Occurrence of Colletotrichum musicola causing anthracnose on Manihot esculenta.

Cassava (Manihot esculenta) is one of the main food sources of energy in developing countries owing to its starch-rich roots (Pinweha et al., 2015). Anthracnose is considered the most destructive disease of the aerial part of this crop (Bragança et al., 2016; Liu et al., 2019), and it is caused by species such as Colletotrichum plurivorum, C. karstii, C. fructicola, C. siamense (Liu et al., 2019), and C. theobromicola (Oliveira et al, 2016). In 2019, leaves with irregular necrotic spots, typical symptoms of anthracnose, were collected in Pará, Brazil. Commercial sampled fields showed 20% of incidence of anthracnose. Colletotrichum strains were isolated and cultured on potato dextrose agar at 25 ºC with a 12-h light photoperiod from surface-disinfected (70% alcohol and 1% sodium hypochlorite) lesion transition area. Five of the obtained isolates exhibited brown colonies on the upper and lower surfaces. Conidia were hyaline, cylindrical and aseptate, 12.82-15.23 µm × 3.52-5.25 µm in size. These phenotypic characters were similar to those belonging to C. orchidearum sensu lato (Damm et al. 2019). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), ß-tubulin (TUB2), chitin synthase 1(CHS-1), and histone HIS3 partial gene were amplified and sequenced for one representative isolate (UFT/Coll89). Sequences were deposited in GenBank [Accession numbers: MT396235 (GAPDH), MT800856 (TUB2), MT800870 (CHS-1), and MT856672 (HIS3)]. BLASTn searches of CHS-1 and HIS3 sequences showed 100% identity to C. musicola. Maximum Likelihood Phylogenetic analysis, including previously published sequences of closely related species, placed the isolate from Cassava in the C. musicola clade with 100% support, and confidently it assigned to this species. Pathogenicity was proven with inoculations by spraying a conidial suspension (106 conida mL-1) on 3-month-old cassava plants (three unwounded leaves per plant). The plants were placed in a humid chamber at 25 °C for 48h, and a 12-h photoperiod. The negative control was represented by plants inoculated with sterile distilled water. The experiment was repeated twice. The same symptoms observed in the field were reproduced only in inoculated leaves, from which the pathogen was reisolated lesions fulfilling Koch's postulates. No symptoms were observed on the negative control. To our knowledge, this is the first report of C. musicola joining a group of new and emergent species of Colletotrichum causing anthracnose in cassava producing regions around the world. The identification of this species causing cassava anthracnose is crucial to improve the disease control strategies and resistance breeding programs.

First report of Colletotrichum truncatum causing anthracnose in cassava in Brazil.

Cassava (Manihot esculenta Crantz) presents significant economic importance in Brazil and other developing countries due to its use in human and animal feeding. In 2019, cassava plants sampled in Pará state (Brazil) presented necrotic and irregular leaf spots, characteristic symptoms of cassava anthracnose. About 90% of the plants were symptomatic, and disease severity was higher during months with high temperature and humidity. Fragments of symptomatic tissues were removed from the lesion transition area, surface disinfested (45 s in 70% ethanol, 1 min in 1% NaOCl, and rinsed twice in sterile water), and plated on potato dextrose agar. Cultures were incubated at 25 °C under continuous light for 7 days. Among the obtained isolates, seven presented grey felt-like mycelium with white sectors, reverse greyish, and hyaline, aseptate, smooth-walled, falcate conidia with average size 20.7-30.7 (26.1 ± 2.1) × 2.4-4.8 (3.5 ± 0.5) µm. Phenotypical features were similar to C. truncatum (Damm et al. 2019). The representative isolate UFT/Coll87 was chosen for further assays. The identity of the isolate was determined by maximum likelihood analysis using sequences of actin (ACT, GenBank accession number MT321653), ß-tubulin (TUB2, MT856673) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH, MT800857) partial regions. Colletotrichum isolate from cassava nested with C. truncatum isolates in a clade with 100% support, being confidently assigned to this species. Koch's postulates were fulfilled to confirm the pathogenicity of UFT/Coll87. Inoculation was carried out in three cassava plants by spraying a conidial suspension (106 conida mL-1) on unwounded leaves (three leaves per plant). Plants sprayed with sterile water represented negative control. Inoculated plants were kept in a humid chamber for 48 h, 25 °C, and a 12-h photoperiod. The experiment was repeated 2 times. Typical cassava anthracnose symptoms were observed 10 days after inoculation. No symptoms were observed in negative control. The pathogen was reisolated from symptomatic leaves and was phenotypically identical to the original isolate UFT/Coll87, fulfilling Koch's postulates. Colletotrichum fructicola, C. karstii, C. plurivorum, and C. siamense were reported causing cassava anthracnose in China (Liu et al. 2019). In Brazil, C. chrysophilum, C. fructicola, C. siamense and C. theobromicola were reported in association with cassava (Bragança et al. 2016; Oliveira et al. 2018; Machado et al. 2020). To our knowledge, this is the first report of C. truncatum causing cassava anthracnose worldwide. Our finding is important for disease management due to the high host range of C. truncatum. The pathogen can reduce the cassava yield, and the crop may serve as a potential inoculum source since it is commonly cultivated near to other crops that are also infected by C. truncatum.

First report of Colletotrichum chrysophillum causing cassava anthracnose in Brazil.

Cassava (Manihot esculenta Crantz) has significant socioeconomic relevance in Brazil and other developing countries, as one of the main sources of carbohydrates for human and animal consumption (De Oliviera et al., 2011). Among the cassava crop diseases, anthracnose is one of the main limiting factors for production and may be caused by species like Colletotrichum plurivorum, C. karstii, C. fructicola, and C. siamense (Bragança et al., 2016; Liu et al., 2019; Oliveira et al., 2016; Sangpueak; Phansak; Buensanteai, 2018). Severity in the field is variable, depending on the resistance of the variety used and is also highly influenced by the climate, being the most severe disease under high humidity and high temperature. Under these conditions, it can cause losses of up to 100%. In 2019, cassava leaves presenting dark brown necrotic injuries of different sizes and irregular borders-typical anthracnose symptoms- were collected from commercial plantations in the states of Pará and Tocantins, Brazil. Symptomatic tissue fragments were superficially disinfected, placed in plates with potato dextrose agar (PDA), and incubated under 25 ± 2 °C for seven days. In the 56 isolates used in the morphological identification, the colonies were white and gray at the top and dark gray in the bottom with sector formation. The conidia were hyaline, cylindrical, and aseptic, 10.04 to 17.83 µm long × 3.29 to 5.75 µm wide. These phenotypical characteristics were similar to those of C. gloeosporioides lato sensu species (Weir et al., 2012). Genomic DNA was extracted from two representative isolates (UFT/Coll69, collected in the municipality of Casa de Tábua-PA; UFT/Coll82, collected in Pau Darco-PA) and the APN2 / MAT-IGS, DNA lyase (Apn2), and glyceraldehyde-3-phosphate dehydrogenase-IGS (GAP2-IG) intergenic spacers were amplified and sequenced. The nucleotide sequences were deposited in the GenBank (accession numbers: MT409462, MT396231, MT759633, MT396239, MT396232, MT800846). The BLASTn (Basic Local Alignment Search Tool) showed a 99 to 100% similarity with Colletotrichum chrysophillum. The maximum likelihood phylogenetic analysis grouped the isolates in the C. chrysophillum clade, with a high bootstrap value (98%). Based on morphocultural characteristics and the phylogenetic analysis, the isolates associated with M. esculenta anthracnose were identified as C. chrysophillum, with a frequency of 6.67% among Colletotrichum colonies isolated from cassava leaves. The inoculation of three isolates was carried out in three plants, three leaves for each plant, by spraying spore solution with a concentration of 1×106 conidia / ml, without wounding the leaves and placed in a humid chamber at 25 ° C for ten days. Control plants were inoculated with sterile distilled water. From the 2nd day after inoculation, small irregular necrotic lesions appeared that increased in size over time, while control plants remained asymptomatic. Both were pathogenic and the symptoms caused after inoculation were similar to each other and to those observed in the field. In Brazil, anthracnose by C. chrysophillum was reported in cashew (Veloso et al., 2018) and banana trees (Vieira et al., 2017). To our knowledge, this is the first report of cassava anthracnose disease by C. chrysophillum.