Final answer:
The most likely group of fungi causing the disease is Basidiomycota.
Step-by-step explanation:
The plant breeder Shelby is trying to identify the cause of a disease in a plant. The given information states that the organism reproduces through spores and has reproductive structures.
Based on this information, the most likely group of fungi causing the disease is Basidiomycota. Basidiomycota is a phylum of fungi that include mushrooms, rusts, and smuts. They reproduce sexually through basidia, which produce basidiospores.
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