In vitro microtuberisation of two improved Ugandan Solanum potato varieties

Abstract

The performance of explants derived from three and six week-old green house-grown potato (Victoria and Kisoro) mother plants was evaluated. The mother plants were fertilized with different combinations of nitrogen, phosphorus, and potassium fertilizers. Explants were cultured on modified Murashige and Skoog's(MS) basal salts, supplemented with appropriate vitamins and growth regulators, for shoot and microtuber induction. Microtubers were induced directly from nodal cuttings inoculated on tuberisation medium and from defoliated in vitro shoots previously grown on shoot propagation medium, before transfer onto the tuberisation medium. In vitro shoot length and node number were significantly (P<0.05) increased by sole N application and retarded by sole P, or K application. Application of N along with P or K showed intermediate effects, but improved shoot growth. Single N application was inimical to microtuber forn1ation, whereas P and K promoted early tuberisation, characterised with significantly (P<0.05) laql'e diameters and fresh weights. Victoria produced bigger and fewer microtubers than Kisoro. Increased number of micro tubers occurred due to combined application ofN,P and K. Microtubers derived from defoliated in vitro shoots showed no significant (P>O.OS) difference in size due to mother plant pre-treatment, unlike the number of microtubers per explant. The six week-old nodal cuttings barely regenerated (5-15%) on the tuber induction medium, and had 30-70% regeneration on shoot induction medium. Better regeneration (60-70%) occurred in theN fertilized mother plants than with P and K (30-50%). Microtubers derived from defoliated in vitro shoots. irrcspecth·e of genotype and pre-treatment produced very few, tiny microtubers and others did not tuberize. Attempts to chemically break dormancy using gibberellic acid gave eratlc results. No significant variation was observed between the conventional mother clones and the in vitro cultures and microtubers.