Genetic Structure of Colletotrichum fructicola Associated to Apple Bitter Rot and Glomerella Leaf Spot in Southern Brazil and Uruguay

Abstract

Colletotrichum fructicola is the main species causing apple bitter rot (ABR) and Glomerella leaf spot (GLS) in southern Brazil, and ABR in Uruguay where GLS remains unnoticed. Thus, this work aimed to determine the genetic structure of C. fructicola isolates of both the countries. A total of 28 out of 31 Brazilian isolates (90.3%) caused typical symptoms of GLS, while only 6 of 25 Uruguayan isolates (24.0%) originating from fruits were able to infect leaves, but causing atypical symptoms. Both populations showed similar levels of Nei's gene diversity (h = 0.088 and 0.079, for Brazilian and Uruguayan populations, respectively), and Bayesian cluster analysis inferred two genetic clusters correlated with the geographical origin of isolates. A principal coordinates analysis scatter plot and an unweighted pair group method with arithmetic mean-based dendrogram also grouped Brazilian and Uruguayan isolates into two groups. By pairwise comparison of nitrate-nonutilizing (nit) mutants with a proposed set of testers, all Uruguayan isolates were grouped into a unique vegetative compatibility group (namely VCG 1), while Brazilian isolates were grouped into four VCGs (VCG 1 to 4). Brazilian and Uruguayan populations of C. fructicola were found to be genetically distinct. Our results suggest that isolates of C. fructicola from Brazil capable of causing GLS and ABR arose independently of those from Uruguay. Possible causes leading to the evolutionary differences between populations are discussed.

Ascospore Infection and Colletotrichum Species Causing Glomerella Leaf Spot of Apple in Uruguay

“…The results of this and other studies ( Rockenbach et al, 2016 ; Velho et al, 2015 ) indicate that C. fructicola have an extremely aggressive behavior; within three days it causes visible symptoms on leaves inoculated with conidia or ascospores and a few days later severe defoliation. Moreover, under favorable conditions, warm temperatures and high relative humidity, abundant reproductive structures are formed on leaf lesions.…”

“…However, C. karstii has not been associated with bitter rot disease in Uruguay ( Alaniz et al, 2015 ). Moreover, Uruguayan populations of C. fructicola causing bitter rot disease were found to be genetically distinct from Brazilian isolates obtained from GLS and bitter rot diseases ( Rockenbach et al, 2016 ). Therefore, new population studies are needed to compare genetic structure of C. fructicola populations causing GLS and bitter rot in Uruguay and Brazil.…”

Extracellular enzymes ofColletotrichum fructicola isolates associated to Apple bitter rot and Glomerella leaf spot

“…in Southern Brazil, i.e. the bitter rot (ABR) and Glomerella leaf spot (GLS) (Velho et al 2015; Rockenbach et al 2016). …”

“…It has been observed that some Colletotrichum isolates exhibit a particular organ specialisation being able to cause either, ABR or GLS (Velho et al 2015, 2016; Rockenbach et al 2016). Causes for such differences remain unknown.…”

“…Causes for such differences remain unknown. In previous studies, it was suggested that genotypes causing GLS probably were originated from ABR-isolates (González et al 2006), favoured mainly by the high production of susceptible apple “Gala” acting as selection force (Rockenbach et al 2016). However, such ability in infect fruits and leaves could be related to a production of fungal extracellular enzymes that degrade the plant cuticle and cell wall components.…”