Relationships between fungal diversity and fruit quality of Yuluxiang pear during low temperature storage

Abstract

Postharvest decay is an urgent problem that affects the storage of pears. Low temperature storage is one of the most important methods to reduce the prevalence of fruit diseases during storage. In this study, the microbial diversity of postharvest Yuluxiang pear (Pyrus × michauxii "Yu Lu Xiang") fruits stored at low temperature for different lengths of times was analyzed. Illumina MiSeq high-throughput sequencing was used to analyze the composition and diversity of fungal communities. The results showed that the fungi within fruit were classified into 6 phyla, 18 classes, 40 orders, 72 families, and 92 genera based on the 97% sequence similarity level. They belonged to 6 phyla, 18 classes, 40 orders, 72 families, and 92 genera. The highest richness of fungi was obtained after 30 d of treatment. The β-diversity index showed that the fungal community composition of these fruit was significantly different at the beginning of storage compared with the different timepoints of samples at low temperature during storage. The comparison of fungal composition at the phylum level indicated that Ascomycota was dominant in the different timepoints of samples at low temperature, while Alternaria was the primary fungus at the genus level. A correlation analysis was used to further explore the correlation between fungi and fruit firmness, titratable acid, and solid soluble contents at low temperatures during storage. Aureobasidium and Didymella positively correlated with the soluble solids and hardness. Phoma positively correlated with the titratable acid, and Aspergillus positively correlated with titratable acid and hardness. This study can guide the industrial production of Yulu pear and also provide a theoretical basis to prevent and control diseases during the storage period of Yulu pear.

Keywords: diversity analysis; fungal diversity; high-throughput sequencing; low temperature; pear.

Figure 1

PCoA of fungal communities in Yuluxiang pears after storage at low temperatures for 30 d(A), 60 d(B), 90 d(C), and 120 d(D). Each point represents a sample, and the dots of different colors indicate different samples (groups). The percentages in the parentheses on the axis represent the proportion of sample difference data (distance matrix) that can be interpreted by the corresponding axis. PCoA, Principal coordinates analysis.

Figure 2

Microbial Venn plot of different samples based on the OTU level. Each ellipse represents a sample (group). The overlapping area between the ellipses indicates the common OTUs between the samples (group), and the number of each block indicates the number of OTUs contained in the block. OTU, operational taxonomic unit.

Figure 3

Analysis of fungal community diversity at the phylum level and genus level of Yuluxiang pears stored at low temperature for 30 d(A), 60 d(B), 90 d(C), 120 d(D), and different colored dots indicated different samples (groups).

Figure 4

A cluster heatmap of the flora at the genus level. The red patch in the figure indicates that the genus is more abundant in this sample than in the other samples, and the blue patch indicates that the genus is less abundant in this sample than in the other samples.

Figure 5

Histogram of the LDA effect values of marker species and differential taxa between groups. The LDA ordinate is a taxa with significant differences between the groups, and the abscissa visually displays the logarithmic score values of the LDA analysis for each taxa in a bar chart. The taxonomic clade shows the taxonomic hierarchical relationships of the main taxa in the sample community from the phylum to genus (from inner circle to outer circle). The node size corresponds to the average relative abundance of that taxa. Hollow nodes represent taxa with insignificant intergroup differences, while the nodes of other colors indicate that these taxa exhibit significant between-group differences and are more abundant in the grouped sample represented by that color. Letters identify the names of taxa that differ significantly between groups. LDA, linear discriminant analysis.

Figure 6

Correlation analysis of the fungi of Yuluxiang pear with fruit hardness, titratable acid, and soluble solids in different storage periods. Each column represents a bacterium. Blue is a negative correlation, and red is a positive correlation. * is a distinctive identifier.