APPLICATION OF GAMMA INDUCED MUTATION IN BREEDING FOR BACTERIAL WILT (Ralstonia solanacearum) DISEASE RESISTANCE IN POTATO (Solanum tuberosum L.)

Abstract

Potato (Solanum tuberosum L.) is the second most important staple food crop in Kenya after maize and fourth in the world, therefore, plays a vital role in food and nutrition security, and sustainable development. Despite its importance, potato production in Kenya is still low due to biotic and abiotic constraints. Of the biotic factors, bacterial wilt in potato is regarded an important disease causing significant yield decline of about 50 to 100 %. It has been reported to affect 77 % of the potato farms in Kenya. Breeding for resistant varieties can play an important role in managing the disease. However, improvement of potato through conventional breeding has been difficult due to the narrow genetic diversity of the crop. Desired genetic variations could be generated through the application of induced mutations from which putative mutants can be selected. The objective of this study was to induce mutation on potato varieties to create variation and identify desirable allelic variants of genes underlying important quantitative traits. The study involved irradiation of three commercially grown high yielding Kenyan potato varieties: Asante, Kenya Mpya and Kenya Sherekea. A total of 570 mutant microtubers were developed using gamma rays from Co60 source under different dose rates (0 – 30 Gray) for the three varieties. The microtubers were then established at M1V1 and developed to M1V2, M1V3, and M1V4 generations at the University of Eldoret. The mutant populations were assessed for morphological, ploidy and genetic diversity. Bacterial wilt resistance screening was carried out at M1V4 generation at KALRO-Kabete station using alpha lattice design. The results showed that the total number of irradiated potato mutants that survived to produce tubers at the M1V1 stage was less than half for each genotype that was initially irradiated in all dosage rates across the three genotypes used. The highest tuber weight was at dosage rates 9 Gy in Asante (22.0 and 57.0 tons/ha), 15 Gy in Kenya Mpya (31.0 and 46.8) and 10 Gy in Kenya Sherekea (48.4 and 49.0) at M1V2 and M1V3 generations respectively. The number of ploidy level distribution was decreasing in diploids and triploids and were increasing in tetraploids from M1V1, M1V2 to M1V3 in all the three potato mutant populations. The reactions of potato mutants to bacterial wilt were varied and there was significant difference in selected agronomic traits and bacterial wilt resistance among varieties and between families of individual varieties. The days to onset of wilting, area under the disease progress curve and percentage of symptomatic tubers of total tuber number per ha was significantly different in all the three potato mutant populations. The genetic variability of the potato mutants showed that 20 SSR primers were polymorphic with 211 alleles (average eleven), Asante, Kenya Mpya and, Kenya Sherekea generating 69, 75 and 67 alleles respectively. The dendrogram and PCoA analyses showed that the 160 potato mutants and three parents were clustered into three groups, though the STRUCTURE analysis supported by the dendrogram confirm that each sub-population affiliate gave six clusters. Success in the use of gamma-induced mutation in the development of new varieties was observed and will lead to improved potato production, which will respond to enhanced food and nutrition security. The information from this study will inform potato variety release for commercial production and sustainable development and for future potato breeding programme.