Novas abordagens para identificação e controle de Choanephora spp. em diferentes hospedeiros

Abstract

Zygomycetes are terrestrial fungi with saprophytic activities and asexual reproduction through the formation of sporangia and sporangioles or sexual reproduction by zygospores; they are taxonomically identical due to the formation of cenocytic mycelium in which spores are produced asexually and development easily favored by hot and humid climate. The climatic conditions of the Amazon region and the Brazilian Cerrado, together with the diversity of plants of agricultural interest that are cultivated annually, are factors that increase the risk of infection by these organisms. The pathogen Choanephora described by Currey in 1873, belongs to this group, infects soybeans, cotton, crotalaria, hibiscus, cucurbits, among others, and is distributed in countries like the USA, Japan, China, Thailand and Brazil, making it necessary to carry out morphological studies and molecular that improve the identification of species and characterization of the disease, aiming at control in their respective hosts. In this work, the total DNA of 27 isolates of the Choanephoraceae family obtained from different hosts were amplified and sequenced to identify gender and species using primers that amplified the regions: Larger Ribosome subunit (LSU), the entire Transcribed Internal Spacer (ITS) region, Actin, second largest Subunit of RNA Polymerase (RPB2), Elongation factor 1 alpha, Elongation factor 1 and Elongation factor 3. Individual and combined data sets were analyzed by Maximum Likelihood to investigate evolutionary relationships within the Choanephoraceae family. The isolates grouped into the genera (Choanephora, Poitrasia and Blakeslea), the isolates that grouped in Choanephora, segregated into three clades (Choanephora cucurbitarum, Choanephora infundibulifera and Choanephora sp.) With the possibility of a new species. In the epidemiology study, plants of Crotalaria breviflora were inoculated with the isolate MN897836 (CCUB 1293) to prove Koch's postulate, the pathogen was identified as Choanephora cucurbitarum, this being the first report of the disease in this host in the world. For the development and control tests, cotton, soybean and sunflower isolates were subjected to analysis of mycelial growth, growth rate, sporulation and descriptive scale to assess development, spore production and antagonistic action of conidial fungi from the Southern Amazon (Gonytrichum sp., Pseudobotrytis terrestris, Brachysporiella sp. and, Ellisembia sp.), Bacillus subtilis, Trichoderma asperellum and Pichia sp. in the control of Choanephora spp. in vitro. Ellisembia sp., Brachysporiella sp. and T. asperellum presented better antagonism results against the three isolates. Pichia sp. presented a halo of inhibition in cotton and crotalaria isolates that permeated for 21 days. Therefore, this work is relevant in the implementation of new approaches for the identification of Choanephora species in different cultures, in addition to biological control using organisms from Amazonian biodiversity, aiming at the control of diseases with low environmental impact.