Tropical soil microflora of spice-based cropping systems as potential antagonists of root-knot nematodes

Metarhizium carneum Formulations: A Promising New Biological Control to Be Incorporated in the Integrated Management of Meloidogyne enterolobii on Tomato Plants

The increase in the populations of root-knot nematode Meloidogyne enterolobii in various vegetables such as tomatoes grown under greenhouse conditions as well as increasing restrictions on the use of certain chemical nematicides have led to the search for new, effective management strategies, preferably ones that are sustainable biological alternatives. In this work, two formulations of the nematophagous fungus Metarhizium carneum, one concentrated suspension and one wettable powder, were evaluated under greenhouse conditions to reduce the M. enterolobii infestation in tomato plants. In addition, the effectiveness of the liquid formulation of M. carneum was compared with two biological and three chemical commercial nematicides. The results show that the two M. carneum formulations reduced the M. enterolobii population density by 78 and 66% in relation to the control treatment. In comparison, the liquid formulation of M. carneum and Purpureocillium lilacinum treatments reduced nematode population density by 72 and 43%, respectively, while for metam sodium preplanting applications followed by M. carneum applications during the tomato growth stage, the reduction was 96%. The alternate use of some chemical compounds plus the application of M. carneum as a biocontrol is a good starting strategy for managing M. enterolobii populations. These results confirm that M. carneum is a serious candidate for the short-term commercialization of an environmentally friendly biological nematicide.

Potencial nematicida de hongos aislados de cultivos de plátano dominico hartón (Musa AAB Simmonds) del suroeste antioqueño

El objetivo de este trabajo fue evaluar el potencial nematicida de aislados fúngicos provenientes de cultivos de plátano de los municipios de Andes y Jardín (Suroeste antioqueño). Se analizaron in vitro diez aislados fúngicos frente a los nematodos fitoparásitos de los géneros Meloidogyne y Radopholus. Los hongos pertenecían a los géneros Paecilomyces, Pochonia, Arthrobotrys, Lecanicillium y Metarhizium. Se realizaron pruebas metabólicas cualitativas con diversos sustratos con el fin de observar la capacidad de degradación de diferentes compuestos característicos en la estructura de huevos o juveniles de nematodos. También, se evaluó la capacidad de colonizar huevos o juveniles de Meloidogyne sp. y, la mortalidad de los aislados frente a los géneros Meloidogyne y Radopholus. Se encontró que la mayoría de los aislados fueron capaces de degradar Tween 80 (90% de los aislados), seguido de caseína (80%), gelatina (80%), Tween 20 (60%), y en menor medida quitina (40% de los aislados); además, el 30% de los aislados presentaron formación de cristales en los medios de Tween. El 70% de los aislados podían infectar huevos, mientras que el 30% restante infectaban juveniles (J2) de Meloidogyne sp., después 24 horas de incubación. En cuanto al porcentaje de mortalidad del hongo y el filtrado, se encontró que todos los aislados difieren del control (p<0.05), siendo aislados de los géneros Pochonia y Paecilomyces quienes presentaron porcentajes de mortalidad superiores al 90%.

Phytohormones selectively affect plant parasitic nematodes associated with Arabidopsis roots

Phytohormones may affect plant-nematode interactions directly as chemo-attractants or -repellents, or indirectly through the root-associated microbiome or through host defense mechanisms. However, the exact roles of phytohormones in these complex plant-soil-nematode interactions are not well understood. We used Arabidopsis thaliana mutants impaired in phytohormone synthesis or sensitivity to elucidate their role in root-nematode interactions. As root-associated microorganisms may modulate these interactions, we explored correlations between the relative abundances of root-associated nematodes, and bacteria and fungi using amplicon sequencing. We found distinct shifts in relative abundances of a range of nematode taxa in the A. thaliana phytohormone mutants. The root knot nematode Meloidogyne hapla, a sedentary endoparasitic species that is in intimate contact with the host, was highly enriched in JA-, SA- and SL-impaired lines, and in an ET-insensitive line. Positive or negative correlations between specific microbial and nematode taxa were observed, but, as the inference of causal relationships between microbiome responses and effects on nematode communities is premature, this should be studied in detail in future studies. In conclusion, genetic derailment of hormonal balances generally rendered plants vulnerable to endoparasitic nematode attack. Furthermore, preliminary data suggest that this effect may be partially modulated by the associated microbiome.

Paecilomyces and Its Importance in the Biological Control of Agricultural Pests and Diseases

Incorporating beneficial microorganisms in crop production is the most promising strategy for maintaining agricultural productivity and reducing the use of inorganic fertilizers, herbicides, and pesticides. Numerous microorganisms have been described in the literature as biological control agents for pests and diseases, although some have not yet been commercialised due to their lack of viability or efficacy in different crops. Paecilomyces is a cosmopolitan fungus that is mainly known for its nematophagous capacity, but it has also been reported as an insect parasite and biological control agent of several fungi and phytopathogenic bacteria through different mechanisms of action. In addition, species of this genus have recently been described as biostimulants of plant growth and crop yield. This review includes all the information on the genus Paecilomyces as a biological control agent for pests and diseases. Its growth rate and high spore production rate in numerous substrates ensures the production of viable, affordable, and efficient commercial formulations for agricultural use.

Fungal evolution: major ecological adaptations and evolutionary transitions

Fungi are a highly diverse group of heterotrophic eukaryotes characterized by the absence of phagotrophy and the presence of a chitinous cell wall. While unicellular fungi are far from rare, part of the evolutionary success of the group resides in their ability to grow indefinitely as a cylindrical multinucleated cell (hypha). Armed with these morphological traits and with an extremely high metabolical diversity, fungi have conquered numerous ecological niches and have shaped a whole world of interactions with other living organisms. Herein we survey the main evolutionary and ecological processes that have guided fungal diversity. We will first review the ecology and evolution of the zoosporic lineages and the process of terrestrialization, as one of the major evolutionary transitions in this kingdom. Several plausible scenarios have been proposed for fungal terrestralization and we here propose a new scenario, which considers icy environments as a transitory niche between water and emerged land. We then focus on exploring the main ecological relationships of Fungi with other organisms (other fungi, protozoans, animals and plants), as well as the origin of adaptations to certain specialized ecological niches within the group (lichens, black fungi and yeasts). Throughout this review we use an evolutionary and comparative-genomics perspective to understand fungal ecological diversity. Finally, we highlight the importance of genome-enabled inferences to envision plausible narratives and scenarios for important transitions.

Isolation and characterization of Aspergillus niger NBC001 underlying suppression against Heterodera glycines

Heterodera glycines is the most pervasive soybean pests worldwide. Biocontrol provides a strategy to sustainably control nematodes. In this study, 22 fungal isolates were obtained and identified from cysts of Heterodera spp. Among them, Aspergillus niger NBC001 showed high nematicidal activity against H. glycines. The 2-fold dilution of NBC001 culture filtrate caused 89% mortality of second-stage juveniles and inhibited more than 98% of egg hatching in vitro. In both pot and field experiments, the numbers of H. glycines cysts in soybean seedlings dressed with the the 5-fold concentrated culture filtrate of NBC001 were significantly reduced by 43% and 28%, respectively. In addition, application of NBC001 remarkably reduced the penetration of nematodes into the roots. Histochemical and fluorometric staining analyses indicate that application of NBC001 stimulated hydrogen peroxide activity in the roots and triggered callose deposition in the leaves and roots. Transcription of the PR1a and EREBP genes in the salicylic acid and ethylene signaling pathways was upregulated in soybean plants treated with NBC001. However, the application of concentrated culture filtrate of NBC001 had no significant impacts on the soil microbial community based on next generation DNA sequencing technology. In summary, NBC001 may be a good biocontrol agent against H. glycines via stimulation of the immunity/defense of the plant host.

Evaluation of Pochonia chlamydosporia and Purpureocillium lilacinum for Suppression of Meloidogyne enterolobii on Tomato and Banana

Meloidogyne enterolobii is one of the most important root-knot nematode in tropical regions, due to its ability to overcome resistance mechanisms of a number of host plants. The lack of new and safe active ingredients against this nematode has restricted control alternatives for growers. Egg-parasitic fungi have been considered as potential candidates for the development of bionematicides. In tissue culture plates, Pochonia chlamydosporia (var. catenulata and chlamydosporia) and Purpureocillium lilacinum strains were screened for their ability to infect eggs of the root-knot nematode M. enterolobii on water-agar surfaces. Reduction in the hatching of J2 varied from 13% to 84%, depending on strain. The more efficacious strains reduced hatchability of J2 by 57% to 84% when compared to untreated eggs, but average reductions were only 37% to 55% when the same strains were applied to egg masses. Combinations of fungal isolates (one of each species) did not increase the control efficacy in vitro. In experiments in which 10,000 nematode eggs were inoculated per plant, reductions in the number of eggs after 12 months were seen in three of four treatments in banana plants, reaching 34% for P. chlamydosporia var. catenulata. No significant reductions were seen in tomato plants after 3 mon. In another experiment with tomato plants using either P. chlamydosporia var. catenulata or P. lilacinum, the number of eggs was reduced by 34% and 44%, respectively, when initial infestation level was low (500 nematode eggs per plant), but tested strains were not effective under a moderate infestation level (5,000 eggs per plant). Under all infestation levels tested in this work, gall and egg mass indexes (MI) did not differ from the untreated controls, bringing concerns related to the practical adoption of this control strategy by farmers. In our opinion, if the fungi P. chlamydosporia and P. lilacinum are to be used as biocontrol tools toward M. entorolobii, they should focus on agricultural settings with low soil infestation levels and within an IPM approach.

Changes in the soil microbial community after reductive soil disinfestation and cucumber seedling cultivation

Reductive soil disinfestation (RSD) has been proven to be an effective and environmentally friendly way to control many soilborne pathogens and diseases. In this study, the RSDs using ethanol (Et-RSD) and alfalfa (Al-RSD) as organic carbons were performed in a Rhizoctonia solani-infected soil, and the dissimilarities of microbial communities during the RSDs and after planting two seasons of cucumber seedlings in the RSDs-treated soil were respectively investigated by MiSeq pyrosequencing. The results showed that, as for bacteria, Coprococcus, Flavisolibacter, Rhodanobacter, Symbiobacterium, and UC-Ruminococcaceae became the dominant bacterial genera at the end of Al-RSD. In contrast, Et-RSD soil involved more bacteria belonging to Firmicutes, such as Sedimentibacter, UC-Gracilibacteraceae, and Desulfosporosinus. For fungi, Chaetomium significantly increased at the end of RSDs, while Rhizoctonia and Aspergillus significantly decreased. After planting two seasons of cucumber seedlings, those bacteria belonging to Firmicutes significantly decreased, but Lysobacter and Rhodanobacter belonging to the phylum Proteobacteria as well as UC-Sordariales and Humicola belonging to Ascomycota alternatively increased in Al- and Et-RSD-treated soils. Besides, some nitrification, denitrification, and nitrogen fixation genes were apparently increased in the RSD-treated soils, but the effect was more profound in Al-RSD than Et-RSD. Overall, Et-RSD could induced more antagonists belonging to Firmicutes under anaerobic condition, whereas Al-RSD could continuously stimulate some functional microorganisms (Lysobacter and Rhodanobacter) and further improve nitrogen transformation activities in the soil at the coming cropping season.

Bio-management of tomato wilt complex caused by Meloidogyne incognita and Fusarium oxysporum f. sp. lycopersici

The potential of biocontrol agentsPurpureocillium lilacinum(Paecilomyceslilacinus) andTrichodermaharzianumwas evaluated against tomato wilt complex, caused by a combination ofMeloidogyne incognitaandFusarium oxysporumf. sp.lycopersici, under both laboratory and field conditions. Biocontrol agents at spore concentration of 1 × 106spores ml−1were applied alone and in combined treatments. The results of combined application revealed maximum mortality and inhibition of hatching ofM. incognitaunderin vitroconditions. Combined application of both antagonistic fungi was found to be more effective in mycelial inhibition ofFusarium oxysporumf. sp.lycopersici. In glasshouse trials, application ofT. harzianumpromoted overall plant growth, followed by combined application ofP. lilacinumandT. harzianum; nematode development parameters and fungus damage were significantly reduced. Under field conditions, the combined application ofP. lilacinumandT. harzianumincreased the number of leaves, shoot length, shoot weight and root length, and decreased root weight, with minimum number of females and egg masses ofM. incognitaper root system and mycelia inhibition ofF. oxysporum.

Efficacy of root-associated fungi and PGPR on the growth of Pisum sativum (cv. Arkil) and reproduction of the root-knot nematode Meloidogyne incognita

The effects of root-associated fungi (Aspergillus awamori and Glomus mosseae) and plant growth promoting rhizobacteria (PGPR) (Pseudomonas putida, Pseudomonas alcaligenes and Paenibacillus polymyxa) were studied alone and in combination in glasshouse experiments on the growth of pea, enzyme activity (peroxidase and catalase) and reproduction of root-knot nematode Meloidogyne incognita. Application of A. awamori, G. mosseae and PGPR caused a significant increase in pea growth and enzyme activities of both nematode inoculated and uninoculated plants. A. awamori was more effective in reducing galling and improving the growth of nematode inoculated plants than P. alcaligenes or P. polymyxa. The greatest increase in growth, enzyme activities of nematode-inoculated plants and reduction in galling and nematode multiplication was observed when A. awamori was used with P. putida or G. mosseae as compared to the other combinations tested. Percentage root colonization was higher when AM fungus inoculated plants were treated with P. putida both in presence and absence of nematode.

Biocontrol of Meloidogyne incognita on tomato using antagonistic fungi, plant-growth-promoting rhizobacteria and cattle manure

BACKGROUND

Biocontrol achieved by a single biocontrol agent is generally inconsistent under field conditions. The aim of the present study was to increase the competitiveness and efficacy of biocontrol agents by using them together with cattle manure.

RESULTS

The effects of antagonistic fungi [Aspergillus niger v. Teigh., Paecilomyces lilacinus (Thom) Samson and Penicillium chrysogenum Thom] and plant-growth-promoting rhizobacteria (PGPR) [Azotobacter chroococcum Beijer., Bacillus subtilis (Ehrenberg) Cohn and Pseudomonas putida (Trev.) Mig.] were assessed with cattle manure on the growth of tomato and on the reproduction of Meloidogyne incognita (Kof. & White) Chitwood. Application of antagonistic fungi and PGPR alone and in combination with cattle manure resulted in a significant increase in the growth of nematode-inoculated plants. The highest increase (79%) in the growth of nematode-inoculated plants was observed when P. putida was used with cattle manure, followed by use of P. lilacinus plus cattle manure. Paecilomyces lilacinus resulted in a high reduction in galling and nematode multiplication, followed by P. putida, B. subtilis, A. niger, A. chroococcum and P. chrysogenum. The combined use of P. lilacinus with cattle manure resulted in a maximum reduction in galling and nematode multiplication.

CONCLUSION

Application of P. lilacinus or P. putida with cattle manure was useful to achieve greater biocontrol of M. incognita on tomato.

Effects of fungal culture filtrates of Verticillium lecanii (Lecanicillium spp.) hybrid strains on Heterodera glycines eggs and juveniles

Many nematode-antagonistic fungi produce secondary metabolites and enzymes that demonstrate toxicity against plant-parasitic nematodes. The objective of this study was to evaluate the effects of fungal culture filtrates of Verticillium lecanii hybrid strains on mature eggs, embryonated eggs (eggs fertilized but without development of juveniles), and second-stage juveniles (J2) of Heterodera glycines and to compare these effects with those of their parental strains. The fungal culture filtrates of certain hybrid strains inhibited egg hatch of mature eggs. Furthermore, the fungal culture filtrates of two hybrid strains, AaF23 and AaF42, exhibited high toxicity against embryonated eggs of H. glycines. However, most of the fungal culture filtrates of V. lecanii did not inactivate J2. These results suggested that enzymes or other active compounds produced by the fungal culture filtrates of V. lecanii exhibit activity against specific stages in the H. glycines life cycle. In addition, based on a visual assessment of the morphological changes in eggs caused by filtrates of each strain, there were differences between the hybrid strains and their respective parental strains with regard to the active substances produced by V. lecanii against the embryonated eggs. As a result of promoting recombination of whole genomes via protoplast fusion, several hybrid strains may have enhanced production of active substances that are different from those produced by their parental strains. It was concluded that natural substances produced by V. lecanii are one of the important factors involved in the suppression of H. glycines damage.