Fungos do gênero Guignardia são frequentemente isolados em diferentes espécies de plantas, sendo muitas vezes caracterizados como fungos endofíticos. Entretanto, algumas espécies deste fungo, a exemplo de G. citricarpa e G. psidii, são causadores de importantes doenças que afetam culturas agrícolas, como a Mancha-Preta dos Citros (MPC) e a podridão dos frutos de goiabeira, respectivamente. Também são apontados como causadores de manchas foliares em diferentes espécies de frutíferas e também em outras culturas. Este trabalho teve o objetivo de isolar, identificar e caracterizar a diversidade genética existente entre isolados de Guignardia oriundos de citros, mangueira, goiabeira, eucaliptos, jabuticabeira e pitangueira através da análise da sequência de DNA do cístron ITS1-5,8-S-ITS2. Verificou-se que os isolados obtidos pertencem às espécies G. citricarpa e G. mangiferae. Entretanto, dois grupos encontrados em mangueira não puderam ser identificados em nível de espécie com base em sua sequência de DNA em função da baixa similaridade com as sequências de diferentes espécies de Guignardia já depositadas em banco de dados. Desta forma, goiabeira, eucaliptos, jabuticabeira e pitangueira são hospedeiras de G. mangiferae, enquanto os citros hospedam duas formas, G. citricarpa e G. mangiferae. Já a mangueira é hospedeira de G. mangiferae e de dois outros grupos ainda não identificados. Verificou-se ainda que isolados de Guignardia obtidos de sintomas de podridão de fruto de goiabeira foram identificados como G. mangiferae.

Fungi of Guignardia genera are commonly isolated from different plant species and most of the time they are characterized as endophytics. However, some species of this genus, as G. citricarpa and G. psidii are known as causal agents of serious diseases that affect cultures, such as the Citrus Black Spot and the guava fruit rot, respectively. They are also responsible for diseases that cause foliar spots in different fruit species and also in other cultures. This work has the objective of isolate, identify and characterize the genetic diversity present among Guignardia isolates obtained from citrus, mango, guava, eucalyptus, Brazilian grape tree and Surinam cherry by analysis of DNA sequence from cístron ITS1-5,8SITS2. It was verified that the obtained isolates belong to G. mangiferae and G. citricarpa species. Two different Guignardia types, that were found in mango, could not be identified in species, and do not belong to none of the species deposited in GenBank. So, this work found that mango, guava, eucalyptus, Brazilian grape tree and Surinam cherry host only G. mangiferae, whereas citrus hosts G. mangiferae and G. citricarpa species. Mango hosts three different Guignardia, G. mangiferae and two others types that remain without identification of the species level. It was also verified that isolates of Guignardia obtained from guava fruit rot symptoms were identified as G. mangiferae.

A series of multilocus sequence-based nuclear DNA markers was developed to infer the phylogeographical history of the Basidiomycetous fungal pathogen Rhizoctonia solani AG-1 IA infecting rice and soybean worldwide. The strategy was based on sequencing of cloned genomic DNA fragments (previously used as RFLP probes) and subsequent screening of fungal isolates to detect single nucleotide polymorphisms (SNPs). Ten primer pairs were designed based on these sequences, which resulted in PCR amplification of 200-320 bp size products and polymorphic sequences in all markers analyzed. By direct sequencing we identified both homokaryon and heterokaryon (i.e. dikaryon) isolates at each marker. Cloning the PCR products effectively estimated the allelic phase from heterokaryotic isolates. Information content varied among markers from 0.5 to 5.9 mutations per 100 bp. Thus, the former RFLP codominant probes were successfully converted into six distinctively variable sequence-based nuclear DNA markers. Rather than discarding low polymorphism loci, the combination of these distinctively variable anonymous nuclear markers would constitute an asset for the unbiased estimate of the phylogeographical parameters such as population sizes and divergent times, providing a more reliable species history that shaped the current population structure of R. solani AG-1 IA.