Virus Diseases

A review of the scientific literature reveals that little potato breeding has been undertaken for resistance to virus diseases. The reason is fairly simple. Single-gene resistances to these diseases are relatively rare, and even when they exist, they provide unstable resistance. It was also argued that the use of certified seed potatoes made their development unnecessary. There was also a fear that their development would damage the certified seed industry. Additionally, potato breeders were not working with quantitative resistance. Virus diseases spread relatively slowly in a screening population, and any plant that got a virus diseases would be discarded, on the grounds that it was susceptible. The potato seedlings that were kept were not resistant, however. They were all susceptible 'escapes'.

Consequently, there is immense scope for amateur potato breeders to produce cultivars that are largely unaffected by these viruses, or any other tuber-borne diseases. Farmers can then keep some of their own harvest for seed. This would reduce the costs of potato production enormously. The certified seed potato industry would then be reduced to providing elite seed stocks of new cultivars, certified as to identity and purity of variety only. Anyone who doubts that this is possible should visit Kenya, where some potato cultivars have been grown for more than sixty vegetative generations without any renewal of seed stocks.

The major seed tuber-borne diseases are:

Potato Leaf Roll Virus. Insect transmitted by Myzus persicae and other aphids. The leaves roll into cup shapes, even cylinders, and become brittle.

Potato Virus X. Mechanical transmission.

Potato Virus Y. Also known as 'Leaf Drop Streak'. Main spread in field is by Myzus persicae but also sap-transmissible.

Spindle Tuber Viroid. Transmitted in true seed.

Other Potato Viruses. Generally unimportant.

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