Soil organisms are a crucial part of the terrestrial biosphere. Despite their importance for ecosystem functioning, few quantitative, spatially explicit models of the active belowground community ...currently exist. In particular, nematodes are the most abundant animals on Earth, filling all trophic levels in the soil food web. Here we use 6,759 georeferenced samples to generate a mechanistic understanding of the patterns of the global abundance of nematodes in the soil and the composition of their functional groups. The resulting maps show that 4.4 ± 0.64 × 10
nematodes (with a total biomass of approximately 0.3 gigatonnes) inhabit surface soils across the world, with higher abundances in sub-Arctic regions (38% of total) than in temperate (24%) or tropical (21%) regions. Regional variations in these global trends also provide insights into local patterns of soil fertility and functioning. These high-resolution models provide the first steps towards representing soil ecological processes in global biogeochemical models and will enable the prediction of elemental cycling under current and future climate scenarios.
Seeds of papaya fruit (
Carica papaya
) are usually unused for the industry, but they have been previously reported to be anthelmintic. However, the effects and mechanisms involved in papaya seeds ...against root-knot nematodes (RKN) are poorly studied in soil incorporation. Here, we investigated soil biofumigation with papaya seeds against the RKN
Meloidogyne incognita
and the effect of their volatile organic compounds (VOCs) separately from non-VOCs. Soil biofumigation reduced the number of galls and eggs of RKN about 100% in tomato roots, by using seeds macerates at 4.0 g 100 mL
−1
, which is a feasible amount for field applications. The VOCs emitted by the seeds killed 80% of
M. incognita
second-stage juveniles after a few hours of exposure. Furthermore, the whole volatilome of the papaya seed was identified by gas chromatography. Some of the compounds have already been studied against RKN. Therefore, we examined the efficacy of all nonstudied compounds against
M. incognita
. The most promising compounds were vinyl acetate, phenylacetaldehyde and benzylacetonitrile with lethal concentrations (LC
50
) of 61.5, 101.3 and 14.4 μg mL
−1
, respectively. When vinyl acetate and phenylacetaldehyde were applied to the soil at the recommended commercial nematicide dose (396 μg mL
−1
), the effect on
M. incognita
was better than the commercial nematicide (Carbofuran), reducing 70% of the number of galls and eggs. However, benzylacetonitrile reduced galls and eggs only by 25%. These results provide evidence for biofumigation with papaya seeds as a sustainable approach to control RKN and the potential use of their VOCs as nematicidal compounds.
•First study on the fungal endophytic community isolated from feijoa fruit.•Two different cultivars host antagonistic fungi against Colletotrichum spp.•The most resistant cultivar hosted more ...biological control fungal agents.•T. harzianum, C. rosea and T. amestolkiae antagonized Colletotrichum spp.
Feijoa sellowiana (O. Berg) Burret is a tropical fruit from South America known as pineapple-guava or feijoa. Anthracnose is a fungal-caused disease that harms feijoa, and may completely reduce fruit production. The endophytic microbiota of feijoa fruits from native cultivars may provide new biocontrol agents against anthracnose. This work aimed to evaluate the diversity of endophytic cultivable fungi in feijoa fruits from two Brazilian native cultivars and verify potential agents against anthracnose pathogens: Colletotrichum nymphaeae and Colletotrichum siamense. The cultivable fungal diversity in feijoa fruits was assessed by fungi isolation, followed by fungal identification, through sequencing the ITS region of rDNA, and estimation of species abundance and frequency. Later, the antagonism of selected isolates was tested against Colletotrichum spp. by direct confrontation. Results demonstrated that isolated fungal communities slightly differed between the two cultivars. There was no difference in the Shannon index between the two cultivars. However, abundance and frequency of endophytes was respectively, 40% and 53% higher in the most resistant cultivar (Mattos), where Trichoderma harzianum, Trichoderma hamatum, Clonostachys rosea and Clonostachys rhizophaga were exclusively found. C. rosea and T. harzianum from cultivar 'Mattos', and Talaromices amestolkiae found in both cultivars ('Mattos' and 'Alcantara'), reduced mycelial growth and sporulation of Colletotrichum spp. Therefore, the endophytic cultivable community was slightly more abundant and rich in the most resistant cultivar of feijoa by encompassing more antagonistic species of fungi. This work also described for the first time the potential of endophytic fungi as biocontrol agents of feijoa pathogens.
Damage caused by plant-parasitic nematodes (PPNs) represents significant losses in agriculture worldwide. Sustainable and non-agrochemical practices have been sought out for the last few years aiming ...the reduction of PPN outbreaks, as such practices represent less interference in the soil health. In addition, certain soils naturally show high levels of suppressiveness against nematodes. Natural suppressive soils do not allow PPN increment by a balance in soil biotic and abiotic conditions. Such soils must be better understood by which components are responsible for their natural suppressiveness. Hence, keeping, stimulating or and even creating suppressive conditions in agricultural rhizosphere has been studied and applied to reduce PPN populations. There are many aspects that implicate in soil suppressiveness against PPN, such as microbiota activities, organic matter amount, chemical composition and physical constitution. However, any of those conditions is a single driver in suppressive soils against PPN. In this context, we intend to bring up an overview concerning the natural occurrence of suppressive soils against the most devastating PPNs worldwide and discuss the means used to induce suppressiveness in agricultural fields by sustainable management practices.
Several plant species are known to control plant-parasitic nematodes in soil by producing nematicidal volatile organic compounds (VOCs). However, the VOCs activity of many plant species against ...root-knot nematodes is still unknown. Here, we investigated VOCs emitted from leaves of citronella (Cymbopogon nardus L.) or black pepper (Piper nigrum L.), broccoli shoots (Brassica oleracea L.) and Brazil nuts (Bertholletia excelsa Bonpl.) against second-stage juveniles (J2) and eggs of Meloidogyne incognita. In vitro assays revealed that VOCs emitted from dry plant macerates decreased J2 motility to almost 0% and reduced egg hatching by 47% in comparison with the control. The water exposed to VOCs from citronella, black paper and Brazil nuts decreased the motility of the J2 by 42%, whereas broccoli reduced it to almost 0%. Furthermore, VOCs from Brazil nuts and broccoli shoots killed J2 and reduced the number of galls and eggs in tomato roots under greenhouse conditions. Purified dimethyl sulfate (DMS), dimethyl disulfide (DMDS) and 3-pentanol, previously identified in the broccoli volatilome, were tested on eggs of M. incognita. DMDS and 3-pentanol were shown to reduce egg hatching by 96.8% at 176 mg/L and by 88.4% at 918 mg/L, respectively, whereas DMS increased egg hatching by 13% at 500 and 1000 mg/L. All plant species produced VOCs toxic to eggs and J2, which are the most important developmental stages in terms of nematode management and should be more exploited to reduce root-knot nematode populations in soils prior to host infection or used for prospection of novel nematicidal products.
•VOCs from different plants reduced the viability of M. incognita J2 and eggs.•Brazil nuts and broccoli VOCs reduced galls and eggs formation of M. incognita.•Dimethyldisulfide (DMDS) and 3-pentanol decreased M. incognita egg hatching.•Dimethylsulfide (DMS) stimulated M. incognita egg hatching.
Meloidogyne
species produce egg masses containing nutrients which may serve as feeding substrate for rhizospheric fungi. In the present work we isolated fungi form
Meloidogyne paranaensis
egg masses. ...Amongst the fungi isolated 67% belonged to the genus
Fusarium
and, within those, 52% of the isolates were of the species
F.
oxysporum. Isolates from
F. oxysporum
and
F. solani
significantly reduced
M. incognita
infectivity and reproduction in tomato when J
2
were exposed to fungal volatiles, causing up to 100% immobility in in vitro tests. Water exposed to the volatile compounds produced by fungi and mixed to the J
2
suspension caused toxicity in
M. incognita
J
2
and reduced infectivity and reproduction of nematodes inoculated in tomato, when compared to the control. Using gas chromatography-mass spectrometry (GC-MS), the volatile compounds produced by
F. oxysporum
and
F. solani
were identified and gathered in six main categories: esters, alcohols, phenols, aldehydes, carboxylic acids and sesquiterpenes, making up a total of 23 molecules. For the first time, 12 molecules from various chemical groups were identified in the water exposed to the volatiles from
F. oxysporum
and
F. solani
. A lower number of molecules were detected in the toxic water when compared with the vapors produced by fungi. Within these molecules, various have been already reported as having high nematicidal activity. Thus,
F. oxysporum
and
F. solani
fungi from
M. paranaensis
egg masses produce volatile compounds with antagonistic activity to
M. incognita
.
We investigated the properties of rhizospheric soils infested with root-knot nematode (RKN) Meloidogyne exigua in 17 coffee (Coffea arabica) farms from the Southern region of Minas Gerais, Brazil. ...Physicochemical (pH, clay and organic matter) and biological properties (RKN parasites and microbiota volatile toxicity on M. exigua) were correlated with the number of second-stage juveniles (J
2
) and the egg hatching of M. exigua extracted from those rhizospheres. In the five most suppressive farms, the number of J
2
was less than 50/100 g of soil and the egg hatching was significantly low. The bacterium Pasteuria penetrans was found in four of the most suppressive farms with an average of 30% of J
2
infected with endospores. By using in vitro experiments the microbiota volatiles emitted from the most suppressive soils killed more than 83% of the J
2
. Additionally, volatiles produced by Fusarium oxysporum, Cladosporium sp. and Syncephalastrum sp. isolated from M. exigua eggs, significantly killed the J
2
. Identification of nematicidal compounds from the soils by GC-MS supported the strong involvement of the microbiota volatile toward RKN suppressiveness. Clay percentage and pH were similar in farms with the most suppressive soils (42.5% and 6.6%, respectively). Finally, the most suppressive soils came from farms with the highest coffee bean yields. Collectively, these results suggest the strong involvement of parasitic microorganisms, clay percentage and the pH suppressing RKN in soils from the major coffee production region in Brazil, and that volatiles emitted from total microbiota and exclusively from egg-isolated fungi are toxic to M. exigua.
ABSTRACT Pecan tree Carya illinoinensis (Wangenh.) K. Koch is a widespread species in the southern region of Brazil and commercially important for nut and wood production. Stem cankers in pecan trees ...negatively impact the orchard, but the biotic causes of cankers are usually not identified. Symptoms of stem canker were observed in about 60% of pecan trees from orchards in the states of Rio Grande do Sul and Paraná. Therefore, this study aimed to analyze the molecular and morphophysiological characteristics of fungi associated with pecan canker in orchards in southern Brazil and to confirm their pathogenicity in pecan seedlings. Samples from symptomatic stems were collected in different municipalities and possible causal agents were isolated. Molecular identification was performed by the Polymerase Chain Reaction technique for amplification of the EF-1α region and subsequent sequencing. The sequencing, followed by morphophysiological aspects of mycelial growth and colony pigmentation, allowed the identification of a species complex included in the Botryosphaeriaceae family. The isolates were classified as Lasiodiplodia theobromae, Pseudofusicoccum kimberleyense and Neofusicoccum parvum. Pathogenicity was tested by inoculating the isolates into pecan seedlings to evaluate the symptoms. All isolates caused canker in the stem, but there was variation in the severity. Therefore, different species of the Botryosphaeriaceae family are responsible for stem canker occurrence in pecan trees in the southern region of Brazil, but at different levels of injury. Thus, it is crucial to identify and understand the behavior of the fungal isolates to best control cankers in pecan orchards.
RESUMO A nogueira-pecã Carya illinoinensis (Wangenh.) K. Koch é uma espécie arbórea amplamente difundida na região sul do Brasil e comercialmente importante devido à produção de nozes e madeira. Cancros do tronco em árvores de noz-pecã impactam negativamente o pomar, mas as causas bióticas dos cancros geralmente não são identificadas. Sintomas de cancro do caule foram observados em cerca de 60% das nogueiras de pomares em municípios do Rio Grande do Sul e Paraná. Assim, este estudo teve como objetivo analisar as características moleculares e morfofisiológicas de fungos isolados de cancros em nogueira-pecã em pomares do sul do Brasil e confirmar sua patogenicidade na planta. Amostras de caules sintomáticos foram coletadas e possíveis agentes causais foram isolados. A identificação molecular foi realizada pela técnica de Reação em Cadeia da Polimerase para amplificação da região EF-1α e posterior sequenciamento. O sequenciamento, seguido de aspectos morfofisiológicos do crescimento micelial e pigmentação da colônia, permitiu a identificação de um complexo de espécies incluído na família Botryosphaeriaceae. Os isolados foram classificados como Lasiodiplodia theobromae, Pseudofusicoccum kimberleyense e Neofusicoccum parvum. A patogenicidade foi testada inoculando os isolados em mudas de nogueira-pecã para avaliar os sintomas. Todos os isolados causaram cancro no caule, mas houve variação na severidade. Portanto, diferentes espécies da família Botryosphaeriaceae são responsáveis pela ocorrência de cancro em tronco de nogueira-pecã na região sul do Brasil, mas em diferentes níveis de dano. Assim, é crucial identificar e compreender o comportamento dos isolados fúngicos para melhor controlar os cancros nos pomares.
PDF
