Evaluating the Efficacy of Essential Oils and EO Blends in Suppressing Potato Sprout Growth.

Abstract

Potatoes (Solanum tuberosum L.) are one of the most important crops globally due to their role as a staple food crop that provides essential nutrients, contributing to human nutrition and food security. However, sprouting in potato during storage poses significant challenges to farmers and producers worldwide, leading to reduce potato quality, economic losses, and storage issues, affecting crop productivity and food security. Synthetic sprout inhibitors such as chlorpropham (CIPC) are commonly used worldwide to suppress potato sprouting during storage. However, the excessive and repeated use of these chemicals can be toxic to both the environment and human health, leading to health concerns if it reaches the food chain. Consequently, the European Union banned the use of CIPC in 2020, and export markets have established zero CIPC residue levels. As a result, there is an increasing interest in developing sustainable alternatives to chemical sprout inhibitors. The use of essential oils (EOs) has emerged as a safe and effective alternative to chemical sprout inhibitors for potato sprout suppression. This work hypothesized that some EOs would suppress and control sprouting in potato. Additionally, we expected that EO treatments would preserve potato quality. The aim of this dissertation was to investigate the effects of selected EOs on sprout suppression in different

potato cultivars stored at room temperature. We started by screening twenty EOs in three potato cultivars, Ranger Russet, Terra Rosa, and Dakota Trailblazer minitubers, over 60 days storage for the suppression of sprouts at room temperature. The experiments were structured in a complete randomized block design with two replications. Of the 20 EOs, Cinnamomum camphora and Origanum majorana were identified as the most effective and promising in suppressing potato sprouts. The study revealed that EO from C. camphora completely inhibited sprout growth in cv. Ranger Russet over 60 days, while suppressing sprouts for 45 days in cv. Terra Rosa and cv. Dakota Trailblazer. O. majorana EO effectively suppressed sprout growth for up to 45 days across the three cultivars. Afterwards, we explored the potential synergistic effects of combining these two EOs with other promising candidates identified in our preliminary experiments, specifically Lavandula x intermedia and Pelargonium graveolens EOs. To do this, we designed two experiments using a simplex centroid mixture design to evaluate the synergistic effects of these EO blends on sprout suppression in three potato cultivars—Ranger Russet, La Ratte, and Norkotah minitubers—over a 90-day storage period at room temperature. In the first blend experiment, a combination of C. camphora, O. majorana, and L. x intermedia EOs was utilized. In the second experiment, a blend of C. camphora, O. majorana, and P. graveolens EOs was examined. The results of these two blend studies indicated that O. majorana and C. camphora consistently suppressed sprouting in all potato cultivars when applied alone throughout the 90 days storage period. L. x intermedia EO reduced and limited sprout growth. The first blending experiment revealed diverse synergistic effects among the three cultivars. The combination of C. camphora and O. majorana EOs significantly reduced sprout length in cv. Ranger Russet and cv. Norkotah minitubers up to 90 days. Moreover, formulations including C. camphora, O. majorana, and L. x intermedia EOs significantly reduced sprout length up to 90 days in both cv.

Ranger Russet and cv. Norkotah minitubers. No significant impact on sprout length was observed for cv. La Ratte. However, the blend of C. camphora and O. majorana significantly reduced sprout number. In the second blend experiment, P. graveolens EO was less effective in reducing sprout growth. Interestingly, the blend of C. camphora and P. graveolens, as well as the blend of O. majorana and P. graveolens, showed synergistic effects, significantly reducing sprout length up to 90 days. Furthermore, the results also demonstrated that all four EOs were superior in suppressing sprouting compared to clove EO. These EO blends also reduced the mold growth on the stored potatoes. Furthermore, optimization analyses identified cultivar-specific formulations, which were further evaluated for safety using the zebrafish embryo model. Toxicity screening revealed that C. camphora-rich blends, such as H2164 (ED50 = 181.21 μg/mL), were more toxic. In addition to sprout inhibition, EO blends have been shown to modulate primary metabolites such as sugars and amino acids in stored tubers. Moreover, GC- MS-FID was utilized to determine the chemical composition of the EOs, revealing that linalool (95.5 %,) was the predominant component in C. camphora EOs, whereas terpinen-4-ol (40.3 %), γ-terpinene (14.6 %), and sabinene (7.2 %) were the main EO constituents of O. majorana, in addition to other compounds. The main compounds identified in L. x intermedia EO were linalool (35.5%), linalyl acetate (35.4%), and camphor (7.4%). Concurrently, P. graveolens EO was rich in β-citronellol (40.5%), geraniol (14.34%), and citronellyl formate (9.13%). Our findings suggest that EOs and their blends could provide a natural, sustainable alternative to chemical sprout inhibitors, offering a practical solution for post-harvest potato storage at room temperature.