Reaction of wild Solanaceae rootstocks to the parasitism of Meloidogyne javanica

ABSTRACT Intensive production of vegetables in greenhouses can increase the amount of inoculum of soil-borne pathogens, such as the root-knot nematode. Thus, in this study we aimed to evaluate the potential of Solanaceae as rootstocks resistant to Meloidogyne javanica nematodes as an alternative to tomato grafting. The experiment consisted of seven treatments: wild species joá-vermelho (Solanum capsicoides), joá-bagudo (Solanum palinacanthum), joá-bravo (Solanum viarum), jurubeba (Solanum spp.) and the commercial tomato cultivars Santa Cruz Kada, Batalha and Guardião. The analyzed variables were gall index; egg mass index; final nematode population; reproduction factor (FR) and reaction: susceptibility, resistance and immunity; fresh shoot and root mass and number of eggs per gram of roots. The wild species joá-vermelho, joá-bagudo and jurubeba showed resistance, with the lowest indexes of galls, egg mass, final population of nematodes and number of eggs per gram of root, not differing from the resistant control treatment (hybrid rootstock Guardião), with a reproduction factor less than 1, showing potential to be used as a resistant rootstock to M. javanica. Joá-bravo species showed susceptibility to the root-knot nematode, with a FR>1, not differing from the susceptible tomato Santa Cruz Kada. These results confirm the resistance of wild species to nematode parasitism, which can prove the viability of use as possible alternative rootstocks, and reinforce the idea that more studies should be carried out aiming to provide more viable options for farmers and plantlet producers.

of approximately 3 hectares, in about 13% of family properties in the state (EMATER, 2016).
In order to meet market demand, farmers use intensive production in protected environment, reducing, partially, the negative effects provided by harsh climatic conditions (Araújo et al., 2009;King et al., 2010;Bisbis et of Parana showed an increase of 77% from 2,000 to 2,016, due to an increase in crop productivity, as a result of the producer organization and investment in technology (Salvador, 2017).According to Instituto Paranaense de Assistência Técnica e Extensão Rural, these vegetables are grown essentially by family farmers, on average areas O ne of the main challenges faced by horticulture these days is to meet the growing demand for food due to global population growth (Rouphael et al., 2018), as well as to produce fresh, high-quality and free-chemical-residue food in order to meet the demands of consumers (Bisbis et al., 2018).
Vegetable production in the state al., 2018).However, intensive vegetable cultivation under greenhouses may increase inoculums of soil pathogen, due to the fact that, when the producer specializes in growing one vegetable species, performs successive cultivation in this environment, limiting crop rotation (King et al., 2010;Rosa et al., 2013;Pinheiro et al., 2014).Among the species, grown in protected environment, the tomato crop stands out due to its high sensitivity to inclement weather (Gusmão et al., 2006;Bergougnoux et al., 2014;Çelik et al., 2017) and susceptibility to several pests and diseases, which makes this cultivation difficult, with economic and environmental risk factors, caused by excessive use of chemical products (Luz et al., 2007;Loos et al., 2008).
Considering soil pathogens, the root-knot nematode belonging to the genus Meloidogyne is of great economic importance for tomato crop (Carvalho et al., 1999;Podestá et al., 2016).Its popular name derives from the main symptom presented by plants when affected by these pathogens, which consists of nourishing cells (gall nematodes), which act as a permanent feeding place, providing nutrients for the nematode development and interfering negatively in nutritional and water absorption by plants (Jones et al., 2013;Karssen et al., 2013;Kepenekci et al., 2018).
The reaction of plants to the rootknot nematode can vary according to species and cultivar, being that the crop rotation, duration of the development cycle, planting season, population density and kind of soil also interfere in damage severity (Jones et al., 2013).Generally, these observed symptoms include reduced fruit yield and quality, slow growth, yellowish leaves, wilting in the hottest hours of the day, and decreased resistance to other biotic and abiotic factors (Jones et al., 2013;Podestá et al., 2016;Kepenekci et al., 2018).
The root-knot nematodes are mandatory endoparasites, which may be native or inserted into new production regions, through contaminated soils, root remnants or infected plants (Louws et al., 2010).Although crop rotation with non-host species and soil fumigation are used to control these pathogens, resistance is still the most employed and sustainable strategy (Louws et al., 2010).
The chemical nematicides generally used to control these pathogens are of high costs and present potential risks for beneficial soil microorganisms (Huang et al., 2014), environment and human health (Fournet et al., 2012;Jones et al., 2013;Becker, 2014;Onkendi et al., 2014;Kyriacou et al., 2017).Moreover, the increasing market for organic tomatoes does not allow the use of agrochemicals (López-Pérez et al., 2006;Lee et al., 2010).
Giving up growing tomato in areas infested with root-knot nematode is not a viable option for the farmer, especially when this area is the only option for cultivation.Thus, more sustainable strategies are necessary to make production in areas infested with these pathogens viable (Huang et al., 2016).
Grafting can be a technique used in an integrated management system aiming to minimize damage caused by root-knot nematode (Peil, 2003;Krumbein & Schwarz, 2013;Verdejo-Lucas et al., 2013).This practice improves the crop quality, with more efficient water and nutritional use, increase in plant vigor and harvest time, making the tomato plant more tolerant to pathogen attack, such as phytonematods (Rizzo, et al., 2004;Lee et al., 2010;Kyriacou et al., 2017).
Although the genetic basis of rootstocks for tomato crop seems to be wide, considering the great quantity of species related to the crop which could be used, the current genetic basis is limited (King et al., 2010).Most commercially available rootstocks are high-cost hybrids, produced by specialized companies (King et al., 2010;Lopes et al., 2015).
T h e s e r o o t s t o c k s m a k e t h e production more expensive for farmers and that is why identifying alternative rootstocks, resistant or tolerant, as an alternative to commercial hybrids, is essential.Wild Solanum species are sources of resistance characteristics to various soil pathogens, fruit quality and other important characteristics to be considered in order to improve crops, being possible alternative rootstocks for tomato crop (Keatinge et al., 2014;Migicovsky & Myles, 2017).
The inoculum of root knot nematode M. javanica used in the experiment was obtained from a pure population kept in tomato plants, grown in a greenhouse.The nematode eggs were obtained according to the methodology described by Hussey & Barker (1973), modified by Bonetti & Ferraz (1981).The seedlings of all wild and commercial species were produced in a greenhouse, in polystyrene trays with 128 cells.Plantlets were transplanted 30 days after emergence, in 1-kg-capacity plastic containers, with substrate, soil and sand in the ratio 2:1 (v:v), autoclaved in advance for 1 h at 120˚C, 1 atm, (Ito et al., 2014).One week after seedling transplant, the nematode was inoculated using 2 mL of suspension containing 5,000 eggs of M. javanica through 4 equidistant holes open in soil, close to the plant stem.
S i x t y d a y s a f t e r n e m a t o d e inoculation, gall index (IG), egg mass index (IMO), final nematode population (Pf); reproduction factor (FR) and reaction of: susceptibility (S), resistance (R) and immunity (I); fresh shoot mass (MPAF); fresh root mass (MRF); number of eggs per gram of root (NOGR) were evaluated.
In order to determine gall index (IG), the scale proposed by Charchar et al. (2003) was used: after being washed, the roots were graded from 1 to 5 (1= without galls; 2= up to 10 small galls; 3= up to 50 small galls; 4= more than 50 small galls and up to 10 big galls; 5= roots with more than 50 small galls and more than 10 big galls).
Final nematode population per root (Pf) was obtained according to the methodology described by Hussey & Barker (1973), modified by Bonetti & Ferraz (1981).
Variable data were submitted to analysis of variance using F test, comparing the treatment averages by Scott-Knott test (p<0.05).For reproduction factor (FR), the averages of treatments using wild Solanaceae were compared to controls (commercial cultivars) by Dunnett test (p<0.05).Analyses were performed using Assistat software (Silva & Azevedo, 2002).

RESULTS AND DISCUSSION
The wild species joá-bagudo and jurubeba showed the lowest gall index values (IG).For egg mass (IMO), jurubeba showed the lowest value, followed by joá-bagudo and joávermelho.On the other hand, joá-bravo showed the highest indexes for both variables (Table 1).
Final nematode population (Pf) and number of eggs per gram of root (NOGR) of joá-vermelho, joá-bagudo and jurubeba showed lower values (Table 1), in comparison to the other species, proving the lowest root-knot nematode multiplication rate.However, the species joá-bravo showed the highest value for both variables, due to high ratio of Pf/MRF, proving the high susceptibility of this species to nematode M. javanica.Silva et al. (2013) found similar values for Pf in another species of the wild Solanaceae, Maria-pretinha (Solanum americanum), which showed to be susceptible with a final population of 34,720 eggs.
Variable MPAF showed lower value for wild Solanaceae joá-bravo, for its high susceptibility to nematode M. javanica, followed by jurubeba.On the other hand, although the species joabagudo presented a higher value when compared to the other wild Solanaceae species, did not differ statistically from joá-vermelho.
The lowest development of shoot area of the plants is related to the highest number of galls which cause interferences on plant roots, which interfere on efficient absorption of nutrients and consequently on plant development (Jones et al., 2013;Karssen et al., 2013;Kepenekci et al., 2018).Therefore, plants showing lower MPAF generally show higher susceptibility to M. javanica.
In relation to MRF, the species joá-bravo showed the lowest value (in relation to the other wild Solanaceae species) and did not differ statistically from jurubeba.These results were obtained due to the slow initial growth of jurubeba, which results in a lower development, considering that this species showed reduced number of galls.
The species joá-bagudo, jurubeba and joá-vermelho showed to be resistant to M. javanica, when compared to the susceptible commercial controls (Batalha and Santa Cruz Kada) and similar to resistant-hybrid rootstock Guardião (Table 2), showing FR<1 according to Oostenbrink (1966).However, the species joá-bravo showed high susceptibility showing FR>1, not differing from susceptible tomato Santa Cruz Kada, which proved viability of the inoculum used in the present study, showing FR>1.
The results found in this study corroborate the ones found by Pinheiro et  These results confirm the resistance of wild species (belonging to this family) to nematode parasitism, which can prove the viability of using them as alternative rootstocks, and reinforce the idea that further studies on grafting should be carried out, aiming to provide more viable options for farmers.
Although the wild Solanaceae species (joá-bagudo, joá-vermelho and jurubeba), evaluated in the present study, showed resistance to the nematode M. javanica, the compatibility of these species is another important factor to be taken into account.In this context, Simões (2014) obtained compatibility of jiló and jurubeba species as rootstocks for tomato cultivar IPA-6.Farias et al.
(2013) obtained S. gilo, S. lycocarpum and S. stramonifolium as alternative rootstocks compatible with tomato and suitable for conditions in Brazilian Amazon Region.This fact demonstrates feasibility of grafting and the importance of further studies aiming to show the efficiency of these species as alternative rootstocks for tomato crop.
Averages followed by same lowercase letter in the column do not differ statistically by Scott-Knott test (p<0.05).

Table 2 .
Average values of reproduction factor (FR) and rootstock reaction of wild Solanaceae species submitted to Meloidogyne javanica parasitism and comparison with susceptible and resistant controls.Pato Branco, UTFPR, 2015.Averages followed by 1, 2 or 3 differ from the controls: Batalha, Santa Cruz Kada and Guardião respectively, by Dunnett test (p<0.05).S= susceptible; R= resistant.