Exogenous melatonin improves pear resistance to Botryosphaeria dothidea by increasing autophagic activity and sugar/organic acid levels

Pear is a perennial deciduous fruit tree of the Rosaceae Pyrus genus, and is one of the main fruit trees worldwide. The pathogen Botryosphaeria dothidea infects pear trees and causes pear ring rot disease. According to our research, exogenous melatonin application enhanced resistance to B. dothidea in pear fruit. Melatonin treatment of pears significantly reduced the diameter of disease spots and enhanced the endogenous melatonin content under B. dothidea inoculation. Compared with H2O treatment, melatonin treatment suppressed the increase in ROS and activated ROS-scavenging enzymes. Treatment with exogenous melatonin maintained AsA-GSH at more reductive status. The expression levels of core autophagic genes and autophagosome formation were elevated by melatonin treatment in pear fruit. The silencing of PbrATG5 in Pyrus pyrifolia conferred sensitivity to inoculation, which was only slightly recovered by melatonin treatment. After inoculation with B. dothidea, exogenous melatonin treatment increased the contents of soluble sugars and organic acids in pear fruits compared with H2O treatment. Our results demonstrated that melatonin enhanced resistance to B. dothidea by increasing the autophagic activity and soluble sugar/organic acid accumulation.

Isolation and Characterization of Bacillus velezensis Strain P2-1 for Biocontrol of Apple Postharvest Decay Caused by Botryosphaeria dothidea

Botryosphaeria dothidea causes apple ring rot, which is among the most prevalent postharvest diseases of apples and causes significant economic loss during storage. In this study, we investigated the biocontrol activity and possible mechanism of Bacillus velezensis strain P2-1 isolated from apple branches against B. dothidea in postharvest apple fruit. The results showed strain P2-1, one of the 80 different endophytic bacterial strains from apple branches, exhibited strong inhibitory effects against B. dothidea growth and resulted in hyphal deformity. B. velezensis P2-1 treatment significantly reduced the ring rot caused by B. dothidea. Additionally, the supernatant of strain P2-1 exhibited antifungal activity against B. dothidea. Re-isolation assay indicated the capability of strain P2-1 to colonize and survive in apple fruit. PCR and qRT-PCR assays revealed that strain P2-1 harbored the gene clusters required for biosynthesis of antifungal lipopeptides and polyketides. Strain P2-1 treatment significantly enhanced the expression levels of pathogenesis-related genes (MdPR1 and MdPR5) but did not significantly affect apple fruit qualities (measured in fruit firmness, titratable acid, ascorbic acid, and soluble sugar). Thus, our results suggest that B. velezensis strain P2-1 is a biocontrol agent against B. dothidea-induced apple postharvest decay. It acts partially by inhibiting mycelial growth of B. dothidea, secreting antifungal substances, and inducing apple defense responses.

High-quality genome assembly and annotation resource of Botryosphaeria dothidea strain BDLA16-7, causing trunk canker disease on Chinese hickory

Botryosphaeria dothidea is a latent pathogen with global importance to woody plant health, which causes serious tree trunk cankers on Chinese hickory. To date, only one Illumina short-read-based genome assembly of strain CK16 is available for host Chinese hickory. To address this problem, we reported a near telomere-to-telomere genome assembly of strain BDLA16-7 (46.05 Mb, N50 3.87 Mb) using Oxford Nanopore Sequencing Technology. Our genome assembly was consisted of 15 contigs, of which, 3 were assembled into chromosomal level and the maximum contig length was 6.19 Mb. The assembly contained 7.96% repeats and 12,815 protein-coding genes (10,274 genes were functional annotated). We also identified 3,642 pathogen-host interaction (PHI) genes, 250 carbohydrateactive enzymes (CAZymes), 252 cytochrome P450 enzymes (CYPs), 752 putative secreted proteins and 63 secondary metabolite biosynthesis gene clusters (SMBGCs). The BUSCO completeness of genome assembly and predicted genes was 99.34% and 97.50%, respectively, at fungal level (n=758). The almost chromosomal-level and well-annotated genome assembly will provide a valuable genetic resource for understanding of the infection mechanisms of B. dothidea in future.

An Integrative Study on Asphondylia spp. (Diptera: Cecidomyiidae), Causing Flower Galls on Lamiaceae, with Description, Phenology, and Associated Fungi of Two New Species

An integrative study on some species of Asphondylia was carried out. Two species of gall midges from Italy, Asphondylia rivelloi sp. nov. and Asphondylia micromeriae sp. nov. (Diptera: Cecidomyiidae), causing flower galls respectively on Clinopodium vulgare and Micromeria graeca (Lamiaceae), are described and illustrated. The characteristics of each developmental stage and induced galls are described, which allowed the discrimination of these new species in the complex of Asphondylia developing on Lamiaceae plants. Molecular data based on sequencing both nuclear (ITS2 and 28S-D2) and mitochondrial (COI) genes are also provided in support of this discrimination. Phylogeny based on nuclear markers is consistent with the new species, whereas COI phylogeny suggests introgression occurring between the two species. However, these species can also be easily identified using a morphological approach. Phenology of host plants and gall midges are described, and some peculiar characteristics allow the complete and confident discrimination and revision of the treated species. Gall-associated fungi were identified as Botryosphaeria dothidea,Alternaria spp., and Cladosporium spp.