Potato genotypes from a breeding population adapted to tropical highlands were analyzed for the stability of late blight resistance and also for marker-phenotype association. We harmonized the historical evaluation data, consisting of observations spanning 6 years from two field sites utilizing a resistance scale constructed by comparing the area under the disease progress curve (AUDPC) values of 172 genotypes with that of susceptible control ‘Yungay’. In total, 70 potato genotypes had a coefficient of variability <0.5 and were considered stable across the environments tested. A principal component analysis demonstrated that the ensemble of experiments formed two distinct groups that reflect the stability of genotype resistance to late blight. Phytophthora infestans isolates present in the experimental fields belonged to the EC-1 clonal lineage and showed variation in virulence beyond the concept of the avirulence determined by the conventionally used R1-R11 differential set. A single-nucleotide polymorphism (SNP) marker on chromosome 9 was associated with late blight resistance and linked to instability. Genotypes with either AACC or AAAC combinations for this SNP were highly resistant only in some environments, while the genotypes with the AAAA combination had more moderate levels of resistance but were stable across environments.

Recurrent drought and late blight disease are the major factors limiting potato productivity in the northwest Ethiopian highlands. Incorporating drought tolerance and late blight resistance in the same genotypes will enable the development of cultivars with high and stable yield potential under erratic rainfall conditions. The objectives of this study were to assess combining ability effects and gene action for tuber yield and traits related to drought tolerance in the International Potato Centre’s (CIP’s) advanced clones from the late blight resistant breeding population B group ‘B3C2’ and to identify promising parents and families for cultivar development. Sixteen advanced clones from the late blight resistant breeding population were crossed in two sets using the North Carolina Design II. The resulting 32 families were evaluated together with five checks and 12 parental clones in a 7 x 7 lattice design with two water regimes and two replications. The experiment was carried out at Adet, in northwest Ethiopia under well-watered and water stressed conditions with terminal drought imposed from the tuber bulking stage. The results showed highly significant differences between families, checks, and parents for growth, physiological, and tuber yield related traits. Traits including marketable tuber yield, marketable tuber number, average tuber weight and groundcover were positively correlated with total tuber yield under both drought stressed and well-watered conditions. Plant height was correlated with yield only under drought stressed condition. GCA was more important than SCA for total tuber yield, marketable tuber yield, average tuber weight, plant height, groundcover, and chlorophyll content under stress. This study identified the parents with best GCA and the combinations with best SCA effects, for both tuber yield and drought tolerance related traits. The new population is shown to be a valuable genetic resource for variety selection and improvement of potato’s adaptation to the drought prone areas in northwest Ethiopia and similar environments.

Potato virus Y (PVY) and Phytophthora infestans (Mont.) de Bary that causes potato late blight (LB), pose serious constraints to cultivated potatoes due to significant yield reduction, and phenotyping for resistance remains challenging. Breeding operations for vegetatively propagated crops can lead to genotype mislabeling that, in turn, reduces genetic gains. Low-density and low-cost molecular marker assessment for phenotype prediction and quality control is a viable option for breeding programs. Here, we report on the development of kompetitive allele specific PCR (KASP) markers for LB and PVY resistance, and for routine quality control assessment of different breeding populations. Two KASP markers for LB resistance and two for PVY Ryadg were validated with an estimated assay power that ranged between 0.65 and 0.88. The developed QC KASP markers demonstrated the capability of discriminating tetraploid calls in breeding materials, including full-sibs and half-sibs. Routine implementation of the developed markers in a breeding program would assist with better allocation of resources and enable precise characterization of breeding material, thereby leading to increased genetic gains.