Identification and Characterization of Penicillium spp. Associated with Storage Rot of Sugar Beet in the Red River Valley of Minnesota and North Dakota, USA

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Sugar beets produced in the Red River Valley of Minnesota and North Dakota, USA are stored in large outdoor piles or sheds for up to 280 days before processing into sugar. During storage, roots often succumb to postharvest rots which reduce the yield of recoverable sucrose from the roots. Penicillium spp. are commonly responsible for postharvest sucrose loss, although the species responsible for postharvest rots and the frequency in their ability to establish infection are largely unknown for this production region. To determine the Penicillium species responsible for storage rot in the Red River Valley, Penicillium isolates were obtained from rotted roots that were collected from storage piles located throughout the Red River Valley in Minnesota and North Dakota after variable times in storage. Morphological characterization and molecular identification of species using the DNA sequence of the internal transcribed spacer (ITS), β-tubulin (tub2), and RNA polymerase II second largest subunit (rpb2) regions of the pathogen genome indicated the presence of four Penicillium species in sugar beet root piles. The four Penicillium strains were identified, in order of their prevalence in piles, as P. cellarum, P. paneum, P. crustosum, and P. polonicum. Regional variations in the distribution of Penicillium species were noticed. Inoculation of healthy roots with isolates of all four Penicillium species caused storage rot symptoms resembling those observed on storage roots from which the Penicillum species were isolated. While P. cellarum has been previously identified in U.S. storage piles, this is the first report of P. paneum and P. crustosum as causal organisms of sugar beet storage rot in the U.S. These findings will be useful for the identification of the pathogens present in the storage piles and the formulation of disease management practices to control the storage rot of sugar beet.