Postbloom Fruit Drop of Citrus and Key Lime Anthracnose Are Caused by Distinct Phylogenetic Lineages of Colletotrichum acutatum

Abstract

Colletotrichum acutatum causes two diseases of citrus, postbloom fruit drop (PFD) and Key lime anthracnose (KLA). PFD is a disease restricted to flowers of sweet orange and most other citrus, and symptoms include petal necrosis, abscission of developing fruit, and the formation of persistent calyces. KLA is a disease of foliage, flowers, and fruits of Key lime only, and symptoms include necrotic lesions on leaves, fruits, twigs, flowers, and blight of entire shoots. The internal transcribed spacers 1 and 2 and the gene encoding the 5.8S ribosomal RNA subunit within the nuclear ribosomal cluster (ITS) and intron 2 of the glyceraldehyde-3-phosphate dehydrogenase gene (G3PD) were sequenced for isolates from PFD-affected sweet orange and KLA-affected Key limes collected in the United States (Florida), Brazil (São Paulo), Mexico, Belize, Costa Rica, and the Dominican Republic to determine if there are consistent genetic differences between PFD and KLA isolates over the geographic area where these diseases occur. Based on the sequence data, isolates clustered into two well-supported clades with little or no sequence variation among isolates within clades. One clade (PFD clade) contained PFD isolates from all countries sampled plus a few isolates from flowers of Key lime in Brazil. The other clade (KLA clade) contained KLA isolates from Key lime foliage from all countries sampled and one isolate from flowers of sweet orange in Mexico. In greenhouse inoculations with PFD and KLA isolates from Florida, isolates from both clades produced PFD symptoms on Orlando tangelo flowers, but KLA-clade isolates produced significantly less severe symptoms. PFD-clade isolates were not pathogenic to Key lime foliage, confirming previous studies. The differentiation of PFD and KLA isolates into two well-supported clades and the pathogenicity data indicate that PFD and KLA are caused by distinct phylogenetic lineages of C. acutatum that are also biologically distinct. PFD is a recently described disease (first reported in 1979) relative to KLA (first reported in 1912) and it had been proposed that strains causing PFD evolved from strains causing KLA eventually losing pathogenicity to Key lime foliage. We reject the hypothesis that PFD strains have diverged from KLA strains recently based on estimated divergence times of haplotypes and it appears that PFD and KLA strains have been dispersed throughout the Americas independently in association with each host.

Chilli anthracnose disease caused by Colletotrichum species

“…Sequences of introns from two genes (glutamine synthase and glyceraldehyde-3-phosphate dehydrogenase) were also used to evaluate a diverse collection of isolates of C. acutatum (Guerber et al, 2003). C. acutatum isolates clustered into groups (Guerber et al, 2003;MacKenzie et al, 2008;Peres et al, 2008). These groups might represent phylogenetically distinct species of C. acutatum sensu lato (Guerber et al, 2003).…”

Colonization of citrus leaves and secondary conidiation response to citrus flower extracts by non-postbloom fruit drop strains of Colletotrichum acutatum

“…Of the four non-PFD isolates examined, only the fern isolate did not produce PFD symptoms on flowers (MacKenzie et al, 2009). Therefore, blueberry, KLA, and strawberry strains could potentially contribute to PFD epidemics, with KLA isolates being the only ones besides PFD isolates that have been recovered from PFD-affected sweet orange flowers (Peres et al, 2008). KLA and blueberry isolates did not colonize vegetative tissue to the extent that the PFD isolate did, which may explain why these strains are not commonly isolated from PFD-affected petals.…”

“…A unique strain of C. acutatum is responsible for epidemics of postbloom fruit drop (PFD) of citrus throughout the Americas (Peres et al, 2008). This strain was described originally as a slow-growing orange (SGO) strain of Colletotrichum gloeosporioides (Fagan, 1979) until it was reclassified as C. acutatum (Brown et al, 1996).…”

Sensitivity of Colletotrichum acutatum Isolates to Selected Fungicides

“…This organism infects fruit plants, vegetables, ornamental plants, oil crops, fodder crops, conifers and weeds (Freeman et al, 2001;Mari et al, 2012;Peres et al, 2008;Sreenivasaprasad and Talhinhans, 2005). Incidence of C. acutatum on strawberry, lupin, saffl ower, cherry, tomato, apple trees, and gooseberry has been confi rmed in the Czech Republic (Novotný et al, 2006;Víchová et al, 2011Víchová et al, , 2012Víchová et al, , 2013.…”