First Report ofColletotrichum truncatumofSolanum lycopersicumin Mexico

Abstract

Tomatoes (Solanum lycopersicum) are among the most economically important vegetables in Mexico. During 2016, more than 52,000 ha of tomatoes were planted, both in open fields and in greenhouses, yielding more than 2,875,164 t nationwide and placing Mexico as one of the main producers and an important exporter of this product worldwide (SAGARPA 2016; SIAP 2016). Anthracnose is a disease caused by several species of the genus Colletotrichum in several economically important hosts, affecting both pre- and postharvest fruits (Damm et al. 2009). During October 2017, 240 tomato fruits with symptoms were collected from an open field in the state of Morelos, Mexico. During this time, anthracnose was also observed in the harvest fruits, with circular and sunken lesions covered with black acervuli containing spores and dark setae in a group. Epidermal tissue sections of 1.0 cm were cut from 30 fruits and disinfested with 1.5% sodium hypochlorite for 3 min. These tissues were washed twice with sterile distilled water and allowed to dry on absorbent paper towels. They were planted in potato dextrose agar (PDA) culture medium and incubated at 25 ± 2°C under white light. Pure cultures were obtained from monosporic cultures on agar-agar and transferred to PDA after 8 days. The initial growth was white, turning pale gray, with numerous black structures (microsclerotia) and setae. Conidia were produced in masses and were hyaline, unicellular, fusiform, and apex-acute and measured 20 to 22.35 μm long and 2.4 to 2.6 μm wide. The setae were 75 to 85 μm long and 4 to 5 μm wide, with elliptic to claviform or slightly lobed appressoria. The cultural and morphological characteristics agreed with descriptions of Colletotrichum truncatum (Sutton 1980). To confirm the molecular identity, DNA was extracted using a DNeasy minikit (Qiagen) and amplified using ITS, actin, GAPDH, and EF1-728 primers. Consensus sequences were deposited in GenBank, and the identity match with C. truncatum was 97% for ITS (MH448905), actin (MH493053), and GAPDH (MH4930952) and 100% for EF1-728 (MH493054). The sequences were aligned with the same species from the NCBI GenBank database. To confirm pathogenicity, 48 tomato fruits were superficially disinfested in a 1.5% sodium hypochlorite solution, washed twice with sterile distilled water, and placed on absorbent presterilized paper towels. A conidial suspension (10⁶ conidia/ml) from the fungus was placed on the tomato’s surface. Nine fruits were used as controls, with only sterile distilled water, and stored in a humidified chamber at temperature 26°C for 8 days. Pathogenicity tests were repeated twice. Symptoms developed 8 days after inoculation, and anthracnose was observed in all inoculated fruits, whereas no symptoms were present in the control fruit. Koch’s postulates were fulfilled when the pathogen was isolated from the tomato fruits but not from the control fruits. C. truncatum is reported to cause anthracnose in different hosts, including Solanaceae species (He et al. 2016; Ranathunge and Sandani 2016). Based on a literature review, this is the first report of C. truncatum affecting S. lycopersicum fruits in Mexico.