Establishment of the fungal entomopathogen Beauveria bassiana as an endophyte in sugarcane, Saccharum officinarum

Enhancing drought tolerance in Malva parviflora plants through metabolic and genetic modulation using Beauveria bassiana inoculation

BACKGROUND

Enhancing crops' drought resilience is necessary to maintain productivity levels. Plants interact synergistically with microorganisms like Beauveria bassiana to improve drought tolerance. Therefore, the current study investigates the effects of biopriming with B. bassiana on drought tolerance in Malva parviflora plants grown under regular irrigation (90% water holding capacity (WHC)), mild (60% WHC), and severe drought stress (30% WHC).

RESULTS

The results showed that drought stress reduced the growth and physiological attributes of M. parviflora. However, those bioprimed with B. bassiana showed higher drought tolerance and enhanced growth, physiological, and biochemical parameters: drought stress enriched malondialdehyde and H2O2 contents. Conversely, exposure to B. bassiana reduced stress markers and significantly increased proline and ascorbic acid content under severe drought stress; it enhanced gibberellic acid and reduced ethylene. Bioprimed M. parviflora, under drought conditions, improved antioxidant enzymatic activity and the plant's nutritional status. Besides, ten Inter-Simple Sequence Repeat primers detected a 25% genetic variation between treatments. Genomic DNA template stability (GTS) decreased slightly and was more noticeable in response to drought stress; however, for drought-stressed plants, biopriming with B. bassiana retained the GTS.

CONCLUSION

Under drought conditions, biopriming with B. bassiana enhanced Malva's growth and nutritional value. This could attenuate photosynthetic alterations, up-regulate secondary metabolites, activate the antioxidant system, and maintain genome integrity.

Endophytic Colonisation of Solanum lycopersicum and Phaseolus vulgaris by Fungal Endophytes Promotes Seedlings Growth and Hampers the Reproductive Traits, Development, and Survival of the Greenhouse Whitefly, Trialeurodes vaporariorum

In the scope of mitigating the negative impacts of pesticide use and managing greenhouse whiteflies, Trialeurodes vaporariorum sustainably, 16 endophytic fungal isolates from five different genera (Beauveria, Trichoderma, Hypocrea, Bionectria, and Fusarium) were screened for their ability to colonise two preferred host plant species, namely, tomato (Solanum lycopersicum L.) and French bean (Phaseolus vulgaris L.), through seed inoculation. Seven and nine isolates were endophytic to P. vulgaris and S. lycopersicum, respectively, where significant differences in the endophytic colonisation rates were observed among the fungal isolates in P. vulgaris and its plant parts, with a significant interaction between the isolates and plant parts in S. lycopersicum. Hypocrea lixii F3ST1, Trichoderma asperellum M2RT4, Trichoderma atroviride F5S21, and T. harzianum KF2R41 successfully colonised all the plant parts of both hosts and therefore were selected and further evaluated for their endophytic persistence, effect on plant growth, and pathogenicity to T. vaporariorum adults and F1 progeny. The four endophytes remained in both host plants for the 5-week assessment with varied colonisation rates related to the strong interaction with the time, isolates, and plant parts in both hosts. The effect of the same endophytes on the different host growth parameters varied in P. vulgaris and S. lycopersicum, with T. asperellum M2RT4 not boosting the growth in both host plants while T. atroviride F5S21 resulted in enhanced shoot biomass in S. lycopersicum. T. atroviride F5S21 and T. harzianum KF2R41 inoculated S. lycopersicum plants and H. lixii F3ST1, T. asperellum M2RT4, and T. harzianum KF2R41 inoculated P. vulgaris plants had significantly lower oviposition, while nymph development in both hosts was significantly prolonged in all the endophytically-colonised plants. The endophytes H. lixii F3ST1 and T. asperellum M2RT4 significantly reduced the longevity/survival of the exposed T. vaporariorum adults and the progeny in both S. lycopersicum and P. vulgaris. The findings demonstrate the attributes of the various endophytes in host plant growth promotion as well as their effects on the life-history parameters of T. vaporariorum and could consequently be developed as potential endophytic fungal-based biopesticides for the sustainable management of the pest in S. lycopersicum and P. vulgaris cropping systems.

Development of Plant-Fungal Endophyte Associations to Suppress Phoma Stem Canker in Brassica

Endophytic microorganisms are found within the tissues of many plants species, with some conferring several benefits to the host plant including resistance to plant diseases. In this study, two putative endophytic fungi that were previously isolated from wild seeds of Brassica, identified as Beauveria bassiana and Pseudogymnoascus pannorum, were inoculated into cultivars of three Brassica species—Brassica napus, Br. rapa and Br. oleracea. Both fungal endophytes were reisolated from above- and below-ground tissues of inoculated plants at four different plant-growth stages, including cotyledon, one-leaf, two-leaf, and four-leaf stages. None of the plants colonised by these fungi exhibited any obvious disease symptoms, indicating the formation of novel mutualistic associations. These novel plant–endophyte associations formed between Brassica plants and Be. bassiana significantly inhibited phoma stem canker, a devastating disease of Brassica crops worldwide, caused by the fungal pathogen Leptosphaeria maculans. The novel association formed with P. pannorum significantly suppressed the amount of disease caused by L. maculans in one out of two experiments. Although biological control is not a new strategy, endophytic fungi with both antiinsect and antifungal activity are a highly conceivable, sustainable option to manage pests and diseases of economically important crops.

Method for observing Beauveria bassiana colonization in plants

Microbes interact in a multitude of ways with host plants, can dwell as endophytes within plants causing no apparent disease, and often provide benefits to their host. Observing microorganism distribution and colonization is a prerequisite for interactive research. To this end, we describe use of fluorescent staining for microorganism labeling and highlight its simplicity, and efficiency. Fluorescein can quickly bind to Beauveria bassiana spores, producing bright green fluorescence that can be observed even inside plant tissues. This method provides an intuitive visual image that can be utilised for subsequent data acquisition and statistical analysis.•Our protocol depends on binding of fluorescein diacetate (FDA) specifically to microorganisms. The fungus hydrolyses and metabolises FDA in cells to produce bright green fluorescent products. This fluorescent signal can easily penetrate plant epidermis and be detected by fluorescence microscopy.•FDA, which itself does not emit light, will emit a fluorescent signal only when combined with B. bassiana. Concomitant genetic testing of the fungal ITS confirmed the high level of the fluorescent staining method for detection of B. bassiana.•Compared with the previous green fluorescent protein (GFP) labeling methods, this protocol improved the labeling efficiency of microorganisms and simplifies the process.

Natural Occurrence of Entomopathogenic Fungi as Endophytes of Sugarcane (Saccharum officinarum) and in Soil of Sugarcane Fields

Simple Summary

Sugarcane, an important cash crop in Malawi, is susceptible to numerous insect pests, and many farmers rely heavily on chemical insecticides for their control. Biopesticides containing insect pathogens are used in several countries outside Malawi; however, the occurrence and use of insect pathogens is limited in Malawi. In this study, we evaluated the natural occurrence of insect pathogenic fungi in sugarcane (Saccharum officinarum) and in soil samples from sugarcane fields in Chikwawa District, southern Malawi. Insect pathogenic fungi from soil were isolated by baiting using larvae of the greater wax moth (Galleria mellonella). Insect pathogenic fungi were also isolated from surface-sterilized sugarcane leaves, stems, and roots. We found three types of insect pathogenic fungi: Beauveria bassiana, Metarhizium spp., and Isaria spp. Beauveria bassiana and Isaria spp. were found mostly from sugarcane leaves and stems, while Metarhizium spp. was mainly found in soils. To the best of our knowledge, this is the first report of B. bassiana and Isaria spp. occurring naturally as endophytes in sugarcane. Further, it is the first report of B. bassiana, Isaria spp. and Metarhizium spp. in the soil of sugarcane fields in Africa.

Abstract

The natural occurrence of entomopathogenic fungal endophytes in sugarcane (Saccharum officinarum) and in soil samples from sugarcane fields was evaluated in Chikwawa District, southern Malawi. Fungi from soil were isolated by baiting using Galleria mellonella larva. Fungal endophytes were isolated from surface-sterilized plant tissue sections. Forty-seven isolates resembled the genus Beauveria, 9 isolates were Metarhizium, and 20 isolates were Isaria. There was no significant difference in the number and type of fungal isolates collected from soil and from plant tissue. There was, however, a significant difference in the part of the plant where fungal species were isolated, which fungal species were isolated, and the number of fungal species isolated at each location. Phylogenetic analysis of 47 Beauveria isolates based on DNA sequencing of the Bloc intergenic region indicated that these isolates all belonged to B. bassiana and aligned with sequences of B. bassiana isolates of African and Neotropical origin. The Malawian B. bassiana isolates formed a distinct clade. No larvae died from infestation by multiple fungi. To the best of our knowledge, this is the first report of B. bassiana and Isaria spp. occurring naturally as endophytes in sugarcane. Further, it is the first report of B. bassiana, Isaria spp., and Metarhizium spp. in the soil of sugarcane fields in Africa.

Fungal isolate and crop cultivar influence the beneficial effects of root inoculation with entomopathogenic fungi in strawberry

BACKGROUND

Root inoculations of crop plants with beneficial fungi constitute a promising strategy for growth promotion and control of above-ground pests and diseases. Here, strawberry roots (cultivar 'Albion' and 'Pircinque') were inoculated with 25 different Brazilian entomopathogenic fungal isolates of three genera and the effects on Tetranychus urticae oviposition and plant growth were evaluated in greenhouse experiments.

RESULTS

Reductions in the number of T. urticae eggs compared to control treatments were observed on both cultivars inoculated with almost all isolates. For the cultivar 'Albion', Metarhizium anisopliae (ESALQ 1604, ESALQ 1669), M. robertsii (ESALQ 1622, ESALQ 1635), Metarhizium sp. Indet. (ESALQ 1684) and Beauveria bassiana (ESALQ 3323) increased dry weight of roots and leaves, and fruit yield, while M. robertsii (ESALQ 1634), Metarhizium sp. Indet. (ESALQ 1637) and (ESALQ 1636) enhanced fruit yield and dry weight of leaves, respectively. For the cultivar 'Pircinque', M. anisopliae (ESALQ 1669) was the only isolate observed to increase dry weight of roots.

CONCLUSION

The results suggest that inoculation of strawberry roots with entomopathogenic fungi may be an innovative strategy for pest management above ground. Furthermore, these inoculations may also stimulate plant growth and strawberry production, but the effects depend on fungal strains and crop cultivar. © 2019 Society of Chemical Industry.

Endophytic Beauveria bassiana promotes drought tolerance and early flowering in corn

Beauveria bassiana (Bals.) Vuillemin (B. bassiana) is an entomopathogenic fungus that establishes endophytic symbiosis with plants. In the present study, the effects of B. bassiana strains colonization in growing Zea mays L. (Z. mays), crop production, and drought tolerance were evaluated. Z. mays seeds were inoculated with B. bassiana strains (GHA, PTG4, and PTG6), using 1 × 10⁶ blastospores/mL and methyl cellulose (MC) or cornstarch (CS) as adherents. Colonization was determined by B. bassiana recovery from plant tissues plated on PDA medium. Plant height, fresh and dry weight, and flowering time were analyzed to assess plant performance. Drought tolerance was evaluated by stopping watering for 10 days, watering again, and determining vigor recovery after 24 h. Results showed 100% endophytic roots colonization, regardless of adherent type or strain tested. Colonization was variable in shoots and leaves, but GHA strain achieved the highest inoculation rates, including 88% in stems and 50% in leaves, which did not depend on adherent type used; for PTG4 strain, adherent type had an important effect (MC = 100% stems and leaves; CS = 63% stems and 25% leaves). For PTG6 strain, the best adherent type was CS (71% stems and 75% leaves), whereas MC showed variable inoculation percentage (25% stems and 75% leaves). Interestingly, only MCPTG4 treatment showed consistent positive effects on germination percentage (day 5 = 46 ± 2%; day 14 = 87 ± 7%) compared with controls (CC = 63 ± 4%, CMC = 50 ± 3%, CCS = 47 ± 0%). In addition, the other treatments showed low germination percentages at day 5 (7 ± 7% to 46 ± 2%), which recovered at day 14 (53 ± 0% to 73 ± 8%), except for MCPTG6 treatment with 23 ± 10% germination. About plant performance, not significant effects on plant height and fresh/dry weight in all the treatments were observed. However, B. bassiana-treated plants, using either GHA, PTG4 or PTG6 strains, and MC as adherent, showed tolerance to drought and flowered one to two weeks earlier, providing evidence supporting further applications of these seed treatments in agricultural systems, for abiotic stress sustainable management practices.

Monitoring of the field application of Metarhizium anisopliae in Brazil revealed high molecular diversity of Metarhizium spp in insects, soil and sugarcane roots

The use of Metarhizium against sugarcane spittlebugs in Brazil is one of the most successful and long lasting biological control programs using entomopathogenic fungus in the world. However, studies to monitor the fate of this fungus on the sugarcane agroecosystem are rare, especially with respect to its persistence, efficacy in pest control and impact on the local populations of Metarhizium. The present study aimed at documenting the efficacy and persistence of M. anisopliae strain ESALQ1604 in a sugarcane field by using microsatellite molecular markers. The species diversity of Metarhizium was characterized in insects, soil and sugarcane roots in a sprayed and an unsprayed plot. Although the infection rates were not very high (≤ 50%), the applied strain was recovered from spittlebugs after 7, 30 and 60 days’ post-application, but accounted for only 50%, 50% and 70.5% of all insects killed by M. anisopliae, respectively. All haplotypes from spittlebug were associated with a single subclade of M. anisopliae. The highest haplotype diversity was found in soil (h = 0.989) and in the smallest in spittlebug (h = 0.779). Metarhizium robertsii, M. anisopliae, M. brunneum; one taxonomically unassigned lineage was found in soil and only M. brunneum and M. anisopliae were isolated from roots. This study revealed the great diversity of Metarhizium spp. in the sugarcane agroecosystem and the importance of the local population of M. anisopliae on spittlebugs management.

Prospects of endophytic fungal entomopathogens as biocontrol and plant growth promoting agents: An insight on how artificial inoculation methods affect endophytic colonization of host plants

Entomopathogenic fungi (EPF) can be established as endophytes in the host plants to offer a long-term preventive measure for pests and diseases. This practice serves as a better alternative to the common practice of periodic direct application of EPF on plants or the target pests as a short-term defense strategy against pests and diseases. These fungal endophytes, aside from their role in pests and diseases prevention, also act as plant growth promoters. Several fungal endophytes have been associated with improvement in plant height, dry and wet weight and other growth parameters. However, many limiting factors have been identified as mitigating the successful colonization of the host plants by EPF. The inoculation methods used have been identified as one, but sadly, this has received little or less attention. Some previous studies carried out comparison between various artificial inoculation methods; foliar application, seedling dipping, soil drenching, seed inoculation, direct injection and others. In separate studies, some authors had suggested different application methods that are best suitable for certain fungal entomopathogens. For instance, leaf inoculation with conidial suspensions was suggested to be the best inoculation method for Beauveria bassiana in sorghum, stem injection was suggested as the most suitable for coffee, while, root dipping method proved the most successful for B. bassiana colonization of tomato plants for the management of Helicoverpa armigera. Here, we discussed entomopathogenic fungal endophytes as bio-control agents, plant growth promoters and highlighted the effect of various artificial inoculation methods on their endophytic colonization of the host plants.