Endoparasitic root-knot (Meloidogyne spp.) and lesion (Pratylenchus spp.) nematodes cause considerable damage in agriculture. Before they invade roots to complete their life cycle, soil microbes can ...attach to their cuticle or surface coat and antagonize the nematode directly or by induction of host plant defenses. We investigated whether the nematode-associated microbiome in soil differs between infective stages of Meloidogyne incognita and Pratylenchus penetrans, and whether it is affected by variation in the composition of microbial communities among soils. Nematodes were incubated in suspensions of five organically and two integrated horticultural production soils, recovered by sieving and analyzed for attached bacteria and fungi after washing off loosely adhering microbes. Significant effects of the soil type and nematode species on nematode-associated fungi and bacteria were revealed as analyzed by community profiling using denaturing gradient gel electrophoresis. Attached microbes represented a small specific subset of the soil microbiome. Two organic soils had very similar bacterial and fungal community profiles, but one of them was strongly suppressive towards root-knot nematodes. They were selected for deep amplicon sequencing of bacterial 16S rRNA genes and fungal ITS. Significant differences among the microbiomes associated with the two species in both soils suggested specific surface epitopes. Among the 28 detected bacterial classes, Betaproteobacteria, Bacilli and Actinobacteria were the most abundant. The most frequently detected fungal genera were Malassezia, Aspergillus and Cladosporium. Attached microbiomes did not statistically differ between these two soils. However, Malassezia globosa and four fungal species of the family Plectosphaerellaceae, and the bacterium Neorhizobium galegae were strongly enriched on M. incognita in the suppressive soil. In conclusion, the highly specific attachment of microbes to infective stages of phytonematodes in soil suggested an ecological role of this association and might be involved in soil suppressiveness towards them.
The influence of the squash hybrid RS841 rootstock (
Cucurbita maxima
x
C. moschata
) on population dynamics of
Meloidogyne incognita
and yield of cucumber cv. Dasher II was assessed during 2013 and ...2014 in a plastic greenhouse. In addition, the relationship between ecophysiological parameters (plant water status, gas exchange, and leaf reflectance) and
Pi
and cucumber yield were also estimated in 2013. Nematode densities were determined at the beginning (
Pi
) and at the end (
Pf
) of each crop, and the relationship between these parameters was used to estimate the maximum multiplication rate (
a
), the maximum population density (
M
) and the equilibrium density (
E
) per grafted and ungrafted cucumber and cropping season. Moreover, the relationship between the multiplication rate (
Pf
/
Pi
) and
Pi
was compared between grafted and ungrafted cucumber per cropping season. Finally, the relative yield of grafted or ungrafted cucumber was plotted against
Pi
to determine the tolerance limit (
T
) and the minimum relative yield (
m
) by the Seinhorst damage function model. Values of
a, M
and
E
in grafted cucumber were higher than in ungrafted one irrespective of the cropping season. These results were supported by comparing the relationship between
Pf/Pi
and
Pi
between grafted and ungrafted cucumber. The relationship between
Pi
and yield fitted the Seinhorst damage function. The values of
T
and
m
did not differ between grafted and ungrafted each year. Predawn water potential, net photosynthetic rate, and leaf chlorophyll index decreased with increasing
Pi
. In addition, relative yield was related to variation in net photosynthetic rate and the leaf chlorophyll index. Under the conditions of this study, RS841 rootstock was neither resistant nor tolerant to
M. incognita
.
The fluctuation of Meloidogyne population density and the percentage of fungal egg parasitism were determined from July 2011 to July 2013 in two commercial organic vegetable production sites (M10.23 ...and M10.55) in plastic greenhouses, located in northeastern Spain, in order to know the level of soil suppressiveness. Fungal parasites were identified by molecular methods. In parallel, pot tests characterized the level of soil suppressiveness and the fungal species growing from the eggs. In addition, the egg parasitic ability of 10 fungal isolates per site was also assessed. The genetic profiles of fungal and bacterial populations from M10.23 and M10.55 soils were obtained by Denaturing Gradient Gel Electrophoresis (DGGE), and compared with a non-suppressive soil (M10.33). In M10.23, Meloidogyne population in soil decreased progressively throughout the rotation zucchini, tomato, and radish or spinach. The percentage of egg parasitism was 54.7% in zucchini crop, the only one in which eggs were detected. Pochonia chlamydosporia was the only fungal species isolated. In M10.55, nematode densities peaked at the end of the spring-summer crops (tomato, zucchini, and cucumber), but disease severity was lower than expected (0.2-6.3). The percentage of fungal egg parasitism ranged from 3 to 84.5% in these crops. The results in pot tests confirmed the suppressiveness of the M10.23 and M10.55 soils against Meloidogyne. The number of eggs per plant and the reproduction factor of the population were reduced (P < 0.05) in both non-sterilized soils compared to the sterilized ones after one nematode generation. P. chlamydosporia was the only fungus isolated from Meloidogyne eggs. In in vitro tests, P. chlamydosporia isolates were able to parasitize Meloidogyne eggs from 50 to 97% irrespective of the site. DGGE fingerprints revealed a high diversity in the microbial populations analyzed. Furthermore, both bacterial and fungal genetic patterns differentiated suppressive from non-suppressive soils, but the former showed a higher degree of similarity between both suppressive soils than the later.
The thermal requirements of
on
in a set of constant soil temperatures were determined and the phenology model was validated at fluctuating soil temperatures. The base temperature (
) and the thermal ...constant (
) from nematode inoculation to females starting to lay eggs were 11.3 °C and 323 accumulated degree days (DD), respectively;
= 10.5 °C and
= 147 DD from egg production to emergence of juveniles; and
= 11.1 °C and
= 476 DD for life cycle completion. At fluctuating soil temperatures in pots with the minimum lower than
and the maximum higher than
(optimal temperature), the DD calculation was carried out by the average daily temperature-
(ADTb) and the single sine method over
(SSTb) with horizontal, intermediate, and vertical cutoffs. The most accurate were the ADTb and the SSTb with horizontal and intermediate cutoffs (93-106% of the predicted value) but the vertical underestimated the accumulated DD (75-82% of the predicted value). When fluctuating soil temperatures were between
and
in a plastic greenhouse, only the ADTb method was used. Life cycle completion was observed around 465 DD (accuracy between 0.95 and 0.99) at four different transplanting dates.
•C. amarus accessions were poorer hosts to RKN than watermelon.•C. amarus accessions improved crop yield when cultivated in nematode infested soils.•The level of resistance to RKN of both C. amarus ...was not affected after two years.
The aims of this study were to determine i) the effect of grafted watermelon cv. Sugar Baby onto C. amarus accessions BGV0005164 and BGV0005167 on M. incognita and M. javanica population growth estimated by means of the values of maximum reproduction rate, maximum nematode density and equilibrium density in pot experiments; ii) the effect of increasing nematode densities on plant productivity in pot experiments; and iii) the effect of repeated cultivation of watermelon cv. Sugar Baby grafted onto both C. amarus accessions and onto C. lanatus ‘Robusta’ during two seasons in a plastic greenhouse on M. incognita reproduction, disease severity, crop yield and selection for nematode virulence. In pot experiments, the values of maximum reproduction rate, maximum nematode density and equilibrium density of M. incognita were 37 %, 72 % and 68 % lower in watermelon grafted onto BGV0005164 than in ungrafted, and 28 %, 76 % and 77 % lower when grafted onto BGV0005167. Regarding M. javanica, the values of maximum reproduction rate, maximum nematode density and equilibrium density in watermelon grafted onto BGV0005164 were 88 %, 65 % and 14 % lower than in ungrafted, and 80 %, 76 % and 33 % lower when grafted onto BGV0005167. Dry shoot weight of ungrafted and grafted watermelon inoculated with a range of nematode densities between 0 and 1200 s-stage juveniles per 100 cm3 of soil was not affected, irrespective of the nematode isolate. In the plastic greenhouse experiment, M. incognita reproduced less in grafted than in ungrafted watermelon. Disease severity was higher in ungrafted than in grafted watermelon. The level of resistance of both C. amarus accessions was not affected after two-year cultivation, but it decreased from moderately resistant in 2017 to slightly resistant in rootstock ‘Robusta’. Watermelon grafted yielded between 2.9 and 5.6 kg more per plant than the ungrafted in 2017, and between 2.0 and 2.7 kg more per plant in 2018. In conclusion, C. amarus accessions BGV0005164 and BGV0005167 performed as poorer hosts to M. incognita and M. javanica. Watermelon grafted onto these C. amarus accessions improved fruit yield when they were cultivated in nematode infested soils without affecting its level of resistance to M. incognita after two consecutive crops.
Plant-parasitic nematodes are a significant cause of yield losses and food security issues. Specifically, nematodes of the genus
can cause significant production losses in horticultural crops around ...the world. Understanding the mechanisms of the ever-changing physiology of plant roots by imaging the galls induced by nematodes could provide a great insight into their control. However, infected roots are unsuitable for light microscopy investigation due to the opacity of plant tissues. Thus, samples must be cleared to visualize the interior of whole plants in order to make them transparent using clearing agents. This work aims to identify which clearing protocol and microscopy system is the most appropriate to obtain 3D images of tomato cv. Durinta and eggplant cv. Cristal samples infected with
to visualize and study the root-nematode interaction. To that extent, two clearing solutions (BABB and ECi), combined with three different dehydration solvents (ethanol, methanol and 1-propanol), are tested. In addition, the advantages and disadvantages of alternative imaging techniques to confocal microscopy are analyzed by employing an experimental custom-made setup that combines two microscopic techniques, light sheet fluorescence microscopy and optical projection tomography, on a single instrument.
spp. are an important threat to horticulture and cause substantial yield losses. Plant resistance is an alternative control method for chemical nematicides. This study highlights the host suitability ...of the lettuces cultivars Grand Rapids and Salinas 88 and the beans cultivars Aporé, Cornell 49242, Macarrão Atibaia and Ouro Negro to four
and seven
isolates from Spain in a pot experiment. Moreover, the response of these cultivars to increasing
densities (
) was assessed in a plastic greenhouse. The lettuce cultivar Regina 71 and the bean cultivar Bolinha were included as susceptible standards for comparison. It was found that Grand Rapids and Salinas 88 lettuces were resistant to the most nematode isolates in the pot experiment but were classified as slightly and moderately resistant, respectively, in the plastic greenhouse at increasing
Regarding the beans, Aporé was resistant to the majority of the
isolates whereas Macarrão Atibaia and Ouro Negro were slightly resistant and Cornell 49242 was susceptible in the pot experiment. In the plastic greenhouse, Aporé was the only cultivar able to effectively suppress the nematode reproduction irrespective of
, while Ouro Negro became less resistant as
increased. These results play an important role in enhancing the effective and ecofriendly
management strategies.
Proximal remote sensing devices are novel tools that enable the study of plant health status through the measurement of specific characteristics, including the color or spectrum of light reflected or ...transmitted by the leaves or the canopy. The aim of this study is to compare the RGB and multispectral data collected during five years (2016–2020) of four fruiting vegetables (melon, tomato, eggplant, and peppers) with trial treatments of non-grafted and grafted onto resistant rootstocks cultivated in a Meloidogyne incognita (a root-knot nematode) infested soil in a greenhouse. The proximal remote sensing of plant health status data collected was divided into three levels. Firstly, leaf level pigments were measured using two different handheld sensors (SPAD and Dualex). Secondly, canopy vigor and biomass were assessed using vegetation indices derived from RGB images and the Normalized Difference Vegetation Index (NDVI) measured with a portable spectroradiometer (Greenseeker). Third, we assessed plant level water stress, as a consequence of the root damage by nematodes, using stomatal conductance measured with a porometer and indirectly using plant temperature with an infrared thermometer, and also the stable carbon isotope composition of leaf dry matter.. It was found that the interaction between treatments and crops (ANOVA) was statistically different for only four of seventeen parameters: flavonoid (p < 0.05), NBI (p < 0.05), NDVI (p < 0.05) and the RGB CSI (Crop Senescence Index) (p < 0.05). Concerning the effect of treatments across all crops, differences existed only in two parameters, which were flavonoid (p < 0.05) and CSI (p < 0.001). Grafted plants contained fewer flavonoids (x¯ = 1.37) and showed lower CSI (x¯ = 11.65) than non-grafted plants (x¯ = 1.98 and x¯ = 17.28, respectively, p < 0.05 and p < 0.05) when combining all five years and four crops. We conclude that the grafted plants were less stressed and more protected against nematode attack. Leaf flavonoids content and the CSI index were robust indicators of root-knot nematode impacts across multiple crop types.
The present research was undertaken to evaluate the effects of soil temperature on the life cycle of root-knot nematodes (RKN) on zucchini-squash in growth chambers and to assess the relationship ...between Meloidogyne incognita soil population densities at planting (Pi), its multiplication rate, and crop losses of zucchini in field conditions. Thermal requirements for M. incognita and M. javanica were determined by cultivating zucchini plants in pots inoculated with 200 second stage juveniles (J2) of each Meloidogyne species at constant temperatures of 17, 21, 25, and 28 °C. Number of days from nematode inoculation until appearance of egg laying females and until egg hatching were separately recorded. For life cycle completion, base temperatures (Tb) of 12 ºC and 10.8 ºC and accumulated degree-days above Tb (S) of 456 and 526, were estimated for M. incognita and M. javanica, respectively. The relationship between fruit weight and M. incognita Pi fits the Seinhorst damage function, but differed accordingly to the cropping season, spring or autumn. Tolerance limits for M. incognita on zucchini were 8.1 J2 per 250 cm³ of soil in spring and 1.5 in autumn cropping cycles, and the minimum relative yields were 0.61 in spring and 0.69 in autumn. Zucchini-squash was a poorer host for M. incognita in spring than in autumn, since maximum multiplication rates (a) and equilibrium densities (E) were lower in spring (a = 16–96; E = 274–484) than in autumn (a = 270–2307; E = 787–1227).
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