Investigating genetic and environmental factors impacting potato dormancy and assessing management strategies to control potato sprouting during storage

Sprouting during potato storage must be controlled as it leads to a decrease in tuber weight, a reduction in nutritional and processing quality, and consequently economic losses. To avoid losses during storage, chlorpropham (CIPC) has been extensively used for decades due to its high efficiency and affordability to mitigate potato sprouting. However, because CIPC and its major metabolite are a potential risk to human health, CIPC has recently been removed from the European market (EU regulation 2019/989). Consequently, the main objective of this thesis was to find economically suitable and sustainable management strategies to control potato sprouting. In this thesis, the influence of year, location and variety factors on potato dormancy was assessed. The analysis was performed using 3,379 records of multi-environment trials collected in Switzerland in five different locations with contrasting environments, over 25 years. In total, 537 genotypes were tested. The potential to predict potato dormancy of 247 predictors (i.e., environmental factors and management during the growing season variables) was evaluated using a forward selection approach to select a model predicting the duration of dormancy. Variety was the most important variable to explain the variability in dormancy (60.3 %), while year and location explained 13.9 % and 5.4 % of the dormancy variability, respectively. The selected predictive model used the variety class and a parameter related to the temperature of the growing season as predictors. The importance of the temperature parameter was confirmed by a greenhouse trial. In order to find alternative anti-sprouting treatments, the potential to control potato sprouting of several synthetic pre- and post-harvest molecules was investigated (i.e., Maleic hydrazide (MH); 1,4-Dimethylnaphtalene (1,4-DMN); 3-decen-2-one and CIPC) and compared to an untreated control. The potential of 1,4-DMN and 3-decen-2-one post-harvest treatments to reinforce the efficacy of MH pre-harvest treatment was also investigated. Residue analyses were performed at the end of the storage. Results showed that all pre- and post-harvest treatments significantly mitigated sprouting for up to seven months of storage. The efficacy of the tested molecules to reduce the sprout weight in comparison to the untreated control was 86.9 %; 77.9 %, 73.6 % and 99.8 % for the MH; 3-decen-2-one, 1,4-DMN and CIPC molecules, respectively. The advantage of the 3-decen-2-one treatment is that it leads to complete necrosis of sprouts within 24 hours after treatment and it can be used as a curative treatment to save potato stocks that have already sprouted. In this study, results showed that there was no benefit to combine pre- and post-harvest treatments to mitigate sprouting. A variety-dependent effect of sprouting and treatment efficacy was observed. In addition, no residue of 1,4-DMN was observed in treated tubers (< LOQ), while residues of both CIPC and MH were found in treated tubers. The efficacy of natural molecules to mitigate sprouting was also evaluated and compared to an untreated control. The tested natural molecules were L-carvone, D-limonene (i.e., mint and orange essential oils, respectively) and ethylene. All the tested molecules efficiently controlled sprouting for up to five months of storage at 8 °C. These natural molecules are advantageous because they are authorized to treat potatoes in organic farming and they can so far be used without a maximum residue limit in the final product. As an alternative or complementary approach, the potential of cold storage (i.e., at 4 °C) to mitigate sprouting after 4.5 months of storage in comparison to storage at a higher temperature (i.e., 8 °C) was evaluated for six processing potato varieties (Lady Claire, Verdi, Kiebitz, Pirol, Agria and Markies). The CIS-ability of these six potato varieties was evaluated by measuring relevant determinant parameters for the industry (e.g., acrylamide content, sucrose content, RS or crisp color quality) after two and/or four months of storage at 4 °C and 8 °C. The potential of reconditioning at 15 °C after a cold storage at 4 °C to decrease total RS, glucose and acrylamide contents in potato tubers was also evaluated. Vacuolar invertase (VInv) gene expression level was measured in tubers stored at 4 °C, at 8 °C and reconditioned at 15 °C. Results showed that a storage at 4 °C efficiently mitigates sprouting in the six tested varieties for up to 4.5 months of storage. Three CIS-resistant varieties were identified (i.e., Lady Claire, Verdi and Kiebitz) and displayed a low total RS and/or glucose content for up to four months of storage at 4 °C. In addition, the reconditioning efficiently reduced the glucose content and the Vinv gene expression in the Markies variety after storage at 4 °C. Several correlations have been observed between glucose or RS content and VInv gene expression. Based on the results obtained in this thesis, several potato management strategies are proposed to mitigate sprouting for different sprouting pressure scenarios.