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 summary This 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.


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Potato (Solanum tuberosum L) is one of the vital food crops that is mostly grown in 58 Nepal's mid-hill region. In most developing countries such as Nepal, Potato is an important cash 59 crop to resolve food insecurity and reduce poverty among smallholder farmers [1]. 60 Several ecological conditions such as temperature, humidity, light, and soil play a key role 61 during several developmental phases of potato such as germination, sprouting, vegetative 62 growth, and maturity. In potato, the tuber germination and establishment stage is highly sensitive 63 to severe cold leading to the tuber's dormancy. 64 Dormancy is defined as the rest period under which sprouts fails to develop from any bud 65 of tuber even though tuber is kept in ideal condition [2]. The tuber's dormancy period is 66 governed by several factors, i.e., potato cultivar, growing condition, storage duration, and tuber 67 size [3,4,5,6]. The tuber's dormancy results in low sprouting and poor establishment of the crop 68 even in favourable growing conditions, which is one of the major causes of the decline in potato 69 production. Also, more extended dormancy of tuber affects the possibility of cultivating potato 70 more than once per year in various regions.

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It is essential to break the dormancy of the potato tuber. Tuber treatment with a chemical 72 such as Gibberellic acid, Thiourea, Ethylene Chlorohydrin, carbon disulfide, and Bromoethane 73 can remove the tuber's dormancy [7,8,9]. In recent years, Thiourea is used for breaking of 74 dormancy of the potato tuber. Still, it is difficult to find research work that compares the 75 effectiveness of various concentrations of Thiourea along with the potato varieties.

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To address this knowledge gap, this research will help compare several levels of Thiourea 77 concentration and determine effective one for breaking dormancy of potato tuber along with 78 different varieties. Thiourea is defined as a catalyze inhibitor, which plays a crucial role in 79 stimulating potato tuber germination. Application of Thiourea at appropriate concentration 80 supports the germination process and develop multiple sprouts per eye of potato tuber [10,11]. 81 Potato tuber producing a primary sprout length of at least 2mm is a reliable confirmation for 82 breaking the dormancy period [12]. It was reported that potato tuber treated with Thiourea and 83 hydrogen peroxide was found to have the early breaking of dormancy, i.e., 6 days and 10 days,     Similarly, 60gm and 90gm Thiourea were dissolved in 3 liters distilled water for 2% and 3% 105 solution.
106 Details of treatment 107 The potato tubers of different varieties were treated with varying concentrations of 108 Thiourea. Each treatment had ten potato tubers of uniform shape and size. The tubers were 109 soaked in the solution for 2 hours. While for control, the tuber was soaked in distilled water for 110 the same period. After that, the soaked tuber was air-dried until all the excess solution in the 111 tuber surface was removed. Then, the tubers were placed in a plastic tray and kept in the 112 darkroom.  The data were collected at an interval of 7 days, and a total of 49 days of data was observed.

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The statistical analysis of data was done by using statistical packages, namely Microsoft Excel