Microbiome of Nodules and Roots of Soybean and Common Bean: Searching for Differences Associated with Contrasting Performances in Symbiotic Nitrogen Fixation.

Biological nitrogen fixation (BNF) is a key process for the N input in agriculture, with outstanding economic and environmental benefits from the replacement of chemical fertilizers. However, not all symbioses are equally effective in fixing N2, and a major example relies on the high contribution associated with the soybean (Glycine max), contrasting with the low rates reported with the common bean (Phaseolus vulgaris) crop worldwide. Understanding these differences represents a major challenge that can help to design strategies to increase the contribution of BNF, and next-generation sequencing (NGS) analyses of the nodule and root microbiomes may bring new insights to explain differential symbiotic performances. In this study, three treatments evaluated in non-sterile soil conditions were investigated in both legumes: (i) non-inoculated control; (ii) inoculated with host-compatible rhizobia; and (iii) co-inoculated with host-compatible rhizobia and Azospirillum brasilense. In the more efficient and specific symbiosis with soybean, Bradyrhizobium presented a high abundance in nodules, with further increases with inoculation. Contrarily, the abundance of the main Rhizobium symbiont was lower in common bean nodules and did not increase with inoculation, which may explain the often-reported lack of response of this legume to inoculation with elite strains. Co-inoculation with Azospirillum decreased the abundance of the host-compatible rhizobia in nodules, probably because of competitiveness among the species at the rhizosphere, but increased in root microbiomes. The results showed that several other bacteria compose the nodule microbiomes of both legumes, including nitrogen-fixing, growth-promoters, and biocontrol agents, whose contribution to plant growth deserves further investigation. Several genera of bacteria were detected in root microbiomes, and this microbial community might contribute to plant growth through a variety of microbial processes. However, massive inoculation with elite strains should be better investigated, as it may affect the root microbiome, verified by both relative abundance and diversity indices, that might impact the contribution of microbial processes to plant growth.

Within-Host Competition between Two Entomopathogenic Fungi and a Granulovirus in Diatraea saccharalis (Lepidoptera: Crambidae).

We provide insights into how the interactions of two entomopathogenic fungi and a virus play a role in virulence, disease development, and pathogen reproduction for an economically important insect crop pest, the sugarcane borer Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae). In our model system, we highlight the antagonistic effects of the co-inoculation of Beauveria bassiana and granulovirus (DisaGV) on virulence, compared to their single counterparts. By contrast, combinations of Metarhizium anisopliae and B. bassiana, or M. anisopliae and DisaGV, have resulted in additive effects against the insect. Intriguingly, most cadavers that were derived from dual or triple infections, produced signs/symptoms of only one species after the death of the infected host. In the combination of fungi and DisaGV, there was a trend where a higher proportion of viral infection bearing conspicuous symptoms occurred, except when the larvae were inoculated with M. anisopliae and DisaGV at the two highest inoculum rates. Co-infections with B. bassiana and M. anisopliae did not affect pathogen reproduction, since the sporulation from co-inoculated larvae did not differ from their single counterparts.

A protocol for determination of conidial viability of the fungal entomopathogens Beauveria bassiana and Metarhizium anisopliae from commercial products.

Techniques for directly determining conidial viability have widespread use but also have limitations for quality control assessments of formulated mycoinsecticides, especially in emulsifiable oil. This study proposes a new method based on adaptations of already established protocols that use the direct viability method to make it more economical and accurate, thus enabling its use in the evaluation of formulated products. Appropriate parameters and conditions were defined using products based on Beauveria bassiana and Metarhizium anisopliae in the forms of pure conidia, fungus-colonized rice, ground fungus-colonized rice and oil dispersion. The established protocol, named ESALQ, consists of the transfer of 150 µL of a suspension containing about 0.7 and 1 × 10(6) conidia/mL onto Rodac® plates with 5 mL of potato dextrose agar culture medium + 5 mg/L of Pentabiotic® and 10 µL/L of Derosal® (Carbendazim) and subsequent counting of germinated and non-germinated conidia. For the ground fungus-colonized rice and oil dispersion formulations, prior to transferring the fungal suspension to the medium, rice should be decanted and the oil removed, respectively. This method was compared with another direct viability method and with the Colony-forming unit (CFU) and Fluorescence viability methods, comparing the accuracy obtained using the coefficient of variation (CV) of the analysis of each method. The results showed that in addition to the ease of application, the developed method has higher accuracy than the other methods (with a CV up to seven times lower than in the Standard method and up to 32 times lower than CFU). The CFU method underestimated the concentration of viable conidia in most of the tested fungal forms, and in the emulsifiable oil products, these values were 54% lower for B. bassiana and 84% lower for M. anisopliae. The adaptations and standardizations proposed in the ESALQ method showed effective improvements for routine quality assessment of mycoinsecticides.

Falsa broca aumenta disseminação de Beauveria bassiana em populações de campo da broca-do-rizoma da bananeira / West Indian Sugarcane Weevil enhances dissemination of Beauveria bassiana on field populations of the banana weevil

A transmissão horizontal de fungos entomopatogênicos tem papel importante na epizootiologia, pois está diretamente associada à disseminação do agente causal da doença de insetos. Em hospedeiros que apresentam restrita mobilidade, a presença de pragas secundárias no agroecossistema pode ajudar na formação de focos secundários da doença e, com isso, aumentar a mortalidade das pragas-chave. Para tanto, a disseminação de Beauveria bassiana, introduzida inoculativamente através de iscas tipo telha, foi avaliada em um bananal infestado por Cosmopolites sordidus (Piracicaba) e outro por C. sordidus e Metamasius hemipterus (Botucatu). Constatou-se que, em Piracicaba, não foram capturados insetos infectados na testemunha, sendo os índices de infecção nas parcelas que receberam B. bassiana de 8 e 15 por cento. Em Botucatu, o índice de infecção dos insetos capturados na testemunha chegou a 17 por cento, enquanto que, nas parcelas tratadas, variou de 28 a 54 por cento. Os resultados obtidos neste trabalho demostram que a presença de M. hemipterus influenciou na disseminação de B. bassiana para a população de C. sordidus, praga-chave dessa cultura.

Horizontal transmission of entomopathogenic fungi plays an important role in the epizootiology, because it is directly associated with the spread of causal agents of insect diseases. In hosts with restricted mobility, the presence of secondary pests in the agroecosystem can help in the formation of secondary disease outbreaks and increase the mortality of the target pest. For this purpose, the dissemination of Beauveria bassiana inoculated using tile-type baits was evaluated in a banana plantation infested with Cosmopolites sordidus (Piracicaba) and one with C. sordidus and Metamasius hemipterus (Botucatu). In Piracicaba, insects contaminated with the pathogen were not found in the control group, and infection rates in the plots that received B. bassiana ranged between 8 and 15 percent. In Botucatu, the infection rate of insects in the control reached 17 percent, whereas in the fungal treatment plots, it varied from 28 to 54 percent. The present results demonstrate the influence of M. hemipterus in the dissemination of B. bassiana in populations of C. sordidus, a target pest of this crop.