Management strategies for breaking tuber dormancy in potato

Abstract

This study was aimed at breaking potato tuber dormancy to facilitate their use as seed potatoes immediately after harvesting. Six genotypes out of 22 were selected in a screening trial based on their dormancy period to investigate the effect of plant growth regulators, i.e. benzyl amino purine or gibberellic acid or both, cold pre-treatment, electric current and irradiation on breaking tuber dormancy and subsequent field evaluation. The sprouted genotypes were categorized into short, medium and long dormant groups. Their weight, sprouting behaviour, antioxidative enzymes, hydrogen peroxide contents, hormonal contents and sugar contents were analysed at one week and three week intervals after subjecting tubers to dormancy breaking methods. This investigation was carried out using completely randomized design (CRD) under factorial settings. Among PGRs, 60 mgL-1 BAP and its combination with 20 mgL-1 GA3 most effectively reduced the dormancy duration. Gibberellic acid produced maximum sprout length with concentration 20 mgL-1 but was statistically comparable to effect of combined application of 60 mgL-1 BAP and 20 mgL-1 GA3. The interaction of PGR × genotype was more pronounced in short-term and medium-term dormancy genotypes and less pronounced in long-term dormancy genotypes. The cold pre-treatment had the greatest effect at 2°C for breaking tuber dormancy and inducing sprout length. However, use of electric current was most effective at 80 volt to shorten tuber dormancy and develop longest sprout. Irradiation proved to be most effective at highest dose, 3.5 kGy. Hydrogen peroxide contents and superoxide dismutase and ascorbate peroxidase activities after treatment with PGRs, low temperature, electric current and irradiation increased from first week to the third week of storage. In contrast, catalase and peroxidase activities were decreased. In hormonal contents, zeatin increased and GA1 and ABA decreased during the storage period of three weeks. The increase in sugar contents with passage of storage time was observed in selected genotypes. Overall, two-way interaction, genotype × storage period was significant for the observed attributes i.e. antioxidative activities and hormonal and sugar contents. The field experiment was conducted with factorial arrangement based on randomized complete block design using three replications. Various physical (days to emergence, emergence percentage, leaf area and number of stems and tubers per plant), physiological (Photosynthetic rate, transpiration rate and stomatal conductance) and biochemical attributes (chlorophyll contents in leaves, specific gravity and tuber dry matter) were studied during the crop growth period. The individual 2

effects of dormancy breaking methods and genotypes were significant (p<0.05) for days to emergence, emergence percentage, number of stems and tubers per plant and leaf area. The combined effect of dormancy breaking methods and genotypes was however nonsignificant. The main and interactive effect of dormancy breaking methods and genotypes significantly affected the plant photosynthetic rate, transpiration rate and stomatal conductance; also the biochemical constituents i.e. leaf chlorophyll contents, tuber specific gravity and tuber dry matter contents. The last experiment involved assessment of relationship between true seed and tuber dormancy in a Solanum tuberosum group phureja - stenotomum hybrid population. The 12 random crosses were selected for this study. For the study of tuber dormancy, parental genotypes were harvested from three different locations Presque Isle, Maine; Plymouth, North Carolina and BARC, Maryland; and kept in cold store of BARC, Maryland, USA at 7 °C. Parental tuber dormancy ranged from 6-10+ weeks. TPS seedling vigor ranged from 9 to 94.2%. The seedling vigor index of all the progenies obtained from the long dormant parent was lower except WHD-7 had the higher value of seedling vigor index with both parents were long-dormant. No correlation (r = 0.01) was found between parental tuber dormancy and seedling vigor index. So, for the selection for early sprouting, offspring in-vitro needs to correlate with short tuber dormancy in subsequent field generations. Overall, from this study we can draw several conclusions. i) The dormancy duration and sprout length varies among genotypes. ii) The use of PGRs has been the most efficient dormancy breaking method, followed by electric current, cold storage and irradiation in order to their effectiveness for breaking dormancy and subsequent field performance. iii) The biochemical attributes i.e. antioxidative enzymes and hormonal and sugar contents changed significantly in different genotypes with the progression of storage period. iv) The parental genotypes harvested from different locations differed significantly in term of dormancy duration and sprouting percentage and there was no correlation (r = 0.01) between parental tuber dormancy and offspring true potato seed.