First report of Colletotrichum siamense causing grape ripe rot in Brazil.

Vitis vinifera cv. BRS Vitória is a seedless black table grape cultivar with an extremely pleasant flavor and is adapted to cultivation in all Brazilian regions. Between November and December 2021, grape berries presenting typical ripe rot symptoms were found in three vineyards located in Petrolina, Pernambuco Brazil. The first symptoms are small and depressed lesions on ripe berries, presenting tiny black acervuli. As the disease progress, lesions enlarge and affect the whole fruit, and abundant orange masses of conidia can be observed. Finally, berries become completely mummified. Symptoms were observed in the three vineyards visited, and disease incidence was above 90%. Some producers are considering eradicating the plantations due to the losses caused by the disease. Control measures used so far are costly and ineffective. Fungal isolation was performed by transferring conidial masses from 10 diseased fruit to plates containing potato dextrose agar medium. Cultures were incubated at 25 °C under continuous light. Seven days after inoculation, three fungal isolates (LM1543-1545) were obtained and subcultivated in pure culture for species identification and pathogenicity test. Isolates presented white to grey cottony mycelia, and hyaline conidia with cylindrical with rounded ends, which resemble the genus Colletotrichum (Sutton 1980). Partial sequences of APN2-MAT/IGS, CAL, and GAPDH loci were amplified, sequenced, and deposited on GenBank (OP643865-OP643872). Isolates from V. vinifera were placed within the clade including the ex-type and representative isolates of C. siamense. The clade was strongly supported (99.8% bootstrap support) in the maximum likelihood multilocus tree of the three loci combined, which confidently assign the isolates to this species. Inoculation on grape bunches was performed to confirm pathogenicity. Grape bunches were surface sterilized for 30 s in 70% ethanol, 1 min in 1.5% NaOCl, rinsed two times with sterile distilled water, and air-dried. Fungal conidial suspensions (106 conidia mL-1) were sprayed to the point of run-off. The negative control was represented by grape bunches sprayed with sterile distilled water. Grape bunches were kept in a humid chamber for 48 h at 25 °C and a light period of 12 h. The experiment was conducted with four replicates (four inoculated bunches per isolate) and repeated once. Typical ripe rot symptoms were observed on grape berries 7 days after inoculation. No symptoms were observed on the negative control. The fungal isolates recovered from inoculated berries were morphologically identical to the C. siamense isolates originally recovered from symptomatic berries collected in the field, fulfilling Koch's postulates. Colletotrichum siamense was reported in association with grape leaves in USA (Weir et al. 2012) and causing grape ripe rot in North America (Cosseboom & Hu 2022). Only C. fructicola, C. kahawae, C. karsti, C. limetticola, C. nymphaeae and C. viniferum were reported causing grape ripe rot in Brazil (Echeverrigaray et al. 2020). To our knowledge, this is the first report of C. siamense causing grape ripe rot in Brazil. This finding is important for disease management because C. siamense has a high phytopathogenic potential due to its wide distribution and host range.

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.