EVALUATION OF POTATO GENOTYPES TO REDEPLOYMENT FOR LATE BLIGHT (Phytophthora infestans) RESISTANCE AND AGRONOMIC PERFORMANCES AT HARAMAYA, ETHIOPIA

Abstract

Late blight, caused by Phytophthora infestans,isa major threat of potato production and productivity worldwide, including Ethiopia. The pathogen has the ability to rapidly evolve and the resistantvarieties become susceptible soon after their release. Thus, screening of large set of potato genotypes to late blight resistance is vital to sustain the productivity of the crop. This research was conducted with the objective to evaluate and estimate genetic variability of potato genotypes for late blight resistance and morpho-agronomic traits, and determine the association of tuber yield, yield-related traits and genotypes reaction to late blight disease. 68 genotypes were evaluated in augmented design with eight blocks at Raare research field of Haramaya University in 2021. Results revealed that genotypes showed significant differences for all traits, except number of leaves and main stems. The test genotypes and check varieties (Bubu, Belete, Gudanie, and Jarso)had also significant differences for all traits, except days of late blight appearance, days to maturity, and average tuber weight. The total (TTY) and marketable (MTY) tuber yield of genotypes ranged between 10.66 and 33.80 t ha–1, and 9.93 and 31.97 t ha–1, respectively. The best performing check variety Belete had 25.21and 21.67 t ha–1TTY and MTY, respectively, and CIP- 388370-12B, CIP-386029-10A, Al-667, CIP-392640-541, CIP-388370-12A, CIP-90162-3, CIP- 383032-15, AL-560, Al-436-1, Al-624-33, Al-624-9, CIP-377838-12, Al-601, CIP-391058-558, CIP-396036-201, and CIP-395017-242 new entries produced higher TTY and MTY than the best performing check variety. Late blight appeared early at 43 days after planting (DAP) on Jarso farmers cultivar and late at 59 DAP on CIP-377808-10A. Percent severity index (PSI) and area under disease progress curve (AUDPC) ranged from 31.45 to 100% and 569.23 to 1704.79%-days in that order. Disease progress rate (r) ranged between 0.024 and 0.158 units day–1. Bubu,and Belete varieties and other 16 genotypes showed moderate resistance to late blight, and reported as MR to late blight. The PSI and AUDPC had negative and significant genotypic correlation coefficient with days to maturity, plant height, average tuber weight, TTY and MTY, but had positive and significant genotypic correlation coefficient with unmarketable tuber yield. Phenotypic and genotypic coefficients of variation ranged from 2.38 to 48.73% and 1.71 to 15.8%, respectively, whereas heritability in broad sense and genetic advance as percent of the mean ranged from 10.52 to 96.5% and 2.49 to 28.8% in that order of presentation. The first principal component (PCs) axis explained 71.67% of genetic variation; of which, PC1 had the largest share of 45.48%. Total and marketable tuber yields, PSI and AUDPC in PC1, unmarketable tuber yield in PC2 and number of tubers per hill in PC3 had the largest contribution. The Euclidean distances (D2) of all possible pairs of genotypes ranged from 0.80 to 9.2 and based on D2 matrix, the 68 genotypes were with the mean, standard deviation and coefficient of variation having the values of 4.44, 1.52 and 34.28%, respectively.Genotypes were clustered based on D2, and cluster I consisted of 31(45.58%) genotypes and the other eight clusters consisted of 1 to 9 genotypes. MR varieties (Bubu and Belete) were grouped in Cluster I. The mean of genotypes in this cluster was greater than grand mean of genotypes for agronomic traits but had PSI and AUDPClower mean than mean of genotypes. This suggested further evaluation of genotypes in Cluster I to develop varieties resistant to late blight and high yield.The PSI and AUDPC had high heritability coupled with high genetic advance suggested selection of genotypes based on phenotypic observation was efficient.This indicated not only from recently developed genotypes but also there is the high chance of selection of resistant genotypes produced before 35 years from true potato seed. Therefore, the 16 genotypes exhibited lower disease severity (moderately resistant), so that these genotypes could be recommended for cultivation and further breeding utilization