Characterization of <i>Colletotrichum gloeosporioides</i> isolates associated with anthracnose and twig dieback on sweet orange ( <i>Citrus sinensis</i> ) in Florida and sensitivity to fenbuconazole, fluopyram and pyraclostrobin

Abstract

Citrus is one of the most economically important crops in Florida. In 2022 surveys of 46 citrus groves in southwest Florida, twig dieback and anthracnose on fruit, leaves and twigs were frequently observed. The occurrence, diversity, pathogenicity and sensitivity to chemical compounds of Colletotrichum strains isolated from symptomatic Citrus sinensis cv. Valencia were investigated. One hundred representative monoconidial isolates were identified as Colletotrichum gloeosporioides by phylogenetic analysis based on five genomic loci (GAPDH, ACT, TUB2, GS and ApMat). Fruit pathogenicity tests performed on seven representative isolates confirmed the pathogenicity of the identified species. This study is the first report of C. gloeosporioides associated with twig dieback and preharvest anthracnose on Ci. sinensis cv. Valencia in Florida. The sensitivity of 100 isolates of C. gloeosporioides to fenbuconazole (DMI), fluopyram (SDHI) and pyraclostrobin (QoI) was assessed by inhibition of conidial germination. Over 50% of tested isolates showed reduced sensitivity to fenbuconazole, fluopyram and pyraclostrobin, providing the first evaluation of the in vitro sensitivity of C. gloeosporioides strains isolated from Ci. sinensis cv. Valencia in Florida. These molecules appear unable to control the spread and development of C. gloeosporioides on Ci. sinensis cv. Valencia in Florida. Due to several citrus diseases that have severely affected Florida's citrus industry over the past 20 years, fungal diseases such as anthracnose have been neglected, but are increasing in importance in recent years worldwide. Our study represents a starting point for the development of new solutions to manage this problem for citrus growers.

Affiliated Institutions

• Virginia Tech US
• University of Turin IT
• University of Catania IT

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