Evaluation of the Fertilizing and Nematicidal Effects of Lixiviate from Banana Rachis and Purpureocillium lilacinum for a Reduction of Fallow Frequency in Dessert Banana Monoculture

The practice of fallowing for one year represents a viable alternative to chemical control of Radopholus similis and Pratylenchus coffeae in dessert banana monoculture. Although necessary, fallowing has an economic disadvantage for farmers. The objective of this work is to evaluate the nematicidal and fertilizing effects of lixiviate from banana rachis and Purpureocillium lilacinum in order to reduce the frequency of fallowing. In this study, we performed a chemical analysis of the lixiviate and then compared the two types (plantain lixiviate and dessert lixiviate) at 25% concentration, Bioact (Purpureocillium lilacinum) at 106 spores/ml) and two mixed treatments (plantain lixiviate + Bioact and dessert lixiviate + Bioact) to an untreated control and a reference nematicide, fluopyram at 10% (Verango) during three cycles of cultivation of the dessert banana seedling Grande naine. At the end of each crop cycle, the evolution of the nematode population and the yield of banana plants were evaluated. Chemical analysis revealed a high potassium content in both products and a more remarkable amount of nitrogen in the plantain lixiviate. The results showed that Bioact did not show antagonistic effect against nematodes and impact on production. On the other hand, despite less nematicidal activity, the lixiviate significantly increased the yield compared to the chemical nematicide treatment. Therefore, only in the plots treated with lixiviate, it was possible to carry out several successive crop cycles. This result was more marked with the plantain lixiviate. The results presented in this work are encouraging for the development of biological control methods of banana nematodes by lixiviate.

Targeted transcriptomics reveals signatures of large-scale independent origins and concerted regulation of effector genes in Radopholus similis

The burrowing nematode, Radopholus similis, is an economically important plant-parasitic nematode that inflicts damage and yield loss to a wide range of crops. This migratory endoparasite is widely distributed in warmer regions and causes extensive destruction to the root systems of important food crops (e.g., citrus, banana). Despite the economic importance of this nematode, little is known about the repertoire of effectors owned by this species. Here we combined spatially and temporally resolved next-generation sequencing datasets of R. similis to select a list of candidates for the identification of effector genes for this species. We confirmed spatial expression of transcripts of 30 new candidate effectors within the esophageal glands of R. similis by in situ hybridization, revealing a large number of pioneer genes specific to this nematode. We identify a gland promoter motif specifically associated with the subventral glands (named Rs-SUG box), a putative hallmark of spatial and concerted regulation of these effectors. Nematode transcriptome analyses confirmed the expression of these effectors during the interaction with the host, with a large number of pioneer genes being especially abundant. Our data revealed that R. similis holds a diverse and emergent repertoire of effectors, which has been shaped by various evolutionary events, including neofunctionalization, horizontal gene transfer, and possibly by de novo gene birth. In addition, we also report the first GH62 gene so far discovered for any metazoan and putatively acquired by lateral gene transfer from a bacterial donor. Considering the economic damage caused by R. similis, this information provides valuable data to elucidate the mode of parasitism of this nematode.

Molecular Diagnosis and Evolutionary Relationship Analysis Of Plant Parasitic Tea Garden Nematodes From Different Tea Estates In Sylhet Region of Bangladesh

Nematodes from plant-parasitic sources are ever-present and incidental to plant growth as well as crop production. The damage of tea gardens caused by nematode is often non-specific and easily confused with symptoms. The present study determined the parasitic and non-parasitic nematodes population in different tea gardens of the Sylhet region by their morphological and partial molecular characterization. Out of 13 tea gardens, it was observed that BTRI, Karimpur, Mathiura, and Tarapur tea garden has the highest number of parasitic and non-parasitic nematodes. After PCR amplification, DNA bands with desired amplicon size were detected by gel electrophoresis. Among thirteen soil samples, nematodes from Malnichara, Karimpur, BTRI, Mathiura , and Finlay had partially confirmed the presence of rootknot nematode (Meloidogyne spp.), root-lesion nematode (Pratylenchus brachyurus), burrowing nematode (Radopholus similis), reniform nematode (Rotylenchulus reniformis) and lance nematode (Hoplolaimus columbus) consequently based on approximately base pair of 1.7, 1.1 and 0.52 kb (different Meloidogyne spp.) 0.52, 0.52, 0.25 and 2.3 kb of specific genes. From evolutionary analysis, it might be said that Meloidogyne species are strongly related with each other making clusters except Meloidogyne natalie where this one is closely related with Hoplolaimus columbus in their evolutionary relationship as remaining others (Rotylenchulus reniformis, Radopholus similis, Pratylenchus brachyurus) are in different clusters in the same clade and this result could be confirmed after sequencing. J. Bio-Sci. 29(1): 101-109, 2021 (June)

A Venom Allergen-Like Protein, RsVAP, the First Discovered Effector Protein of Radopholus similis That Inhibits Plant Defense and Facilitates Parasitism

Radopholus similis is a migratory endoparasitic nematode that is extremely harmful to host plants. Venom allergen-like proteins (VAPs) are members of the cysteine-rich secretory protein family that are widely present in plants and animals. In this study, we cloned a VAP gene from R. similis, designated as RsVAP. RsVAP contains an open reading frame of 1089 bp encoding 362 amino acids. RsVAP is specifically expressed in the esophageal gland, and the expression levels of RsVAP are significantly higher in juveniles than in other life stages of R. similis. This expression pattern of RsVAP was consistent with the biological characteristics of juveniles of R. similis, which have the ability of infection and are the main infection stages of R. similis. The pathogenicity and reproduction rate of R. similis in tomato was significantly attenuated after RsVAP was silenced. In tobacco leaves transiently expressing RsVAP, the pathogen-associated molecular pattern-triggered immunity (PTI) induced by a bacterial flagellin fragment (flg22) was inhibited, while the cell death induced by two sets of immune elicitors (BAX and Gpa2/RBP-1) was repressed. The RsVAP-interacting, ras-related protein RABA1d (LeRabA1d) was identified in tomato hosts by yeast two-hybrid and co-immunoprecipitation assays. RsVAP may interact with LeRabA1d to affect the host defense response, which in turn facilitates nematode infection. This study provides the first evidence for the inhibition of plant defense response by a VAP from migratory plant-parasitic nematodes, and, for the first time, the target protein of R. similis in its host was identified.

Attraction and penetration of Musa by the burrowing nematode, Radopholus similis, in an autotrophic bipartite culture system

Summary Our objective was to discover the stages (pre- or post-infection) in which the resistance to burrowing nematode (Radopholus similis) occurs in two resistant banana (Musa spp.) cultivars. An autotrophic in vitro culture system was used to compare R. similis migration towards, and penetration into, the banana roots. A new two-compartment autotrophic in vitro model system was developed using agar-based medium to examine the migration of R. similis to either the susceptible ‘Grande Naine’ or the resistant ‘Yangambi km5’ (‘Ykm5’), when both the Musa genotypes were present at equal distance. The autotrophic in vitro model system was advantageous, because it supported continuous root growth due to the actively photosynthesising shoots growing in the open air, while the in vitro root conditions make it possible to observe and assess the nematode chemotaxis in the transparent medium. Significantly fewer nematodes migrated towards the resistant ‘Ykm5’ plants when compared to both the susceptible ‘Grande Naine’, and another resistant cultivar, ‘Saba’, at 1 h after infection. This signals a possibility of a lower concentration or different composition of nematode attractants in ‘Ykm5’ root exudates. No significant differences were observed in the percentage of R. similis that migrated towards the roots of the susceptible and resistant banana plants at 3, 4 and 6 h after inoculation. No significant differences were observed in the percentages of female penetration in the resistant and susceptible plant roots at 1 and 2 days after inoculation. The results of the two-compartment system confirmed that when a choice is given to migrate towards the resistant and susceptible genotypes, no differences were observed in the percentage of female migration towards both the genotypes.

Poblaciones de fitonematodos asociados al vigor de plantas de plátano

Introducción. La fracción biótica del suelo es el componente esencial en los procesos ecológicos y pueden ejercer influencia en la productividad agrícola de los cultivos. Objetivo. Identificar la población de fitonematodos asociados al vigor de las plantas de plátano en la zona de sur del lago de Maracaibo, Venezuela. Materiales y métodos. Se seleccionaron ocho lotes de plantas de plátano (Musa AAB cv. Hartón) de 2 ha, ubicados en el sur del lago de Maracaibo, los cuales se dividieron en dos áreas o lotes de 1 ha, durante octubre y diciembre del año 2018. La designación de los lotes por vigor (AV= alto vigor y BV= bajo vigor) se realizó con base en los parámetros del número de manos por racimo, circunferencia de la planta madre y altura del hijo de sucesión, en veinte plantas próximas a la cosecha, por cada uno. La muestra de suelo se recolectó a 15 cm de profundidad en tres plantas recién florecidas por lote y para las raíces se realizó una microcalicata por planta hasta 30 cm de profundidad. Para la extracción nematológica en suelo se empleó el método de levigación de oostenbrink con embudo de Baermann y en raíz el método de licuado. Posteriormente, se cuantificó por género los especímenes encontrados. Resultados. Se encontró una población en el suelo (14 140 individuos) más significativa (p<0,05) que en la raíz (2670 individuos). Al comparar la población total por vigor no se observó diferencia estadística entre AV (395) y BV (305). Se determinaron doce géneros taxonómicos en las muestras de raíz y en suelo. Los especímenes más predominantes en AV fueron Helicotylenchus multicinctus y Radopholus similis y en los lotes BV fue Pratylenchus sp. Conclusión. Se observó una alta diversidad de la nematofauna presente tanto en los suelos como en raíces del cultivo.