ABSTRACT
Plant pathogens may be disseminated/transmitted in different ways. Fungal and bacterial pathogens may be disseminated largely by wind or water and in some cases with the help of insects. Viruses and phytoplasmas on the other hand, predominantly depend on vectors such as insects, mites, nematodes, and fungi for their natural spread under in vivo conditions. The infected seeds or vegetatively propagated seed materials form the most important primary sources of infection, irrespective of the nature of the pathogen. The infected seeds/seed materials may exhibit some symptoms or show the presence of the fungal or bacterial pathogens when incubated. But infection of seeds by viruses or viroids or phytoplasmas may not be discernible, unless special methods of detection are employed. Transmission of some of the viruses and viroids through pollen, leading to seed infection, is also recognized.
