Conventional breeding of potatoes for resistance to bacterial wilt (Ralstonia solanacearum): Any light in the horizon?

Potato (Solanum tuberosum L.) is the third most important food crop in the world after wheat and rice while bacterial wilt is the second most important disease of potatoes after late blight. In high latitudes and high altitudes in the tropics, bacterial wilt is caused by race 3/biovar 2A (R3bv2A) (phylotype IIB, sequevar 1) while in the tropical lowlands, the disease is caused mainly by race 1 and biovar 2T. Control of bacterial wilt has proven to be very difficult. Breeding for resistance has been going on for long in many places such as the International Potato Center (CIP), University of Wisconsin, Brazilian Agricultural Research Corporation (Embrapa Hortaliças, Brazil), Uruguay and Peru. Classical breeding has achieved moderate unstable level of resistance/tolerance due to host-pathogen-environment interaction. In addition, hybridisation of the cultivated potato with the wild relatives have showed wild traits such as high glycoalkaloid content in addition to moderate levels of resistance to bacterial wilt. In recent years, genetic engineering for disease resistance has been employed such as the use of potent antimicrobial peptides and pattern recognition receptors. However, most of this work is in experimental stages. The purpose of this review is to document the progress made in breeding for resistance to bacterial wilt of potatoes. Though great strides have been made, there is still a long way to go before varieties with stable resistance coupled with good agronomic characteristic are released. There is light in the horizon though a bit far.