Caracterização de fungos associados a sementes e à antracnose da carnaubeira

Abstract

The carnauba (Copernicia prunifera) has great socio-economic importance for its integral use, where the leaves, fruits, flowers, stem and roots are completely useful, giving rise to industrial and artisanal products. A large extraction of these palm trees in their native areas threatens the present natural ecosystems, compromising the microbiota, local fauna and flora. Seeds are the most efficient means of dissemination of pathogens into new areas which may cause serious losses if contaminated seeds are used for the seedling production. The production of healthy seedlings to the restoration of landscapes can be hampered by the association of pathogens with seeds, which can be transmitted to plants, compromising their development and leading to death. The objective of this study was to characterize morphologically and molecularly fungi associated with seeds and to test the pathogenicity of Colletotrichum isolates associated with carnauba fruit (C. prunifera). Fruits in a stage of physiological maturation were collected in three municipalities of the Ceará State: Bela Cruz, Caucaia and Paraipaba, where the remaining natural populations are found. The filter paper method or the blot test method was used to evaluate the healthy of 400 carnauba seeds from each sampled region. The direct isolation method was used to obtain Colletotrichum isolates associated with anthracnose. For this, fruits from each region, with symptoms of anthracnose, were washed with neutral detergent and disinfested with sodium hypochlorite and conditioned in a humid chamber until sporulation on the lesions. Three isolates from diseased fruits were obtained as representatives of each collection site (UFCM 0630-Caucaia, UFCM 0631-Bela Cruz and UFCM 0632- Paraipaba). Sequencing of DNA fragments from the internal transcribed spacer of ribosomal DNA was performed for seed isolates, and DNA fragments from the regions ITS, actin (ACT), β-tubulin), glyceraldehyde-3-phosphate dehydrogenase (GPDH), and glutamine synthetase (GS), were sequenced for molecular characterization and determination of phylogenetic relationships of the Colletotrichum isolates obtained from carnauba fruits. A morphological and cultural characterization of all isolates was carried out. Isolates UFCM 0630, UFCM 0631 and UFCM 0632 were submitted to the pathogenicity test on healthy fruits of carnauba (C. prunifera) and mango cv. Tommy Atkins, and on cashew plantlets BRS 265. After characterization of the seed isolates, it was possible to identify the genera Alternaria, Aspergillus, Fusarium, Lasiodiplodia, Penicillium, Phomopsis, Rhizopus and Schizophyllum. In the Colletotrichum characterization, the isolates UFCM 0630 and UFCM 0632 were identified as Colletotrichum tropicale, and the UFCM 0631 isolate as Colletotrichum theobromicola, species belonging to the Colletotrichum gloeosporioides species complex. Koch's postulates were completed to confirm the pathogenicity of the three Colletotrichum species isolates on healthy carnauba fruits. Only isolates UFCM 0630 and UFCM 0632 were pathogenic on mango fruits and cashew plantlets. All the fungi identified on seeds in the present study represent the first report for C. prunifera. Colletotrichum tropicale and C. theobromicola are reported for the first time as etiological agents of carnauba anthracnose.