Pathogenicity of fungus strains isolated from medicinal Fritillaria przewalskii Maxim. bulb rot

Abstract

Background: Bulb rot causes loss of the perennial medicinal plant Fritillaria przewalskii Maxim., is exacerbated with growth years and seriously constrains plant productivity, but the pathogens responsible for the disease were still unknown, very few reports were presented before.Methods: To determine potential pathogenic sources, fungus strains were isolated from diseased plant samples with bulb rot symptom of the 3- to 5-year-old F. przewalskii plants by tissue separation, and assayed for pathogenicity according to Koch’s Law.Results: Seven pathogenic strains (F1-F7) were detected in5-year-old rot bulbs, six (F1-F6) in 4-year-old rot bulbs, and four (F1, F2, F5, F6) in 3-year-old rot bulbs. All of the strains were able to infect bulbs by stabbing and some exhibited varying levels of aggressiveness. Relative to the non-stabbing controls, the bulbs stab-inoculated with F5, F2, F7, F4, F1, F6, and F3 showed 76.65%, 75.15%, 71.44%, 40.37%, 39.09%, 36.87%, and 34.93% rot after 8 days, respectively. Phylogenetic analysis revealed that theses trains (deposited in GenBank under accessions MH917682 to MH917688) were clustered into Bionectria ochroleuca (F1, F3, F4), Fusarium oxysporum (F2, F7), Fusarium tricinctum (F5), and Clonostachys rosea (F6). The two species of Fusarium had the strongest pathogenicity, followed by Bionectria ochroleuca and Clonostachys rosea. Although leading to low bulb rot incidence by stab-inoculation, F1 showed the highest isolation rate (48.9%) among all strains. Conclusions: Thus, the edible and medicinal bulbs of F. przewalskii are susceptible to synergetic contamination by these seven pathogenic strains at some point after their third year of growth, which has contributed to the species endangered status, with the two strains of Fusarium being the predominant pathogens. To our knowledge, this is the first report on the seven strains of four fungal species causing in F. przewalskii bulb rot in China.

Research progress of rhizosphere microorganisms in Fritillaria L. medicinal plants

“…As planting years increased, the relative abundances of the genera Lactobacillus , Gemmatimonas , Bryobacter , and Bacteroides gradually decreased, whereas the relative abundances of the genera Methylotera , Sphingobacterium , and Pseudomonas gradually increased ( Mu, 2019 ). Wu (2021a , Wu 2021b) reported that the composition of phyla and genera within soil bacterial communities changed alongwith the growth years of F. kansuensis . Among them, for the relative abundance, Actinomycetes (23.58%–32.08%), Proteobacteria (22.00%–28.80%), Acidobacteria (13.82%–20.86%) and Chloroflexi (8.43%–15.08%) belonging to the dominant phyla, and the continuous planting of Fritillaria kansuensis for 5 years would significantly reduce the diversity of bacterial communities in the soil rhizosphere.…”

“…Common soil borne diseases, such as root rot disease, sclerotium disease, ray mold disease, rust disease, and yellow rot rust, occurred frequently and caused serious harm ( Wang, 2010 ). This made it very easy for Fritillaria to develop bulb rot and lose its medicinal value ( Liu et al, 2020 ; Wu, 2021a ). Using morphological identification method, the pathogen of sclerotium disease and root rot disease of F. pallidiflora was identified as Stromatinia rapulum ( Supi et al, 2012 ) and Fusarium solani var.…”

“…could cause leaf spot disease ( Wang, 2017 ). But the pathogens of root rot disease of F. przewalskii were F. oxysporum , F, tricinctum , Bionectria ochroleuca and Clonostachys rosea ( Wu et al, 2021a ). Botrytis cinerea was identified as the pathogen of ray mold disease of F. thunbergia, and not the Botrytis elliptica which was generally considered as the pathogen in the past (Li et al, 2022).…”

“…At present, pathogens of main diseases of Fritillary medicinal plants have been reported ( Supi et al, 2012 ; Supi et al, 2015 ; Song et al, 2016a ; Wang, 2017 ; Wu et al, 2021 ; Li et al, 2022), but some pathogens are only identified by morphological identification method, and need to be further identified by molecular biology method. The pathogen of a certain plant of Fritillaria may be speculated from the incidence of other Fritillaria plants, but the pathogen of the same disease in different Fritillaria plants are not exactly the same.…”