Resistance to Viruses in Potato

The European cultivated potato (Solanum tuberosum ssp tuberosum) is a self-compatible outbreeding tetraploid species (2n = 4x = 48) and ranks fourth after wheat, rice and maize in terms of importance to human nutrition. It was introduced into Europe in the late 16th century from the Andes of South America and later transported to the rest of the world. By the end of the 18th century, it had been adapted to long-day conditions through selection by its early cultivators for early-tubering and high yields. Potato is susceptible to a wide range of fungal, bacterial and virus diseases as well as various insect and nematode pests. As its importance as a staple food crop increased, so did problems associated with its clonal means of multiplication, notably caused by various virus diseases, described as a degeneration of seed tubers due to ‘the curl’ (reviewed by Salaman, 1926). In time it was realized that some of the viruses were transmitted by aphids. This led to the development of seed industries in many countries where highgrade virus-free seed tubers were produced in areas that are climatically and geographically suitable with regards to isolation from sources of infection and reduced numbers of virus vectors.