The Control of Fusarium Root Rot and Development of Coastal Pine (Pinus thunbergii Parl.) Seedlings in a Container Nursery by Use of Bacillus licheniformis MH48

The Prospect of Hydrolytic Enzymes from Bacillus Species in the Biological Control of Pests and Diseases in Forest and Fruit Tree Production

Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Bacillus amyloliquefaciens AK-12 Helps Rapeseed Establish a Protection against Brevicoryne brassicae

Aphids are a serious threat to rapeseed (Brassica napus L.) production, and cause unmanageable loss. Therefore, effective prevention and management strategies are urgently required to avoid losses. Bacillus amyloliquefaciens AK-12 isolated from a dead aphid with aphicidal activity was tagged with a green fluorescent protein through a natural transformation. The transformed strains were checked for stability and growth, and the best-performing strain was tested for its colonization inside and outside the rapeseed plant. The stability of AK-12-GFP reached more than 95%, and the growth curve was consistent with that of AK-12. After 30 days of treatment, the colonization of 1 × 106 CFU/g was recorded in rapeseed leaves. Interestingly, AK-12 reduced the aphid transmission rate compared with the control and improved the growth of the rapeseed seedlings. Meanwhile, the AK-12 strain also exhibited phosphorus, potassium-solubilizing, and nitrogen-fixing activity, and produced 2.61 µg/mL of IAA at 24 h. Regulation in the activity of four enzymes was detected after the AK-12 treatment. Phenylalanine ammonia lyase (PAL) was recorded at a maximum of 86.84 U/g after 36 h, and catalase (CAT) decreased after 48 h; however, peroxidase (POD) and polyphenol oxidase (PPO) reached the maximum within 12 h of AK-12 application. Additionally, important resistance genes related to these enzymes were upregulated, indicating the activation of a defense response in the rapeseed against aphids. In conclusion, defense enzymes and defense-related gene activation could improve the pest resistance in rapeseed, which has good application prospects for the future to be developed into biopesticide.

Taxonomical, functional, and cytopathological characterization of Bacillus spp. from Lake Magadi, Kenya, against Rhizoctonia solani Kühn in Phaseolus vulgaris L

A decline in common bean production and the ineffectiveness of synthetic chemical products in managing plant pathogens has led to exploiting Kenyan soda lakes as an alternative search for biocontrol agents. This study aimed to identify phylogenetically Bacillus spp. from Lake Magadi and their antagonistic activity against Rhizoctonia solani under in vitro and in vivo conditions. The 16 S ribosomal RNA (rRNA) subunit sequences of six bacterial strains isolated from Lake Magadi showed diversity similar to the Bacillus genus; Bacillus velezensis, Bacillus subtilis, and Bacillus pumilus. In vitro, antagonism showed varied mycelium inhibition rates of fungi in the coculture method. Enzymatic assays showed the varied ability of isolates to produce phosphatase, pectinase, chitinase, protease, indole-3-acetic acid (IAA), and hydrogen cyanide (HCD). The in vivo assay showed M09 (B. velezensis) with the lowest root mortality and incidence of postemergence wilt. Pre-emergence wilt incidence was recorded as lowest in M10 (B. subtilis). Isolate M10 had the highest phenylalanine ammonia-lyase (PAL) for defense enzymes, while polyphenol oxidase (PPO) and peroxidase were recorded as highest in M09. For the phenolic content, M10 recorded the highest phenolic content. In conclusion, Lake Magadi harbors Bacillus spp, which can be used as a potential biocontrol of R. solani.

Bacterial consortium (Priestia endophytica NDAS01F, Bacillus licheniformis NDSA24R, and Priestia flexa NDAS28R) and thiourea mediated amelioration of arsenic stress and growth improvement of Oryza sativa L

The present study analyzed the effects of individual microbes and their consortium (Priestia endophytica NDAS01F, Bacillus licheniformis NDSA24R, and P. flexa NDAS28R) either alone or in interaction with thiourea (TU) on growth and responses of rice plants subjected to As stress (50 mg kg^-1 in soil) in a pot experiment. The bacteria used in the experiment were isolated from As contaminated fields of Nadia, West Bengal and showed significant As removal potential in in vitro experiment. The results revealed significant growth improvement, biomass accumulation, and decline in malondialdehyde levels in rice plants in bacterial and TU treatments as compared to control As treatment. The best results were observed in a bacterial consortium (B1-2-3), which induced a profound increase of 65%, 43%, 127% and 83% in root length, shoot length, leaf width and fresh weight, respectively. Sulfur metabolism and cell wall synthesis were stimulated upon bacterial and TU amendment in plants. The maximum reduction in As concentration was observed in B2 in roots (-55%) and in B1-2-3 in shoot (-83%). The combined treatment of B1-2-3 + TU proved to be less effective as compared to that of B1-2-3 in terms of As reduction and growth improvement. Hence, the usage of bacterial consortium obtained in the present work is a sustainable approach, which might find relevance in field conditions to achieve As reduction in rice grains and to attain higher growth of plants without the need for additional TU supplementation.

Control of Fungal Diseases and Fruit Yield Improvement of Strawberry Using Bacillus velezensis CE 100

Due to the increasing health and environmental risks associated with the use of fungicides in agriculture, alternatives—such as using plant growth-promoting bacteria (PGPB) to suppress phytopathogens—that simultaneously improve plant yield, are important. This study evaluated the biocontrol efficiency of Bacillus velezensis CE100 against Macrophomina phaseolina and Fusarium oxysporum f. sp. fragariae, the respective causal agents for charcoal rot and fusarium wilt diseases in strawberry, and its potential to enhance strawberry growth and fruit production. B. velezensis CE 100 produced fungal cell wall-degrading enzymes, chitinases, and β-1,3-glucanases; and inhibited the mycelial growth of M. phaseolina and F. oxysporum f. sp. fragariae by 64.7% and 55.2%, respectively. The mycelia of both phytopathogenic fungi showed severe swelling and rupturing of the hyphae compared to the smooth, normal growth in the control group. Moreover, B. velezensis CE100 produced up to 2.8 units/mL of indole-3-acetic acid (IAA) during incubation and enhanced root biomass in strawberries. Consequently, B. velezensis CE 100 not only increased the fruit yield of strawberries by controlling the fungal diseases but also through enhancing plant growth. The findings of this study indicate that B. velezensis CE100 could be a safe, ecofriendly biocontrol alternative to chemical fungicides in strawberry production.

Biological Control of Leaf Blight Disease Caused by Pestalotiopsis maculans and Growth Promotion of Quercus acutissima Carruth Container Seedlings Using Bacillus velezensis CE 100

Leaf blight disease caused by Pestalotiopsismaculans lead to deleterious losses in the quality of forest container seedlings. The use of plant growth-promoting bacteria provides a promising strategy to simultaneously control diseases and enhance forest seedling production. This study investigated the biocontrol of leaf blight disease and growth promotion potential of Bacillus velezensis CE 100 in Quercus acutissima Carruth seedlings. B. velezensis CE 100 produced cell wall degrading enzymes, such as chitinase, β-l,3-glucanase, and protease, which caused cell wall lysis and hyphae deformation of P. maculans, leading to mycelial growth inhibition by 54.94%. Inoculation of B. velezensis CE 100 suppressed P. maculans infection and increased seedling survival rate by 1.6-fold and 1.3-fold compared to chemical fertilizer and control, respectively. In addition, B. velezensis CE 100 produced indole-3-acetic acid, which improved root development and nutrient uptake compared to chemical fertilizer and control. Especially, inoculation with B. velezensis CE 100 increased the total nitrogen content of Q. acutissima seedlings, improved the chlorophyll index in the leaves, and increased seedling biomass by 1.3-fold and 2.2-fold compared to chemical fertilizer and control, respectively. Thus, B. velezensis CE 100 could be applied in the eco-friendly production of high-quality forest seedlings.

Antifungal Activity of Bacillus velezensis CE 100 against Anthracnose Disease (Colletotrichum gloeosporioides) and Growth Promotion of Walnut (Juglans regia L.) Trees

Walnut anthracnose caused by Colletotrichum gloeosporioides is a deleterious disease that severely affects the production of walnut (Juglans regia L.). The aim of this study was to assess the antifungal and growth promotion activities of Bacillus velezensis CE 100 as an alternative to chemical use in walnut production. The crude enzyme from B. velezensis CE 100 exhibited chitinase, protease, and β-l,3-glucanase activity and degraded the cell wall of C. gloeosporioides, causing the inhibition of spore germination and mycelial growth by 99.3% and 33.6% at 100 µL/mL, respectively. The field application of B. velezensis CE 100 culture broth resulted in a 1.3-fold and 6.9-fold decrease in anthracnose disease severity compared to the conventional and control groups, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (up to 1.4 µg/mL) and exhibited the potential for ammonium production and phosphate solubilization to enhance the availability of essential nutrients. Thus, field inoculation of B. velezensis CE 100 improved walnut root development, increased nutrient uptake, enhanced chlorophyll content, and consequently improved total biomass by 1.5-fold and 2.0-fold compared to the conventional and control groups, respectively. These results demonstrate that B. velezensis CE 100 is an effective biocontrol agent against anthracnose disease and a potential plant growth-promoting bacteria in walnut tree production.

Potential Role of Rhizobacteria Isolated from Citrus Rhizosphere for Biological Control of Citrus Dry Root Rot

Citrus trees face threats from several diseases that affect its production, in particular dry root rot (DRR). DRR is a multifactorial disease mainly attributed to Neocosmospora (Fusarium) solani and other several species of Neocosmospora and Fusarium spp. Nowadays, biological control holds a promising control strategy that showed its great potential as a reliable eco-friendly method for managing DRR disease. In the present study, antagonist rhizobacteria isolates were screened based on in vitro dual culture bioassay with N. solani. Out of 210 bacterial isolates collected from citrus rhizosphere, twenty isolates were selected and identified to the species level based on the 16S rRNA gene. Molecular identification based on 16S rRNA gene revealed nine species belonging to Bacillus, Stenotrophomonas, and Sphingobacterium genus. In addition, their possible mechanisms involved in biocontrol and plant growth promoting traits were also investigated. Results showed that pectinase, cellulose, and chitinase were produced by eighteen, sixteen, and eight bacterial isolates, respectively. All twenty isolates were able to produce amylase and protease, only four isolates produced hydrogen cyanide, fourteen isolates have solubilized tricalcium phosphate, and ten had the ability to produce indole-3-acetic acid (IAA). Surprisingly, antagonist bacteria differed substantially in their ability to produce antimicrobial substances such as bacillomycin (five isolates), iturin (ten isolates), fengycin (six isolates), surfactin (fourteen isolates), and bacteriocin (subtilosin A (six isolates)). Regarding the PGPR capabilities, an increase in the growth of the bacterial treated canola plants, used as a model plant, was observed. Interestingly, both bacterial isolates Bacillus subtilis K4-4 and GH3-8 appear to be more promising as biocontrol agents, since they completely suppressed the disease in greenhouse trials. Moreover, these antagonist bacteria could be used as bio-fertilizer for sustainable agriculture.

Bacillus velezensis CE 100 Inhibits Root Rot Diseases (Phytophthora spp.) and Promotes Growth of Japanese Cypress (Chamaecyparis obtusa Endlicher) Seedlings

Root rot diseases, caused by phytopathogenic oomycetes, Phytophthora spp. cause devastating losses involving forest seedlings, such as Japanese cypress (Chamaecyparis obtusa Endlicher) in Korea. Plant growth-promoting rhizobacteria (PGPR) are a promising strategy to control root rot diseases and promote growth in seedlings. In this study, the potential of Bacillus velezensis CE 100 in controlling Phytophthora root rot diseases and promoting the growth of C. obtusa seedlings was investigated. B. velezensis CE 100 produced β-1,3-glucanase and protease enzymes, which degrade the β-glucan and protein components of phytopathogenic oomycetes cell-wall, causing mycelial growth inhibition of P. boehmeriae, P. cinnamomi, P. drechsleri and P. erythoroseptica by 54.6%, 62.6%, 74.3%, and 73.7%, respectively. The inhibited phytopathogens showed abnormal growth characterized by swelling and deformation of hyphae. B. velezensis CE 100 increased the survival rate of C. obtusa seedlings 2.0-fold and 1.7-fold compared to control, and fertilizer treatment, respectively. Moreover, B. velezensis CE 100 produced indole-3-acetic acid (IAA) up to 183.7 mg/L, resulting in a significant increase in the growth of C. obtusa seedlings compared to control, or chemical fertilizer treatment, respectively. Therefore, this study demonstrates that B. velezensis CE 100 could simultaneously control Phytophthora root rot diseases and enhance growth of C. obtusa seedlings.

Bacillus licheniformis PR2 Controls Fungal Diseases and Increases Production of Jujube Fruit under Field Conditions

There is a growing interest in using biocontrol agents to control fungal diseases and increase the production of jujube fruit (Zizyphus jujua Miller var. inermis Rehder). The purpose of this study was to use Bacillus licheniformis PR2 to inhibit fungal diseases and promote fruit production in jujube orchards. B. licheniformis PR2 secreted 92.4 unit/mL of chitinase, which inhibited fungal phytopathogens through hyphal alterations with swelling and bulbous structures. B. licheniformis PR2 also inhibited mycelial growths of fruit fungal pathogens Botrytis cinerea, Colletotrichum gloeosporioides, and Phytophthora nicotianae by 81.3%, 60.1%, and 67.0%, respectively. B. licheniformis PR2 increased jujube fruit yield by 17.9 kg/tree by reducing rotting damage caused by fungal pathogens, with a yield 3.2 times higher than that achieved by the control without PR2 treatment. In addition, B. licheniformis PR2 produced auxin, which promoted cell division after flower fertilization, thus increasing fruit length and diameter by 1.2-fold compared to those of the control. These results confirmed that eco-friendly B. licheniformis PR2 could effectively control fungal diseases in jujube orchards and improve its fruit size and yield.

Antifungal Activity of Cyclic Tetrapeptide from Bacillus velezensis CE 100 against Plant Pathogen Colletotrichum gloeosporioides

The aim of this study was to investigate the antifungal activity of a cyclic tetrapeptide from Bacillus velezensis CE 100 against anthracnose-causing fungal pathogen Colletotrichum gloeosporioides. Antifungal compound produced by B. velezensis CE 100 was isolated and purified from ethyl acetate extract of B. velezensis CE 100 culture broth using octadecylsilane column chromatography. The purified compound was identified as cyclo-(prolyl-valyl-alanyl-isoleucyl) based on mass spectrometer and nuclear magnetic resonance analyses. This is the first report of the isolation of a cyclic tetrapeptide from B. velezensis CE 100 culture filtrate. Cyclic tetrapeptide displayed strong antifungal activity at concentration of 1000 µg/mL against C. gloeosporioides mycelial growth and spore germination. Our results demonstrate that the antifungal cyclic tetrapeptide from B. velezensis CE 100 has potential in bioprotection against anthracnose disease of plants caused by C. gloeosporioides.

Influence of Mean Leaf Angles and Irrigation Volumes on Water Capture, Leaching, and Growth of Tropical Tree Seedlings

Research Highlights: The mean leaf angle and crown projection area can be used as criteria for grouping tree seedling species in different irrigation zones in tree nurseries with overhead microsprinkler systems, preventing water and fertilizer waste, and increasing growth. Background and Objectives: There are important gaps in current functional knowledge about how plant architecture, especially the mean leaf angles of tree seedlings, affect water and nutrient solution capture in overhead microsprinkler systems. These gaps contribute to water and fertilizer waste in tree nurseries. This research aimed to ascertain how mean leaf angles affect irrigation water capture, leaching, and the growth of tree seedlings given different volumes of irrigation. Materials and Methods: Nine species of tree seedlings with different mean leaf angles were submitted to four irrigation volumes (8, 10, 12, and 14 mm) applied daily by overhead microsprinklers in a split-plot design completely randomized. The variables leaching fraction, height, stem diameter, shoot, root, and total dry mass, Dickson quality index, crown projection area, root system quality, and leachate electrical conductivity were evaluated. Results: For species with mean leaf angles of −54, 31, 38, 42, 55, 57, and 58°, the 8 mm irrigation volume was sufficient to produce greater growth and less leaching. For species with angles of −56 and −14°, the 14 mm irrigation volume was required to produce greater growth. Conclusions: The tree seedling species with positive mean leaf angles facilitate irrigation water and nutrient solution capture, allowing the application of lower irrigation volume. On the other hand, some tree seedling species with negative mean leaf angles hinder irrigation water and nutrient solution capture, requiring the application of higher irrigation volume. When the tree seedling species have a negative mean leaf angle, but the crown projection area is small, the difficulty of water and nutrient solution reaches directly the substrate is attenuated.

Control of Fungal Diseases and Increase in Yields of a Cultivated Jujube Fruit (Zizyphus jujuba Miller var. inermis Rehder) Orchard by Employing Lysobacter antibioticus HS124

The objective of this study is to investigate the inhibitory effects of Lysobacter antibioticus HS124 on fungal phytopathogens causing gray mold rot, stem rot, and anthracnose. Another objective of this study is to promote the yield of fruit in jujube farms. L. antibioticus HS124 produces chitinase, a lytic enzyme with the potential to reduce mycelial growth of fungal phytopathogens involving hyphal alterations with swelling and bulbous structures, by 20.6 to 27.3%. Inoculation with L. antibioticus HS124 decreased the appearance of fungal diseases in jujube farms and increased the fruit yield by decreasing fruit wilting and dropping. In addition, L. antibioticus HS124 produced the phytohormone auxin to promote vegetative growth, thereby increasing the fruit size. The yield of jujube fruits after L. antibioticus HS124 inoculation was increased by 6284.67 g/branch, which was 2.9-fold higher than that of the control. Auxin also stimulated fine root development and nutrient uptake in jujube trees. The concentrations of minerals, such as K, Ca, Mg, and P in jujube fruits after L. antibioticus HS124 inoculation were significantly increased (1.4- to 2.0-fold greater than the concentrations in the control). These results revealed that L. antibioticus HS124 could not only control fungal diseases but also promote fruit yield in jujube farms.