Genetic Diversity, Transmission and Understanding of Seed-Borne Viruses and Phytoplasma

Seed-borne plant viruses and phytoplasma are the major constraints in reducing the yield of many agricultural and horticultural crops worldwide. In this chapter, we have discussed about the genetic diversity, transmission and distribution of some plant viruses and phytoplasma originating from different geographical locations. At present, more than 200 plant viruses, phytoplasma and viroids are known to be seed-transmitted of which most of them were reported from crops belonging to Leguminosae family. Seed-transmitted viruses were reported from various genera including Poty-, Tospo-, Begomo-, Nepo-, Crypto-, Ilar-, Tobamo-, Potex-, Como-, Carla-, Carmo-, Cucumo-, Sobemo-, Furo-, Bromo- and Tymoviruses. Besides seed-transmission, more than 100 viruses are known to be transmitted through vegetative planting materials in different crops. Although the rate of infection due to seed-borne viruses is less as compared with those viruses transmitted by different insect vectors, the seed-borne viruses cause enormous quality and economic losses in various crops ranging from 4 to 100%. To manage these seed-borne viral diseases, understanding about their spread and population structure of viruses is very much required. In view of this, certain seed-borne viruses including Cucumber mosaic virus (CMV), Pea seed-borne mosaic virus (PSbMV), Soybean mosaic virus (SbMV), Zucchini yellow mosaic virus (ZYMV) and some viruses propagated through vegetative cuttings including Sugarcane mosaic virus (SCMV) and Sugarcane yellow leaf virus (SCYLV) have been discussed in this chapter.