Genetic Variability in Potato (Solanum tuberosum L.) Genotypes for Late blight [Phytophthora infestans (Mont.) de Bary] Resistance and Yield at Haramaya, Eastern Ethiopia

Late blight (Phytophthora infestans de Bary) is the most important and destructive disease of potato (Solanum tuberosum L). The pathogen has the ability to rapidly evolve and overcome resistance genes, leading commercial potato varieties to succumb to it too soon. As a result, evaluation of commercial potato varieties for resistance should not be a one-time task, but a routine breeding activity. This study was, therefore, conducted to determine the genetic variability of potato varieties in terms of resistance to the late blight disease and yield potential during the 2013/14 cropping season under natural epiphytotic conditions. A total of 21 potato genotypes (Alemaya 624, Araarsaa, Belete, Bubu, Bulle, Chala, Chiro, CIP-384321/3A, CIP-384321/3B, Gabbisa, Gera, Gorebela, Guasa, Gudanie, Jalanie, Jarso, Mara Charre, Moti, and Zemen) were evaluated using a randomized complete block design (RCBD) with three replications. The genotypes showed highly significant (P < 0.01) differences in reaction to the disease (disease intensity, severity, score and AUDPC) and yield potential. Only three varieties (Bubu, Belete and Bulle) were found to be resistant to the disease, with other three varieties (Gera, Araarsaa, and Mara Charre) being moderately resistant. The remaining 15 varieties (Al-624, Badhasa, Batte, Chala, Chiro, CIP-384321/3A, CIP-384321/3B, Gabbisa, Gorebela, Guasa, Gudanie, Jalenie, Jarso, Moti, and Zemen) were found to be susceptible to the disease. The highest marketable tuber yields ranging from 32.89 to 35.85 t ha-1 were recorded for Bubu, CIP-384321/3A, CIP-384321/3B, and Gudanie whilst the lowest marketable tuber yields ranging from 5.04 to 11.85 t ha-1 were recorded for Batte, Guasa, Jarso, Moti and Zemen. The marketable tuber yields of the other varietis lay variably in the intermediate ranges. High broad sense heritability (H2) (47.78 to 91.02%) and genetic advance in percent mean (GAM) (58.87 to 96.31%) were computed for both disease and yield parameters. High genotypic and phenotypic variances were recorded with low magnitude of differences for all parameters, and the environmental variance was much lower than the two other variances. Strong and positive genotypic and phenotypic correlations were observed among the disease score parameters and unmarketable tuber yield while strong and negative correlations were observed between disease score and the two yield parameters (total and marketable tuber yields). This indicated that the traits are highly heritable with the involvement of more additive gene action and are amenable for selection. The dendrogram of the 21 potato genotypes using Unweighted Pair-group Method with Arithmetic means (UPGMA) analysis and Euclidean distances separated the genotypes into three clusters and four sub-groups where resistant and moderately resistant varieties with high yield potential were grouped into Cluster I (Belete, Bubu, Gera, Mara Charre, and Bulle) while Gudanie, CIP-384321/3-A, and CIP-384321/3-B were grouped into Cluster II. All susceptible and low yielding genotypes were grouped into Cluster III. The resistant varieties were found to be the most distant from many of the genotypes but were closer to each other. However, genetic similarities were observed among the susceptible genotypes. In conclusion, the results of the study have revealed that the potato varieties markedly varied in resistance to the late blight disease as well as in yield potential. The genetic variability and the high heritability, coupled with high genetic gain of the traits, indicate the potential of improving the crop for disease resistance and yield through selection. The results have also demonstrated that farmers could profitably cultivate the resistant and moderately resistant high-yielding potato varieties under rain-fed conditions with limited integrated management efforts against the disease.Keywords: AUDPC (Area under Disease Progress Curve); Broad sense heritability; Euclidean distance; Genetic distance; Genetic variability; Varietie