The first report about Fusarium falciforme that causes root rot in cassava cv Rosinha, in Alagoas state, Brazil

The aim of this study was identifying the root rot causal agents in cassava, cv Rosinha, in Alagoas state, Brazil. Pathogen species were studied, which are responsible for root rot in cassava, through isolation, morphological characterization and pathogenicity confirmation. Fusarium sp was emphasized among other isolated genera, which is pathogenic to cassava roots and plants. The phylogenetic study was based on the ITS region of the constructed DNA, using the ‘‘maximum Likelihood Tree’’ method, with a base of 1000 “bootstrap” replicas, what showed 100% of genetic similarity to Fusarium falciforme géneros aislados, se destacó Fusarium sp., patógeno de las raíces y plantas de yuca. El estudio filogenético se basó en la región ITS de la construcción de ADN, utilizando el método de "Árbol de Máxima Verosimilitud", con una base de 1000 réplicas bootstrap, que mostró un 100% de similitud genética con Fusarium falciforme


Introduction
Root rot (Manihot esculenta Crantz) is the disease that most limits cassava production (Azevedo et al., 2021) in the North and Northeast regions of Brazil, notably in Alagoas state, where losses reach 70% approximately. The cassava is mainly used in human and animal feeding, as material for the biofuel, biodegradable plastic, meat processing, pasta production, textile and modified starch industries (Oliveira et al., 2011;Silva, et al., 2020). The losses caused by the root rot are limiting factors in the North and Northeast in the country (Machado et al., 2014;Nascimento Junior, 2015;Paiva et al., 2022). However, records about the main plant pathogens that cause root rot are incipient, even though their importance as a tool to make decisions about the best management strategy to be implemented (Baayen et al., 2000;Nalim et al., 2011;O'Donnell et al., 2008;Oliveira et al., 2011).The aim of this study is identifying the root rot causal agents in cassava, cv Rosinha, in Alagoas state, Brazil.

Methodology
Soil and roots were collected in the cities Arapiraca, Campo Alegre, Penedo, São Miguel dos Campos and São Sebastião in Alagoas state, Brazil in 2015, where cassava, cv Rosinha, was produced and presented root rot problems. In order to isolate the microorganisms, the serial dilution technique was used and in accordance to Tuite, (1969) methodology, 1.0 mL of the suspension was transferred to the petri dishes with BDA culture medium. Mycelial discs of isolated Fusarium sp. were used for DNA extraction, using CTAB protocol according to Doyle and Doyle, (1987). PCR reactions were prepared subsequently, and after that, the product was sent to purification and sequencing with the same primers that were used in the amplification to Macrogen Inc. (Seoul, South Korea). Multiple alignments of nucleotide sequence were prepared (Ronquist et al., 2012), using MUSCLE algorithm (Edgar, 2004) and manually adjusted in MEGA6 package (Tamura et al., 2013). Os isolados obtidos foram amplificados com o gene que codifica para a região ITS-rDNA (Table 1).

Results and Discussion
The structures that were produced by the pathogen were observed in the BDA medium, showing macroconidia with 3-7 septa and the size varying from 27-60 µm x 3-5 µm and microconidia with and without septa, measuring 8-16 µm x 2-4 µm, from cylindrical to oval and chlamydospore with an average diameter of 4.7-9.4µm (Figure 1). Obtained after 21 days of growth in BDA in the dark at room temperature (28 ± 2 ° C). The images were captured by a digital camera (Olympus IX2-SLP) coupled to an optical microscope with a magnification of 100 to 200x, projected on a computer monitor, using the Cellsenses Standard software (SAMSUNG SDC-415®). 50 measurements were made of each type of structure produced. Source: Authors (2022). The phylogenetic analysis based on the genic sequences of the ITS (Chehri et al., 2011;Chhetri et al., 2015;Hyde et al., 2014;O'Donnell et al., 2013) region of the DNA of the isolated material, using the ''maximum Likelihood Tree'' method with base on 1000 "bootstrap" replicas, showed 100% reliability that the isolated material belongs to the genus Fusarium and 99% similar to the Fusarium falciforme sequence that was deposited at GenBank (CBS128812). The confirmation is possible from the studied genomic region and the formed phylogenetic tree (Figure 2). Research, Society andDevelopment, v. 11, n. 12, e221111234369, 2022 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v11i12.34369  Thus, it is possible to affirm that from the studied genomic region and the formed phylogenetic tree, the isolated FUS is F. falciforme and not F. solani as the causal agent of cassava root rot (Alves et al., 2020;Paiva et al., 2022;Silva, et al., 2020aSilva, et al., , 2020bSilva, et al., 2020) . So, this is the first report about this specie as the causer of root rot in cassava.

Conclusion
Based on the genomic region (ITS) studied, we can conclude that Fusarium falciforme is another species of phytopathogen that causes root rot in cassava.
The morphophysiological characteristics of a phytopathogen together with the molecular tools make the identification more assertive and the decision making in the control of the disease faster.
Other work needs to be carried out to assess the epidemiology and severity of the disease in our state.