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 ($\overline{\mathrm{x}}$ = 1.37) and showed lower CSI ($\overline{\mathrm{x}}$ = 11.65) than non-grafted plants ($\overline{\mathrm{x}}$ = 1.98 and $\overline{\mathrm{x}}$ = 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.

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.

The management of Meloidogyne spp. in tomato crops presents significant challenges for sustainable agriculture. This study evaluates the potential of Nesidiocoris tenuis, Macrolophus pygmaeus, and (Z)-3-hexenyl propanoate—two zoophytophagous mirid species and one of the herbivore-induced plant volatiles (HIPVs) they trigger—to induce systemic resistance against Meloidogyne incognita and M. javanica in tomato plants (cv. Bodar). To this end, we assess the expression of the PIN2 and PR1 genes, related to the jasmonic acid (JA) and salicylic acid (SA) pathways, respectively. Exposure of tomato plants to 15 nymphs of either N. tenuis or M. pygmaeus for 24 or 48 h, and to (Z)-3-hexenyl propanoate for 24 h, before inoculation with 200 second-stage juveniles of the nematodes significantly reduced nematode infectivity and reproduction. Notably, PIN2 gene expression in leaves was upregulated nine- and 14-fold by N. tenuis and M. pygmaeus, respectively, zero days after nematode inoculation (DANI) and was repressed by the nematode seven DANI with a nine-fold decrease, but not when the plants were exposed to M. pygmaeus or N. tenuis, indicating a strong early defense response. However, PR1 expression levels showed no significant changes, suggesting a predominant role of the JA pathway over the SA pathway in the induced resistance. We conclude that induction of systemic resistance in tomato plants by N. tenuis, M. pygmaeus, and (Z)-3-hexenyl propanoate before nematode exposure is a promising strategy for nematode management, at least to suppress nematode infection by the primary inoculum and later reproduction.

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. Among these, RGB images can provide spatially detailed information about crop status including estimates of biomass, chlorophyll (and chlorosis) and fractional vegetation cover. The aim of this study is to compare the RGB 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, RKN) infested soil in a greenhouse. The proximal remote sensing of plant health status data collected were 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). Thirdly, we assessed plant level water stress, as a consequence of the root damage by nematodes, directly using stomatal conductance measured with a porometer, and indirectly using plant temperature with an infrared thermometer and also the stable carbon and nitrogen isotope composition of leaf dry matter. Among the measured parameters, carbon and nitrogen percentage exhibited the highest positive correlation (r = 0.90), whereas flavonoids and NBI (Nitrogen Balance Index) showed the highest inverse correlation (r = −0.87). It was found that the interaction between treatments and crops (ANOVA) was statistically different for only 4 of 17 parameters (flavonoid (p = 0.002), NBI (p = 0.044), NDVI (p = 0.004) and CSI (RGB-based Crop Senescence Index) (p = 0.002). Concerning the effect of treatments across all crops, differences existed only in two parameters, which were flavonoids (p = 0.003) and CSI (p = 0.001). Grafted plants contained less flavonoids ($\bar{\mathrm{x}}$ = 1.37) and showed lower CSI ($\bar{\mathrm{x}}$ = 11.65) than non-grafted plants ($\bar{\mathrm{x}}$ = 1.98 and $\bar{\mathrm{x}}$ = 17.28, respectively, p = 0.020 and p = 0.029) 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 and the RGB indexes (CSI) were robust indicators of root-knot nematode impacts across multiple crop types.