Leonardo S. S. Oliveira

Species or Genotypes? Reassessment of Four Recently Described Species of the Ceratocystis Wilt Pathogen, Ceratocystis fimbriata, on Mangifera indica.

Ceratocystis wilt is among the most important diseases on mango (Mangifera indica) in Brazil, Oman, and Pakistan. The causal agent was originally identified in Brazil as Ceratocystis fimbriata, which is considered by some as a complex of many cryptic species, and four new species on mango trees were distinguished from C. fimbriata based on variation in internal transcribed spacer sequences. In the present study, phylogenetic analyses using DNA sequences of mating type genes, TEF-1α, and β-tubulin failed to identify lineages corresponding to the four new species names. Further, mating experiments found that the mango isolates representing the new species were interfertile with each other and a tester strain from sweet potato (Ipomoea batatas), on which the name C. fimbriata is based, and there was little morphological variation among the mango isolates. Microsatellite markers found substantial differentiation among mango isolates at the regional and population levels, but certain microsatellite genotypes were commonly found in multiple populations, suggesting that these genotypes had been disseminated in infected nursery stock. The most common microsatellite genotypes corresponded to the four recently named species (C. manginecans, C. acaciivora, C. mangicola, and C. mangivora), which are considered synonyms of C. fimbriata. This study points to the potential problems of naming new species based on introduced genotypes of a pathogen, the value of an understanding of natural variation within and among populations, and the importance of phenotype in delimiting species.

Mapping Global Potential Risk of Mango Sudden Decline Disease Caused by Ceratocystis fimbriata.

The Mango Sudden Decline (MSD), also referred to as Mango Wilt, is an important disease of mango in Brazil, Oman and Pakistan. This fungus is mainly disseminated by the mango bark beetle, Hypocryphalus mangiferae (Stebbing), by infected plant material, and the infested soils where it is able to survive for long periods. The best way to avoid losses due to MSD is to prevent its establishment in mango production areas. Our objectives in this study were to: (1) predict the global potential distribution of MSD, (2) identify the mango growing areas that are under potential risk of MSD establishment, and (3) identify climatic factors associated with MSD distribution. Occurrence records were collected from Brazil, Oman and Pakistan where the disease is currently known to occur in mango. We used the correlative maximum entropy based model (MaxEnt) algorithm to assess the global potential distribution of MSD. The MaxEnt model predicted suitable areas in countries where the disease does not already occur in mango, but where mango is grown. Among these areas are the largest mango producers in the world including India, China, Thailand, Indonesia, and Mexico. The mean annual temperature, precipitation of coldest quarter, precipitation seasonality, and precipitation of driest month variables contributed most to the potential distribution of MSD disease. The mango bark beetle vector is known to occur beyond the locations where MSD currently exists and where the model predicted suitable areas, thus showing a high likelihood for disease establishment in areas predicted by our model. Our study is the first to map the potential risk of MSD establishment on a global scale. This information can be used in designing strategies to prevent introduction and establishment of MSD disease, and in preparation of efficient pest risk assessments and monitoring programs.

Genetic variation, morphology and pathogenicity of Ceratocystis fimbriata on Hevea brasiliensis in Brazil

Ceratocystis fimbriata causes diseases on a wide variety of plants in Brazil, including rubber tree (Hevea brasiliensis), on which it causes gray mold or moldy rot on tapping panels affecting latex yield. However, C. fimbriata isolated from rubber tree have not been critically studied. Phylogenetic analyses of sequences of ITS rDNA and a mating type gene placed rubber tree isolates from Acre and Bahia among Brazilian isolates of C. fimbriata from other hosts. In the analyses of 14 microsatellite loci, the rubber tree isolates from Bahia were identical to each other and had alleles similar to those of Brazilian isolates from mango and eucalyptus. The microsatellite alleles of the Acre rubber tree isolates were identical to each other but distinct from other Brazilian isolates. The rubber tree isolates were morphologically indistinguishable from each other and very similar to the isolates of C. fimbriata on Ipomoea batatas, on which the species was originally described. Based on inoculation experiments results, the Bahia and Acre rubber tree isolates do not appear to be host specialized, which is typical for Brazilian isolates of C. fimbriata sensu stricto.

Ceratocystis tiliae sp. nov., a wound pathogen on Tilia americana

Species in the North American clade (NAC) of the Ceratocystis fimbriata complex are mostly weak pathogens that infect native tree hosts through fresh wounds. Isolations from discolored tissue of wounded Tilia americana (basswood) in Iowa and Nebraska yielded a Ceratocystis species that was similar to but distinct from isolates of C. variospora from other hosts. Sequences of 28S rDNA showed that isolates from basswood did not differ from C. variospora, but there were minor differences in ITS rDNA sequences. The DNA sequences of a portion of the Cerato-platanin gene and TEF1α showed the basswood fungus to be a unique lineage. Cross inoculations in two experiments showed that the basswood isolates and C. variospora isolates from Quercus spp. were most aggressive to their respective hosts. Isolates from basswood grew slower and were less pigmented than C. variospora isolates from Quercus spp. The basswood fungus thus is distinguished from C. variospora based on phylogenetic analyses and phenotype and is herein described as C. tiliae sp. nov.

Canker disease caused by Chrysoporthe doradensis and C. cubensis on Eucalyptus sp. and Tibouchina spp. in Brazil

Chrysoporthe species are known to cause canker on hosts belonging to Myrtaceae and Melastomataceae families. Cankers occur on tree trunks and branches and may reduce growth and lead to plant death. In this study, the incidence and pathogenicity of Chrysoporthe cubensis and other species causing canker on Eucalyptus sp., Tibouchina heteromalla and T. granulosa were examined. The isolates were collected in Maranhão (MA) and Minas Gerais (MG) in Brazil. Sequence analysis of beta-tubulin and actin genomic regions confirmed the presence of C. cubensis and C. doradensis on clones of the hybrid Eucalyptus grandis x E. urophylla, T. granulosa, and T. heteromalla in Brazil. Morphological characterization enabled the identification of the isolates from both genera primarily based on differences in conidial size and shape. The isolates were pathogenic to ten Eucalyptus clones and Tibouchina plants. Our results contribute new knowledge of Chrysoporthe species causing diseases of woody plants in Brazil of importance to Eucalyptus breeding programs when screening for resistance. Furthermore, this is the first report of C. doradensis infecting Eucalyptus and T. granulosa, as well as the first record of C. cubensis infecting T. heteromalla in Brazil.

Ceratocystis fimbriata isolates on Mangifera indica have different levels of aggressiveness

Mango is amongst the most exported fruits worldwide and the mango tree has been cultivated in many countries with tropical and subtropical climates. Currently, Ceratocystis wilt caused by Ceratocystis fimbriata is among the most important diseases on mango tree. Planting of resistant genotypes is the best strategy for disease control. In the selection of resistant plants a highly aggressive isolate should be used in inoculations under controlled conditions. Thus, the objective of this study was to evaluate whether there are differences in aggressiveness among isolates of C. fimbriata obtained from diseased mango trees in Brazil. Before inoculation, five randomly selected isolates were tested for sporulation and mycelial growth in different culture media in order to select the best conditions for inoculum production. Twenty-four isolates from the States of São Paulo, Rio de Janeiro, Minas Gerais and Mato Grosso do Sul were inoculated in the susceptible mango cultivar Espada. Subsequently, the four most aggressive isolates were inoculated in other five different mango cultivars. The culture media MEA provided the best levels of sporulation and mycelial growth for four of the five tested isolates. Isolates SEMG1-1 from Minas Gerais and SESP8-3 from São Paulo were the most aggressive. The response of cultivars to the most aggressive isolates tested in the present work varied from highly resistant to highly susceptible, ‘Ubá’ being the most resistant regardless of the isolate tested. These results demonstrate that there are significant differences in aggressiveness among C. fimbriata isolates from mango in Brazil, as well as cultivar × isolate interaction.