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.
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.
This study aimed to investigate the effects of crop rotation with Macrotyloma axillare ‘Java’, Crotalaria spectabilis and Crotalaria ochroleuca combined with green manure application or biological treatment, on the control of Meloidogyne javanica in soybean. An initial greenhouse study was conducted in a 4 × 2 factorial design, with four rotation crops (M. axillare ‘Java’, C. spectabilis, C. ochroleuca and soybean) in the presence and absence of green manure. A second greenhouse study was carried out using a 4 × 5 factorial design, with four rotation crops and five biocontrol treatments (Pochonia chlamydosporia, Purpureocillium lilacinum + Trichoderma harzianum, Bacillus methylotrophicus, Bacillus subtilis + Bacillus licheniformis and untreated control). Both experiments consisted of two independent trials (Trials 1 and 2) conducted at different times of the year. The experimental field soil was infested by growing soybean infected with M. javanica for 50 days prior to the assays. Then, seeds of rotation crops were sown and biocontrols applied. Rotation crops were removed 70 days after sowing, and soybean seeds were sown immediately afterwards. Total nematodes, nematode per gram of root and soil biological activity were assessed 60 days after soybean sowing. In the first study, all rotation systems and green manure treatments reduced M. javanica population. In the second study, all biological treatments were effective, except B. methylotrophicus and M. axillare ‘Java’ combined with P. chlamydosporia in Trial 1 and C. spectabilis combined with P. lilacinum +T. harzianum in Trial 2. Macrotyloma axillare ‘Java’ combined with B. methylotrophicus and C. spectabilis combined with B. subtilis +B. licheniformis resulted in higher soil metabolic activity. The association of biological control agents with crop rotation generally did not present additive effects in the reduction in M. javanica populations, except for one combination of M. axillare ‘Java’ with B. subtilis +B. lichneniformis.
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