elocation-id: e3610
The use of weeds as an agroecological management strategy for phytonematodes has gained importance due to their implementation as trap plants that interfere with their biological cycle; therefore, this research aimed to evaluate the percentage of reproduction of Meloidogyne enterolobii and Nacobbus aberrans in five weeds. This experiment was carried out at the College of Postgraduates, Montecillo Campus, State of Mexico, Mexico, in 2023. The chili genotype CM-334 (control) was used as a susceptibility reference and each experimental unit was inoculated with 1000 J2 of each nematode species. The response variables were galling, egg masses, eggs, number of females and juveniles per g of root at 35 days after inoculation (dai) for Meloidogyne enterolobii and 45 dai for Na. A completely randomized experimental design with factorial arrangement was used. The weeds Tagetes erecta, Portulaca oleracea, Dysphania ambrosioides, Malva parviflora, and Oxalis corniculata showed a 100% decrease in the number of galls, egg masses, and eggs per g of root for Nacobbus aberrans, compared to the control. These last two parameters were similar for Meloidogyne enterolobii. All weeds evaluated showed a differential reproduction percentage for both nematodes in the number of females and individuals per g of root (7.34-100%). The results obtained indicate that these weeds can be used as a potential trap crop for the management of the nematodes Meloidogyne enterolobii and Nacobbus aberrans.
Dysphania ambrosioides,Malva parviflora, Oxalis corniculata, Portulaca oleracea, Tagetes erecta.
The root-knot nematodes Meloidogyne spp., present in several agricultural areas of Mexico, attack vegetables, fruit trees, ornamentals, and staple crops, causing losses in their yield (Cid del Prado et al., 2001); studies have focused on both M. incognita and Nacobbus aberrans (Na) (Moens et al., 2009) because they are polyphagous species; however, in recent years, the incidence of M. enterolobii (Me) (Villar-Luna et al., 2016) has been reported in Sinaloa, which is one of the largest chili producers in Mexico (SIAP, 2019).
The losses in production and in the income of producers caused by these nematodes make it necessary to search for control alternatives. Among these, the implementation of weedy or cultivated plants has been chosen since they can act as susceptible or resistant hosts to phytoparasitic nematodes (Rich et al., 2009; Ntidi et al., 2016). This characteristic can be used in phytosanitary management through the use of trap plants, either as indicators or differentials between nematode species, considering local conditions such as predominant nematode species, availability of sowing material, and geographical distribution of the evaluated species.
Additionally, some weeds can act as antagonists to phytoparasitic nematodes, whose properties affect their biological cycle, and it is attributed to nematicide/nematostatic metabolites present in the tissues of these species (Ferraz and Valle, 1997); these compounds can be released into the external environment or act only within the plant (Moreira et al., 2015). These plants can also be used as green cover or organic matter, or to improve overall soil quality (Moreira et al., 2015).
The use of species with antagonistic characteristics, such as Tagetes spp., Phyllanthus amarus, Trianthema portulacastrum, Solanum xanthocarpum, Coccinia grandis, and Leucas cephalotes, can have a significant impact on the reduction of the galling index caused by root-knot nematodes mediated by their phytochemical and physiological composition (Khan et al., 2019). This potentially inhibitory action on the mechanisms of host-nematode interaction, either individually or interspersed with other antagonist species, is proposed as a strategy for the control of root-knot nematodes in agricultural systems.
In this sense, it is suggested that the use of weeds could have a positive impact on the reduction of reproductive parameters of phytopathogenic nematodes and consequently on the damage caused by these species in agricultural crops. The research aimed to evaluate the percentage of reproduction of Nacobbus aberrans and Meloidogyne enterolobii in five weeds.
At the College of Postgraduates, Montecillo Campus, State of Mexico, Mexico, in 2023, the reproduction factor of the nematodes N. aberrans (Na) and M. enterolobii (Me) was evaluated on the following weeds: Tagetes erecta L., Asteraceae, Portulaca oleracea L., Portulacaceae, Dysphania ambrosioides L., Amaranthaceae, Malva parviflora L., Malvaceae, and Oxalis corniculata L., Oxalidaceae grown in pots with 236 cm3 of substrate (peat most:black soil:sand; 1:0.5:1) and they were kept under greenhouse conditions (38 °C max and -7 °C min). The chili genotype Criollo de Morelos CM-334 (CM-334) was used as a reference of susceptibility to Me and Na (Villar-Luna et al., 2015).
The inoculum of Me and Na was maintained in plants of chili (cv. California Wonder) and tomato (Río Grande) in a greenhouse at the College of Postgraduates, Montecillo Campus. Egg was extracted according to Vrain (1977) methodology; the juveniles of the second instar (J2) were obtained from eggs incubated at 27 ±1 °C in Petri dishes with sterilized distilled water. Each plant species was inoculated when they had 3-4 pairs of leaves with an inoculum level of 1000 J2 per plant (Filialuna et al., 2022).
The experimental unit consisted of an inoculated plant with five replications per plant species evaluated. It was established under a completely randomized design with factorial arrangement, where one factor was the species of nematode and another factor was the species of weed; five variables were evaluated: 1) galling; 2) egg masses; 3) eggs; 4) females and 5) juveniles per g of root at 35 days after inoculation (dai) for Me and 45 dai for Na. Subsequently, in the substrate containing the weeds, a cherry tomato seedling with 3-4 pairs of true leaves was planted in order to evaluate the presence of inoculum in said substrate. At 35 days after the extraction (dae) of the weeds inoculated with Me, the same parameters mentioned above were evaluated in the same way as occurred for Na at 45 dae.
Egg masses were stained with phloxine B (Hussey and McGuire, 1987) and acid fuchsin was used for the number of nematodes present in the root system (Byrd et al., 1983). The number of egg masses per root was counted under a magnifying glass with a 5x magnification and the number of masses per root was recorded. The number of nematodes present in the root was obtained with the use of a stereoscopic microscope (Zeiss Stemi DV4).
Eggs were extracted using Vrain (1977) method and the number of eggs per gram of root of each species evaluated was determined. The evaluation of the categorization of host, good host or non-host, was carried out according to the criteria reported by Oostenbrink (1966) with modifications, who establishes the reproduction factor RF= 0-0.09 as non-host; 0.1-0.9, poor host; 1-2, moderate host and >2, adequate host. Where the RF was determined by dividing the final population (Pf) by the initial population (Pi).
The reproductive parameters of the nematode were estimated in each experimental unit according to Kanchan et al. (2023), who indicate that the percentage of reduction in reproductive parameters is equal to: [(number of p in the control - number of p in the treatment)/number of p in the control] x 100%. Where: p= galls/number of egg masses/eggs per g of root/number of females and juveniles inside the root.
The data of the evaluated variables were subjected to an analysis of variance (Anova) with a confidence interval of 95%; the statistical differences between the means were compared using Tukey’s test (p≥ 0.05) with the statistical program of Sas version 9.0 (SAS Institute Inc, 2002).
Significant differences (p≥ 0.05) were observed in all evaluated variables caused by M. enterolobii and N. aberrans. Me presented greater galling and number of juveniles per gram of root compared to Na (Tables 1 and 2). There was a differential galling among the weed species evaluated and the severity caused by the root-knot nematodes evaluated (Figures 1 and 2).
Malva parviflora, Portulaca oleracea, and Dysphania ambrosioides exhibited a greater susceptibility to Me infection; nevertheless, this behavior was different for Na, whose weeds did not present galling for this species (Table 2, Figure 2). On the other hand, Oxalis corniculata showed galling only for M. incognita (Figure 1), with an average of 270 galls per plant. In addition to a greater galling caused by Me (Table 1), a greater presence of J2-J3 juveniles was observed in all weeds evaluated compared to Na (Tables 1 and 2); the positive control CM-334 presented a greater number of juveniles in both species of root-knot nematodes (Tables 1 and 2).
Lower virulence was observed based on the number of Me juveniles in the weeds Oxalis corniculata (1.6) and Tagetes erecta (0), compared to the rest of the weeds evaluated (Table 1). In the case of Na, the weed Oxalis corniculata (0) and Tagetes erecta (0) were not susceptible to this nematode (Table 2). No mature females of Me or Na were observed in the weeds Portulaca oleracea, Dysphania ambrosioides, Tagetes erecta, and Oxalis corniculata (Figures 1 and 2, Tables 1 and 2).
All weeds evaluated showed no egg masses, except for Malva parviflora inoculated with Me, although this was not reflected in the galling of the second cycle, which corresponded to tomato plants (Table 1). On the other hand, Oxalis corniculata recorded an average of 77 egg masses per plant and 767 eggs per plant of M. incognita.
The virulence caused by Na had the same behavior in the production of eggs per gram of root (Table 2) and the reproduction factor that was equal to 0 in all weeds evaluated; that is, there was no presence of eggs, so all weeds evaluated according to Oostenbrink (1966) behaved as non-host species for both root-knot nematodes.
Although Me form galls in the weeds Portulaca oleracea and Dysphania ambrosioides, no adult stages were found; these findings are similar to those reported by Groover et al. (2019) as they found differences in galling in cotton (Fibermax 1944), corn (Mycogen 2R042) and soybean (Asgrow 5935) plants caused by species of the genus Meloidogyne, demonstrating that the differentiation of root-knot nematode species, through the implementation of hosts that show the variability of nematode populations in the same field, can contribute in a practical way to decision-making for the management of these species through the crop rotation thanks to the decrease in the reproductive factor, which would indicate that the formation of galls is not essential or indicative of the adequate development of the nematode (Cook and Starr, 2006).
The behavior of the weeds Portulaca oleracea, Tagetes erecta, Dysphania ambrosioides, and Oxalis corniculata may be related to what was pointed out by Villar-Luna et al. (2015) in the CM-334 chili, who reported a low penetration of J2 of M. incognita at 21 days after inoculation, which is highly resistant to this species, attributing it to a restriction in its establishment.
They also point out that this incompatible interaction (Mi-CM-334) may be involved in the overexpression of the EAS, HMG2, WRKY-a, PR-1 and POX genes associated with plant defense mechanisms, as well as with the accumulation of bioactive compounds, which they related them to the restriction of the establishment and reproduction of the nematode.
The inhibition of the development of adult females of Me and Na observed in plants of Portulaca oleracea, Dysphania ambrosioides, and Oxalis corniculata (Tables 1 and 2, Figures 1 and 2) could be based on a hypersensitivity response (HR), which plays a crucial role in immunity to plant pathogenic nematodes by influencing migration directly or indirectly through the release of nematostatic chemicals, nematicides or damage-associated molecular patterns that can activate other immune responses, such as creating a physical barrier between surrounding cells, inhibiting the supply of nutrients in the nematode’s feeding cells, causing a reduction in fecundity in females and therefore in the reproduction factor (Sato et al., 2019), as observed in Portulaca oleracea, which presented only immature females for Me (Table 1).
This is consistent with Proita et al. (2008) results, who analyzed the post-infection development and histopathology of Meloidogyne arenaria race 1 on three species of Arachis spp. and observed a hypersensitive reaction with the formation of necrotic zones in the vascular cylinder and there were no giant cells or juvenile development until the second stage (J2); in the same way, in our results, there was only the presence of juveniles of different stages of Me and Na in Dysphania ambrosioides (Tables 1 and 2), of Na in Portulaca oleracea and Malva parviflora (Table 2), and of Me in Oxalis corniculata (Table 1).
In Portulaca oleracea, flavonoid levels have been reported to vary depending on the part of the plant, with the highest levels being present in the root followed by the stem and leaf (Zhou et al., 2015); likewise, seven different flavonoids have been found present in this plant, including kaempferol, myricetin, luteolin, apigenin, quercetin, genistein and genistin (Uddin et al., 2014), the same compounds that, in recent research, have been identified as chemicals that show high mortality and inhibition of hatching of eggs and juveniles of Meloidogyne incognita species (Wuyts et al., 2006; Khan et al., 2019).
Nonetheless, it has been reported as a host for M. incognita, as well as for Me and Na (Rich et al., 2009; Cid del Prado et al., 2018), which does not agree with what was observed in this work. On the contrary, we agree with what Manzanilla et al. (2002) report for N. aberrans, where they indicate that, although some species of Poaceae (= Gramineae) are reported as hosts, in these plants, there is usually only the presence of vermiform juveniles and females without the presence of obese females.
This behavior indicates that some species of weeds can serve as trap plants since they penetrate the infective stages but do not allow the biological cycle of the nematode to be completed as adult females are not found, which induce the formation of galls and interfere with the absorption of water and nutrients (Triviño, 2004).
Similarly, the action of secondary metabolites present in these species can affect the behavior of M. incognita, acting as attractants or repellents, inducing the inhibition of motility, reducing incubation, and causing its death (Yang et al., 2016). Wuyts (2006) observed that salicylic acid accumulates at the sites of nematode location, being able to migrate through tissues, acting as an elicitor that triggers the signal systems of plant cells, in such a way that endogenous salicylic acid induces gene expression, which results in the formation of proteins related to pathogenesis and the production of phytoalexins (Hussey and Janssen, 2004).
On the other hand, it could be related to what was reported by Kirwa et al. (2018), who found that M. incognita can be attracted to five compounds (zeatin, quercetin, luteolin, solasodine, and tomatidine) isolated from tomato rhizosphere extract and that chemotaxis activity depended on concentration; some of these compounds, such as quercetin and luteolin, have been reported in the phytochemical profile of all weed species evaluated and their concentration depends on the host species.
Meloidogyne enterolobii (Me) induced galls in Portulaca oleracea, Dysphania ambrosioides and Malva parviflora, but the presence of galls by Nacobbus aberrans (Na) was not evident; for its part, in Oxalis corniculata, there was only the presence of galls by Meloidogyne incognita (Mi); this behavior suggests that these weeds can be used as differential species according to the presence of galls.
On the other hand, Portulaca oleracea, Dysphania ambrosioides, and Oxalis corniculata can be used as trap species given the presence of juveniles without adult females of the nematode’s species Me and Na.
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