It’s difficult to control potato late blight
In the early 20th century, the breeder found that hexaploid S. demissum had resistance genes (R genes)
and could directly cross with tetraploid S. tuberosum. So it was considered as the main resistance
resource, and 11 R genes (R1-R11) have been introgressed into potato cultivars[2]. But resistance
breakdown was found in cultivars carrying one or few R genes in monoculture, and P. infestans isolates
that could infect all specificities of 11 R genes were occasionally found[4]. Disappointed by the nondurable
resistance of the S. demissum R genes, researchers and breeders either turned to other species for
durable R genes [7-11], or adopted so-called ‘R-gene-free’ approaches to explore partial resistance [12-
13]. However, both alternatives appeared to be problematic: sexual barriers made the flow of R genes
from other wild species time-consuming and partial resistance was often unfavorably linked to late
maturity and low vigor [14-15]. For example, Dutch breeder utilized double bridgecrossing using S.
acaule (2n=4x=48) and S. phureja (2n=2x=24) to introgress late blight R genes from S. bulbocastanum
(2n=2x=24) into S. tuberosum, and in early 1970’s this resulted in the ABPT clones[11]. It was not until
2004 that the first potato cv. Biogold (Van RijnBV) carrying gene(s) from the ABPT clones was released,
but unfortunately these materials were overcome less then one year.