RESUMO
Hemileia vastatrix, causal agent of coffee leaf rust (CLR), is an aggressive pathogen of coffee plants worldwide. Conventional fungicides play a major role in the suppression of this disease, but a recent shift toward eco-friendly farming practices has occurred and additional novel, effective, and sustainable strategies for CLR control are needed. Naturally occurring fungal antagonists could be well-positioned to meet this demand, but these fungi need to be isolated and tested for efficacy to identify organisms with potential. In this study, a survey of fungi associated with CLR lesions in four districts of Hawai'i Island, HI, USA (Kona, Ka'u, Hamakua, and Hilo) was conducted. Coffee leaves infected with CLR were collected from 22 locations and over 600 lesions were plated on ½ APDA and CTC 4T media. DNA was extracted from purified isolates and the internal transcribed spacer region (ITS) was sequenced and analyzed by BLASTn. In total, 194 isolates comprising 50 taxa were recovered. Several of the genera are known antagonists of CLR or other plant pathogens, including Simplicillium, Akanthomyces, Cladosporium, Fusarium, and Clonostachys. The wide diversity of fungi associated with CLR lesions provide a wealth of possibilities for identifying potential CLR antagonists that could serve as a valuable tool for coffee farmers as part of an integrated pest management plan.
Assuntos
Coffea , Doenças das Plantas , Folhas de Planta , Coffea/microbiologia , Havaí , Doenças das Plantas/microbiologia , Doenças das Plantas/prevenção & controle , Folhas de Planta/microbiologia , Fungos/classificação , Fungos/isolamento & purificação , Fungos/genética , Fungos/efeitos dos fármacos , Basidiomycota/isolamento & purificação , Basidiomycota/genética , Basidiomycota/classificação , AntibioseRESUMO
Blueberry (Vaccinium spp.) has great economic importance in Chile, which currently has about 8,500 ha being cultivated. Recently, the presence of canker and dieback symptoms has been observed along the productive blueberry zone of Chile. Species of Pestalotiopsis and Truncatella were consistently isolated from diseased samples in 22 different locations. Therefore, the objective of this study was to identify and characterize the species of Pestalotiopsis and Truncatella associated with canker and twig dieback symptoms on blueberry. Forty-nine isolates were obtained on acidified potato dextrose agar in 2006 and 2007. These isolates were identified as Pestalotiopsis clavispora, P. neglecta, and Truncatella (=Pestalotia) angustata on the basis of colony characteristics and conidial morphology. This identification was verified by internal transcribed spacer analysis of DNA. Isolates of P. clavispora, P. neglecta, and T. angustata were pathogenic on apple, kiwifruit, and blueberry fruit. Similarly, isolates of P. clavispora were pathogenic on detached blueberry twigs of cv. O'Neal. Additionally, three selected isolates of P. clavispora induced light-brown canker lesions, surrounded by a reddish halo, and shoot dieback after twig inoculations on 2-year-old twigs of blueberry cvs. O'Neal, Bluecrop, Brightwell, Brigitta, Duke, Elliot, and Misty. Among blueberry cultivars, Brightwell and O'Neal were the most susceptible and Bluecrop and Misty the least susceptible, while Elliot, Brigitta, and Duke were moderately susceptible to P. clavispora. These pathogens were isolated consistently from inoculated plants, confirming Koch's postulates. P. clavispora was highly sensitive to fludioxonil and pyraclostrobin with a median effective concentration of 0.06 to 0.08 and 0.04 to 0.8 µg/ml, respectively. Therefore, the results of this study indicate that P. clavispora, P. neglecta, and T. angustata are primary pathogens that can cause canker lesions and dieback symptoms on blueberry not previously described in Chile. However, these results do not exclude that other species of these genera or other plant-pathogenic fungi (e.g., Botryosphaeria, Pestalotia, and Phomopsis spp.) may eventually be involved in this syndrome of blueberry.