Can an infectious diseases come from a plant?
This is a great biological question! I'm glad we encourage such questions from curious people who want to learn more about modern biology.
Much as other animals can be vectors for diseases that infect humans, plants can be vectors for pathogenic infectious agents.
You may occasionally read news stories of disease-causing strains of Escherichia coli which contaminate vegetables and force product recalls. There is currently a CDC advisory to not eat clover sprouts, as an example, because of contamination with E. coli O103, a strain which can cause a variety of health problems (including kidney damage, in severe cases).
This kind of contamination is becoming more common, largely as a consequence of how we produce food:

Fresh fruits and vegetables once were thought to be relatively free of disease-producing pathogens. In recent years, however, outbreaks of foodborne illness linked to fruits and vegetables have become more common. These outbreaks come from produce grown both in the United States and in other countries. Outbreaks have been linked to Escherichia coli O157:H7 and Salmonella on apples, lettuce, cantaloupe and sprouts; Listeria monocytogenes on cabbage and cantaloupe; Shigella on parsley and lettuce; and Cyclospora on imported raspberries.
Changes in microorganisms have undoubtedly contributed to this increase, as have changes in growing, harvesting, distribution, processing and consumption practices. Listeria monocytogenes, Clostridium botulinum and Bacillus cereus are naturally present in some soils. Their presence on fresh produce is not uncommon. Salmonella, E. coli O157:H7, Campylobacter jejuni, Vibrio cholerae, parasites and viruses can contaminate produce through raw or improperly composted manure, irrigation water containing untreated sewage or manure, and contaminated wash water. Contact with mammals, reptiles, fowl, insects and unpasteurized animal products are other sources of contamination.

Wash your fruits and veggies!