The spore fungus, (Phytophthora infestans) is a microorganism that causes the potato disease known as dry rot. The egg spore fungus is still the most devastating disease for potatoes worldwide. Many wild-type potatoes have higher resistance to P. infestans than cultivated potatoes. This resistance to the disease originates from certain genes which are generally called R genes in potatoes. These ´R´ genes are also used for bioprospecting. New species or cultivated potatoes with R genes can create new opportunities for genetic modification. In the last two decades, several different R genes have been discovered and tested.
19 different incidents have been recorded with potatoes where disease resistance stems from genetic modifications, four of which are against dry rot (P. infestans). One is the potato SP951 (Solanum tuberosum L.). Three other potatoes registered with genetic modification for resistance to late blight (P. infestans var.) are; W8, X17, Y9.
A gene for resistance to dry rot has been identified in the wild-type potato (Solanum bulbocastanum). The gene was isolated and introduced via bacterium (Agrobacterium tumefaciens) into the potato Katahdin (Solanum tuberosum). The RB gene from S. bulbocastanum was inserted into Katahdin, and has been genetically modified and developed to be able to form new resistant hybrids.
The potato SP591 with an inserted RB gene from the potato (S. bulbocastanum) has been tested against different varieties of P. infestans in different countries in 2017. In Bangladesh, a genetically modified Katahdin has been crossed with the varieties Kardinal and Diamant. Also in West Java, Katahdin SP904 and SP951 were tested with the RB gene. These potatoes showed little sign of resistance to the P. infestans variant.
The genetically modified potato Katahdin has also been crossed with the varieties Granola and Atlantic in the Philippines. These cultivated potatoes and many others inserted with the R gene were apparently defeated by an evolution over time of matching virulences of P. infestans.
In the USA, the company Simplot has developed three different lines with an inserted Rpi-vnt1 gene. These lines have the names W8, X17 and Y9 and all three originate from the potato (Solanum venturii) which has had the gene Rpi-vnt1 inserted to form a product with "late blight resistance protein". This is a genetic modification to give their potatoes resistance to dry rot.
There are several species of wild-type potatoes with resistance to P. infestans infection. Genes that contribute to resistance have been identified and isolated from e.g. S. bulbocastanum, S. pinnatisectum, and S. venturii. The R gene from these will work to varying degrees and are dependent on the different types of potatoes into which they are inserted.
GMO-free hybrids such as Sarpo mira tested in Ireland have proven to be as resistant as a GMO potato with an inserted R gene. Phytophthora infestans HERB 1, was the cause of the famine in Ireland around 1847. Repeated waves of infectious P. infestans destroyed all the potato crops and led to approx. one million deaths and displaced around two million from their lands.