Occurrence of fungal pathogens of carrots on wooden boxes used for storage

Infested wooden boxes, previously used for carrot storage, were sampled in four commercial carrot production farms in Bradford Marsh, Ontario, and screened for fungal occurrence. At least 128 and 465 fungal isolates were recovered from these boxes in 2001 and 2002, respectively, and were classified into 10 taxonomic groups, including Alternaria spp., Aspergillus spp., Botrytis cinerea , Fusarium spp., Mucor spp., Penicillium spp., Rhizoctonia carotae , Rhizopus spp., Sclerotinia sclerotiorum and Trichoderma spp. A subsample of 27 putative pathogenic isolates was further tested for the ability to cause disease on carrots and to colonize wood surfaces under growth room and cold storage conditions. Approximately 60% of the taxa growing on wood caused lesions upon contact with intact carrots in cold storage. Isolates of S. sclerotiorum , B. cinerea and R. carotae caused the most severe diseases, developed most extensively on wooden surfaces in cold storage, and represented 12% of the recovered fungi. Isolates of Alternaria spp., Aspergillus spp., Fusarium spp., Mucor spp., Penicillium spp., Rhizopus spp. and Trichoderma spp. caused negligible or no disease on carrots and represented 88% of recovered fungi. Several of these fungi, however, showed potential to colonize wooden surfaces and cause disease on sliced carrots. This study suggests that pathogenic inocula occurring on used wooden boxes can initiate disease upon contact with healthy carrots and reusing infested boxes can affect carrots in storage.