Anthracnose stalk rot (ASR) of maize results in millions of dollars in losses annually in the United States. ASR, together with anthracnose leaf blight and anthracnose top dieback, is caused by the fungus Colletotrichum graminicola. Current ASR management recommendations emphasize host resistance and reduction of plant stressors, e.g., drought, heat, low fertility, or soil acidity. Stress reduction may be more difficult to achieve in the future due to more high-intensity production protocols and climate change. Moreover, cultural and chemical management practices may conflict with other important goals including environmental sustainability and maximization of yield potential. Thus, future ASR management may rely more heavily on host resistance, for which there are relatively few highly effective sources. The last comprehensive review of C. graminicola and maize anthracnose was written over two decades ago. The genomic age has brought important new insights into mechanisms governing the host-pathogen interaction from the application of molecular and cytological technologies. This review provides a summary of our current model of maize anthracnose etiology, including how increased knowledge of molecular and cellular events could contribute to better ASR management. Improved understanding of C. graminicola taxonomy has confirmed that the fungus is specific to Zea mays, and that it colonizes living maize tissues via a critical biotrophic phase. Successful biotrophic establishment relies on an array of secreted protein effectors and secondary metabolites produced at different stages of infection and dispersed to multiple locations. These molecules could provide therapeutic targets for the next generation of transgenic or gene-edited ASR-resistant hybrids.
Brazil is the leader in the global ranking of forest productivity; however, one of the major challenges to eucalyptus production is the existence of fungal diseases. A severe epidemic caused by pestalotiopsis‐like fungi was observed in a forest nursery in Brazil, causing a huge impact on the eucalyptus micropropagation stages. The aims of the present study were to identify the causal agents associated with pestalotiopsis leaf spot and dieback in eucalyptus, assess their pathogenicity to different commercial clones, and evaluate which conditions favour conidial germination and infection by the pathogens. Multilocus phylogenetic analyses using ITS, TEF and TUB identified the isolates as members of Neopestalotiopsis and segregated them into three species. Isolates from all Neopestalotiopsis spp. caused symptoms on unwounded eucalyptus leaves and disease development was strongly dependent on long leaf wetness periods (≥72 h). All four commercial clones tested were susceptible to the pathogen. These results clearly dispute the commonly held assumption that pestalotioid fungi are weak and opportunistic pathogens. This is the first report of different phylogenetic species of Neopestalotiopsis causing dieback, leaf and stem lesions in eucalyptus cuttings and provides a basis for developing novel disease management strategies in forest nurseries.
Pachira glabra (Malvaceae) occurs naturally in Brazil's Atlantic Forest and is used to recover degraded areas of permanent preservation. Symptoms of leaf spot caused by Diaporthe spp. have been observed in P. glabra saplings in a Brazilian forest nursery. The aim of this study was to identify the fungal species employing morphological characteristics, pathogenicity tests, and DNA sequence comparisons for the internal transcribed spacer region (ITS), β-tubulin (TUB), translation elongation factor 1-α (TEF1), and calmodulin (CAL) gene regions. A novel species was identified and described, named here as Diaporthe pachirae. Furthermore, this is the first report of a species belonging to Diaporthe on P. glabra in Brazil. The current study revealed that documentation of new fungi is a relevant forerunner to any research with natural forests.
This study aimed to develop and validate a standard area diagram set (SADs) to help assess rust severity caused by Austropuccinia psidii on eucalyptus leaves. The SADs has eight colour images of leaves with severity values ranging from 0.97% to 37.3%. The SADs were validated by 16 raters, who assessed the same set of 50 images twice: the first without the SADs and the second using it as an aid. Accuracy and precision of the estimates were determined based on Lin's concordance correlation coefficient, and the inter‐rater reliability was measured using the coefficient of determination (R2) and intraclass correlation. The estimates of severity of eucalyptus rust were more accurate, precise and reliable using SADs. These results demonstrate the value of SADs for several activities, including epidemiological studies, treatments comparison, disease monitoring, decision‐making in eucalyptus rust management measures, and in breeding programs.
Cedrela fissilis is a tree species belonging to the family Meliaceae with a large occurrence in Brazil and can also be found in Argentina,
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