Soybean, the most important agricultural product in Brazil, is widely cultivated all over the country. The occurrence of green stem and foliar retention (GSFR) has been reported since the beginning of the soybean cultivation in Brazil and its potential causes were attributed to severe attack of stinkbugs or plant nutritional disorders. About two decades ago, a new type of GSFR was reported in Brazilian tropical regions of soybean production, also of an unknown cause. Several possible causes were investigated, but the presence of the nematode Aphelenchoides sp. in symptomatic plants was frequently observed. Koch's postulates were conducted to check whether this nematode could be the cause of the syndrome. Specimens of Aphelenchoides sp. were isolated from soybean plants and multiplied in colonies of the fungus Fusarium sp. in PDA culture medium. Nematode suspensions were inoculated onto healthy soybean plants and the typical GSFR symptoms were observed. The nematode was recovered from the inoculated plants. Based on both morphological and molecular data, we suggest that Aphelenchoides besseyi is the causal agent of GSFR of soybeans in Brazil, a syndrome popularly known as "Soja Louca II".

No abstract

Rationale The nematode Aphelenchoides besseyi is the causal agent of green stem and foliar retention, a soybean disease recently described in Brazil. This condition can reduce soybean yield by up to 100%. However, little is known about chemical interactions between the plant and pathogen. Therefore, this work aimed to investigate metabolites from healthy soybean roots and from soybean roots that were inoculated with A. besseyi. Methods A. besseyi were multiplied in vitro with Fusarium sp. colonies in Petri dishes for 25 days, and were axenically inoculated into hydroponics healthy soybean plants. The metabolites were extracted from the roots of healthy and A. besseyi‐infected plants 16 days post‐inoculation. These extracts were analyzed using an untargeted metabolomic method with an ultra‐high‐performance liquid chromatography/electrospray ionization /tandem mass spectrometry (UHPLC/ESI‐MS/MS) and molecular networking approach. Results Roots from infected plants showed morphological alterations such as shrinkage, darkening, and arching. Similarly, they also showed an increased presence of flavonoids, compared with healthy roots. Compounds such as neobavaisoflavone, glycitin, genistin, and genistein were putatively identified and had greater intensity in inoculated roots. These compounds are linked to the defensive mechanisms in plants against nematodes. Moreover, coumaric acid, also exclusively putatively identified in inoculated roots, shows activity related to inhibition of root growth. Conclusions Liquid chromatography, mass spectrometry, and molecular networking approaches proved to be a powerful tool for the metabolomic study of GSFR. This study showed metabolomics differences of protective substances in the roots, evidencing a quick response of the plant to the attack of A. besseyi.

Summary Aphelenchoides besseyi is a concern to Brazilian agriculture, since the losses caused by the green stem and foliar retention syndrome in soybean, especially in hot and humid climates, could reach high levels. However, limited information is available regarding the host-parasite relationship. The objective of this study was to evaluate the capacity of A. besseyi to penetrate soybean roots and its movement in soybean tissues until reaching the top parts. Plants inoculated with 1000 A. besseyi were evaluated for root penetration from 1-28 days after inoculation (DAI), and post-penetration and movement inside tissues by staining them with acid fuchsin. Plant development, chronology of the symptoms and the number of pods were also evaluated at 60 DAI. Aphelenchoides besseyi was found in the cortex and xylem vessels of roots from 1 DAI. During the experimental period, the number of nematodes from roots to shoots increased more than 123, 330 and 430%, respectively, for roots, stems + petioles + inflorescences, and leaves, demonstrating the ascendent movement of A. besseyi. Necrotic lesions in young leaves and apical tissues were observed from 8 DAI; the typical symptom of ‘amachamiento’ was observed from 10 DAI, with enlargement of nodes and lesions in inflorescences and, at 30 DAI, stunted plants were detected. At 60 DAI, inoculated plants had lower numbers of pods and exhibited severe symptoms including abortion of flowers and tissue splitting and cortical lesions in a few pods and roots. These observations emphasise the importance of A. besseyi for Brazilian soybean production.

Aphelenchoides besseyi is the causal agent of soybean green stem and foliar retention syndrome known as Soja Louca II. This nematode has recently been reported parasitizing cotton in Brazil. In Costa Rica, it causes the symptoms known as “amachamiento” and false angular spots in common bean (Phaseolus vulgaris). Due to the great importance of beans to Brazilian agriculture, the objective of this research was to study the pathogenicity of A. besseyi in common bean under greenhouse conditions, including its endoparasitic relationships by staining root and shoot system tissues with fuchsin acid. In addition, A. besseyi was collected and quantified from shoot systems 30 days after inoculation by washing the tissue in water and blender centrifugal-flotation. We observed the symptoms of “amachamiento”, leaf and vein deformation in the expanded trifoliate leaves, and also leaves with necrotic, brown to reddish and angular lesions, characteristics from false angular spot, and deformed stems characterized by enlargement of nodes, retortions and necrotic lesions. High numbers of nematodes were found inside common bean plants. This is the first report of the pathogenicity and symptoms caused by A. besseyi in common bean in Brazil. These findings are important for development of management strategies to avoid losses on bean cropped in infested areas.

No abstract

DIVERSIDADE DE HIMENÓPTEROS PARASITÓIDES (HYMENOPTERA) NA ESTAÇÃO ECOLÓGICA DE JATAÍ, LUIZ ANTÔNIO, SP, BRASIL

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was recently described causing damages on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. The present study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using as inoculum two A. besseyi populations, obtained from symptomatic soybean and cotton plants collected in naturally infested fields. Cultivars ‘Imponente’, ‘Aracê’, ‘Guariba’, ‘Tumucumaque’, ‘Nova Era’, and ‘Tracuateua’ were inoculated with 500 A. besseyi of each population, separately, into soil and after 30 days from the inoculation nematodes were extracted from shoot systems. Both populations were able to parasitize all the cowpea cultivars. Independently of the cultivar, cowpea plants exhibited symptoms of leaf deformation similar to those described for soybean, cotton, and common bean and, in addition, severe brooming was observed and the interior of the stems was porous and necrotic. To our knowledge, this is the first report of parasitism by A. besseyi of cowpea in Brazil, under greenhouse conditions, increasing the list of hosts of this nematode.