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

ABSTRACT: Glomerella leaf spot (GLS) caused by Colletotrichum spp. is a destructive disease of apple restricted to a few regions worldwide. The distribution and evolution of GLS symptoms were observed for two years in Uruguay. The recurrent ascopore production on leaves and the widespread randomized distribution of symptoms throughout trees and orchard, suggest that ascospores play an important role in the disease dispersion. The ability of ascospores to produce typical GLS symptom was demonstrated by artificial inoculation. Colletotrichum strains causing GLS did not result in rot development, despite remaining alive in fruit lesions. Based on phylogenetic analysis of actin, β-tubulin and glyceraldehyde-3-phosphate dehydrogenase gene regions of 46 isolates, 25 from fruits and 21 from leaves, C. karstii was identified for the first time causing GLS in Uruguay and C. fructicola was found to be the most frequent (89%) and aggressive species. The higher aggressiveness of C. fructicola and its ability on to produce abundant fertile perithecia could help to explain the predominance of this species in the field.

SUBMITTER: Alaniz S

PROVIDER: S-EPMC6464197 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Glomerella leaf spot (GLS), caused by Colletotrichum fructicola, is a rapidly emerging disease leading to defoliation, fruit spot, and storage fruit rot on apple in China. Little is known about the mechanisms of GLS pathogenesis. Early transcriptome analysis revealed that expression of the zinc finger transcription factor Ste12 gene in C. fructicola (CfSte12) was upregulated in appressoria and leaf infection. To investigate functions of CfSte12 during pathogenesis, we constructed gene deletion mutants (ΔCfSte12) by homologous recombination. Phenotypic analysis revealed that CfSte12 was involved in pathogenesis of nonwounded apple fruit and leaf, as well as wounded apple fruit. Subsequent histological studies revealed that loss of pathogenicity by ΔCfSte12 on apple leaf was expressed as defects of conidium germination, appressorium development, and appressorium-mediated penetration. Further RNA sequencing-based transcriptome comparison revealed that CfSte12 modulates the expression of genes related to appressorium function (e.g., genes for the tetraspanin PLS1, Gas1-like proteins, cutinases, and melanin biosynthesis) and candidate effectors likely involved in plant interaction. In sum, our results demonstrated that CfSte12 is a key regulator of early apple GLS pathogenesis in C. fructicola In addition, CfSte12 is also needed for sexual development of perithecia and ascospores.IMPORTANCE Glomerella leaf spot (GLS) is an emerging fungal disease of apple that causes huge economic losses in Asia, North America, and South America. The damage inflicted by GLS manifests in rapid necrosis of leaves, severe defoliation, and necrotic spot on the fruit surface. However, few studies have addressed mechanisms of GLS pathogenesis. In this study, we identified and characterized a key pathogenicity-related transcription factor, CfSte12, of Colletotrichum fructicola that contributes to GLS pathogenesis. We provide evidence that the CfSte12 protein regulates many important pathogenic processes of GLS, including conidium germination, appressorium formation, appressorium-mediated penetration, and colonization. CfSte12 also impacts development of structures needed for sexual reproduction which are vital for the GLS disease cycle. These results reveal a key pathogenicity-related transcription factor, CfSte12, in C. fructicola that causes GLS.

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

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