Abstract
Sweet potato (Ipomoea batatas (L.) Lam.) is an important staple food in several regions of the world. Water scarcity is the most devastating abiotic stress, with a great impact on crop productivity, food security, and subsistence. Drought restricts the nutrient intake and transport into the plant. Tolerant crops have morphological mechanisms of drought avoidance and/or phenotypic flexibility, showing also good water and nutrient efficiency. However, that information is scarce for sweet potato, which is usually based on physiological traits of plant productivity. Here, we show the physiological responses of eight sweet potato accessions subjected to a 3 months’ drought period, by recording their differences for nutrient and leaf chlorophyll content, biomass and stress level. Our results showed that the differences in water use efficiency (WUE, +68.1%), chlorophyll content index (CCI, -5.3%), total plant biomass (TPB, -55.4%), nutrient efficiency (NER, +38.1%) and nutrient harvest index (NHI, +2.9%) where significantly correlated with the water regime. The water shortage led to a drought avoidance response, with TPB loss in all accessions. Distinct phenotypic flexibility responses were also recorded and explained by the root:shoot ratio (R:S) and stress index (SI) variation of the storage root and shoot growth. This information could be relevant for the development of sweet potato breeding programs, adapting this crop to climate change.
 
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 In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 4, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue.
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Highlights
Roots and tubers are the second-most cultivated group of species after cereals, contributing significantly to food and nutritional security
Cultivars are considered to be under drought stress when they face water limitation in the soil, and when they are subjected to the constant loss of water through evapotranspiration triggered by atmospheric conditions (Motsa et al, 2015a)
All sweet potato accessions decreased their biomass, showing a drought avoidance behaviour during stress. They showed a variation in their physiological responses, according to water allocation, chlorophyll rate and nutrient use at the whole-plant level (Table 2)
Summary
Roots and tubers are the second-most cultivated group of species after cereals, contributing significantly to food and nutritional security. Sweet potato (Ipomoea batatas (L.) Lam.) is a tropical crop tuber, and a worldwide important staple food (Sharma and Kaushal 2016). Asia had the highest sweet potato production in 2017, with 79.6 Mt, representing 71% of worldwide production (FAOSTAT database, www.fao.org, 2019). Water scarcity is one of the main collateral abiotic consequences of climate change, which is increasingly affecting worldwide crop production. This lack of water decreases productivity, jeopardizing subsistence and food security (Lebot, 2009; Ganança et al, 2015; Ganança et al, 2018). Cultivars are considered to be under drought stress when they face water limitation in the soil, and when they are subjected to the constant loss of water through evapotranspiration triggered by atmospheric conditions (Motsa et al, 2015a)
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