Santiago-Charneco, Jose Luis

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    Antifungal analysis of synthetic fungicide against Neocosmopara falciformis (syn. of Fusarium falciforme) isolated from Solanum lycopersicum in Puerto Rico
    (2021-05-14) Santiago-Charneco, Jose Luis; Rivera-Vargas, Lydia I.; College of Agricultural Sciences; Feliciano-Rivera, Merari; Ortiz-Bermúdez, Patricia; Department of Crops and Agro-Environmental Sciences; Rodríguez-Román, Daniel
    Worldwide Solanum lycopersicum is the most important vegetable crop. In 2019 a total production of 37.38 million metric tonnes (mT) tomatoes were produced. In Puerto Rico, according to the most recent agricultural census, approximately 18,000 mt of tomatoes were produced in 2019 contributing closely to $20 million to the island agricultural gross income. Puerto Rico's tropical climate, characterized by warm and humid conditions with annual temperatures oscillating between 21° to 32°C, promote a favorable and diverse environment for soil microorganisms. The fungal genus Fusarium spp. includes a diverse group of species responsible for soil-borne plant diseases of agricultural importance. For this reason, the first objective of this research was to identify Fusarium spp. associated with tomato production at the southern region of Puerto Rico. The second objective was to evaluate in-vitro, the sensitivity of Fusarium spp. isolates to a conventional synthetic fungicide (i.e., chlorothalonil). Three Fusarium spp. isolates were obtained from tomato plants (Skyway) showing necrotic or chlorotic tissue, delayed root development, stunted growth, and stem rot. For fungal identification, morphological characteristics were examined, and phylogenetic analysis were conducted using three genes: translation elongation factor (Tef), DNA-directed RNA polymerase II subunit(RPB1) and the internal transcribed spacer (ITS) . All isolates were identified as Fusarium falciforme, of the Fusarium solani species complex, more recently reappraised as Neocosmopora falciformis. Pathogenicity tests conducted in wounded roots of three-month-old tomato plants (cv. Skyway) tested negative. In addition, pathogenicity tests performed on wounded and unwounded tomato fruits under laboratory conditions, promoted mycelia development and fruit rot in wounded areas, for all Neocosmopara falciformis isolates evaluated. Subsequently, in-vitro fungicide sensitivity test showed statistical differences between isolates. Cell viability was measured by calculating percentage (%) reduction which is needed to maintain cellular structures and associated functions, after 48 hours of exposure to the fungicide, chlorothalonil. Neocosmopara falciformis showed resistance to the highest doses tested 128 ppm. No statistical differences were observed when compared to the non-treated control. Fusarium oxysporum f. sp. cubense did show statistical differences to the non-treated control and fungal cell activity was diminish by 84% compared to the non-treated control. This research is the first report of N. falciformis associated with an agricultural important crop and exhibiting resistance to a commonly used fungicide (chlorothalonil) in Puerto Rico. This study will provide a base of identification for future monitoring as a possible pathogen and also shows the importance of developing new effective methods for the management of this organism.