PM 7/18(2): Monilinia fructicola

Tracking of Diversity and Evolution in the Brown Rot Fungi Monilinia fructicola, Monilinia fructigena, and Monilinia laxa

Monilinia species are among the most devastating fungi worldwide as they cause brown rot and blossom blight on fruit trees. To understand the molecular bases of their pathogenic lifestyles, we compared the newly assembled genomes of single strains of Monilinia fructicola, M. fructigena and M. laxa, with those of Botrytis cinerea and Sclerotinia sclerotiorum, as the closest species within Sclerotiniaceae. Phylogenomic analysis of orthologous proteins and syntenic investigation suggest that M. laxa is closer to M. fructigena than M. fructicola, and is closest to the other investigated Sclerotiniaceae species. This indicates that M. laxa was the earliest result of the speciation process. Distinct evolutionary profiles were observed for transposable elements (TEs). M. fructicola and M. laxa showed older bursts of TE insertions, which were affected (mainly in M. fructicola) by repeat-induced point (RIP) mutation gene silencing mechanisms. These suggested frequent occurrence of the sexual process in M. fructicola. More recent TE expansion linked with low RIP action was observed in M. fructigena, with very little in S. sclerotiorum and B. cinerea. The detection of active non-syntenic TEs is indicative of horizontal gene transfer and has resulted in alterations in specific gene functions. Analysis of candidate effectors, biosynthetic gene clusters for secondary metabolites and carbohydrate-active enzymes, indicated that Monilinia genus has multiple virulence mechanisms to infect host plants, including toxins, cell-death elicitor, putative virulence factors and cell-wall-degrading enzymes. Some species-specific pathogenic factors might explain differences in terms of host plant and organ preferences between M. fructigena and the other two Monilinia species.

Rapid Detection of Monilinia fructicola and Monilinia laxa on Peach and Nectarine using Loop-Mediated Isothermal Amplification

Monilinia laxa and M. fructicola are two causal agents of brown rot, one of the most important diseases in stone fruit. Two species cause blight on blossoms and twigs and brown rot on fruit in pre- and postharvest. Both species are distributed worldwide in North and South America, Australia, and Japan. In Europe, M. laxa is endemic, while M. fructicola was introduced in 2001 and it is now widespread in several countries. Currently, both species coexist in European stone fruit orchards. Monilinia spp. overwinter in cankers and mummified fruit. Mummy monitoring during winter permits growers to understand which species of Monilinia will be prevalent in an orchard during the following season, permitting planning of an appropriate crop protection. Traditionally, the identification has been carried out using morphological features and even with polymerase chain reaction (PCR)-based assays that requires time and well-equipped laboratories. In this study, two isothermal-based methods were designed to identify these pathogens in a faster way than using traditional methods. The loop-mediated amplification (LAMP) assays were validated on some isolates of Monilinia spp. coming from the mummy monitoring according to the international European and Mediterranean Plant Protection Organization standard (PM7/98), taking into account specificity, sensitivity, repeatability, and reproducibility. The sensitivity of both assays was checked by monitoring (at different time points) two nectarine varieties artificially inoculated and stored at two different temperatures. The reliability of both LAMP assays against the quantification of the inoculum was compared with previously published quantitative PCR assays. Both LAMP methods were able to detect a low number of cells. These LAMP methods could be a useful tool for monitoring brown rot causal agents in the field and during postharvest.

Characterization of Monilinia spp. Populations on Stone Fruit in South Italy

Monilinia spp. are responsible for brown rot decay of stone and pome fruit in the field as well as in postharvest. Monilinia laxa and M. fructigena are considered indigenous to Europe, while M. fructicola is a quarantine pathogen in the European and Mediterranean Plant Protection Organization area included in the A2 List. In Italy, it was first reported in 2009 in Piedmont (northern Italy) and rapidly spread to central Italy. We carried out a monitoring program on the occurrence of Monilinia spp. in southern Italy and a comparative characterization of the three main fungal pathogens. Molecular assays based on direct polymerase chain reaction (PCR) and real-time quantitative PCR for molecular identification of Monilinia spp. from rotted fruit were set up, validated, and applied in a monitoring program. Of the tested 519 isolates from 26 orchards, 388 (74.8%) were identified as M. fructicola, 118 (22.7%) as M. laxa, 10 (1.9%) as M. fructigena, and 3 (0.6%) were M. polystroma. M. fructicola colonies grew faster and had a higher optimal temperature for growth (26°C) than M. laxa (23°C) and M. fructigena (20°C). No relevant difference in virulence could be observed on artificially inoculated apricot, cherry, and peach fruit. The fungal species showed different responses to fungicides, because M. fructicola was more sensitive than M. laxa, especially to cyflufenamid, and M. fructigena revealed a lower sensitivity to succinate dehydrogenase inhibitors (boscalid, fluopyram, and fluxapyroxad) and quinone outside inhibitors (mandestrobin). In summary, the two species M. fructicola and M. polystroma were first detected in southern Italy where M. fructicola has largely displaced the two indigenous pathogens M. laxa and M. fructigena; the relative proportions of the three pathogens in orchards should be considered when defining the management of brown rot of stone fruit due to differences in their responses to fungicides.

Distribution and Characterization of Monilinia spp. Causing Apple Fruit Decay in Serbia

Brown rot, caused by Monilinia spp., is an economically important pre- and postharvest disease of pome and stone fruits worldwide. In Serbia, apple is the most widely grown pome fruit, and the distribution of economically important Monilinia spp. responsible for apple brown rot is unknown. Hence, we conducted a three year survey, from 2010 to 2012, where 349 isolates were obtained from six orchards and four storage facilities from five different apple cultivars with brown rot symptoms. Morphological characterization of the isolates, multiplex PCR, and phylogenetic analysis revealed four species: M. fructigena, M. laxa, M. fructicola, and Monilia polystroma. All species were found in the orchard and in storage, with M. fructigena predominating, followed by M. polystroma. Representative isolates were analyzed in vitro and in vivo where differences in growth rate, sporulation, and virulence on apple fruit were observed. Findings from this investigation demonstrate diversity in the species responsible for pre- and postharvest apple brown rot, which has significant implications for pathogen detection and for developing disease-specific management strategies.

Detection of Latent Monilinia Infections in Nectarine Flowers and Fruit by qPCR

Most stone fruit with a latent brown rot infection caused by Monilinia do not develop visible signs of disease until the arrival of fruit at the markets or the consumer's homes. The overnight freezing-incubation technique (ONFIT) is a well-established method for detecting latent brown rot infections, but it takes between 7 to 9 days. In this report, we inform on the advantages of applying a qPCR-based method to (i) detect a latent brown rot infection in the blossoms and fruit of nectarine trees (Prunus persica var. nucipersica) and (ii) distinguish between the Monilinia spp. in them. For applying this qPCR-based method, artificial latent infections were established in nectarine flowers and fruit using 10 Monilinia fructicola isolates, 8 M. fructigena isolates, and 10 M. laxa isolates. We detected greater amounts of M. fructicola DNA than M. laxa and M. fructigena DNA in latently infected flowers using qPCR. However, greater DNA amounts of M. laxa than M. fructicola were detected in the mesocarp of latently infected nectarines. We found that the qPCR-based method is more sensitive, reliable, and quicker than ONFIT for detecting a latent brown rot infection, and could be very useful in those countries where Monilinia spp. are classified as quarantine pathogens.

Genera of phytopathogenic fungi: GOPHY 1

Genera of Phytopathogenic Fungi (GOPHY) is introduced as a new series of publications in order to provide a stable platform for the taxonomy of phytopathogenic fungi. This first paper focuses on 21 genera of phytopathogenic fungi: Bipolaris, Boeremia, Calonectria, Ceratocystis, Cladosporium, Colletotrichum, Coniella, Curvularia, Monilinia, Neofabraea, Neofusicoccum, Pilidium, Pleiochaeta, Plenodomus, Protostegia, Pseudopyricularia, Puccinia, Saccharata, Thyrostroma, Venturia and Wilsonomyces. For each genus, a morphological description and information about its pathology, distribution, hosts and disease symptoms are provided. In addition, this information is linked to primary and secondary DNA barcodes of the presently accepted species, and relevant literature. Moreover, several novelties are introduced, i.e. new genera, species and combinations, and neo-, lecto- and epitypes designated to provide a stable taxonomy. This first paper includes one new genus, 26 new species, ten new combinations, and four typifications of older names.

One-Step Detection of Monilinia fructicola, M. fructigena, and M. laxa on Prunus and Malus by a Multiplex Real-Time PCR Assay

Brown rot is an economically important fungal disease affecting stone and pome fruit orchards, as well as harvested fruit during storage and on the market. Monilinia fructicola, M. laxa, and M. fructigena are the main causal agents of this disease and each have a different regulatory status depending on regional regulations. In this study, a new multiplex tool based on real-time polymerase chain reaction was developed to detect the three pathogenic fungi in a single reaction on fruit, twigs, and flowers of Prunus and Malus spp. Species-specific primer-hydrolysis probe combinations were designed to amplify a region located in a previously described MO368 sequenced characterized amplified region marker, and used in a quadruplex format coupled with the 18S Uni universal primer-probe test in order to check the quality of the DNA template. The assay was designed and optimized with the objective to provide high performance values. Experimental data supported its sensitivity, specificity, reproducibility, and robustness. In addition, a set of quality controls was implemented to minimize the risk of false-positive and false-negative results, thus making this new test fit for use in serial analyses and reliable in the framework of official controls.