In vitro symptom induction of Colletotrichum abscissum infection in detached sweet orange flowers

The citrus industry is economically important in several countries around the world, and its primary challenges include pests and diseases, especially in Brazil. Post-bloom fruit drop (PFD), caused by Colletotrichum abscissum , a fungus that belongs to the C . acutatum species complex, is one of the most severe citrus crop diseases, causing damage to blossoms and interfering in the fruit viability, consequently contributing to early drop of the fruit. Little is known about the pathogenic mechanisms of C . abscissum in the flowers of citrus species, so finding an experimental model to study symptom development and gene function under controlled conditions is essential. However, the complexity of the PFD pathosystem in the field does not allow adequate experimental control, and due to regulations, evaluating genetically modified fungi under natural environmental conditions requires prior approval. Studies of gene function can be performed by knockdown, knockout, or deletion in C . abscissum mutants with a focus on symptom development in flowers. We developed a reliable in vitro system as an alternative for symptom induction of C . abscissum infection in detached citrus flowers. Inoculated citrus flowers were placed on Petri dishes with a water-agar substrate and kept in BOD chambers for 72 h. All C . abscissum inoculations resulted in the typical symptoms of PFD, proving the effectiveness of this large-scale screening system, which is fast and reliable and requires less space than that required for greenhouse or open-field experiments.