New guarana fungus can affect other economically important plants

A new species of fungus found in guarana plants (Paullinia cupana), with characteristic symptoms like leaf spots that resemble anthracnose, can cause leaf diseases in açaí and African oil palm trees. The discovery was made in a study based on field observation, fungus isolation, and laboratory analyses with morphological and molecular characterization, performed at Embrapa Western Amazon's Laboratory of Molecular Biology.

The new species belongs to a group called pestalotioid fungi, which comprises three genera (Pestalotiopsis, Pseudopestalotiopsis and Neopestalotiopsis) and causes diseases in a broad range of hosts. In guarana trees, the researchers identified species that belong to two of the three pestalotioid genera. Out of six strains analyzed, they identified three as the fungal species Neopestalotiopsis formicarum, while the other three isolates were described as a new species that was baptized Pseudopestalotiopsis gilvanii. The study also makes the first report of Neopestalotiopsis formicarum as a guarana plant pathogen.

The new fungus was observed in guarana clones, which indicates that the new pathogen needs to be monitored so as not to become an issue for the crop in the future. Photo: Ronaldo Rosa

Pseudopestalotiopsis gilvanii was isolated in guarana plants and raised concerns about how it affects the crop, since it causes symptoms that burn the leaf, reducing photosyntheses and thus harming plant development. “Moreover, the fungus was observed in guarana clones that are launched cultivars, which indicates that this new pathogen needs to be monitored so that it does not become a problem for guarana cultivation in the future”, warns the Embrapa researcher Gilvan Ferreira da Silva, coordinator of the local Laboratory of Molecular Biology.

The scientist underscores that the discovery is important not only because it has revealed a new species, but also because it has identified a new pathogen that can become a problem for several economically important crops in tropical regions. However, the researcher clearly states that growers can stay calm, since the new pathogen is not a threat at the moment yet; the fungus has been seldom observed in the fields; and further monitoring is required to better understand the pathogen's behavior.

Ferreira reports that at first they suspected it was anthracnose, another disease that affects guarana plants, caused by the fungus Coletotrichum guaranicola. However, the scientists verified the occurrence of the disease in anthracnose-resistant plants developed through breeding and genetic improvement. They even suspected a breach in plant resistance to the fungus that causes anthracnose.

Other results nevertheless showed that it was a new pathogen. And the molecular studies combined with the morphological characterization indicated that part of the isolates did not show correspondence with the literature, pointing to a new species. The discovery was later confirmed and described in a paper published in the journal Phytotaxa magazine, which specializes in taxonomy.

Publication of the discovery

The discovery of the new pathogen was published in the scientific journal Phytotaxa as a paper entitled "Pseudopestalotiopsis gilvanii sp. nov. and Neopestalotiopsis formicarum leaves spot pathogens from guarana plant: a new threat to global tropical hosts", and authored by: Gilvana F. Gualberto; Aricléia de M. Catarino, postdoctoral scholar at the National Institute of Amazonian Research's Graduate Program on Agriculture in Wet Tropics; Rogério E. Hanada, a researcher at the National Institute of Amazonian Research (Inpa); Gilvan Ferreira da Silva, researcher at Embrapa Western Amazon; Thiago Fernandes Sousa, master's student of Microbiology from the Federal University of Viçosa (UFV) advised by Gilvan at Embrapa Western Amazon; Fernanda F. Caniato, professor at the Amazonas Federal University (Ufam); and Jeferson Cruz, technician at Embrapa Western Amazon's Laboratory of Molecular Biology.

Phytopathogenic potential for several crops

After they confirmed that they were dealing with phytopathogenic species in guaraná plants, they decided to investigate the pathogens' potential to affect other plants that are economically important for the tropics. In controlled research conditions, the fungus was inoculated in samples of plants that are studied at Embrapa Western Amazon: açaí palms (both Euterpe precatoria and Euterpe oleracea), African oil palms, banana plants and rubber trees.

The results verified that the fungus Ps. gilvanii was pathogenic to both Euterpe oleracea and E. precatoria açaí palms. It also affected African oil palm (Elaeis guineensis), but did not have pathogenic effect on banana plants (Musa paradisiaca var. pacovan) or rubber trees (Hevea brasiliensis).

The research also indicated that the fungus N. formicarum was not pathogenic to rubber trees but was pathogenic to other species tested. The symptoms caused by pestalotioid fungi in those crops also resembled the anthracnose ones, as they showed leaf spots that harm plants' photosynthetic capacity.

Agricultural importance of this fungal group has been growing

Ferreira clarifies that he is not talking about the frequency of such diseases or the losses they cause, as the pathogen has been described too recently and studies in that sense have not been performed yet. However, he comments that the discovery of this new plant pathogen comes at a time that studies indicate the pestalotioid group can now be classified as emerging pathogens.

While in the 1980s and 1990s this group of pathogens was considered without much importance, in recent years the scientific literature on them has increased a lot. Dozens of papers about such pathogens have been published annually and in 2021 alone, there were 61 studies in the PubMed database. In fact, recently published studies show the agricultural importance of diseases caused by the fungal group with examples demonstrating that it affects production, as is the case of the Pinus bungeana pine and the tea plant Camelliae sinensis in China, or coconut palms (Cocos nucifera) in Bangladesh.

Preventive strategies

New studies are being conducted towards prevention and to establish strategies of disease control. “We are seeing the elaboration and approval of new projects to expand investigation to the scope of molecular, genomic and transcriptomic biology”, the Embrapa researcher announces.

Since the new fungi were verified in some of the clonal cultivars of guaraná, which endangers materials that offer high yield, new research to assess their resistance and susceptibility levels will be conducted on those cultivars in light of the new pathogens.

The researcher explains that, in partnership with the Ufam researcher Fernanda Caniato, the Ps. gilvanii fungus will be studied at a genomic level, including the identification of the microorganism's genes and guarana plant defense genes against it.

There will be studies with the transcriptome (full set of RNA transcripts) of the interaction between the pathogen and both susceptible and resistant guarana clones, in order to verify transcripts that are differentially expressed in resistant plants and in susceptible plants.

They also initiated another line of research to assess the potential of bacteria and fungi to fight and control the pathogenic fungi. This work, which focuses on the development of phytopathogen biocontrol, is funded by the Amazonas State Foundation for Research Support (Fapeam) and coordinated by Caniato, at Ufam, in partnership with Embrapa.