Host status of soybean genotypes to Meloidogyne species

: This study aimed to evaluate the host status of soybean genotypes to Meloidogyne javanica (Est J3), Meloidogyne sp.0 (Est R0), and M. graminicola (Est VS1). In the first experiment, all tested genotypes (BMX Potência RR, BMX Valente RR, BMX Icone IPRO, PELBR10-6049 RR, and TECIRGA 6070 RR) were susceptible to M. javanica, with reproduction factor (RF) >1.0, and resistant to Meloidogyne sp.0 (0.01 > RF < 0.15), whereas in the second experiment, all genotypes (BRS 246 RR, PELBR11-6038 RR, PELBR11-6001 RR, PELBR10-6005 RR, BMX Apolo RR, PELBR11-6028 RR, PF11651, PF103251, PELBR11-6035 RR, PELBR10-6050 RR, PELBR11-6042 RR, PELBR10-6017 RR, PELBR11-6007 RR, PELBR10-6016 RR, and PELBR10-6049 RR) were resistant to M. graminicola (0.06 > RF < 0.43).

http://doi.org/10.1590/0103-8478cr20190637Soybean (Glycine max L. Merril) is one of the most important legumes crops in the world, contributing to 25% of the edible oil production and providing approximately 67% of the protein concentrate for animal feed worldwide (AGARWAL et al., 2013).
However, intensive planting and expansion of croplands to new areas have intensified phytosanitary problems, particularly those related to plant parasitic nematodes.In this context, the species Meloidogyne javanica and M. incognita are widely distributed in the soybean growing areas of Brazil (DIAS et al., 2010).Other species have been reported in different regions of the world, such as M. graminicola in China (LONG et al., 2017).This must be taken into consideration when planting soybeans in areas previously destined for the rice sector.In addition, recently, there have been frequent reports of an atypical population, called Meloidogyne sp.0, in southern Brazil (MATTOS et al., 2017).Therefore, the objective of this study was to evaluate the response of soybean genotypes to M. javanica, Meloidogyne sp.0, and M. graminicola, under greenhouse conditions.
Two experiments were conducted in a greenhouse (25℃ ± 5℃) at Embrapa Clima Temperado -Pelotas / RS (31°42ʹS 52°24ʹW), from November 2018 to February 2019 (70 days).In the first experiment, five genotypes were evaluated against M. javanica (Est J3) and Meloidogyne sp.0 (Est R0) (Tables 1 and 2), and in the second experiment, fifteen genotypes were evaluated against M. graminicola (Est VS1) (Table 3).The first experiment was performed in a completely randomized factorial design (5 genotypes × 2 species × with or without nematodes).The second experiment was also performed in a completely randomized design with 15 genotypes.Tomato (Lycopersicon esculentum Mill.'Santa Cruz') seedlings for M. javanica, and irrigated rice (EPAGRI SCS112 and BR IRGA 403) for Meloidogyne sp.0 and M. graminicola, were included to verify the viability of the inoculum.Specimens of Meloidogyne were obtained following the methodology of CooLEN and D'HERDE (1972).Ten days after emergence, each seedling, grown in a 3,500 mL pot containing previously sterilized soil, was inoculated with a suspension containing 5,000 specimens (eggs + J2) from each Meloidogyne population separately (initial population = Pi).Two evaluations were performed, 30 and 60 days after inoculation (dai), to determine the average chlorophyll content of the leaves, using a portable chlorophyll meter (SPAD-502 Plus ® , KONICA MINOLTA OPTICS, INC., Marunouchi, Chiyoda, Tokyo, Japan, © 2009).The plants were removed from the soil after 60 days, and the fresh mass of the root system (FMRS), fresh mass of the aerial part (FMAP), and number of galls (NG) were determined.Subsequently, the nematodes were then extracted from the roots according to the aforementioned methodology, and the final population (Pf) and reproduction factor of each nematode species (RF = Pf / Pi) were estimated.Genotypes were classified as resistant (R; RF < 1.0) or susceptible (S; RF > 1.0) (ooSTENBRINK, 1966).
For data from the first experiment, the values of the different variables were subjected to analysis of variance (ANOVA) and compared with Tukey's test (1953) (α = 0.05), using SAS ® software (SAS 9.3, SAS Institute, Cary, North Carolina, USA).Data from the second experiment were compared with the Scott-Knott grouping test (1974) (α = 0.05), using the SASM program.
There were significant interactions between the inoculation-genotype factors for the chlorophyll content assessed 30 dai in plants inoculated with Meloidogyne sp.0.For the effect of inoculation within each genotype, differences were observed only for BMX Potência RR.In plants inoculated with M. javanica, the effects were significant only for genotypes; however, after 60 dai, the effects were significant for both genotypes and inoculation.The chlorophyll content did not differ between the genotypes inoculated with M. javanica and Meloidogyne sp.0 (Table 1).

Márquez et al.
M. javanica, the effects were significant only for genotypes and inoculation.Gall formation was evident in all soybean genotypes inoculated with M. javanica.In plants inoculated with Meloidogyne sp.0, lower NG values were recorded for all genotypes.Based on RF analysis, all tested genotypes were found to be susceptible to M. javanica and resistant to Meloidogyne sp.0 (Table 2).
In the second experiment (Table 3), root galls were observed in all soybean genotypes; however, they presented reduced RF values (0.06 > RF <0.43).ASMUS and FERRAZ (2001) studied the relationship between M. javanica and soybean and reported little influence of M. javanica on the leaf chlorophyll content.The FMRS results of the present study were similar to those reported by these authors, and also to those of CARNEIRo et al. (1999), who found that the increase in FMRS was associated with the formation of root galls and the emergence of secondary roots.
Despite the reports of M. graminicola pathogenicity in soybean (LONG et al., 2017), the genotypes evaluated in the present study were resistant (0.06 > RF < 0.43).The genotypes included in this experiment, which assessed their susceptibility to the two root-knot nematode species, are currently cultivated in lowland regions, in rotation with irrigated rice.This study confirmed that these genotypes can be safely cultivated in this region, as they are resistant to both Meloidogyne sp.0 and M. graminicola.

Table 2 -
Response of soybean genotypes to Meloidogyne javanica and Meloidogyne sp.0.
Means followed by the same letter in the same column are not significantly different, based on the Tukey test at 5%; * ** original values transformed into [√ (x + 0.5)]; R = resistant; S = susceptible; CV = Coefficient of variation; RF = reproduction factor; 1 indicates susceptible host.

Table 3 -
Response of soybean genotypes to Meloidogyne graminicola.
Means followed by the same letter in the same column are not significantly different, based on the Scott & Knott test at 5%; * ** original values transformed into [√ (x + 0.5)]; R = resistant; S = susceptible; CV = Coefficient of variation; RF = reproduction factor; 1 indicates susceptible host.