Reaction of wild solanaceae species to Meloidogyne incognita ¹

ABSTRACT

The quest for resistance sources against Meloidogyne incognita as a control measure is essential in tomato. Thus, this study aimed to evaluate the reaction of six species of wild solanaceae to M. incognita. The species of wild solanaceae studied were Solanum capsicoides, S. asperolanatum, S. americanum, S. viarum, S. palinacanthum and Nicandra physaloides. Seedlings of wild solanaceae species were transplanted and inoculated with M. incognita. The experiment was performed in a completely randomized design with eight replicates. The analyzed variables were: height of the aerial portion, fresh weight of the aerial portion, fresh weight and length of the root system, gall index, number of galls/g of root, number of egg masses/g of root, number of eggs/g of root and the nematode reproduction factor. Based on gall index and reproduction factor criteria the species S. capsicoides, S. americanum, S. palinacanthum and N. physaloides were classified as resistant against M. incognita. These species also showed a significant increase in height and fresh weight of the aerial portion, length of the root system and fresh weight of the root system. Therefore, these species of wild solanaceae may contribute to the management of M. incognita in future applications.

Keywords:
Solanum spp.; Solanaceae; tomato; root-knot nematodes.

INTRODUCTION

Tomato (Solanum lycopersicum L.) is one of the main vegetables produced and marketed in Brazil, a country which is placed tenth in world production (FAO, 2018). Among the main phytosanitary problems jeopardizing tomato crops are the nematode species Meloidogyne incognita (Kofoid & White) Chitwood and M. javanica (Treub) (Chitwood), the first being widely disseminated (Pinheiro et al., 2014a). In tomato, M. incognita causes losses that vary between 44.3 to 70% of the production (Charchar et al. 1998; Sharma & Sharma, 2015), reaching 100% depending on the susceptibility of the cultivar and the soil and climate factors.

Planting resistant cultivars is one of the main approaches for the management of Meloidogyne spp. in tomato, due to its efficiency, cost and less environmental impact. The Mi gene confers resistance to M. incognita, M. javanica, M. arenaria (Neal) Chitwood (Cook, 1991), but there are few resistant commercial cultivars and the Mi gene does not confer resistance to new species such as M. brasiliensis Charchar & Eisenback and M. enterolobii Yang & Eisenback (formerly M. mayaguensis Rammah & Hirschmann) (Charchar et al. 2010; Pinheiro et al., 2014b). Thus, the identification of new resistance sources similar to Mi gene in the Solanaceae family are fundamental for the management of Meloidogyne in tomato.

The use of rootstocks, mainly from the Solanaceae family, resistant to Meloidogyne species is an efficient and promising technique (Peil, 2003; Pinheiro et al., 2014a), allowing cultivation in infested areas and making tomato production feasible. Species of wild solanaceae have been reported as resistant against M. javanica, M. incognita race 1 and M. enterolobii (Mattos et al., 2011; Cardoso et al., 2019). Therefore, the search for new wild resistant solanaceae against M. incognita contributes as a strategy to develop resistant rootstocks and genetic sources of resistance for tomato. Thus, the objective of this work was to evaluate the reaction of six species of wild solanaceae to M. incognita.

MATERIAL AND METHODS

The experiment was performed in a greenhouse at the Federal Institute of Northern Minas Gerais (IFNMG), Campus Almenara-MG, with geographical coordinates 16º13'52”S, 40°44'30”W and altitude of 270 m, from September to October 2019. The following wild solanaceae species were studied: Joá-de-capote (Nicandra physaloides (L.) Gaertn.), Jurubeba (Solanum palinacanthum Dun.), Joá-Vermelho (S. capsicoides All.), Jurubeba-grande (S. asperolanatum Ruiz & Pav.), Maria-pretinha (S. americanum Mill.) and Joá-bravo (S. viarum Dun.). Seeds of the first and second species were collected in the municipalities of Montes Claros and Almenara, state of Minas Gerais, respectively, and the others were acquired from the company Agro Cosmos. The identification of wild solanaceae was carried out based on specific literature (Lorenzi, 2008).

To obtain the seedlings, seeds were placed in plastic cups with 180 mL capacity, containing substrate composed of plaster sand (coarse washed river sand) and soil (Oxisol) at a proportion of 2:1 (v/v) and autoclaved at 121 ^oC for 1 hour to eradicate any plant-parasitic nematodes. Analyses of a composite soil sample of the studied site showed the following pysico-chemical characteristics: 33% clay, 13% silt, 54% sand, pH in water of 4.5 and 0,54% organic matter. The cups were kept in a greenhouse at 28 ± 2 ^oC temperature and irrigated manually. Seedlings for transplanting and carrying out the experiment were obtained 36 days after sowing. Seedlings of the wild solanaceae were transplanted to plastic pots with a 2 L capacity, containing a mixture of the same substrate mentioned above. Single seedlings were transplanted to pots after being selected by size and development of root system.

Twenty-four hours after transplanting, seedlings were inoculated with a suspension containing eggs of M. incognita. The suspension of M. incognita eggs was obtained from pure tomato root cv. Kada, infected with M. incognita and grown in a greenhouse from the Phytopathology Research Laboratory (PRL) at Federal University of Minas Gerais-UFMG. The identification of M. incognita was performed by the perineal configuration of females under light microscope and (-esterase phenotyping performed according to Taylor & Sasser (1978), Esbenshade & Triantaphyllou (1985) and Hartman & Sasser (1985). The eggs were obtained according to Hussey & Barker (1973), modified by Bonetti & Ferraz (1981). The eggs were cleaned according to Coolen & D’Herde (1972). The eggs suspension was kept at room temperature to stimulate the hatching of second-stage juveniles (J2) of M. incognita and to verify the quality of the inoculum (Rocha et al., 2015). Then, with the aid of a light microscope, the suspension was calibrated (569 eggs/mL + 384 J2/mL), obtaining the inoculum concentration used in the experiment. To carry out the inoculation, 2.6 mL of the suspension were, distributed in three 1.5 cm deep holes, made with the aid of a glass rod around the seedlings, in the rhizosphere projection. After inoculation, the pots were kept in a greenhouse under the same conditions mentioned above, keeping the soil at field capacity. The experiment consisted of seven treatments, six species of wild solanaceae and the susceptible tomato Santa Cruz cv. Kada (Control). A completely randomized design was used with eight replicates, totaling 56 plots.

Thirty-eight days after inoculation, the height of the aerial portion (HAP) of the plants was measured from the ground level until the last internode with the aid of a tape measure. Then, the aerial portion was cut and the root system was collected, washed in a bucket containing water and placed in a plastic bag with a capacity of three liters, previously identified, according to each treatment. Subsequently, the fresh weight of the aerial portion (FWAP), the length of the root system (LRS) and the fresh weight of the root system (FWRS) were evaluated with a precision electronic scale. The LRS was determined with a tape measure, evaluating the length of the pivoting root. Infectivity and reproduction evaluations were carried out in the PRL at UFMG. The percentage of infection severity was estimated by the following gall index criteria: Gall Index 1 (¹GI) in a scale of 0 to 10 (Bridge & Page, 1980), where 0 = no galls; 1 = few small, almost imperceptible galls; 2 = small but noticeable galls; 3 = some large galls; 4 = greater number of large galls; 5 = 50% of the infested roots and some main roots with galls; 6 = galls on the main roots; 7 = almost all roots with galls; 8 = all roots with galls; 9 = all roots with large galls; 10 = all roots with large galls, without root system, dead plant. Gall Index 2 (²GI) was also based on a scale of grades from 0 to 5, but based on the percentage of the root system with galls according Taylor & Sasser (1978), where 0 = no galls; 1 = 1 to 2; 2 = 3 to 10; 3 = 11 to 30; 4 = 31 to 100; and 5 = more than 100 galls. Next, egg masses in the root systems were colored red, in a solution containing artificial stain used in food manufacturing, according to the technique of Rocha et al. (2005). After staining, the roots were placed on paper towels for 10 minutes, and the number of egg masses and number of galls was counted in the root system. To quantify the number of eggs per root system, the roots were cut into pieces of approximately 2 cm in length and the eggs obtained by extraction according to Hussey & Barker (1973), modified by Bonetti & Ferraz (1981). Under light microscope, the number of M. incognita eggs was quantified in the root system using a Peters slide to estimate the number of eggs per gram of root. The calculation of the Reproduction factor (Rf) was achieved by dividing the final (Pf) and initial (Pi) population densities for each treatment (Rf = Pf/Pi), as proposed by Oostenbrink (1966). The classification of plants according to the resistance reaction to M. incognita was based on the criteria of Oostenbrink, (1966) and Taylor & Sasser (1978). Plants with Rf ≥ 1.0 were considered susceptible, with Rf < 1 resistant and Rf = 0 immune (Oostenbrink, 1966). Based on gall index at a scale of 0 to 5 (Taylor & Sasser, 1978), plants with a number of galls ≤ 10 (grades 0 to 2) were considered resistant and the number of galls > 10 (grades 3 to 5) were susceptible. The correlation between gall indexes (¹GI and ²GI) and the number of galls per root system and between ²GI and Rf was evaluated.

Infectivity and reproduction data were transformed in order to attain homogeneity of variances and normality of data. The averages were subjected to analysis of variance and compared by Scott-Knott test at 5% probability by the SISVAR software (Ferreira, 2007). To calculate the Pearson correlation coefficient between gall indexes and the number of galls per gram of root and Rf, the statistical software GENES (Cruz, 2016) was used. All analyzes of mean comparison between treatments were performed with SISVAR and Pearson's correlations by GENES.

RESULTS AND DISCUSSIONS

The studied wild solanaceae showed some variable behaviors in relation to the reaction to M. incognita (infectivity and reproducibility) and to the development of the aerial part and the root system (Tables 1 and 2). Among the studied wild solanaceae, the species S. capsicoides, S. americanum, S. palinacanthum and N. physaloides inoculated with M. incognita were considered resistant (Table 1). With the exception of S. americanum, the resistant species showed less infectivity and reproduction, expressed by the number of galls and masses of eggs per gram of root and the number of eggs per gram of root, respectively, in comparison with S. lycopersicum, control (Table 1). Similar behavior to infectivity was verified through the evaluation of ²GI, but according to ¹GI S. asperolanatum and S. americanum also showed a lower percentage of infestation of the root system. Nicandra physaloides and S. palinacanthum also showed greater height and fresh weight of the aerial portion (Table 2). The species S. palinacanthum, S. viarum and S. capsicoides had higher fresh weight of the root system, while higher length of the root system occurred in these last two species and in S. asperolanatum and S. americanum (Table 2).

Table 1:
Infectivity and reproduction expressed by gall indexes (GI), number of galls per gram of root (NG), number of egg masses per gram of root (NEM), number of eggs per gram of root (NE), reproduction factor (Rf) and classification of the reaction of wild solanaceae species to Meloidogyne incognita

Species	1 GI	2 GI	NG	NEM	NE	Rf	Reaction
							2 GI	3 Rf
S. capsicoides	0.75b	2.37b	2.73b	2.13b	8.90a	0.07b	S	R
S. asperolanatum	1.25b	4.62a	10.03a	9.62a	9.62a	4.11a	S	S
S. americanum	1.12b	3.12a	6.83a	5.62a	5.62a	0.86b	S	R
S. viarum	2.25a	4.25a	11.95a	10.99a	10.98a	4.50a	S	S
N. physaloides	0.75b	1.50b	1.49b	1.08b	1.08b	0.25b	R	R
S. palinacanthum	0.38b	1.50b	0.42b	0.19b	0.20b	0.23b	R	R
S. lycopersicum	2.63a	4.63a	7.35a	7.20a	7.19a	4.27a	S	S

• Averages followed by the same lowercase letter within the column do not differ statistically from each other by the Scott-Knott test at 5% probability. ¹GI: gall index based on a scale of 0 to 10 (Bridge & Page, 1980). ²GI: gall index based on a scale from 0 to 5 and reaction classification (Taylor & Sasser, 1978). ³Classification of the reaction based on the Rf (Oostenbrink, 1966). S: susceptible; R: resistant.

Table 2:
Average height of the aerial portion (HAP), fresh weight of the aerial portion (FWAP), length of the root system (LRS) and fresh weight of the root system (FWRS) of wild solanaceae inoculated with Melodoigyne incognita

Species	HAP (cm)	FWAP (g)	LRS (cm)	FWRS (g)
S. capsicoides	9.75 c	12.38 c	60.50 a	19.63 a
S. asperolanatum	8.13 c	9.13 c	52.75 a	12.00 b
S. americanum	25.13 b	7.38 c	47.13 a	6.50 b
S. viarum	12.75 c	11.63 c	49.25 a	18.50 a
N. physaloides	39.63 a	14.50 b	23.50 c	8.25 b
S. palinacanthum	24.75 b	16.63 b	35.88 b	17.13 a
S. lycopersicum	42.88 a	21.63 a	40.38 b	15.50 a

• Averages followed by the same lowercase letter, within the column, do not differ statistically from each other by the Scott-Knott test at 5% probability.

The species S. capsicoides, S. americanum, S. palinacanthum and N. physaloides showed Rf of 0.07, 0.86, 0.23 and 0.25, respectively, being considered resistant to M. incognita by the criteria of Oostenbrink, (1966). Cardoso et al. (2019) previously verified the species S. capsicoides, S. palinacanthum and Solanum spp. were resistant to M. javanica. Mattos et al. (2011) also reported resistance from S. asperolanatum, S. stramonifolium, Solanum sp. against M. incognita race 1 and the species S. stramonifolium, S. paniculatum and S. subinerme against M. enterolobii. In another study, Mônaco et al. (2008) verified resistance of S. americanum to M. paranaensis. Therefore, it seems that the species studied, S. capsicoides, S. americanum and S. palinacanthum, have sources of resistance to the aforementioned Meloidogyne species and M. incognita, and S. asperolanatum only to M. incognita race 1. In addition to the species reported in the literature, we demonstrate resistance from S. americanum and N. physaloides to M. incognita.

The primary purpose for grafting is the control of soil-borne diseases, such as bacterial wilt, Fusarium wilt and root-knot nematodes, which have been selected by screening tomato cultivars and resistant wild species (Yamakawa, 1982; King et al., 2010). Genes for Meloidogyne spp. have been identified from solanaceous, such as tomato (Barbary et al., 2015) and pepper (Capsicum annuum L.) (Changkwian et al., 2019). However, no study has been reported on the identification of resistant genes from the wild solanaceous plants tested in the present study against root-knot nematodes.

The studied species of wild solanaceae showed different behavior when we observed the resistance classification criteria, with the four species S. capsicoides, S. americanum, S. palinacanthum and N. physaloides classified as resistant by the Rf, while only two species (S. palinacanthum and N. physaloides) were resistant according to the gall index criterion according to Taylor & Sasser (1978). Considering both criteria, S. palinacanthum and N. physaloides were the most promising species to be investigated as rootstocks for tomato in further studies. Similar behavior was also observed when we compared the evaluation of the percentage of infestation severity of the root system of the species S. asperolanatum and S. americanum by the gall index of Bridge & Page (1980), that resulted in scores of 1.2 and 1.1 (few small galls, almost imperceptible), but according to Taylor & Sasser (1978) scale of scores 4.6 and 3.1, which are considered susceptible (Table 1). We also observed that there was no correlation between the ²GI and the Rf, and between the ¹GI and the number of galls per root system, which partially explains the results obtained. The lack of correlation between the ¹GI and the number of galls per root system may be related to the scale of grades that varies from 0 to 10, which makes the precision/accuracy difficult to the evaluator, in relation to the scale of grades 0-5 proposed by Taylor & Sasser (1978). In addition, the parasitism of M. incognita in the host plant induces gall formation, but the reaction of the plant due to the attack of the nematode may express differently in relation to the reproduction factor (number of eggs), which can classify it as susceptible or resistant according to the method used in the evaluation. Thus, the reaction estimation must be evaluated by the Rf and/or gall index.

The ²GI correlated positively with the number of galls per root system (r = 0.94) and with the ¹GI (r = 0.79). That is to say, the choice of the method to evaluate the severity of plant infestation by M. incognita by gall index of Taylor & Sasser (1978) and Bridge & Page (1980), or by direct quantification of the number of galls per root system and vice versa, showed similar results.

The quality, level and type of inoculum and the evaluation period and the development of the plants can interfere with the evaluation results concerning the plant reaction to the nematode. Dong et al. (2007) evaluated peanut (Arachis hypogaea L.) genotypes with three levels of resistance to M. arenaria, the type and concentration of the inoculum and the evaluation period, verifying that inoculation with 8,000 eggs or 2,000 J2 of M. arenaria per plant does not differ statistically by the gall index method when evaluated in the period of 2 and 10 weeks after inoculation, with similar results for the type of inoculum in relation to the classification of resistance. The same authors also found that the three levels of resistance can be separated based on gall indexes from four weeks with inoculum ranging from 1,000 to 6,000 eggs per plant. In our study, we used a suspension at a concentration of 2,478 eggs and J2 of M. incognita per plant and resistance evaluation period of five weeks after inoculation. In addition, we evaluated the quality of the inoculum by hatching and the dark color of the J2's body related to infectivity (Rocha et al., 2015), demonstrating that the factors mentioned above did not affect negatively the reaction classification of the species studied.

Another factor that can interfere in the process of infection and infectivity is the growth and development of the root system due to the chances of the infective juvenile to find the root. Only N. physaloides showed lower fresh weight and length of the root system, while S. asperolanatum and S. americanum showed only lower fresh weight of the root system, when compared to tomato (Table 2). However, S. asperolanatum and S. americanum were susceptible by the criterion of ²GI, with significant values ​​in the number of galls per gram of root, yet by the criterion of Rf only S. americanum was resistant, but with Rf of 0.86, close to 1.0 (susceptible plant). Therefore, the selection of seedlings of the studied species was important so that growth and development did not interfere in the process of infection by the infective juvenile of M. incognita. However, some species considered resistant showed less development of the aerial portion, requiring future studies to verify their viability and compatibility as resistant rootstocks in tomato against M. incognita.

CONCLUSION

The wild species joá-vermelho (Solanum capsicoides), maria-pretinha (S. americanum), jurubeba (S. palinacanthum) and joá-de-capote (Nicandra physaloides) were considered resistant to M. incognita.

ACKNOWLEDGEMENTS AND FULL DISCLOSURE

The authors declare that there is no conflict of interests in carrying the study and publishing this manuscript.

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Publication Dates

• Publication in this collection
  13 June 2022
• Date of issue
  May-Jun 2022

History

• Received
  10 Aug 2020
• Accepted
  29 Sept 2021