First Report of Brown Rot Caused by Monilia mumecola on Chinese Sour Cherry in Chongqing Municipality, China

Prediction of the Potential Distributions of Prunus salicina Lindl., Monilinia fructicola, and Their Overlap in China Using MaxEnt

Prunus salicina Lindl. (P. salicina) is an essential cash crop in China, and brown rot (BR) is one of its most important diseases. In this study, we collected geographic location information on P. salicina and Monilinia fructicola (G. Winter) Honey (M. fructicola), one of the BR pathogenic species, and applied the MaxEnt model to simulate its potential suitable distribution in China. There have been discussions about the dominant environmental variables restricting its geographical distribution and their overlap. The results showed that the mean temperature of the coldest quarter, precipitation of the warmest quarter, precipitation in July, and minimum temperatures in January and November were the main climatic variables affecting the potential distribution of P. salicina, while the coldest quarter, precipitation of the driest month, precipitation of March, precipitation of October, maximum temperatures of February, October, and November, and minimum temperature of January were related to the location of M. fructicola. Southern China had suitable conditions for both P. salicina and M. fructicola. Notably, the overlap area of P. salicina and M. fructicola was primarily located southeast of 91°48' E 27°38' N to 126°47' E 41°45' N. The potential overlap area predicted by our research provided theoretical evidence for the prevention of BR during plum planting.

Morphological and Molecular Identification of Peach Brown Rot Disease in Tibet and Exploration of the Biocontrol Efficiency of Trichoderma

Brown rot caused by the pathogen of the genus Monilinia is the most destructive disease in peaches worldwide. It has seriously reduced the economic value of the peach (Prunus persica (L.) Batsch) in Nyingchi and Qamdo, Tibet, China. Monilinia fructicola, Monilia mumecola, and M. yunnanensis have been reported as the causal agents of brown rot disease on stone fruits in China. In this study, we report on the identification of M. yunnanensis in peach orchards in Nyingchi and Qamdo, Tibet. From twenty-three isolates with the same characteristics, we identified the representative single-spore isolates T8-1, T8-8, and T8-20 as M. yunnanensis and confirmed that the Tibet brown rot disease was caused by M. yunnanensis based on the morphological characteristics and molecular analyses. The phylogenetic analysis of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) and β-tubulin (TUB2) nucleotide sequences and the multiplex PCR identification revealed that the representative isolates T8-1, T8-8, and T8-20 were more closely related to M. yunnanensis than other Monilinia species. Furthermore, the biocontrol strain of Trichoderma T6 presented significant antagonistic activity on the M. yunnanensis T8-1 isolate (T8-1) among the five Trichoderma strains. The highest inhibitory rates for Trichoderma T6 and its fermentation product against T8-1 mycelial growth were 72.13% and 68.25%, respectively. The obvious inhibition zone displayed on the colony interaction area between the colony of T8-1 isolate and Trichoderma T6 and the morphological characterization of the T8-1 hyphae were enlarged and malformed after inoculation with the Trichoderma T6 fermentation product at 20-fold dilution. Our results indicate that the strain of Trichoderma T6 could be considered as a beneficial biocontrol agent in managing brown rot of peach fruit disease.

Phylogenetic divergences in brown rot fungal pathogens of Monilinia species from a worldwide collection: inferences based on the nuclear versus mitochondrial genes

Background

Phylogenetic analyses for plant pathogenic fungi explore many questions on diversities, relationships, origins, and divergences of populations from different sources such as species, host, and geography. This information is highly valuable, especially from a large global sampling, to understand the evolutionary paths of the pathogens worldwide. Monilinia fructicola and M. laxa are two important fungal pathogens of stone fruits that cause the widespread disease commonly known as brown rot. Three nuclear genes (Calmodulin, SDHA, TEF1α) and three mitochondrial genes (Cytochrome_b, NAD2, and NAD5) of the two pathogen species from a worldwide collection including five different countries from four different continents were studied in this work.

Results

Both Maximum Likelihood and Bayesian approaches were applied to the data sets, and in addition, Maximum Parsimony based approaches were used for the regions having indel polymorphisms. Calmodulin, SDHA, NAD2, and NAD5 regions were found phylogenetically informative and utilized for phylogenetics of Monilinia species for the first time. Each gene region presented a set of haplotypes except Cytochrome_b, which was monomorphic. According to this large collection of two Monilinia species around the world, M. fructicola showed more diversity than M. laxa, a result that should be carefully considered, as M. fructicola is known to be a quarantine pathogen. Moreover, the other two mitochondrial genes (NAD2 and NAD5) did not have any substitution type mutations but presented an intron indel polymorphism indicating the contribution of introns as well as mobile introns to the fungal diversity and evolution. Based on the concatenated gene sets, nuclear DNA carries higher mutations and uncovers more phylogenetic clusters in comparison to the mitochondrial DNA-based data for these fungal species.

Conclusions

This study provides the most comprehensive knowledge on the phylogenetics of both nuclear and mitochondrial genes of two prominent brown rot pathogens, M. fructicola and M. laxa. Based on the regions used in this study, the nuclear genes resolved phylogenetic branching better than the mitochondrial genes and discovered new phylogenetic lineages for these species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02079-6.

Phylogenetic Analysis and Fungicide Baseline Sensitivities of Monilia mumecola in China

Monilia mumecola is one of the causal agents of peach brown rot in China. In this study, M. mumecola isolates from different locations and hosts were used to analyze the genetic diversity and to assay the sensitivity to four generally used fungicides: carbendazim, tebuconazole, azoxystrobin, and boscalid. Results showed that isolates from different locations tended to be separated. Interestingly, isolates from different hosts (e.g., peach and apricot) at the same locations generally clustered together, indicating that the M. mumecola isolates may infect different hosts in the same areas. The fungicide sensitivity assay of 93 M. mumecola isolates showed that the average effective concentration for 50% mycelial growth inhibition values for carbendazim, tebuconazole, azoxystrobin, and boscalid were 0.103, 0.034, 0.325, and 0.419 µg/ml, respectively. The sensitivity distributions of the tested isolates to the four fungicides showed continuous unimodal curves, indicating no qualitative shift of resistance. No significant difference of sensitivity to tested fungicides was observed among isolates from either different locations or different hosts.

Monilinia Species Associated with Brown Rot of Cultivated Apple and Pear Fruit in China

Monilinia isolates were collected from major apple and pear production regions in China from 2004 to 2011 and identified based on their morphological characteristics and three highly conserved loci. The 247 isolates belonged to three species: Monilinia fructicola, Monilia yunnanensis, and Monilia polystroma. M. yunnanensis was the most prevalent (77%), followed by M. polystroma (20%) and Monilinia fructicola (3%). Monilia yunnanensis is primarily distributed in the south, north, and west of China; M. polystroma is limited to the north and east; and Monilinia fructicola was detected only from a few samples from the north and east. Phylogenetic analysis based on internal transcribed spacer, β-tubulin, and laccase (lcc2) genes suggested that Monilia yunnanensis, M. polystroma, and Monilinia fructigena are closely related, and Monilia yunnanensis is more distantly related. We also found that these three species do not show consistent differences in morphological characteristics, including colony morphology, colony expansion rate, conidial characteristics, and the amount of stroma produced in culture. Thus, these three species are more like phylogenetic species in the process of speciation. In addition, a set of species-specific primers based on single-nucleotide polymorphisms and deletions in the lcc2 gene region were designed and a conventional polymerase chain reaction method successfully developed for differentiating Monilinia fructicola, Monilia yunnanensis, M. polystroma, and Monilinia laxa from the other species.

Identification and Characterization of Three Monilinia Species from Plum in China

In total, 112 Monilinia spp. single-spore isolates were collected from plum fruit (Prunus salicina) symptomatic for brown rot disease from Yunnan, Hubei, and Zhejiang provinces and Chongqing municipality, China between 2012 and 2014. Three distinct colony morphologies (phenotypes) were observed on potato dextrose agar and two isolates per phenotype were selected for further analysis. Colony color, colony shape, conidia size, number of germ tubes per conidia, and pathogenicity on plum were investigated. The ribosomal internal transcribed spacer regions 1 and 2 as well as a polymerase chain reaction-based method that amplified fragments of the glyceraldehyde-3-phosphate dehydrogenase (G3PDH) and β-tubulin (TUB2) genes were used to identify the isolates to the species level. The three phenotypes were identified to be three different species: Monilinia fructicola, Monilia mumecola, and Monilia yunnanensis. Phylogenetic analysis based on G3PDH and TUB2 nucleotide sequences revealed that isolates within species clustered together regardless of host or geographical origin, suggesting that these factors did not play an important role for the evolutionary separation of the described species.