Host status of eucalypt species to Pratylenchus brachyurus and Meloidogyne incognita

Plant parasitic nematodes are major threats to Brazilian and world agriculture. Among them, Pratylenchus brachyurus and Meloidogyne incognita stand out as major pests for several crops, including corn, cotton, soybean among others, which can be components of integrated crop-livestock-forestry systems (ICLFs). In this context, information about the host status of eucalypts (Corymbia spp. and Eucalyptus spp.) to plant parasitic nematodes becomes more relevant in Brazil, due to the use of eucalypts in ICLFs. If tree components used on this system increase the population density of P. brachyurus and M. incognita, it is possible that these pathogens could damage shorter-cycle crops. Since information about the host status of eucalypts to plant parasitic nematodes is scarce, this study evaluated the host status of some eucalypt species to P. brachyurus and M. incognita. Two greenhouse trials were done to evaluate the reproduction of P. brachyurus and one to M. incognita, using some of the most cultivated species and hybrids of eucalypts in Brazil. The population growth of P. brachyurus increased on Corymbia citriodora, Eucalyptus grandis, Eucalyptus dunnii × Eucalyptus urophylla, and E. grandis × E. urophylla after ~90 days of inoculation. Conversely, despite M. incognita reproducing well in the control plants, no individuals were recovered from C. citriodora, E. urophylla and E. grandis × E. urophylla, which were classified as resistant plants. Based on both obtained and available data, M. incognita poses no threat to eucalypt species today. However, P. brachyurus is suggested to be a threat to eucalypts.

Phytonematodes infesting common bean fields in Brazil, and pathogenicity tests with Pratylenchus brachyurus

Phytonematodes are among the main pathogens of the common bean. In general, control practices that aim to control these pathogens have not been regularly adopted in Brazil. The objectives of the present study were to evaluate the occurrence of phytonematodes in dry bean fields in Paraná and São Paulo states and estimate the pathogenicity of Pratylenchus brachyurus to dry bean in glasshouse experiments. Root and soil were sampled for nematode extraction, identification and estimation of population density. Four glasshouse experiments with different initial population densities were carried out to evaluate the effect of P. brachyurus on the growth of dry bean plants. Six species of phytonematodes were detected, namely Helicotylenchus dihystera, P. brachyurus, Pratylenchus crenatus, Meloidogyne javanica, Meloidogyne incognita and Rotylenchulus sp. The spiral nematode H. dihystera was found in all samples and was the most abundant species in both states. The lesion nematode P. brachyurus was also frequent, reaching 94% in Paraná and 100% in São Paulo. The root-knot nematodes and Rotylenchulus sp. were reported only in São Paulo fields (45% and 18% frequency, respectively), and P. crenatus only in Paraná (12%). The most abundant nematode in the soil was H. dihystera, and in roots was P. crenatus. It was demonstrated that densities of 6.66 specimens of P. brachyurus per cm3 of soil provoke visible and measurable root decay. In conclusion, survey data showed low phytonematode densities and pathogenicity tests demonstrated that densities above 6.67 specimens of P. brachyurus per cm3 of soil cause damage to the dry bean roots.

Host suitability of grain sorghum and sudangrass for Pratylenchus brachyurus / Suscetibilidade do sorgo granífero e capim-sudão a Pratylenchus brachyurus

Nowadays, the root-lesion nematode Pratylenchus brachyurus (Godfrey) is a major pest of soybean in Brazil, mainly in areas using double cropping with maize or cotton, which are suitable hosts for P. brachyurus. A great effort has been made to find cash crops for P. brachyurus management. Grain sorghum [Sorghum bicolor (L.)] was classified as a non-host for P. brachyurus but based on a single trial. It would be a valuable option as a culture for double cropping with soybean, as it is profitable and can be used in root-lesion nematode management. Sudangrass (S. bicolor var. sudanense) is not directly profitable, but Brazilian farmers favor it because it can produce pasture, green chop, silage, or hay under unfavorable hydric conditions. However, no information is available regarding the suitability of sudangrass for P. brachyurus. Thus, the current study aimed to assess the suitability of grain sorghum and sudangrass for P. brachyurus in two glasshouse trials. The first trial tested sudangrass and grain sorghum 'DKB 510', 'Dow 740', 'Dow 822', 'DKB 599', and 'AG 1040'. The second trial retested sudangrass and grain sorghum 'Dow 740' and 'DKB 599'. The results demonstrated that sudangrass and grain sorghum were suitable hosts for P. brachyurus. These results, in addition to those obtained for other types of sorghum, emphasize that S. bicolor and sudangrass should be avoided in fields infested with P. brachyurus, as they increase the nematode population.(AU)

Atualmente, o nematoide das lesões radiculares Pratylenchus brachyurus Godfrey é um dos principais patógenos para a soja no Brasil, principalmente em áreas com sucessão de milho ou algodão, que também são suscetíveis a P. brachyurus. Grandes esforços têm sido feitos a fim de encontrar uma cultura rentável que possa ser utilizada no manejo de P. brachyurus. O sorgo granífero (Sorghum bicolor L.) é relatado como resistente a P. ­brachyurus, porém com base em apenas um ensaio. Adicionalmente, o capim-sudão (S. ­bicolor var. sudanense) não é diretamente rentável, mas é apreciado pelos agricultores brasileiros por produzir pasto, material verde picado, silagem ou feno, mesmo sob condições hídricas desfavoráveis. Entretanto, não há nenhuma informação sobre a suscetibilidade dessa cultura a P. brachyurus. Dentro desse contexto, o objetivo do presente trabalho foi avaliar a suscetibilidade de cultivares de sorgo granífero e capim-sudão a P. brachyurus em dois ensaios em casa de vegetação. No primeiro experimento, foram testados o capim-sudão e os sorgos graníferos DKB 510, Dow 740, Dow 822, DKB 599 e AG 1040. No segundo experimento, capim-sudão e os cultivares de sorgo granífero Dow 740 e DKB 599 foram testados novamente. Os resultados de ambos os ensaios demonstraram que o capim-sudão e o sorgo granífero são suscetíveis a P. ­brachyurus. Esses resultados, mais os obtidos para outros tipos de sorgo, demonstram que S. ­bicolor e o capim-sudão devem ser evitados em áreas infestadas com P. ­brachyurus, já que essas culturas aumentam dramaticamente as densidades populacionais do nematoide das lesões no solo.(AU)

Host Transcriptional Profiling at Early and Later Stages of the Compatible Interaction Between Phaseolus vulgaris and Meloidogyne incognita.

The root-knot nematode (Meloidogyne incognita) is one of most devastating pathogens that attack the common bean crop. Although there is evidence that some cultivars have race-specific resistance against M. incognita, these resistance sources have not proved effective, and nematodes are able to circumvent the host's defense system. We constructed RNA-seq based libraries and used a high-throughput sequencing platform to analyze the plant responses to M. incognita. Assessments were performed at 4 and 10 days after inoculation corresponding to the stages of nematode penetration and giant cell development, respectively. Large-scale transcript mapping to the common bean reference genome (G19833) resulted in the identification of 27,195 unigenes. Of these, 797 host genes were found to be differentially expressed. The functional annotation results confirm the complex interplay between abiotic and biotic stress signaling pathways. High expression levels of the wounding-responsive genes were observed over the interaction. At early response, an overexpression of the N gene, a TIR-NBS-LRR resistance gene, was understood as a host attempt to overcome the pathogen attack. However, the repression of heat shock proteins resulted in a lack of reactive oxygen species accumulation and absence of a hypersensitive response. Furthermore, the host basal response was broken by the repression of the ethylene/jasmonate pathway later in the response, resulting in a continuous compatible process with consequent plant susceptibility.

A method to estimate the population level of Aceria litchii (Prostigmata: Eriophyidae) and a study of the population dynamics of this species and its predators on litchi trees in southern Brazil.

Litchi (Litchi chinensis Sonnerat) is native to Southeast Asia, where most of the world cultivation of this crop is done. Its commercial cultivation in Brazil is recent and concentrated in the state of São Paulo. This crop has been severely damaged in Asia and Brazil by the litchi erineum mite, Aceria litchii (Keifer) (Eriophyidae). The objectives of this study were the adaptation of a method to estimate the density of A. litchii, an evaluation of the population dynamics of this pest and of its associated predators in the state of São Paulo, and an estimation of its injury levels to litchi trees. To estimate the density of A. litchii, an adaptation of a method commonly used to evaluate nematode densities in plant roots was performed. This method was shown to be adequate for the estimation of the number of A. litchii, and it might also be useful for similar evaluations of other erineum forming mites. Field samples to determine the pest population dynamics were collected monthly from August 2011 to July 2012. Sampled leaves were examined under a stereomicroscope for removal of predators and subsequent extraction ofA. litchii by the adapted method. A. litchii reached maximum densities in November 2011 and June 2012, being found at low densities between January and March 2012. The pattern of variation of A. litchii injury levels was similar to that of the density of A. litchii. The main predatory mite co-occurring with A. litchii was the phytoseiid Phytoseius intermedius Evans and McFarlane. However, high injury levels due toA. litchii suggest that the predator was unable to prevent visible damages to the trees, indicating that control activities should be adopted by growers.

Seed treatment affects Meloidogyne incognita penetration, colonization and reproduction on cotton / Tratamento de sementes afeta a penetração, colonização e reprodução de Meloidogyne incognita em algodão

The effect of abamectin, applied as seed treatment, on Meloidogyne incognita penetration, colonization, and reproduction on cotton was evaluated in two greenhouse experiments. Second stage juveniles (J2) penetration was evaluated 3, 9 and 15 days after germination (dag), whereas the nematode colonization was evaluated 27dag, by counting the total number of galls and egg masses per root system. Eggs and J2 were extracted from the roots to assess the nematode reproduction at 50 and 100dag. The seed treatment caused a decrease in J2 penetration in the roots, resulting in lower colonization and reproduction of M. incognita. These findings are discussed considering the environmental aspects of abamectin in the soil and the current practices for the crop management.

O efeito de abamectina em tratamento de sementes na penetração, colonização e reprodução de Meloidogyne incognita, em algodão, foi avaliado em dois experimentos de casa de vegetação. A penetração de juvenis de segundo estádio (J2) foi avaliada aos três, nove e 15 dias após a germinação (dag), enquanto que a colonização 27dag foi avaliada por meio da contagem do número total de galhas e massas de ovos por sistema radicular. Ovos e J2 de M. incognita foram extraídos das raízes para determinar a reprodução do nematoide aos 50 e 100dag. O tratamento de sementes diminuiu a penetração dos J2 nas raízes, resultando em menor colonização e reprodução de M. incognita. Os resultados obtidos são discutidos tendo em vista os aspectos ambientais da presença de abamectina no solo e as práticas agrícolas em uso.