Apple core rot, an economically important disease worldwide, appears both before and during harvest. Current gaps in understanding of the infection cycle impede progress toward more effective management of this disease. The fungus Trichothecium roseum is the main pathogen of core rot on apple in China. In this study, we used fluorescent labeling to trace colonization of T. roseum in floral tissues, characterizing routes of penetration to the core of ‘Fuji’ apples. T. roseum infected petals, anthers, filaments, stigmas and separated styles of flowers, and floral debris served as inoculum for core infection. In field inoculations, T. roseum entered styles initially through stylar fissures and colonized pluricellular hairs of these fissures during early stages of fruit development. Subsequently, hyphae grew along the extending fissures, which are continuations of stylar fissures located between stylar bases and carpel cavities. The hyphae remained in the extending fissures from mid-June to late July. When fruit developed an open sinus in late July, the sinus eventually fused with extending fissures and carpel cavities in late August, hyphae invaded carpel cavities, and ultimately fruit flesh via cracks on carpel cavity walls. Our results revealed for the first time the routes by which T. roseum penetrates apple fruit, and provided significant insights for strategic management of core rot.

Malus asiatica (Rosaceae, Malus) is a small deciduous tree, which has been cultivated in China more than 450 years (Jin, 2019). M. asiatica is deeply favored by consumers because of its sweet taste...

Glomerella leaf spot (GLS), mainly caused by Colletotrichum fructicola, is a destructive disease of apple. However, the underlying pathogenesis mechanisms of GLS are still largely obscure. Previous infection transcriptome analysis showed that transcription factor CfGti1 was induced during leaf infection. The present study confirms that the CfGti1 gene is strongly expressed in conidia and early infection. To identify functions performed, we generated gene deletion mutant ΔCfGti1 by homologous recombination. Phenotypic analysis revealed that ΔCfGti1 lost pathogenicity to apple leaves by blocking appressorium-mediated host penetration, although penetration pegs still developed on cellophane. In addition, ΔCfGti1 colonization and hyphal extension in wounded apple fruit were dramatically decreased. The ΔCfGti1 mutant exhibited defects in growth and development of hyphae, which may be partly responsible for its inability to colonize apple. Comparative transcriptome and qRT-PCR analyses suggested that CfGti1 regulated appressorium-mediated host penetration by modulating genes related to metabolism of appressorial lipid droplets. Interestingly, CfGti1 also regulated the expression of ybtS and AKT1 or AFT1-1 related to biosynthesis of AK and AF host-specific toxins. This study demonstrated that CfGti1 is a pivotal regulator for apple GLS pathogenesis in C. fructicola.