Survey of fungi associated with cassava root rot from different producing regions in Brazil

Abstract

Although root rot is one of the major diseases affecting Brazilian cassava (Manihot esculenta Crantz.), little is known about the diversity of root rot pathogens. In this study, diseased plants exhibiting root rot symptoms were collected from cassava-producing regions in five Brazilian states: Bahia, Sergipe, Paraíba, Maranhão, Tocantins, and Paraná. Seventy isolates were obtained and assigned to species complexes based on rDNA's ITS (internal transcribed spacer of the ribosomal DNA) region (ITS1, ITS2 and 5.8S). A total of seven species complexes was found belonging to the genus Fusarium (56/74), followed by Lasiodiplodia (8/74), Neoscytalidium (6/74), and Diaporthe/Phomopsis complex (2/74), Phytophthora, and Corallomycetella (1/74 each). These species were distributed differently according to sample locations and states, but overall, the F. solani species complex (FSSC) was the most prevalent. A number of phylogenetic lineages had not been previously reported as being associated with cassava-root rot disease, such as: F. graminearum (FGSC), F. incarnatum-equiseti (FIESC) and F. chlamydosporum (FCSC) complexes, and a phylogenetic lineage most closely related to P. phaseolorum.Results suggest the need to improve knowledge of the species associated with cassava, including multilocus phylogeny for a more specific characterization, and differences in the resistance background associated with these species, as a strategy to incorporate resistance to multiple pathogens in cassava breeding programs.

Methodologies for selecting cassava with resistance to dry and black root rot under controlled conditions

“…All evaluated methodologies used an isolate of Fusarium solani (CBPPR0057) and Neoscytalidium hyalinum (CBPPR1011), which causes DRR and BRR, respectively, previously characterized both as pathogenic to cassava and the most aggressive of the two groups of pathogens studied (Vilas Boas et al 2017). These fungi belong to the cassava root rot pathogen collection at the Plant Pathology Laboratory in Embrapa Mandioca e Fruticultura.…”

“…Different cassava varieties were used across the experiments, and they were choose based on previous works aiming the selection of resistant varieties, and the behavior of the cassava genotypes in the field (Oliveira et al 2013;Vilas Boas et al 2016;Vilas Boas et al 2017).…”

“…Dry (DRR) and black (BRR) root rot are two of the most destructive pathologies in cassava (Manihot esculenta Crantz), whose economic importance is increasing in major producing countries (Onyeka et al 2005a;Vilas Boas et al 2017). The increase in DRR and BRR is causing a progressive decline in yield and affecting subsequent crop cycles (Vilas Boas et al 2016).…”

“…The most frequent species causing DRR and BRR in the North and Northeast regions of Brazil are those associated with dry root rot and black root rot (Vilas Boas et al 2017). Based on these results, it is necessary to develop strategies for the identification of multiple sources of resistance against the major pathogens associated with DRR and BRR, taking into consideration the different resistance mechanisms in plant tissues.…”

Modelling growth characteristics and aggressiveness of Neoscytalidium hyalinum and Fusarium solani associated with black and dry root rot diseases on cassava

“…For the experiments involving the comparison of the aggressiveness of pathogen isolates on roots of the commercial variety 'Fécula branca', susceptible to root rot disease under field conditions, the roots were washed in tap water and disinfested with sodium hypochlorite solution (0.5%) for 3 min (Vilas Boas et al 2016b). The trials were conducted based on the root slice method, as described by Onyeka et al (2005b), to screen for resistance in the cassava plants.…”