Bacterial wilt resistance from Solanum tuberosum + S. commersonii somatic hybrids

This work reports the first successful transfer of bacterial wilt resistance from Solanum commersonii into the potato background. Bacterial wilt, caused by Ralstonia solanacearum, is an important potato disease but there are few sources of wilt resistance available to breeders. The wild S. commersonii is sexually incompatible with S. tuberosum, but possesses several desirable agronomic traits. It was reported to possess some wilt resistance. To overcome sexual incompatibility, protoplasts from the two species were fused to produce vigorous somatic hybrids, but the fertility and resistance levels of these somatic hybrids were unknown.Through a series of crosses, we determined that the somatic hybrids are male and female fertile, and they are self-compatible. More importantly, they are sexually compatible with S. tuberosum. We successfully backcrossed cultivated potato lines twice with a bacterial wilt resistant S. tuberosum + S. commersonii somatic hybrid.We tested six somatic hybrids and two backcross populations for bacterial with resistance. All somatic hybrids were more resistant than the potato cultivars we tested, and resistance segregated in the backcross populations. Full S. commersonii wilt-resistance levels were recovered in both BC1 and BC2 populations.Disease tolerance and strain specificity of resistance are epidemiologically important. Tolerant plants can produce latently infected seed potatoes, which are significant means of disease spread. Strain specificity limits resistance usefulness to areas devoid of compatible pathogens. We measured bacterial colonization of stems and found that under our experimental conditions, none of the lines were tolerant of large bacterial populations in their vascular system, regardless of resistance level. We challenged the resistant S. commersonii and susceptible cv. Superior with genetically diverse strains of R. solanacearum. The resistance was overcome by two strains of Race 1 Biovar 1 (R1Bv1), but withstood 10 other strains, including two more R1Bv1 strains. Thus, like resistance from other potato species, resistance from S. commersonii is strain-specific however, S. commersonii resistance withstands genetically diverse strains of R. solanacearum.