Botrytis cinerea is a necrotrophic fungus causing disease on many important agricultural crops. Two novel mycoviruses, namely Botrytis cinerea hypovirus 1 (BcHV1) and Botrytis cinerea fusarivirus 1 (BcFV1), were fully sequenced. The genome of BcHV1 is 10,214 nt long excluding a poly-A tail and possesses one large open reading frame (ORF) encoding a polyprotein possessing several conserved domains including RNA-dependent RNA polymerase (RdRp), showing homology to hypovirus-encoded polyproteins. Phylogenetic analysis indicated that BcHV1 may belong to the proposed genus Betahypovirus in the viral family Hypoviridae. The genome of BcFV1 is 8411 nt in length excluding the poly A tail and theoretically processes two major ORFs, namely ORF1 and ORF2. The larger ORF1 encoded polypeptide contains protein domains of an RdRp and a viral helicase, whereas the function of smaller ORF2 remains unknown. The BcFV1 was phylogenetically clustered with other fusariviruses forming an independent branch, indicating BcFV1 was a member in Fusariviridae. Both BcHV1 and BcFV1 were capable of being transmitted horizontally through hyphal anastomosis. Infection by BcHV1 alone caused attenuated virulence without affecting mycelial growth, significantly inhibited infection cushion (IC) formation, and altered expression of several IC-formation-associated genes. However, wound inoculation could fully rescue the virulence phenotype of the BcHV1 infected isolate. These results indicate the BcHV1-associated hypovirulence is caused by the viral influence on IC-formation-associated pathways.

Here, we characterized a negative single-stranded (−ss)RNA mycovirus, Botrytis cinerea mymonavirus 1 (BcMyV1), isolated from the phytopathogenic fungus Botrytis cinerea. The genome of BcMyV1 is 7863 nt in length, possessing three open reading frames (ORF1–3). The ORF1 encodes a large polypeptide containing a conserved mononegaviral RNA-dependent RNA polymerase (RdRp) domain showing homology to the protein L of mymonaviruses, whereas the possible functions of the remaining two ORFs are still unknown. The internal cDNA sequence (10-7829) of BcMyV1 was 97.9% identical to the full-length cDNA sequence of Sclerotinia sclerotiorum negative stranded RNA virus 7 (SsNSRV7), a virus-like contig obtained from Sclerotinia sclerotiorum metatranscriptomes, indicating BcMyV1 should be a strain of SsNSRV7. Phylogenetic analysis based on RdRp domains showed that BcMyV1 was clustered with the viruses in the family Mymonaviridae, suggesting it is a member of Mymonaviridae. BcMyV1 may be widely distributed in regions where B. cinerea occurs in China and even over the world, although it infected only 0.8% of tested B. cinerea strains.

Melon (Cucumis melo L.) is a member of the Cucurbitaceae family, an important economical and horticultural crop, which is widely grown in China. In May 2020, fruit rot disease with water-soaked les...

Rhizosphere microorganisms play pivotal roles in mitigating the challenges associated with continuous cropping in melon cultivation. While grafting and plant growth-promoting rhizobacteria (PGPR) independently influence rhizosphere microbial communities, their combined effects remain largely unexplored. This study investigates the synergistic regulation of Paenibacillus polymyxa NBmelon-1 inoculation and grafting on rhizosphere microbiome assembly, plant performance, and disease resistance in melon self-rootstocks. Field experiments demonstrated that NBmelon-1 inoculation significantly enhanced rootstock stem diameter (95.3% increase in spring) and root development, achieving a graft survival rate exceeding 95%. The combined treatment (NB+GJ) increased scion fruit yield by 29.8% in autumn and 36.5% in spring, as well as the single-fruit weight by 22.5% in autumn and 37.3% in spring, while maintaining fruit morphology. Integrated 16S rRNA and ITS sequencing revealed that the NB+GJ treatment selectively enriched antagonistic bacterial phyla (e.g., Firmicutes and Actinobacteriota) and suppressed pathogenic fungi (e.g., Fusarium and Melanconiella). Seasonal shifts in microbial diversity and functional gene profiles underscored the dynamic interplay between treatments and environmental factors. These findings establish a novel strategy for optimizing melon self-rootstock grafting systems and sustainably managing soil-borne diseases.

In May of 2020, November of 2021 and May of 2022, a preharvest fruit rot with white mycelia was observed inside and outside of the fruits of thick skin muskmelon (Cucumis melo L.) growing in about ten greenhouses (each greenhouse had about 320 muskmelons) with disease incidence of 70% in Ningbo, Zhejiang Province of China. In order to identify the causal agent, plant tissues from the margin of the symptomatic tissue were sterilized for 1 min with 1% sodium hypochlorite (NaClO), 2 min with 75% ethyl alcohol, rinsed in sterile distilled water three times (Zhou et al 2019), and then placed on potato dextrose agar (PDA) plates containing streptomycin sulfate (100 μg/mL) at 25℃ for 4 days. Only Fusarium colonies were isolated from all the plant tissues. The growing hyphae were transferred to new PDA plates using the hyphal tip method, putative Fusarium colonies were purified by single-sporing. Six fungal isolates (Fi-1~6) were obtained. The average radial mycelial growth rate of Fusarium isolate Fi-3 was 4.6 mm/day at 25℃ in the dark on PDA, and like other five isolates. The colonies are abnormal, producing lots of aerial hyphae, each isolate was white to light orange. Isolate Fi-3 produced macroconidia with 4 to 6 septa, tapered with pronounced dorsiventral curvature and measured 21 to 30 μm long 4 to 5 μm wide on Spezieller Nährstoffarmer Agar (SNA) medium at 25℃ for 10 days (Leslie and Summerell 2006), but polyphialides and chlamydospores were still not available for 30 days. The pathogen species was further identified by translation elongation factor-1 alpha (EF-1α) sequencing. The EF-1α of six isolates were sequenced, and their EF-1α sequences were 100% identical to each other, and the sequence of strain Fi-3 was deposited in GenBank with accession no. OL782040 and was also compared with sequences in the FUSARIUM-ID database (Geiser et al. 2004), which indicated that it was 100% identical to those of F. pernambucanum strain NRRL 32864 (GenBank accession GQ505613), F. pernambucanum strain LC7040 (GenBank accession MK289626), and F. pernambucanum strain LC12149 (GenBank accession MK289588) within the Fusarium incarnatum - F. equiseti species complex 17 (FIESC17). Two phylogenetic trees were established based on the TEF1-α sequences of Fi-1~6 and other Fusarium spp., Fi-1~6 was clustered with the sequences of F. pernambucanum within the FIESC17. Thus, both morphological and molecular criteria supported identification of the strain as F. pernambucanum. A pathogenicity test was conducted to verify Koch's postulates, mycelium agar plugs (6 mm in diameter) were removed from the colony margin of a 3-day-old culture of strain Fi-3, healthy melon fruits were surface-sterilized with 70% ethanol and rinsed twice with sterile-distilled water. Then, the melons were wounded using a sterile inoculating needle to stab and inoculated by a mycelium agar plug of strain Fi-3 on the wound sites. 5 fruits were inoculated in each treatment, and a mycelium-free PDA plug was used as a negative control, repeated 3 times, at 25℃ with high relative humidity for 10 days. The results show disease symptoms similar to those naturally infected fruits on all inoculated melon fruits. The fungus re-isolated from the diseased fruits, showed the same colony morphology as the original isolate. Koch's postulates were repeated three times with the same results. Strain Fi-3 inoculated fruits without wounding remained healthy. To our knowledge, this is the first report of fruit rot of melon caused by F. pernambucanum in China.

Squash leaf curl China virus (SLCCNV) belongs to the species Begomovirus cucurbitachinaense in the genus Begomovirus and can infect some Cucurbitaceae crops except for watermelon (Citrullus lanatus). In this study, watermelon plants showing symptoms typical to begomovirus infection in field were observed in Zhejiang Province of China, and SLCCNV presence was identified through PCR and next-generation sequencing (NGS). The pairwise sequence identity of the DNA-A genome shows that SLCCNV watermelon isolate belongs to the SLCCNV/CN strain and shares 96% nucleotide identity with the previously sequenced SLCCNV/CN. An infectious clone of SLCCNV watermelon isolate was constructed using the tandem repeat fragment method. Through agrobacterium-mediated inoculation, the clone could induce systemic infection with typical symptoms in watermelon, melon (Cucumis melo), squash (Cucurbita pepo), pumpkin (Cucurbita maxima), wax gourd (Benicasa hispida), cucumber (Cucumis sativus), and N. benthamiana. It was further demonstrated that the progeny virions derived from the cloned watermelon isolate could be transmitted by whitefly rather than the sap. To the best of our knowledge, this is the first report of a natural infection of SLCCNV on watermelon in China, and the first complete report on the molecular characteristics and pathogenicity of watermelon-infecting SLCCNV in the world.