Host Suitability of Lettuce and Bean Germplasm for Meloidogyne incognita and M. javanica Isolates from Spain.

Meloidogyne 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 Meloidogyne incognita and seven M. javanica isolates from Spain in a pot experiment. Moreover, the response of these cultivars to increasing M. incognita densities (Pi) 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 Pi. Regarding the beans, Aporé was resistant to the majority of the Meloidogyne 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 Pi, while Ouro Negro became less resistant as Pi increased. These results play an important role in enhancing the effective and ecofriendly Meloidogyne management strategies.

Development of Microscopic Techniques for the Visualization of Plant-Root-Knot Nematode Interaction.

Plant-parasitic nematodes are a significant cause of yield losses and food security issues. Specifically, nematodes of the genus Meloidogyne 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 Meloidogyne incognita 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.

Cucumis metuliferus reduces Meloidogyne incognita virulence against the Mi1.2 resistance gene in a tomato-melon rotation sequence.

BACKGROUND: Susceptible tomato cv. Durinta, ungrafted or grafted onto cv. Aligator resistant rootstock, both followed by the susceptible melon cv. Paloma, ungrafted or grafted onto Cucumis metuliferus BGV11135, and in the reverse order, were cultivated from 2015 to 2017 in the same plots in a plastic greenhouse, infested or not with Meloidogyne incognita. For each crop, soil nematode densities, galling index, number of eggs per plant and crop yield were determined. Virulence selection was evaluated in pot experiments. RESULTS: In the tomato-melon rotation, nematode densities increased progressively for the grafted tomato, being higher than for ungrafted plants at the end of the study; this was not the case in the melon-tomato rotation. Grafted crops yielded more than ungrafted crops in the infested plots. Virulence against the Mi1.2 gene was detected, but not against C. metuliferus. Reproduction of M. incognita on the resistant tomato was ∼ 120% that on the susceptible cultivar after the first grafted tomato crop, but this decreased to just 25% at the end of the experiment. CONCLUSION: Alternating different resistant plant species suppresses nematode population growth rate and yield losses. Although this strategy does not prevent virulence selection, the level was reduced. © 2018 Society of Chemical Industry.

Population Densities of Tylenchulus semipenetrans Related to Physicochemical Properties of Soil and Yield of Clementine Mandarin in Spain.

A survey was conducted from April to June 2002 in 62 orchards of clementine mandarin grafted on Troyer or Carrizo citrange rootstock in Catalonia (northeastern Spain) to determine the relationship between physicochemical soil properties and Tylenchulus semipenetrans population densities. Soil was analyzed to determine texture, pH, electric conductivity, organic matter content, N, P, K, Mg, calcium carbonate, and calcium oxide. Also, trials were conducted in 2003 and 2004 in three drip-irrigated orchards of clementine mandarin cv. Clemenules (El Pla and Mariclaire) or cv. Hernandina (Martorella) to determine the relationship between citrus nematode densities and yield of mandarin. T. semipenetrans was detected in 77% of the surveyed orchards. The number of second-stage juveniles + males in soil was related to N and K soil content (3.57953 - 0.001305 N + 0.00113 K, R2 = 0.1620, P < 0.0157). The relationship between relative yield of clementine mandarin cv. Clemenules and densities of females per gram of root in spring was described by the Seinhorst damage function model (0.035 + 0.965 (0.9995)(Pi - 287), R2 = 0.4782, P < 0.0001).

Microbiomes associated with infective stages of root-knot and lesion nematodes in soil.

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.