Enhanced resistance to Spodoptera litura in endophyte infected cauliflower plants

Effect of male parental gamma irradiation on host suitability of its F1 progeny of a lepidopteran tropical pest, Spodoptera litura (Fabr.) towards development and virulence of entomopathogenic nematodes, Steinernema thermophilum

The suitability of F1 progeny insect larvae of the irradiated male parent, Spodoptera litura (Fabr.) for infective juveniles (IJs) of entomopathogenic nematodes (EPN), Steinernema thermophilum was assessed to comprehend the feasibility of combining EPNs with nuclear pest control tactic. As compared to the control, the IJs induced faster host mortality with reduced proliferation in F1 host larvae. IJs derived from F1 host larvae exhibited almost similar proliferation capacity on normal hosts as in control. Further, the molecular basis of EPNs induced mortality in F1 host larvae was evaluated. Dual stress of EPN infection and irradiation induced downregulation of the relative mRNA expression of antimicrobial genes and upregulated expression of antioxidative genes. A pronounced effect of EPNs in association with irradiation stress was apparent on host mortality. Radiation induced sterile F1 insect larvae of S. litura acted as a reasonably suitable host for EPNs and also provided the environment for developing viable EPNs for their potential use as biocontrol agents.

Role of Endophytic Entomopathogenic Fungi in Mediating Host Selection, Biology, Behavior, and Management of Tarnished Plant Bug, Lygus lineolaris (Hemiptera: Miridae)

Non-insecticidal control strategies using entomopathogens, nematodes, and endophytes provide sustainable and safer alternatives for managing crop pests. This study investigated the potential of different fungal endophytes, specifically Beauveria bassiana strains, in colonizing cotton plants and their efficacy against tarnished plant bug, Lygus lineolaris. The effect of endophytes on plant growth parameters and cotton yield were measured during different plant growth stages. The entomopathogenicity of these fungi was studied in diet cup bioassays using L. lineolaris adults. The behavior of adult males and females toward endophytic cotton squares was analyzed using olfactometer assays. The experiments showed that the fungal endophytes colonized the plant structures of cotton plants, which resulted in an increase in the number of cotton squares, plant height, and weight compared to control plants. B. bassiana strains/isolates such as GHA, NI-8, and JG-1 caused significant mortality in Lygus adults compared to controls. Also, male and female Lygus adults exhibited repellence behavior towards endophytic cotton squares containing JG-1 isolate of B. bassiana and to other B. bassiana strains such as NI-8, GHA, and SPE-120. No differences were observed in the survival and development of L. lineolaris second-instar nymphs on endophytic cotton, and no yield differences were observed in the field experiments.

Cladosporium-Insect Relationships

The range of interactions between Cladosporium, a ubiquitous fungal genus, and insects, a class including about 60% of the animal species, is extremely diverse. The broad case history of antagonism and mutualism connecting Cladosporium and insects is reviewed in this paper based on the examination of the available literature. Certain strains establish direct interactions with pests or beneficial insects or indirectly influence them through their endophytic development in plants. Entomopathogenicity is often connected to the production of toxic secondary metabolites, although there is a case where these compounds have been reported to favor pollinator attraction, suggesting an important role in angiosperm reproduction. Other relationships include mycophagy, which, on the other hand, may reflect an ecological advantage for these extremely adaptable fungi using insects as carriers for spreading in the environment. Several Cladosporium species colonize insect structures, such as galleries of ambrosia beetles, leaf rolls of attelabid weevils and galls formed by cecidomyid midges, playing a still uncertain symbiotic role. Finally, the occurrence of Cladosporium in the gut of several insect species has intriguing implications for pest management, also considering that some strains have proven to be able to degrade insecticides. These interactions especially deserve further investigation to understand the impact of these fungi on pest control measures and strategies to preserve beneficial insects.

Impact of Plant Symbiotic Endophytic Fungus, Aspergillus terreus on Insect Herbivore Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae)

Herbivorous insects are known to be resistant to fungal endophytes that asymptomatically inhabit plant tissues. The insecticidal ability of the endophytic fungus Aspergillus terreus isolated from Catharanthus roseus against Spodoptera litura (Fabricius) was assessed in the current study. The survival and growth of S. litura were adversely impacted by the ethyl acetate extract of endophytic A. terreus. Fungal extract supplemented diet caused 14 to 94% larval mortality in comparison to 2% in control. Additionally, retarded insect growth was observed after ingestion of supplemented diet. The fungal metabolites were also observed to have an inhibitory influence on the adult emergence and reproductive potential of adults. Phytochemical analysis revealed the presence of phenolic compounds in the crude extract of endophytic fungus which may be responsible for toxicity. It was also determined how endophyte-infected cauliflower plants affected S. litura's survival and growth. Endophyte-infected plants exhibited resistance to S. litura by causing 54% larval mortality and delaying development by 5.2 days. In comparison to uninfected plants, adult emergence, lifespan, fecundity and egg hatchability of insects was significantly decreased on infected plants. There was a significant decrease in relative growth and consumption rates as well as in the efficiency of food conversion, which indicates toxic and antifeedant effect of the fungus on S. litura. This suggests that endophyte-inoculated plants exhibit antibiosis against S. litura. In conclusion, the endophytic fungi having insecticidal activity could be used to develop alternative ecologically safe control strategies.

Lethal and sublethal effects of flubendiamide and spirotetramat against the leaf worm, Spodoptera litura(Fabricius) under laboratory conditions

The leaf worm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) is a notorious insect pest of many economically important cultivated crops like cotton, maize, tobocco and vegetables causing severe economic losses from 50-100%. In most crops, damage arises due to voracious feeding by the larvae and leads to the skeletonizing of leaves. Toxicological studies were performed to estimate lethal and sublethal levels of flubendiamide and spirotetramat against S. litura. Effects of these estimated values were assessed on different biological traits of S. litura including life duration, survival and next generation potential. Both flubendiamide and spirotetramat showed toxic responses against second instar larvae of S. litura under laboratory conditions. Larval duration and survival rate of S. litura to were significantly different. Exposure to test insecticides resulted in negative effect on the demography of S. litura as longer life cycle and decreased fecundity. Changes in net reproductive rate and intrinsic rate of increase also helped to decide the fate of these insecticides. Low reproductive potential and low hatching percentage due to exposure to test insecticides can help to manage next generation of target pest. These two new chemistry insecticides can be recommended for their effective and long-term utilization against this important leaf feeder which may help its management and decrease economic losses faced by the growers. Their impact on larval duration and low survival rate at lethal levels guides about their potential in pest control.

Two Cladosporium Fungi with Opposite Functions to the Chinese White Wax Scale Insect Have Different Genome Characters

Insects encounter infection of microorganisms, and they also harbor endosymbiosis to participate in nutrition providing and act as a defender against pathogens. We previously found the Chinese white wax scale insect, Ericerus pela, was infected and killed by Cladosporium sp. (pathogen). We also found it harbored Cladosporium sp. (endogensis). In this study, we cultured these two Cladosporium fungi and sequenced their genome. The results showed Cladosporium sp. (endogensis) has a larger genome size and more genes than Cladosporium sp. (pathogen). Pan-genome analysis showed Cladosporium sp. (endogensis)-specific genes enriched in pathways related to nutrition production, such as amino acid metabolism, carbohydrate metabolism, and energy metabolism. These pathways were absent in that of Cladosporium sp. (pathogen). Gene Ontology analysis showed Cladosporium sp. (pathogen)-specific genes enriched in the biosynthesis of asperfuranone, emericellamide, and fumagillin. These terms were not found in that of Cladosporium sp. (endogensis). Pathogen Host Interactions analysis found Cladosporium sp. (endogensis) had more genes related to loss of pathogenicity and reduced virulence than Cladosporium sp. (pathogen). Cytotoxicity assay indicated Cladosporium sp. (pathogen) had cytotoxicity, while Cladosporium sp. (endogensis) had no cytotoxicity. These characters reflect the adaptation of endosymbiosis to host-restricted lifestyle and the invader of the entomopathogen to the host.

Does the Infectious Status of Aphids Influence Their Preference Towards Healthy, Virus-Infected and Endophytically Colonized Plants?

Aphids (Hemiptera: Aphididae) cause significant damage and transmit viruses to various crop plants. We aimed to evaluate how the infectious status of aphids influences their interaction with potential hosts. Two aphid (Myzus persicae and Rhopalosiphum padi) and plant (Nicotiana tabacum and Triticum aestivum) species were used. The preferences of aphids towards healthy, virus-infected (Potato Leafroll Virus (PLRV) and Barley Yellow Dwarf virus (BYDV)), and endophytic entomopathogenic fungi (EEPF)-inoculated (Beauveria bassiana and Metarhizium acridum) plants were investigated in dual-choice tests. The headspace volatiles of the different plant modalities were also sampled and analyzed. Viruliferous and non-viruliferous aphids were more attracted to EEPF-inoculated plants compared to uninoculated plants. However, viruliferous aphids were more attracted to EEPF-inoculated plants compared to virus-infected plants, while non-viruliferous insects exhibited no preference. Fungal-inoculated plants released higher amounts of aldehydes (i.e., heptanal, octanal, nonanal and decanal) compared to other plants, which might explain why viruliferous and non-viruliferous aphids were more abundant in EEPF-inoculated plants. Our study provides an interesting research perspective on how EEPF are involved in behavior of virus vector, depending on the infectious status of the latter.

Endophytic effects of Aspergillus oryzae on radish (Raphanus sativus) and its herbivore, Plutella xylostella

We provide evidence that Aspergillus oryzae not only acts as an endophyte in Raphanus sativus, but also works as a plant growth promoter and provides some protection against its herbivore, Plutella xylostella affecting its feeding rate, mortality and fitness parameters, thereby contributing to the pest population suppression. Seed inoculation of radish seeds with the fungus Aspergillus oryzae allowed its establishment as an endophyte promoting plant growth and negatively affecting fitness parameters of its major herbivore, diamondback moth, Plutella xylostella. Endophytic fungi may contribute to the growth of their host plants and enhance resistance to herbivores and diseases. We evaluated the effect of A. oryzae (Ahlburg) E. Cohn as an endophyte in radish (Raphanus sativus L.) on growth and development of the plants themselves and their major herbivore, the diamondback moth P. xylostella (L). A. oryzae colonization rates in leaves were significantly higher than in roots and stems, with a rate of 80% in leaves, 40% in stems and 20% in roots 1 week after seed inoculation. Colonization gradually decreased in the various plant tissues, and disappeared completely in roots, stems and leaves within 2, 5 and 7 weeks, respectively. A. oryzae did not affect seed germination; however, it promoted radish growth with endophytic plants attaining average heights of 116 mm compared to 99.6 mm in the controls at the third week post-inoculation. The P. xylostella fitness parameters, consumption, larval and pupal weights, and feeding on the endophytic plants were significantly lower than the controls, while larval mortality was significantly higher. Larvae fed on endophytic plants consumed 0.46 mg less leaf matter in the first week post seed inoculation and weighed 0.83 mg less as mature 4th instars than controls. We have demonstrated that A. oryzae can establish as an endophyte in R. sativus through seed inoculation providing some plant growth promotion and protection against its herbivore by increasing its mortality and negatively affecting its fitness parameters, suggesting that adopting seed treatments with A. oryzae may be beneficial in the commercial cultivation of radish.

Endophytic fungi alter sucking bug responses to cotton reproductive structures

All plants including cotton host a wide range of microorganisms as endophytes. There is a growing appreciation of the prevalence, ecological significance and management potential of facultative fungal endophytes in protecting plants from pests, pathogens and environmental stressors. Hemipteran sucking bugs have emerged as major pests across the U.S. cotton belt, reducing yields directly by feeding on developing reproductive structures and indirectly by vectoring plant pathogens. We used no-choice and simultaneous choice assays to examine the host selection behavior of western tarnished plant bugs (Lygus hesperus) and southern green stink bugs (Nezara viridula) in response to developing flower buds and fruits from cotton plants colonized by 1 of 2 candidate beneficial fungal endophytes, Phialemonium inflatum or Beauveria bassiana. Both insect species exhibited strong negative responses to flower buds (L. hesperus) and fruits (N. viridula) from plants that had been colonized by candidate endophytic fungi relative to control plants under both no-choice and choice conditions. Behavioral responses of both species indicated that the insects were deterred prior to contact with plant tissues from endophyte-colonized plants, suggesting a putative role for volatile compounds in mediating the negative response. Our results highlight the role of fungal endophytes as plant mutualists that can have positive effects on plant resistance to pests.

Endophytes from medicinal plants and their potential for producing indole acetic acid, improving seed germination and mitigating oxidative stress

Medicinal plants have been used by marginal communities to treat various ailments. However, the potential of endophytes within these bio-prospective medicinal plants remains unknown. The present study elucidates the endophytic diversity of medicinal plants (Caralluma acutangula, Rhazya stricta, and Moringa peregrina) and the endophyte role in seed growth and oxidative stress. Various organs of medicinal plants yielded ten endophytes, which were identified as Phoma sp. (6 isolates), Alternaria sp. (2), Bipolaris sp. (1), and Cladosporium sp. (1) based on 18S rDNA sequencing and phylogenetic analysis. The culture filtrates (CFs; 25%, 50%, and 100% concentrations) from these endophytes were tested against the growth of normal and dwarf mutant rice lines. Endophytic CF exhibited dose-dependent growth stimulation and suppression effects. CF (100%) of Phoma sp. significantly increased rice seed germination and growth compared to controls and other endophytes. This growth-promoting effect was due to the presence of indole acetic acid in endophytic CF. The gas chromatography/mass spectrometry (GC/MS) analysis showed the highest indole acetic acid content ((54.31±0.21) µmol/L) in Bipolaris sp. In addition, the isolate of Bipolaris sp. exhibited significantly higher radical scavenging and anti-lipid peroxidation activity than the other isolates. Bipolaris sp. and Phoma sp. also exhibited significantly higher flavonoid and phenolic contents. The medicinal plants exhibited the presence of bio-prospective endophytic strains, which could be used for the improvement of crop growth and the mitigation of oxidative stresses.

Transient endophytic colonizations of plants improve the outcome of foliar applications of mycoinsecticides against chewing insects

The current work reports how spray application of entomopathogenic fungi on alfalfa, tomato and melon plants may cause an additional Spodoptera littoralis larvae mortality due to a temporal colonization of the leaves and subsequent ingestion of those leaves by the larvae. Most entomopathogenic fungi (EF) (Ascomycota: Hypocreales) endophytes seem to colonize their host plants in a non-systemic pattern, in which case at least a transient endophytic establishment of the fungus should be expected in treated areas after spray application. In this work, all strains were able to endophytically colonize roots, stems and leaves during the first 96h after inoculation. Whilst the treatment of S. littoralis larvae with a 10(8)ml(-1) conidial suspension resulted in moderate to high mortality rates for the Metarhizium brunneum EAMb 09/01-Su (41.7-50.0%) and Beauveria bassiana EABb 01/33-Su (66.7-76.6%) strains, respectively, an additive effect was detected when these larvae were also fed endophytically colonized alfalfa, tomato, and melon leaves, with mortality rates varying from 25.0% to 46.7% as a function of the host plant and total mortality rates in the combined treatment of 75-80% and 33-60% for B. bassiana and M. brunneum, respectively. Fungal outgrowth was not detected in any of the dead larvae feeding on colonized leaves, whereas traces of destruxin A were detected in 11% of the insects fed tomato discs endophytically colonized by M. brunneum. The combined effects of the fungal spray with the mortality caused by the feeding of insects on transient EF-colonized leaves have to be considered to estimate the real acute impact of field sprays with entomopathogenic fungi on chewing insects.

Plant-fungal interactions: What triggers the fungi to switch among lifestyles?

Up till now various plant-fungal interactions have been extensively studied in the form of mycorrhizal, parasitic or endophytic lifestyles. Many of those interactions are beneficial to the host plants and a few are detrimental. Several investigations have pointed towards the interconversion of one fungal lifestyle into another while interact the plant system meaning endophyte may become parasite or vice versa. In such case, it is necessary to realize whether these different lifestyles are interconnected at some points either by physiological, biochemical or molecular routes and to identify the factors that trigger the change in fungal lifestyle, which is entirely different than earlier one and affects the host plant significantly. This review highlights the possible mechanisms of switching among the lifestyles of fungi based on recent findings and discusses the factors affecting plant fungal interactions. It also underlines the need for studying this important facet of plant-fungal interactions in depth which may in future help to fetch more advantages and to avoid the severe consequences in agriculture and other related fields.