots and the virus level in mycorrhizal plants. We found that two AMF species colonized plant roots to varying degrees (ca. 38% for R. irregularis vs. 20% for F. mosseae). Rhizophagus irregularis had a more positive effect on potato growth parameters, causing a significant increase in the total fresh and dry weight of tubers, along with virus-challenged plants. Furthermore, this species lowered hydrogen peroxide levels in PVY-infected leaves and positively modulated the levels of nonenzymatic antioxidants, i.e., ascorbate and glutathione in leaves and roots. Finally, both fungal species contributed to reduced lipid peroxidation and alleviation of virus-induced oxidative damage in plant organs. We also confirmed an indirect interaction between AMF and PVY inhabiting the same host. The two AMF species seemed to have different abilities to colonize the roots of virus-infected hosts, as R. irregularis showed a stronger drop in mycorrhizal development in the presence of PVY. At the same time, arbuscular mycorrhiza exerted an effect on virus multiplication, causing increased PVY accumulation in plant leaves and a decreased concentration of virus in roots. In conclusion, the effect of AMF-plant interactions may differ depending on the genotypes of both symbiotic partners. Additionally, indirect AMF-PVY interactions occur in host plants, diminishing the establishment of arbuscular mycorrhiza while changing the distribution of viral particles in plants.