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.

No abstract

No abstract

RESUMOO polissacarídeo algal ulvana induz resistência em macieira à mancha foliar de Glomerella. Porém, modificações no processo pré-infeccioso de Colletotrichum gloeosporioides vêm sendo relatadas em plantas previamente tratadas com ulvana. Assim, este trabalho objetivou verificar se o polissacarídeo interfere diretamente no desenvolvimento de estruturas pré-infectivas. Para tanto, depositou-se gotas de 10 µL de suspensão de 2x10 5 conídios.mL -1 em segmentos de papel celofane, assentados sobre lâminas de vidro. A suspensão conidial foi preparada com solução aquosa contendo ou não ulvana (10 mg.mL -1 ). As amostras foram incubadas a 25°C e 100% de humidade relativa. A cada duas horas, 100 conídios por gota foram examinados microscopicamente (200x), por um período de 16h. As taxas de germinação de conídios, formação e melanização de apressórios foram quantificadas. A germinação dos conídios não foi afetada. Ulvana estimulou o alongamento do tubo germinativo, mas retardou a diferenciação do primeiro apressório (séssil). O polissacarídeo acelerou a formação do segundo apressório, mas inibiu a sua melanização. Palavras-chave: Ulva fasciata, apressório, germinação, macieira, melanina, polissacarídeo. ABSTRACT Interference of ulvan on apressoria development and melanization of Colletotrichum gloeosporioidesThe algal polysaccharide ulvan induces resistance in apple to Glomerella leaf spot. However, changes in the pre-infectious process of Colletotrichum gloeosporioides have been reported in apple plants previously treated with ulvan. Thus, this study aimed to verify if the polysaccharide interferes directly in the development of pre-infective structures. For this, 10 µL drops of spore suspension (2x10 5 conidia.m L -1 ) were distributed on cellophane paper segments settled on glass slides. The conidial suspension was prepared with aqueous solution with (10 mg.mL -1 ) or without ulvan. Samples were incubated at 25°C and 100% relative humidity. At every two hours of incubation and over a period of 16 hours, 100 conidia per drop were microscopically (200x) examined. The rates of conidia germination, apressoria formation and melanization were quantified. Germination of conidia was not affected. Ulvan stimulated the elongation of the germ tube but retarded the differentiation of the first apressorium (sessile). The polysaccharide accelerated the formation of second apressorium, but inhibited its melanization.