A New Disease of Kumquat (fortunella Margarita) Caused by Colletotrichum Karsti: Twig and Branch Dieback

. Citrus fruit crops are important in many countries. Anthracnose, post bloom fruit drop, fruit stem-end rot, twig and branch dieback and gummosis, caused by Colletotrichum spp., are diseases that seriously threaten citrus production. Surveys of kumquat (Fortunella margarita) orchards were conducted in Eastern Sicily, Southern Italy, during 2022-23. Fungi isolated from twig and branch dieback of F. margarita were identified as Colletotrichum karsti through multi-locus (gapdh, tub2 and act) phylogeny. Pathogenicity and aggressiveness on detached apple fruit and kumquat plants were confirmed for a selection of representative isolates, although with different levels of disease incidence observed. This is the most comprehensive study on identification of C. karsti as the causal agent of twig and branch dieback of kumquat.