Potential Short-Term Memory Induction as a Promising Method for Increasing Drought Tolerance in Sweetpotato Crop Wild Relatives [ Ipomoea series Batatas (Choisy) D. F. Austin]

Abstract

Crop wild relatives of sweetpotato [Ipomoea series Batatas (Choisy) D. F. Austin] are a group of species with potential for use in crop improvement programs seeking to breed for drought tolerance. Stress memory in this group could enhance these species' physiological response to drought, though no studies have yet been conducted in this area. In this pot experiment, drought tolerance, determined using secondary traits, was tested in 59 sweetpotato crop wild relative accessions using potential short-term memory induction. For this purpose, accessions were subjected to two treatments, i) non-priming: full irrigation (up to field capacity, 0.32 w/w) from transplanting to harvest and ii) priming: full irrigation from transplanting to flowering onset (FO) followed by a priming process from FO to harvest. The priming process consisted of three water restriction periods of increasing length (8, 11, and 14 days) followed each by a recovery period of 14 days with full irrigation. Potential stress memory induction was calculated for each accession based on ecophysiological indicators such as senescence, foliar area, leaf-minus-air temperature, and leaf ¹³C discrimination. Based on total biomass production, resilience and production capacity were calculated per accession to evaluate drought tolerance. Increase in foliar area, efficient leaf thermoregulation, improvement of leaf photosynthetic performance, and delayed senescence were identified in 23.7, 28.8, 50.8, and 81.4% of the total number of accessions, respectively. It was observed that under a severe drought scenario, a resilient response included more long-lived green leaf area while a productive response was related to optimized leaf thermoregulation and gas exchange. Our preliminary results suggest that I. triloba and I. trifida have the potential to improve sweetpotato resilience in dry environments and should be included in introgression breeding programs of this crop. Furthermore, I. splendor-sylvae, I. ramosissima, I. tiliacea, and wild I. batatas were the most productive species studied but given the genetic barriers to interspecific hybridization between these species and sweetpotato, we suggest that further genetic and metabolic studies be conducted on them. Finally, this study proposes a promising method for improving drought tolerance based on potential stress-memory induction, which is applicable both for wild species and crops.

Keywords: 13C discrimination; Batatas complex; drought stress memory; foliar area; leaf temperature; senescence delay.

Figure 1

Timeline representation for the watering treatments per accession: non-primed plants (no water restriction) and primed plants (water restriction periods). Gray and white blocks mean substrate watering with full irrigation or no irrigation, respectively. Duration of every period during the priming process is indicated in days within the blocks. The priming process started after flowering onset (FO).

Figure 2

Short-term memory (STM) values per accession for senescence (STM_S) (A), foliar area (STM_FA) (B), leaf-minus-air temperature (STM_dT) (C) and leaf ¹³C discrimination (STM_Δ) (D). Red dashed line indicates STM occurrence.

Figure 3

Boxplot of short-term memory (STM) values per crop wild relatives (CWR) species and sweetpotato cultivars (orange boxplots) for senescence (STM_S) (A), foliar area (STM_FA) (B), leaf-minus-air temperature (STM_dT) (C) and leaf ¹³C discrimination (STM_Δ) (D). Red dashed line indicates the STM occurrence. In each specie’s boxplot, black line represents the median value. Boxplot contains the variation between 25 and 75% and gray circles are the outlier values.

Figure 4

Clustering analysis and 2D ordination of sweetpotato cultivars and its CWR species based on Principal Component Analysis for component loadings (STM traits, PCI and RCI). Clusters I, II and III correspond to Fernandez's (1992) Groups B, C, and D, respectively.

Figure 5

Boxplot of short-term memory (STM) effect on leaf ¹³C discrimination (STM_∆) for each cluster. Red dashed line indicates the STM occurrence (STM_Δ > 1). In each cluster’s boxplot, black line represents the median value. Boxplot contains the variation between 25 and 75% and gray circles are the outlier values.