No abstract

Apple ring rot, caused by Botryosphaeria dothidea, is one of the most serious diseases affecting apple industry in East Asia. To study the correlation between fruit natural exocarp structures and susceptibility to B. dothidea, lesion length of Malus domestica cultivars and Malus germplasm accessions was measured 14 days after in vitro inoculation with B. dothidea mycelia at different developmental stages. Area per fruit surface (APFS) of lenticels and microcracks and thickness of cuticular wax were observed. Lesion length, lenticel APFS and cuticular wax thickness varied significantly among the 11 cultivars studied. A positive correlation between lesion length and lenticel APFS and a negative correlation between lesion length and cuticular wax thickness were detected among cultivars and during fruit development. In addition, similar correlations were validated in nine Malus germplasm accessions. Numerous microcracks were observed on surfaces of Golden Delicious and Golden Spur fruit, accounting for 90 % of the natural openings. The hyphae of B. dothidea penetrated into exocarp through both lenticels and microcracks. Fruit bagging with double-layered paper bags and exogenous GA 4+7 reduced lenticel APFS, thickened cuticular wax and elevated resistance to disease. Natural openings on fruit exocarp are an important factor affecting susceptibility of apple to B. dothidea.

Pathogen-induced decay is one of the most common causes of fruit loss, resulting in substantial economic loss and posing a health risk to humans. As an ethylene action inhibitor, 1-methylcyclopropene (1-MCP) can significantly reduce fruit decay, but its effect on fruit pathogens remains unclear. Herein, the change in microbial community structure was analyzed using the high-throughput sequencing technology, and characteristics related to fruit quality were determined after 1-MCP (1.0 M l L–1) treatment in “Doyenne du Comiceis” pear fruit during storage at ambient temperature. Overall, 1-MCP was highly effective in reducing disease incidence and induced multiple changes of the fungal and bacterial microbiota. At day 15, the microbial diversity of fungi or bacteria was reduced significantly in the control fruit (non-treated with 1-MCP), which had the most severe decay incidence. For fungi, in addition to Alternaria being the most abundant in both 1-MCP treatment (59.89%) and control (40.18%), the abundances of Botryosphaeria (16.75%), Penicillium (8.81%), and Fusarium (6.47%) increased significantly with the extension of storage time. They became the primary pathogens to cause fruit decay in control, but they were markedly decreased in 1-MCP treatment, resulting in reduced disease incidence. For bacteria, the abundance of Gluconobacter (50.89%) increased dramatically at day 15 in the control fruit, showing that it also played a crucial role in fruit decay. In addition, Botryosphaeria, Fusarium fungi, and Massilia, Kineococcus bacteria were identified as biomarkers to distinguish 1-MCP treatment and control using Random Forest analysis. The redundancy analysis (RDA) result showed that the amount of Botryosphaeria, Penicillium, and Fusarium were positively correlated with disease incidence and respiration rate of pear fruits while negatively correlated with fruit firmness. This investigation is the first comprehensive analysis of the microbiome response to 1-MCP treatment in post-harvest pear fruit, and reveals the relationship between fruit decay and microbial composition in pear fruit.

‘Huangguan’ pear (Pyrus bretschneideri Rehd) fruit is susceptible to cold, characterized by developing peel browning spots (PBS) during cold storage. Additionally, ethylene pretreatment reduces chilling injury (CI) and inhibits PBS occurrence, but the mechanism of CI remains unclear. Here, we deciphered the dynamic transcriptional changes during the PBS occurrence with and without ethylene pretreatment via time-series transcriptome. We found that ethylene suppressed the cold-signaling gene expression, thereby decreasing the cold sensitivity of the ‘Huangguan’ fruit. Moreover, the “Yellow” module closely correlated with PBS occurrence was identified via weighted gene co-expression network analysis (WGCNA), and this module was related to plant defense via Gene Ontology (GO) enrichment analysis. Local motif enrichment analysis suggested that the “Yellow” module genes were regulated by ERF and WRKY transcription factors. Functional studies demonstrated that PbWRKY31 has a conserved WRKY domain, lacks transactivation activity, and localizes in the nucleus. PbWRKY31-overexpressed Arabidopsis were hypersensitive to cold, with higher expression levels of cold signaling and defense genes, suggesting that PbWRKY31 participates in regulating plant cold sensitivity. Collectively, our findings provide a comprehensive transcriptional overview of PBS occurrence and elucidate the molecular mechanism by which ethylene reduces the cold sensitivity of ‘Huangguan’ fruit as well as the potential role of PbWRKY31 in this process.