Study area

The present work was carried out in 2012, in a Batisierra type greenhouse, located in the Chaparrosa community of the municipality of Villa de Cos, Zacatecas. The community is located at 23^o 06’ north latitude and 102^o 22’ west longitude, at 1 900 meters above sea level. Its climate is subtropical arid temperate, with an average annual temperature of 17 ^oC and frosts from the end of october to the beginning of april. The average annual precipitation varies from 400 to 500 mm (^{Medina et al., 2003}). Predominantly flat soils of Feozem and Litosol type, whose chemical characteristics are: pH= 7.6, CE= 0.83 dS m^-1, N-NO₃= 62 mg kg^-1, MO= 1.51%.

Treatments, design and experimental unit

Eight treatments were tested: 1) plants of cempasuchil (Tagetes erecta) (C), located alternately with tomato plants; 2) solarization of the floor with transparent plastic gauge 620 gauge, equivalent to 155 μm thick, placed at the beginning of the work covering the width of the bed and 40 m in length (S); 3) application of the nematode Vidate (N) in the dose of 4 L ha^-1, applied at the moment of the transplant using the drip irrigation system; 4) S+C; 5) S+N; 6) N+C; 7) C+S+N; and 8) witness (without any treatment) (T). The cempasuchil plants were transplanted when they were 30 days old, on February 2 and seven days later the tomato was transplanted. An experimental design was used in complete blocks at random with four repetitions, the experimental unit consisted of a tomato plant.

Experiment management

The work was carried out in natural soil in a Batisierra type greenhouse, which has a drip irrigation system and fertilizer injection. The variety of tomato “El Cid” was used, with Saladette type fruits, because it is one of the varieties that are most cultivated in Zacatecas. A seedling developed in polystyrene trays with alveoli of 25 mL was used in the greenhouse; the transplant was performed on February 9, 2012.

Practices carried out

The population of plants that was established, in the ship where the experiment was developed, was 24 000 per hectare; the distance between beds was 1.40 m and between plants 30 cm. The cultivation practices that were carried out were the same in the experimental plot and in the commercial plantation and consisted mainly in the application of fertilizer from the transplant and then every week, by means of fertigation. When transplanting, 300 kg ha^-1 of di-ammonium phosphate (18-46-00) were applied, after which the dose was applied in total: 280-00-200 in the following weeks, based on soluble fertilizers; 100 units of CaO and 50 units of MgO were also applied, based on calcium nitrate and magnesium sulfate, respectively.

A daily watering of one hour was applied until the fifth bunch was taken (July 6, 2012); from which were applied two daily irrigations of 1.5 h each, until the end of the harvest. Weeding was done manually, three weeding was done: April 7, may 4 and June 8. At the time of the appearance of the pests whitefly (Bemisia tabaci), mite or red spider (Tetranychus urticae), paratrioza or jumping aphid (Bactericera cockerelli), soldier worm (Spodoptera exigua) and thrips (Frankliniella occidentalis), were controlled with application of agrochemicals, Cyromazine (Trigard), Abamectin, Imidacloprid (Confidor), Thiodicarb (larvin 375) and Abamectin, respectively in its commercial dose, as well as the control of crown rot by Fusarium (Fusarium oxisporum), Verticillium wilt (Verticillium dahliae), ashtray (Leveillula taurica), bacteria (Clavibacter, Pseudomonas and Xanthomonas), early blight (Alternaria solani) and late blight (Phytophthora infestans), were controlled with the application of agrochemicals: Carbendazim (Derosal + Previcur), Cimoxanil + Mancozeb (Curathane), Bayleton, Dithane M-45, Carbendazin and Propamocarb+mancozeb (Bavistin 500 SC), respectively, in their commercial doses.

Plant management

Pruning of axillary and leaf buds was performed each time they were required; in a cycle in which 8 to 10 bunches were developed. The tutored was made with raffia and rings on the stem to avoid hanging it. The blunting was done when the plant had 8 to 10 clusters tied the thinning of fruits was not carried out.

Measured variables

Populations of nematodes and galling. Nematode populations in the soil (males and juveniles) were determined before starting the treatments and at the end of the crop cycle, for which soil samples were analyzed by centrifugation and sugar flotation technique, proposed by ^{Zuckerman et al. (1985)}. The percentage of galling in plants attacked by Meloidogyne was also determined, according to the scale proposed by ^{Bridge and Page (1980)}: 0= no gills; 1= small gills, hardly visible, the main roots, clean; 2= only small but clearly visible gills, with clean main roots; 3= some large gills, visible and clean main roots; 4= large gills predominate, but the main roots remain clean; 5= 50% of the roots infested, gills in parts of the main roots, reduced root system; 6= galling at the main roots; 7= most of the main roots grounded; 8= all the main roots grounded, few visible clean roots; 9= all roots severely gilled, the plant is usually dying; and 10= all severely rooted roots, radical system destroyed, the plant is dead.

Production evaluation. Approximately every week, as of June 9, a cluster was cut, the fruits produced by each experimental unit were weighed and quantified and classified by quality according to the following scale: First (more than 99 g fruit^-1), second (between 90 and 99 g) and third (less than 90 g). The cuts are made in the phase of grated maturation.

Statistical analysis

The measured variables were subjected to analysis of variance and in those that were statistically significant, the means test was applied by the minimum significant difference (DMS) with p< 0.05. A correlation analysis between the variables was also performed. The computer program Statistical Analysis System ^{(SAS) version 2002} was used.

Acceptance of applied survey

To evaluate the acceptance or rejection of adoption of other control strategies and especially the presence of cempasuchil plants, together with tomato plants, a survey was applied, one month before the end of the crop cycle, to the technical manager of the greenhouse, as the workers and the producer, which consisted of the following points.

Survey for workers. 1) the work in the management of the cempasuchil plants was difficult; 2) The work in the treatments was more laborious than in the witness; and 3) how did you think having worked with these new treatments?

Survey for the person in charge of the personnel. 1) labor was increased in some of the treatments; 2) there were problems regarding the orders that were given to the staff; and 3) there were problems on the part of the workers in handling the treatments.

Survey for the producer. 1) how he thought the establishment of cempasuchil plants; 2) proposal to improve treatments; and 3) obstacles to working with cempasuchil.

The evaluation of results. At the beginning of the investigation soil tests were made (February 3, 2012), to know the population of nematodes, at the end of the investigation (august 10, 2012) the second soil test was made, which allowed to determine if the population of Meloidogyne spp., decreased or increased based on the treatments applied. The results obtained were analyzed by means of a variance analysis, DMS (p( 0.05) and a correlation test was performed with the ^{SAS version 2002} program.

Variance analysis

The analysis of variance that was made to the 12 variables showed that there was no statistical significance (p> 0.05) for the variation factor in repetitions and if there were in seven variables of the treatments factor (Table 1). The non-statistical significance for repetitions is attributed to the fact that the experiment was carried out in a homogeneous environment, which is understandable, since it was carried out in the greenhouse.

Mean test of the variables that showed statistical significance

The greatest reduction in the number of nematodes occurred with the Cempasuchil treatment, although it was statistically the same as the treatments: cempasuchil + solarization + nematicide, solarization + cempasuchil, nemacidia, and solarization + nematicide (Table 2).

In all the variables where there were statistical differences, the treatment with cempasuchil was the most favorable, since it presented higher amount of fruits per cluster (R1 and R2), greater fruit weight (P1, P2 and P3), higher plant height, in addition to the lower population of nematodes, although in all the variables the treatment with cempasuchil was not different from other treatments in each variable (Table 2).

These results are evidence of the positive effect that the cempasuchil had on the control of nematodes, on the development of the plant and on the production of fruits. In the treatment with cempasuchil, regarding the control treatment, the population of nematodes was reduced 188%, the clusters per plant increased 33 and 10% for the first and second counting, in the weights per fruit the increase was 18, 33 and 13% for the first, second and third evaluations, respectively. The average weight of the fruits of the three evaluations where there were differences was 128 g in the treatment with cempasuchil and 104 g in the control.

With cempasuchil, in addition to reducing the number of nematodes in the evaluation at the end of the crop cycle, it also reduced the presence of root galls in a greater degree compared to the other treatments, the cempasuchil and the combinations C + S + N and S + C obtained a degree of galling of 3 according to the scale of ^{Bridge and Page (1980)} compared to the treatments solarization, vidate, N + C and S + N that presented a degree of galling of 4 and the control of 7, which it is attributed, according to ^{Gomez and Zavaleta (2001)}; ^{Natarajan et al. (2006)}; ^{Wang et al. (2007)}, to which the plant exudes thiophenol compounds that scare away phytopathogenic nematodes.

By sharing the space of soil, water and nutrients, the roots of the tomato plants with those of cempasuchil, there was no negative effect on the growth or production of the plants, on the contrary, there was a favorable effect for the tomato, which is confirmed by ^{Gómez and Zavaleta (2001)} and ^{Natarajan et al. (2006)}, it cannot be said that synergism was present because the biomass of the cempasuchil plants was not evaluated, because the main objective was to evaluate the effect on the tomato plants. Therefore, when these two species coexist during development in nematode infested soil under greenhouse conditions was expressed according to the evaluated variables, a positive effect on the development of the tomato plants.

In the control treatment, the number of nematodes remained high, possibly due to favorable conditions for the development of the nematodes in the soil; even under these conditions, the plants remained productive, which can be attributed to the adequate availability of nutrients and water; since the tomato plants affected with Meloidogyne spp., can produce well when the plant is not subjected to a stress condition (^{Salazar and Guzman, 2013}), although infested soils without any type of control gradually become infested until they are made unproductive.

The variables of juvenile nematodes 2, adult 1 and adult 2, gave the same result referring to the population presented in the seven treatments. The treatments of cempasuchil and cempasuchil + solarization were the lowest in terms of the number of nematodes (Table 3), this indicates that these two treatments are the best, both to have low populations of the Meloidogyne spp. nematode, and to obtain a high yield of fruits. This is confirmed based on the results presented in Table 3, since the correlation coefficients between variable J2 and P3 are negative, as well as between M2 and P3, in both cases the coefficients are highly significant. These cases show the tendency that a higher fruit weight corresponds to a lower number of nematodes.

The results obtained in the present work agree with those obtained by ^{Castro et al. (1990)}, ^{Zavaleta et al. (2002)}, ^{Natarajan et al. (2006)}, due to the effect of the compounds exuded by allelopathic plant species such as cempasuchil on Meloidogyne in the tomato crop, as well as when the cempasuchil is combined with plastic for solarization. ^{Castro et al. (1990)} indicate that the population of nematodes decreases when there are cempasuchil plants interspersed between tomato plants, meanwhile, ^{Katan (1981)}, ^{Pullman et al. (1989)}, ^{Devay (1992)} and ^{Candido et al. (2008)}, point out that the plastic gives rise to temperatures above 40 °C in the soil, which are lethal for nematodes, however, it was not possible to reach those temperatures in the place where the experiment was carried out. that inside the greenhouse the solar rays do not enter directly and the temperature only increased to 30 °C in the soil, in these conditions it is not possible for the solarization treatment to perform the correct function because the climatological conditions in which the experiment was established were not they allowed to reach temperatures higher than 30 °C, possibly there could also be an increase in moisture retention and that favored that the plant was not stressed and had no nematode attack.

It was not possible to determine the mechanism by which the combined effect of cempasuchil + solarization + nematicide, had a low yield of tomato fruits in the first and second cut dates, weight 1 and weight 2 (P1 and P2, Table 2), as well as few clusters, cluster 1 and cluster 2 (R1 and R2), although there was a low number of nematodes; Maybe there was some kind of antagonism between the components of the treatments that gave rise to those results. The explanation of the reasons why in the treatments of cempasuchil and cempasuchil + solarization there was a high yield of fruits and in the height of the plant (Table 2), is attributed to the effect of the exudates of the roots of the cempasuchil in the treatment with only this product, and in the treatment with the combination of cempasuchil + solarization, it can be due to the favorable effect that could be presented between the combination of the conditions generated by the plastic of the solarization, in the increase of the temperature and the soil moisture, and exudation of compounds of the tertienyl group, which have a nematicidal effect (^{Zavaleta et al., 2002}; ^{Wang et al., 2007}; ^{Salazar and Guzmán, 2013}). Another evidence obtained from the results reported in Table 2 is that the lowest values in these variables were obtained with the four treatments in which the nematicide is involved: cempasuchil + nematicide, cempasuchil + solarization + nematicide, solarization + nematicide, and nematicide, for which Vidate did not have a favorable effect on growth and fruit production.

Appreciation of the staff that helped in the work

The head of the staff that works in the greenhouse where the experiment was carried out and the worker who carried out the practices, indicated that it was not difficult for them to carry out the new practices, but it took them more hours of work, mainly where there was cempasuchil; the treatments seemed good because their observations confirmed the good yield and quality fruits. In addition, they mentioned that the best treatment was solarization + cempasuchil, which stood out in the height of the plant, in fruits of greater size and uniformity, since they are the variables that could be seen with the naked eye compared to the rest of the treatments.

In the same way, the producer agreed with the results obtained, although he did not agree with the fact of having intercalary plants. Given this situation, some alternatives to control the nematodes in the tomato crop without the need to grow the cempasuchil plants next to the tomato plants is to apply extracts from the cempasuchil plants (^{Natarajan et al., 2006}), or the rotation between tomato crops with cempasuchil plants (^{Hooks et al., 2010}), in these ways significant effects have been reported in the control of nematodes in the tomato crop compared to the control treatment and even with respect to the chemical treatment.