Location: Food Quality Laboratory2018 Annual Report
1a. Objectives (from AD-416):
Objective 1: Identify key genes regulating virulence and toxin production in Penicillium species, the causal agents of blue mold, to develop novel gene or protein targets for control in commercially stored pome fruit. Sub-objective 1.A: Identify new Penicillium spp. virulence and toxin biosynthetic genes via comparative genomics and transcriptomics. Sub-objective 1.B: Characterize fungal virulence and toxin genes in Penicillium spp. using a targeted gene deletion approach. Objective 2: Integrate genomic-based strategies and evaluate novel tools to manage postharvest blue mold decay in commercial storage caused by Penicillium species on pome fruit. Sub-objective 2.A: Determine difenoconazole baseline sensitivity and characterize resistant blue mold isolates. Sub-objective 2.B: Identify Penicillium spp. genes associated with difenoconazole resistance and develop a molecular-based detection system.
1b. Approach (from AD-416):
Multiple approaches are outlined in this project that encompass both basic and applied methodologies to maintain pome fruit quality, deliver effective strategies to manage blue mold decay, and eliminate mycotoxins from processed pome fruit products. Comparative genomics and transcriptome sequencing will be used to discover new fungal virulence genes and pathways that regulate Penicillium spp. virulence, and toxin production to develop pathogen-specific management strategies. Additionally, mechanisms of postharvest fungicide resistance in Penicillium spp. will be determined using a genomics approach to develop molecular-based management tools for producers. Our applied research focus will utilize standard microbiological methods to determine baseline sensitivity to a new postharvest fungicide currently used to manage blue mold decay and will help producers monitor future shifts in sensitivity indicative of resistance. Characterization of fungicide-resistant isolates will provide practical information on the viability and persistence of such isolates in the packing and storage environments and their impact on control using currently available chemical tools labeled for pome fruits. Results from the current study will also guide growers in making decisions for use of the most efficacious fungicides to control blue mold.
3. Progress Report:
We have accomplished the following research progress during FY18 for both objectives in the parent project plan. Efforts to determine genetic factors regulating fungal virulence in the blue mold fungus are underway. Using molecular methods, new genes have been identified in P. expansum mutants with virulence defects in apple. We have assessed multiple processes that affect pathogen survival, reproduction, and fitness using select P. expansum mutants. Comparisons between P. expansum (R19) and P. solitum (RS1) genomes have yielded the identity of unique genes between the species. Additionally, a comparative proteomics study using mutant and wild type strains has been performed to elucidate the roles of secreted proteins in fungal virulence during apple fruit decay. Evaluation of novel tools to reduce blue mold decay during storage of apple fruit are in progress. Ninety-Seven Penicillium spp. isolates, previously unexposed to difenoconazole, have been characterized genetically, morphologically, and in vivo on apple fruit. Cross resistance between difenoconazole and active ingredients in other postharvest fungicides have been tested along with parameters critical for pathogen survival in the storage environment. Efficacy of a new postharvest fungicide to control Penicillium spp., including multiple postharvest fungicide resistant P. expansum isolates, have been executed using conditions that mimic commercial storage. Progress has been made to integrate genomic-based strategies and evaluate new approaches to abate blue mold decay in storage using a Penicillium expansum isolate with corresponding genome sequence. We have examined physical (steam) and chemical (postharvest fungicides, natural products) treatments that were beneficial at killing blue mold spores (at different inoculum levels) on wooden and plastic crates. Reduction in spore loads also corresponded with significant reductions in blue mold when apples were inoculated with spores recovered from treated bin surfaces.
1. Characterization of apple rot fungi in Serbia. Apples are one of the main tree fruits produced, stored, and exported in Serbia. The fruit are kept for several months without the use of postharvest fungicides. Hence, fungal diseases reduce quality and contribute to food waste. A multi-year study to identify and characterize apple decay-causing pathogens was conducted. ARS researchers in Beltsville, Maryland, in collaboration with the University of Belgrade, sampled apples for 3 years from 7 different locations. Four species of fungi were found, including one that is a quarantine species in North America and Australia, and a molecular diagnostic test was developed. Findings from this study aid in pathogen detection to prevent movement of quarantine species and provides baseline data on pathogen diversity in Serbia that contributed to development of disease-specific management strategies to maintain apple fruit quality in storage.
Dejonge, R., Ebert, M., Huitt-Roehl, C., Pal, P., Suttle, J.C., Spanner, R.E., Neubauer, J., Jurick II, W.M., Stott, K.A., Secor, G.A., Thomma, B.P., Van De Peer, Y., Townsend, C.A., Bolton, M.D. 2018. Gene cluster conservation provides insight into cercosporin biosynthesis and extends production to the genus Colletotrichum. Proceedings of the National Academy of Sciences. 115(24):E5459-E5466.