Aphelenchoides besseyi Parasitizing Tobacco Cultivars in Brazil.

Foliar nematodes (Aphelenchoides spp.) are known to be parasites of tobacco in restricted areas, but symptoms caused by A. besseyi in tobacco are not well characterized, despite the great importance of this nematode worldwide. This study aimed to evaluate the host reaction of four Nicotiana tabacum cultivars (Comum, Xanthi, Samsun, and TNN) and N. benthamiana cultivar Comum to A. besseyi and to characterize the symptoms and the parasitism of this nematode. Two experiments were conducted under greenhouse conditions with controlled humidity and temperature, in which the plants were inoculated with 600 A. besseyi. At 30 days after inoculation (DAI), nematodes present in the soil, roots, and shoot parts were extracted, and roots and shoot tissues were stained with acid fuchsin. A high number of A. besseyi was obtained per gram of shoot tissues (125 to 2,169 nematodes), and severe symptoms were observed in leaves and inflorescences of all cultivars. The symptoms included foliar distortion and deformation, necrotic spots delimited by the veins, flower abortion, and poor development of plants. In addition, A. besseyi was observed to penetrate tobacco roots at 30 DAI, and nematodes were also observed in the foliar mesophyll, inflorescences, and stems, a parasitism that has not been previously reported in tobacco plants. The disease caused by A. besseyi in tobacco could be a concern for growers in southern and northeastern Brazil because this nematode can cause severe damage to the marketable leaves of tobacco, reducing its commercial value.

Aphelenchoides besseyi Parasitizing Cowpea (Vigna unguiculata) in Brazil.

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was described as causing damage on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. This study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using two A. besseyi populations as inocula, 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, with the interior of the stems being 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.

Pre-inoculation with arbuscular mycorrhizal fungi affects essential oil quality and the reproduction of root lesion nematode in Cymbopogon citratus.

Cymbopogon citratus (lemongrass) is an important medicinal and aromatic plant containing citral-rich essential oil, of which the quality and quantity may be affected by nematode infection. Research has shown that arbuscular mycorrhizal fungi (AMF) may act as nematode biocontrol agents and improve the chemical composition of plants. Three experiments were conducted to assess the effects of AMF inoculation on vegetative growth, essential oil composition, induction of defense-related proteins, and control of Pratylenchus brachyurus in C. citratus. Seedlings were transplanted into pots inoculated with one of two AMF species (Rhizophagus clarus or Claroideoglomus etunicatum). At 30 days after AMF inoculation, plants were inoculated with P. brachyurus. Evaluations were performed at 75 days after nematode inoculation. Although both AMF treatments led to effective root colonization (> 84%), fungus inoculation was not effective in reducing P. brachyurus population density. Nevertheless, C. etunicatum promoted an increase in shoot weight, and AMF treatments contributed to preserving essential oil composition in nematode-infected plants. In addition, both AMF treatments enhanced polyphenol oxidase activity and R. clarus increased peroxidase activity after nematode inoculation.

Aphelenchoides besseyi Parasitizing Common Bean in Brazil.

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.