Concentration of Thiourea is effective in breaking the dormancy of potato (Solanum tuberosum L.) varieties

Potato germination is highly sensitive to ecological conditions. High altitude and low annual average temperature result in tuber dormancy and poor sprouting. Dormancy has become a significant constraint for lowering potato production, which hinders the possibility of growing two crop cycles per year. An experiment was conducted from February to April 2020. Two major potato varieties (Desiree and Cardinal) were treated with four Thiourea concentrations (0, 1, 2, and 3%) in a two factorial, completely randomized block design with three replications. Tubers were soaked for 2 hours in different Thiourea solution as per treatments, air dried until excess solution was removed and kept in a dark room on plastic trays. With the progress of experiment dormancy breaking and sprouting parameters like early sprouting, dormancy breaking, sprout length and sprout density were recorded. It was found that Thiourea has a significant effect on all observed attributes as per varieties of potato. For Desiree variety, Thiourea (1%) decreased dormancy period by 22 days compared to control (Desiree*Thiourea 0%) and produced the longest average sprout of 7.36cm at 49 days after treatment (DAT). On the other hand, for the Cardinal variety, Thiourea (3%) decreased tuber dormancy by 27 days compared to control (Cardinal*Thiourea 0%) and produced sprout of 7.75 cm at 49 DAT. In case of sprouts/tuber 1% and 3% Thiourea produced 4.13 and 1.91 sprouts/tubers in Desiree and Cardinal, respectively. The overall mean finding indicate that, 1% and 3% Thiourea concentration was significantly superior for breaking dormancy and enhancing sprouting of potato varieties of Desiree and Cardinal respectively.

Physiology of tuber dormancy and its mechanism of release in potato

The tuber dormancy is an important aspect of tuber’s physiological age and begins with tuber initiation. It is largely dependent on genotype, environmental conditions, and tuber age. The group Phureja among diploid potatoes, has a very short or no tuber dormancy while the tubers of Solanum jamesii, a wild potato species, may remain dormant for more than eight years and have the tendency to sprout in favourable conditions. The dormancy breakage in potato is accompanied by many physiological changes such as changes in the ratios of abscisic acid (ABA)/ cytokinin and ABA/ gibberellic acid (GA3), catalase inhibition and accumulation of soluble sugars. These all changes are interlinked and occur in the same time frame. The dormant buds have 77% of their nuclei in the growth phase (G1), compared to only 13% in the preparation phase for mitosis (G2), resulting in slower development of active buds. This paper reviews various factors involved in natural and forced dormancy breakage of potato tuber in relation to their use as seed potatoes immediately after harvesting and implementation of different exogenous dormancy breaking methods like cold pre-treatment, growth regulators, electric current and irradiation to induce sprouting in potatoes.

The Cysteine-Rich Peptide Snakin-2 Negatively Regulates Tubers Sprouting through Modulating Lignin Biosynthesis and H2O2 Accumulation in Potato

Potato tuber dormancy is critical for the post-harvest quality. Snakin/Gibberellic Acid Stimulated in Arabidopsis (GASA) family genes are involved in the plants’ defense against pathogens and in growth and development, but the effect of Snakin-2 (SN2) on tuber dormancy and sprouting is largely unknown. In this study, a transgenic approach was applied to manipulate the expression level of SN2 in tubers, and it demonstrated that StSN2 significantly controlled tuber sprouting, and silencing StSN2 resulted in a release of dormancy and overexpressing tubers showed a longer dormant period than that of the control. Further analyses revealed that the decrease expression level accelerated skin cracking and water loss. Metabolite analyses revealed that StSN2 significantly down-regulated the accumulation of lignin precursors in the periderm, and the change of lignin content was documented, a finding which was consistent with the precursors’ level. Subsequently, proteomics found that cinnamyl alcohol dehydrogenase (CAD), caffeic acid O-methyltransferase (COMT) and peroxidase (Prx), the key proteins for lignin synthesis, were significantly up-regulated in silencing lines, and gene expression and enzyme activity analyses also supported this effect. Interestingly, we found that StSN2 physically interacts with three peroxidases catalyzing the oxidation and polymerization of lignin. In addition, SN2 altered the hydrogen peroxide (H2O2) content and the activities of superoxide dismutase (SOD) and catalase (CAT). These results suggest that StSN2 negatively regulates lignin biosynthesis and H2O2 accumulation, and ultimately inhibits the sprouting of potato tubers.

Effect of chemical treatments used for dormancy breaking on the number of stems and tubers of Hungarian potato varieties

The length of tuber dormancy of potato varieties is an important factor in the profitability of the potato sector. Under temperate climatic conditions longer dormancy is more advantageous. However, in case of multiple planting within one growing season, in seed multiplication programs or during rapid post-harvest disease testing, breaking or shortening of dormancy is often needed. Numerous ways for chemical regulation of dormancy period were developed, but the efficiency of such methods is strongly genotype dependent. Recently a comparative study of chemical treatments for breaking tuber dormancy of some new Hungarian potato varieties was carried out. Continuing this work, here we report about the effects of chemical treatments used for breaking dormancy on the number of stems and tubers of progeny plants. The experiment was conducted in three consecutive vegetation period, with three varieties having different maturity type and different dormancy period: Balatoni rózsa, Botond and Démon. Treatments were performed using gibberellic-acid, benzyl-adenine and Rindite in different concentrations and combinations. After the dormancy period, tubers were planted into pots and grown under controlled conditions. Number of developed stems and tubers was counted. According to the results, applied treatments had a large effect on the number of developing stems and tubers of the progeny plants. Combined treatments of Rindite+gibberellic-acid, and gibberellic-acid at 100 ppm increased significantly the number of stems and tubers. Correlation between the efficiency of dormancy breaking and the number of developed tubers was found. Based on our data, Rindite and gibberellic-acid have an important role not only in breaking dormancy, but also in increasing the tuber number/plant. This positive effect could be utilized in seed potato production.

CONCENTRATION OF THIOUREA IS EFFECTIVE IN BREAKING THE DORMANCY OF POTATO VARIETIES

Potato germination is highly sensitive to ecological conditions. High altitude and low annual average temperature results in tuber dormancy and poor sprouting. Dormancy has become a significant constraint for lowering potato production that hinders the possibility of growing two crops per year. An experiment was conducted from February to April 2020, where two major potato varieties (Desiree and Cardinal) were treated with four concentrations of Thiourea (0, 1, 2, and 3%) in a two factorial completely randomized block design with three replications. Results showed that Thiourea has a significant effect on all observed attributes as per varieties of potato. For Desiree variety, Thiourea (1%) decreased breaking of dormancy by 22 days compared to control (Desiree*Thiourea 0%) and produced the longest average sprout of 7.36cm at 49 days after treatment (DAT). On the other hand, for the Cardinal variety, Thiourea (3%) decreased tuber dormancy by 27 days compared to control (Cardinal*Thiourea 0%) and produced a sprout of 7.75 cm at 49 DAT. In conclusion, for breaking dormancy and enhancing sprouting of potato varieties Desiree and Cardinal, Thiourea concentration of 1% and 3% is recommended, respectively.Author summaryThis work is the combined effort of all the authors; conceptualization and designing the plot experiments, S.R. and M.D.; performing the experiment and data collection, S.R. and A.A.; statistical analysis and preparation of presentation table and figure, S.R. and B.A.; writing the original draft and editing the whole manuscript, S.R., M.D., R.S., S.S., and A.A. All the author have read and agreed to the published version of the manuscript.

The Effect of Chemical Treatments on the Tuber Dormancy of Hungarian Potato Cultivars

The length of tuber dormancy of potato (Solanum tuberosum L.) is an important property of cultivars, which significantly determines the duration of storage period, the storage conditions, the economy of storage and the earliest time of planting. Potato cultivars can largely differ in the duration of dormancy period. Under temperate climatic conditions, longer dormancy is more advantageous. However, in case of multiple planting within one calendar year or in case of specific needs, it can be necessary to artificially break the dormancy of tubers. In this study, we investigated the effect of chemical treatments on the tuber dormancy of three Hungarian potato cultivars (Balatoni rózsa, Démon, Botond) having different dormancy periods. The experiment was conducted in three consecutive years (growing periods). Treatments were performed using gibberellic acid, benzyl-adenine and Rindite in different concentrations and combinations. Results showed that the treatments largely influenced the length of tuber dormancy. Rindite and its combination with gibberellic acid treatments largely and significantly reduced the dormancy period for all the cultivars in all growing season, with an average 65% reduction (1906 to 669 °C). Treatments had the greatest impact on the cultivar Balatoni rózsa, with an average 33% reduction of dormancy, while they had the least impact on the cultivar Démon, with an average 25% reduction. We did not observe significant relationship between cultivar maturity type and the reduction of tuber dormancy. We found that the weather conditions of growing period influence the duration of dormancy and the efficiency of chemical treatments.